Guida tecnica all'accesso utente in React Native con Parse

accesso e disaccesso utente per react native introduzione dopo aver implementato un componente che gestisce la registrazione utente in parse nell'ultima guida, ora imparerai come accedere e disconnettere gli utenti utilizzando la stessa parse user parse user classe imparerai anche a installare e configurare react navigation react navigation in modo da poter navigare l'utente attraverso i tuoi nuovi schermi e componenti il parse user login parse user login metodo memorizza nel tuo storage locale una sessione utente valida, quindi future chiamate a metodi come currentasync currentasync recupereranno con successo i tuoi dati utente d'altra parte, logout logout cancellerà questa sessione dal disco e disconnetterà da qualsiasi servizio collegato nel tuo server parse in qualsiasi momento, puoi accedere al progetto android completo costruito con questo tutorial nei nostri repository github https //github com/templates back4app/android parse sdk kotlin https //github com/templates back4app/android parse sdk java requisiti per completare questo tutorial, avrai bisogno di un'app react native creata e https //www back4app com/docs/react native/parse sdk/react native sdk completa le guide precedenti in modo da avere una migliore comprensione di https //www back4app com/docs/react native/parse sdk/working with users/react native login obiettivo per costruire una funzionalità di accesso e disaccesso utente utilizzando parse per un'app react native 1 installazione delle dipendenze a un certo punto, ogni applicazione in react native avrà bisogno di navigazione tra le schermate ora imparerai come installare e configurare la libreria più utilizzata in react native per questo, react navigation react navigation vai nella directory principale del tuo progetto e installa le seguenti dipendenze cd yourapp yarn add @react navigation/native react native reanimated react native gesture handler react native screens react native safe area context @react native community/masked view se stai sviluppando per ios, devi installare i pod per completare l'auto collegamento della tua app cd ios npx pod install nota il collegamento è automatico per react native 0 60+ 0 60+ per tutte le piattaforme, quindi se stai ancora utilizzando una versione precedente di rn, dai un'occhiata alla documentazione di react native https //reactnative dev/docs/linking libraries ios nel file di ingresso della tua app ( app tsx app tsx o app js app js ), aggiungi questa riga di importazione in cima al file ora devi spostare i tuoi componenti all'interno del react navigation react navigation container, che incapsulerà la tua app all'interno di un navigationcontainer navigationcontainer app tsx/app js 1 import "react native gesture handler"; 2 // your other imports go here 3 import { navigationcontainer } from "@react navigation/native"; 4&#x9; 5 const app = () => { 6 return \<navigationcontainer>{/ your app code /}\</navigationcontainer>; 7 } 8&#x9; 9 export default app; la libreria di navigazione principale ha diversi moduli di navigazione aggiuntivi come stack, schede, cassetto, altri lo stack navigator è il più semplice e quello che utilizzerai in questa guida procedi con l'installazione \# questo è il navigatore che utilizzerai yarn add @react navigation/stack 2 creare un stacknavigator ora creiamo e impostiamo un stacknavigator stacknavigator questo modulo gestirà e gestirà la navigazione tra le schermate della tua app poiché non è un obiettivo qui darti una comprensione approfondita di react navigation comprensione approfondita di react navigation , ti preghiamo di visitare le https //reactnavigation org/docs/hello react navigation/ , per saperne di più nel tuo app js app js ( app tsx app tsx se stai usando typescript) file, importa e crea un stacknavigator stacknavigator , crea una funzione contenente la schermata di registrazione dell'utente e inserisci il navigatore all'interno della tua app navigationcontainer navigationcontainer il tuo file principale dovrebbe apparire così app tsx/app js 1 import 'react native gesture handler'; 2 import react from 'react'; 3 import {image, safeareaview, statusbar, text, view} from 'react native'; 4&#x9; 5 import asyncstorage from '@react native async storage/async storage'; 6 import parse from 'parse/react native'; 7 import {navigationcontainer} from '@react navigation/native'; 8 import {createstacknavigator} from '@react navigation/stack'; 9 import {userregistration} from ' /userregistration'; 10 import styles from ' /styles'; 11&#x9; 12 // your parse initialization configuration goes here 13 parse setasyncstorage(asyncstorage); 14 const parse application id string = 'application id'; 15 const parse host url string = 'host url'; 16 const parse javascript id string = 'javascript id'; 17 parse initialize(parse application id, parse javascript id); 18 parse serverurl = parse host url; 19&#x9; 20 // wrap your old app screen in a separate function, so you can create a screen 21 // inside the navigator; you can also declare your screens in a separate file, 22 // export and import here to reduce some clutter 23 function userregistrationscreen() { 24 return ( 25 <> 26 \<statusbar /> 27 \<safeareaview style={styles login container}> 28 \<view style={styles login header}> 29 \<image 30 style={styles login header logo} 31 source={require(' /assets/logo back4app png')} 32 /> 33 \<text style={styles login header text}> 34 \<text style={styles login header text bold}> 35 {'react native on back4app '} 36 \</text> 37 {' user registration'} 38 \</text> 39 \</view> 40 \<userregistration /> 41 \</safeareaview> 42 \</> 43 ); 44 } 45&#x9; 46 // create your main navigator here 47 const stack = createstacknavigator(); 48&#x9; 49 // add the stack navigator to your navigationcontainer 50 // and in it you can add all your app screens in the order you need 51 // them on your stack 52 const app = () => { 53 return ( 54 \<navigationcontainer> 55 \<stack navigator> 56 \<stack screen name="sign up" component={userregistrationscreen} /> 57 \</stack navigator> 58 \</navigationcontainer> 59 ); 60 }; 61&#x9; 62 export default app; se esegui la tua app ora, noterai l'inclusione di un'intestazione nella parte superiore dello schermo contenente il nome dello schermo 3 creazione di un componente di accesso costruiamo ora il userlogin userlogin componente funzionale nella tua app crea un nuovo file nella tua directory principale chiamato userlogin js userlogin js ( userlogin tsx userlogin tsx se stai usando typescript) e aggiungi gli elementi di input utilizzando gli state hooks per gestire i loro dati userlogin js 1 import react, {fc, reactelement, usestate} from 'react'; 2 import { 3 image, 4 text, 5 textinput, 6 touchableopacity, 7 view, 8 } from 'react native'; 9 import parse from 'parse/react native'; 10 import styles from ' /styles'; 11&#x9; 12 export const userlogin = () => { 13 const \[username, setusername] = usestate(""); 14 const \[password, setpassword] = usestate(""); 15&#x9; 16 return ( 17 \<view style={styles login wrapper}> 18 \<view style={styles form}> 19 \<textinput 20 style={styles form input} 21 value={username} 22 placeholder={'username'} 23 onchangetext={(text) => setusername(text)} 24 autocapitalize={'none'} 25 keyboardtype={'email address'} 26 /> 27 \<textinput 28 style={styles form input} 29 value={password} 30 placeholder={'password'} 31 securetextentry 32 onchangetext={(text) => setpassword(text)} 33 /> 34 \<touchableopacity onpress={() => {}}> 35 \<view style={styles button}> 36 \<text style={styles button label}>{'sign in'}\</text> 37 \</view> 38 \</touchableopacity> 39 \</view> 40 \<view style={styles login social}> 41 \<view style={styles login social separator}> 42 \<view style={styles login social separator line} /> 43 \<text style={styles login social separator text}>{'or'}\</text> 44 \<view style={styles login social separator line} /> 45 \</view> 46 \<view style={styles login social buttons}> 47 \<touchableopacity> 48 \<view 49 style={\[ 50 styles login social button, 51 styles login social facebook, 52 ]}> 53 \<image 54 style={styles login social icon} 55 source={require(' /assets/icon facebook png')} 56 /> 57 \</view> 58 \</touchableopacity> 59 \<touchableopacity> 60 \<view style={styles login social button}> 61 \<image 62 style={styles login social icon} 63 source={require(' /assets/icon google png')} 64 /> 65 \</view> 66 \</touchableopacity> 67 \<touchableopacity> 68 \<view style={styles login social button}> 69 \<image 70 style={styles login social icon} 71 source={require(' /assets/icon apple png')} 72 /> 73 \</view> 74 \</touchableopacity> 75 \</view> 76 \</view> 77 \</view> 78 ); 79 }; userlogin tsx 1 import react, {fc, reactelement, usestate} from 'react'; 2 import { 3 image, 4 text, 5 textinput, 6 touchableopacity, 7 view, 8 } from 'react native'; 9 import parse from 'parse/react native'; 10 import styles from ' /styles'; 11&#x9; 12 export const userlogin fc<{}> = ({}) reactelement => { 13 const \[username, setusername] = usestate(""); 14 const \[password, setpassword] = usestate(""); 15&#x9; 16 return ( 17 \<view style={styles login wrapper}> 18 \<view style={styles form}> 19 \<textinput 20 style={styles form input} 21 value={username} 22 placeholder={'username'} 23 onchangetext={(text) => setusername(text)} 24 autocapitalize={'none'} 25 keyboardtype={'email address'} 26 /> 27 \<textinput 28 style={styles form input} 29 value={password} 30 placeholder={'password'} 31 securetextentry 32 onchangetext={(text) => setpassword(text)} 33 /> 34 \<touchableopacity onpress={() => {}}> 35 \<view style={styles button}> 36 \<text style={styles button label}>{'sign in'}\</text> 37 \</view> 38 \</touchableopacity> 39 \</view> 40 \<view style={styles login social}> 41 \<view style={styles login social separator}> 42 \<view style={styles login social separator line} /> 43 \<text style={styles login social separator text}>{'or'}\</text> 44 \<view style={styles login social separator line} /> 45 \</view> 46 \<view style={styles login social buttons}> 47 \<touchableopacity> 48 \<view 49 style={\[ 50 styles login social button, 51 styles login social facebook, 52 ]}> 53 \<image 54 style={styles login social icon} 55 source={require(' /assets/icon facebook png')} 56 /> 57 \</view> 58 \</touchableopacity> 59 \<touchableopacity> 60 \<view style={styles login social button}> 61 \<image 62 style={styles login social icon} 63 source={require(' /assets/icon google png')} 64 /> 65 \</view> 66 \</touchableopacity> 67 \<touchableopacity> 68 \<view style={styles login social button}> 69 \<image 70 style={styles login social icon} 71 source={require(' /assets/icon apple png')} 72 /> 73 \</view> 74 \</touchableopacity> 75 \</view> 76 \</view> 77 \</view> 78 ); 79 }; ora puoi implementare la funzione che chiamerà il parse user login parse user login metodo, utilizzando variabili di stato javascript 1 const douserlogin = async function () { 2 // note that these values come from state variables that we've declared before 3 const usernamevalue = username; 4 const passwordvalue = password; 5 return await parse user login(usernamevalue, passwordvalue) 6 then(async (loggedinuser) => { 7 // login returns the corresponding parseuser object 8 alert alert( 9 'success!', 10 `user ${loggedinuser get('username')} has successfully signed in!`, 11 ); 12 // to verify that this is in fact the current user, currentasync can be used 13 const currentuser = await parse user currentasync(); 14 console log(loggedinuser === currentuser); 15 return true; 16 }) 17 catch((error) => { 18 // error can be caused by wrong parameters or lack of internet connection 19 alert alert('error!', error message); 20 return false; 21 }); 22 };1 const douserlogin = async function () promise\<boolean> { 2 // note that these values come from state variables that we've declared before 3 const usernamevalue string = username; 4 const passwordvalue string = password; 5 return await parse user login(usernamevalue, passwordvalue) 6 then(async (loggedinuser parse user) => { 7 // login returns the corresponding parseuser object 8 alert alert( 9 'success!', 10 `user ${loggedinuser get('username')} has successfully signed in!`, 11 ); 12 // to verify that this is in fact the current user, currentasync can be used 13 const currentuser parse user = await parse user currentasync(); 14 console log(loggedinuser === currentuser); 15 return true; 16 }) 17 catch((error object) => { 18 // error can be caused by wrong parameters or lack of internet connection 19 alert alert('error!', error message); 20 return false; 21 }); 22 }; inserisci questa funzione all'interno del userlogin userlogin componente, appena prima della return return chiamata, per essere chiamata e testata ricorda di aggiornare il pulsante di accesso del modulo onpress onpress azione in () => douserlogin() () => douserlogin() e di importare alert alert da react native react native il tuo componente dovrebbe ora apparire così userlogin js 1 import react, {fc, reactelement, usestate} from 'react'; 2 import { 3 alert, 4 image, 5 text, 6 textinput, 7 touchableopacity, 8 view, 9 } from 'react native'; 10 import parse from 'parse/react native'; 11 import styles from ' /styles'; 12&#x9; 13 export const userlogin = () => { 14 const \[username, setusername] = usestate(''); 15 const \[password, setpassword] = usestate(''); 16&#x9; 17 const douserlogin = async function () { 18 // note that these values come from state variables that we've declared before 19 const usernamevalue = username; 20 const passwordvalue = password; 21 return await parse user login(usernamevalue, passwordvalue) 22 then(async (loggedinuser) => { 23 // login returns the corresponding parseuser object 24 alert alert( 25 'success!', 26 `user ${loggedinuser get('username')} has successfully signed in!`, 27 ); 28 // to verify that this is in fact the current user, currentasync can be used 29 const currentuser = await parse user currentasync(); 30 console log(loggedinuser === currentuser); 31 return true; 32 }) 33 catch((error) => { 34 // error can be caused by wrong parameters or lack of internet connection 35 alert alert('error!', error message); 36 return false; 37 }); 38 }; 39&#x9; 40 return ( 41 \<view style={styles login wrapper}> 42 \<view style={styles form}> 43 \<textinput 44 style={styles form input} 45 value={username} 46 placeholder={'username'} 47 onchangetext={(text) => setusername(text)} 48 autocapitalize={'none'} 49 keyboardtype={'email address'} 50 /> 51 \<textinput 52 style={styles form input} 53 value={password} 54 placeholder={'password'} 55 securetextentry 56 onchangetext={(text) => setpassword(text)} 57 /> 58 \<touchableopacity onpress={() => douserlogin()}> 59 \<view style={styles button}> 60 \<text style={styles button label}>{'sign in'}\</text> 61 \</view> 62 \</touchableopacity> 63 \</view> 64 \<view style={styles login social}> 65 \<view style={styles login social separator}> 66 \<view style={styles login social separator line} /> 67 \<text style={styles login social separator text}>{'or'}\</text> 68 \<view style={styles login social separator line} /> 69 \</view> 70 \<view style={styles login social buttons}> 71 \<touchableopacity> 72 \<view 73 style={\[ 74 styles login social button, 75 styles login social facebook, 76 ]}> 77 \<image 78 style={styles login social icon} 79 source={require(' /assets/icon facebook png')} 80 /> 81 \</view> 82 \</touchableopacity> 83 \<touchableopacity> 84 \<view style={styles login social button}> 85 \<image 86 style={styles login social icon} 87 source={require(' /assets/icon google png')} 88 /> 89 \</view> 90 \</touchableopacity> 91 \<touchableopacity> 92 \<view style={styles login social button}> 93 \<image 94 style={styles login social icon} 95 source={require(' /assets/icon apple png')} 96 /> 97 \</view> 98 \</touchableopacity> 99 \</view> 100 \</view> 101 \</view> 102 ); 103 }; userlogin tsx 1 import react, {fc, reactelement, usestate} from 'react'; 2 import { 3 alert, 4 image, 5 text, 6 textinput, 7 touchableopacity, 8 view, 9 } from 'react native'; 10 import parse from 'parse/react native'; 11 import styles from ' /styles'; 12&#x9; 13 export const userlogin fc<{}> = ({}) reactelement => { 14 const \[username, setusername] = usestate(''); 15 const \[password, setpassword] = usestate(''); 16&#x9; 17 const douserlogin = async function () promise\<boolean> { 18 // note that these values come from state variables that we've declared before 19 const usernamevalue string = username; 20 const passwordvalue string = password; 21 return await parse user login(usernamevalue, passwordvalue) 22 then(async (loggedinuser parse user) => { 23 // login returns the corresponding parseuser object 24 alert alert( 25 'success!', 26 `user ${loggedinuser get('username')} has successfully signed in!`, 27 ); 28 // to verify that this is in fact the current user, currentasync can be used 29 const currentuser parse user = await parse user currentasync(); 30 console log(loggedinuser === currentuser); 31 return true; 32 }) 33 catch((error object) => { 34 // error can be caused by wrong parameters or lack of internet connection 35 alert alert('error!', error message); 36 return false; 37 }); 38 }; 39&#x9; 40 return ( 41 \<view style={styles login wrapper}> 42 \<view style={styles form}> 43 \<textinput 44 style={styles form input} 45 value={username} 46 placeholder={'username'} 47 onchangetext={(text) => setusername(text)} 48 autocapitalize={'none'} 49 keyboardtype={'email address'} 50 /> 51 \<textinput 52 style={styles form input} 53 value={password} 54 placeholder={'password'} 55 securetextentry 56 onchangetext={(text) => setpassword(text)} 57 /> 58 \<touchableopacity onpress={() => douserlogin()}> 59 \<view style={styles button}> 60 \<text style={styles button label}>{'sign in'}\</text> 61 \</view> 62 \</touchableopacity> 63 \</view> 64 \<view style={styles login social}> 65 \<view style={styles login social separator}> 66 \<view style={styles login social separator line} /> 67 \<text style={styles login social separator text}>{'or'}\</text> 68 \<view style={styles login social separator line} /> 69 \</view> 70 \<view style={styles login social buttons}> 71 \<touchableopacity> 72 \<view 73 style={\[ 74 styles login social button, 75 styles login social facebook, 76 ]}> 77 \<image 78 style={styles login social icon} 79 source={require(' /assets/icon facebook png')} 80 /> 81 \</view> 82 \</touchableopacity> 83 \<touchableopacity> 84 \<view style={styles login social button}> 85 \<image 86 style={styles login social icon} 87 source={require(' /assets/icon google png')} 88 /> 89 \</view> 90 \</touchableopacity> 91 \<touchableopacity> 92 \<view style={styles login social button}> 93 \<image 94 style={styles login social icon} 95 source={require(' /assets/icon apple png')} 96 /> 97 \</view> 98 \</touchableopacity> 99 \</view> 100 \</view> 101 \</view> 102 ); 103 }; 4 creare una schermata di accesso creiamo ora una nuova schermata per la tua app che utilizzerà il tuo userlogin userlogin componente aggiungi la nuova schermata come la prima (o superiore) schermata del tuo stacknavigator stacknavigator anche app tsx/app js 1 // 2&#x9; 3 // add this new screen function below the userregistrationscreen 4 function userloginscreen() { 5 return ( 6 <> 7 \<statusbar /> 8 \<safeareaview style={styles login container}> 9 \<view style={styles login header}> 10 \<image 11 style={styles login header logo} 12 source={require(' /assets/logo back4app png')} 13 /> 14 \<text style={styles login header text}> 15 \<text style={styles login header text bold}> 16 {'react native on back4app '} 17 \</text> 18 {' user login'} 19 \</text> 20 \</view> 21 \<userlogin /> 22 \</safeareaview> 23 \</> 24 ); 25 } 26&#x9; 27 // 28&#x9; 29 // add the screen as the top one at your stacknavigator 30 const app = () => { 31 return ( 32 \<navigationcontainer> 33 \<stack navigator> 34 \<stack screen name="login" component={userloginscreen} /> 35 \<stack screen name="sign up" component={userregistrationscreen} /> 36 \</stack navigator> 37 \</navigationcontainer> 38 ); 39 }; 40&#x9; 41 // procedi e testa il tuo schermo e componente nota che la tua app mostrerà ora la schermata di accesso dell'utente invece di quella di registrazione, a causa della loro posizione nella stacknavigator stacknavigator dell'elenco degli schermi vedrai un messaggio come questo dopo aver effettuato l'accesso 5 creare una schermata principale e gestire la navigazione dopo aver effettuato l'accesso, generalmente vorrai portare l'utente alla schermata principale della tua app crea questa schermata nel file principale della tua app app tsx/app js 1 // 2&#x9; 3 // add this new screen function below the userregistrationscreen 4 function userloginscreen() { 5 return ( 6 <> 7 \<statusbar /> 8 \<safeareaview style={styles login container}> 9 \<view style={styles login header}> 10 \<image 11 style={styles login header logo} 12 source={require(' /assets/logo back4app png')} 13 /> 14 \<text style={styles login header text}> 15 \<text style={styles login header text bold}> 16 {'react native on back4app '} 17 \</text> 18 {' user login'} 19 \</text> 20 \</view> 21 \<userlogin /> 22 \</safeareaview> 23 \</> 24 ); 25 } 26&#x9; 27 // 28&#x9; 29 // add the screen as the top one at your stacknavigator 30 const app = () => { 31 return ( 32 \<navigationcontainer> 33 \<stack navigator> 34 \<stack screen name="login" component={userloginscreen} /> 35 \<stack screen name="sign up" component={userregistrationscreen} /> 36 \</stack navigator> 37 \</navigationcontainer> 38 ); 39 }; 40&#x9; 41 // ora devi usare ‘react navigation’ per navigare l'utente dopo che ha effettuato l'accesso, aggiungendo questo nuovo codice all'interno del userlogin userlogin componente userlogin js 1 // 2 // add this import 3 import {usenavigation} from '@react navigation/native'; 4&#x9; 5 export const userlogin = () => { 6 // add this to use usenavigation hook 7 const navigation = usenavigation(); 8 9 // 10&#x9; 11 const douserlogin = async function () { 12 const usernamevalue = username; 13 const passwordvalue = password; 14 return await parse user login(usernamevalue, passwordvalue) 15 then(async (loggedinuser) => { 16 alert alert( 17 'success!', 18 `user ${loggedinuser get('username')} has successfully signed in!`, 19 ); 20 const currentuser = await parse user currentasync(); 21 console log(loggedinuser === currentuser); 22 // add this to navigate your home screen; navigation navigate takes 23 // the user to the screen named after the one passed as parameter 24 navigation navigate('home'); 25 return true; 26 }) 27 catch((error) => { 28 alert alert('error!', error message); 29 return false; 30 }); 31 }; 32 // userlogin tsx 1 // 2 // add this import 3 import {usenavigation} from '@react navigation/native'; 4&#x9; 5 export const userlogin fc<{}> = ({}) reactelement => { 6 // add this to use usenavigation hook 7 const navigation = usenavigation(); 8&#x9; 9 // 10 11 const douserlogin = async function () promise\<boolean> { 12 const usernamevalue string = username; 13 const passwordvalue string = password; 14 return await parse user login(usernamevalue, passwordvalue) 15 then(async (loggedinuser parse user) => { 16 alert alert( 17 'success!', 18 `user ${loggedinuser get('username')} has successfully signed in!`, 19 ); 20 const currentuser parse user = await parse user currentasync(); 21 console log(loggedinuser === currentuser); 22 // add this to navigate your home screen; navigation navigate takes 23 // the user to the screen named after the one passed as parameter 24 navigation navigate('home'); 25 return true; 26 }) 27 catch((error object) => { 28 alert alert('error!', error message); 29 return false; 30 }); 31 }; 32&#x9; 33 // verrai reindirizzato alla tua nuova homescreen homescreen dopo aver effettuato l'accesso puoi aggiornare questa schermata aggiungendo questo hellouser hellouser componente che mostra il nome utente dell'utente attuale hellouser js 1 import react, {fc, reactelement, useeffect, usestate} from 'react'; 2 import {text} from 'react native'; 3 import parse from 'parse/react native'; 4 import styles from ' /styles'; 5&#x9; 6 export const hellouser = () => { 7 // state variable that will hold username value 8 const \[username, setusername] = usestate(''); 9&#x9; 10 // useeffect is called after the component is initially rendered and 11 // after every other render 12 useeffect(() => { 13 // since the async method parse user currentasync is needed to 14 // retrieve the current user data, you need to declare an async 15 // function here and call it afterwards 16 async function getcurrentuser() { 17 // this condition ensures that username is updated only if needed 18 if (username === '') { 19 const currentuser = await parse user currentasync(); 20 if (currentuser !== null) { 21 setusername(currentuser getusername()); 22 } 23 } 24 } 25 getcurrentuser(); 26 }, \[username]); 27&#x9; 28 // note the condition operator here, so the "hello" text is only 29 // rendered if there is an username value 30 return ( 31 \<view style={styles login wrapper}> 32 \<view style={styles form}> 33 {username !== '' && \<text>{`hello ${username}!`}\</text>} 34 \</view> 35 \</view> 36 ); 37 }; hellouser tsx 1 import react, {fc, reactelement, useeffect, usestate} from 'react'; 2 import {text} from 'react native'; 3 import parse from 'parse/react native'; 4 import styles from ' /styles'; 5&#x9; 6 export const hellouser fc<{}> = ({}) reactelement => { 7 // state variable that will hold username value 8 const \[username, setusername] = usestate(''); 9&#x9; 10 // useeffect is called after the component is initially rendered and 11 // after every other render 12 useeffect(() => { 13 // since the async method parse user currentasync is needed to 14 // retrieve the current user data, you need to declare an async 15 // function here and call it afterwards 16 async function getcurrentuser() { 17 // this condition ensures that username is updated only if needed 18 if (username === '') { 19 const currentuser = await parse user currentasync(); 20 if (currentuser !== null) { 21 setusername(currentuser getusername()); 22 } 23 } 24 } 25 getcurrentuser(); 26 }, \[username]); 27&#x9; 28 // note the condition operator here, so the "hello" text is only 29 // rendered if there is an username value 30 return ( 31 \<view style={styles login wrapper}> 32 \<view style={styles form}> 33 {username !== '' && \<text>{`hello ${username}!`}\</text>} 34 \</view> 35 \</view> 36 ); 37 }; nota puoi dare un'occhiata migliore agli useeffect useeffect di react https //reactjs org/docs/hooks effect html dopo aver chiamato questo componente all'interno del tuo homescreen, la tua app dovrebbe apparire così 6 creazione di un componente di disconnessione il userlogout userlogout componente è più semplice rispetto al login poiché il parse user logout parse user logout metodo non richiede argomenti e cancella automaticamente i dati di currentuser currentuser memorizzati localmente crea questo componente nella directory principale della tua app userlogout js 1 import react, {fc, reactelement} from 'react'; 2 import {alert, text, touchableopacity, view} from 'react native'; 3 import parse from 'parse/react native'; 4 import {usenavigation} from '@react navigation/native'; 5 import {stackactions} from '@react navigation/native'; 6 import styles from ' /styles'; 7&#x9; 8 export const userlogout = () => { 9 const navigation = usenavigation(); 10&#x9; 11 const douserlogout = async function () { 12 return await parse user logout() 13 then(async () => { 14 // to verify that current user is now empty, currentasync can be used 15 const currentuser = await parse user currentasync(); 16 if (currentuser === null) { 17 alert alert('success!', 'no user is logged in anymore!'); 18 } 19 // navigation dispatch calls a navigation action, and poptotop will take 20 // the user back to the very first screen of the stack 21 navigation dispatch(stackactions poptotop()); 22 return true; 23 }) 24 catch((error) => { 25 alert alert('error!', error message); 26 return false; 27 }); 28 }; 29&#x9; 30 return ( 31 \<view style={styles login wrapper}> 32 \<view style={styles form}> 33 \<touchableopacity onpress={() => douserlogout()}> 34 \<view style={styles button}> 35 \<text style={styles button label}>{'logout'}\</text> 36 \</view> 37 \</touchableopacity> 38 \</view> 39 \</view> 40 ); 41 }; userlogout tsx 1 import react, {fc, reactelement} from 'react'; 2 import {alert, text, touchableopacity, view} from 'react native'; 3 import parse from 'parse/react native'; 4 import {usenavigation} from '@react navigation/native'; 5 import {stackactions} from '@react navigation/native'; 6 import styles from ' /styles'; 7&#x9; 8 export const userlogout fc<{}> = ({}) reactelement => { 9 const navigation = usenavigation(); 10&#x9; 11 const douserlogout = async function () promise\<boolean> { 12 return await parse user logout() 13 then(async () => { 14 // to verify that current user is now empty, currentasync can be used 15 const currentuser parse user = await parse user currentasync(); 16 if (currentuser === null) { 17 alert alert('success!', 'no user is logged in anymore!'); 18 } 19 // navigation dispatch calls a navigation action, and poptotop will take 20 // the user back to the very first screen of the stack 21 navigation dispatch(stackactions poptotop()); 22 return true; 23 }) 24 catch((error object) => { 25 alert alert('error!', error message); 26 return false; 27 }); 28 }; 29&#x9; 30 return ( 31 \<view style={styles login wrapper}> 32 \<view style={styles form}> 33 \<touchableopacity onpress={() => douserlogout()}> 34 \<view style={styles button}> 35 \<text style={styles button label}>{'logout'}\</text> 36 \</view> 37 \</touchableopacity> 38 \</view> 39 \</view> 40 ); 41 }; aggiungi questo nuovo componente a homescreen homescreen in modo da poterlo testare dopo aver effettuato l'accesso la schermata principale della tua app apparirà così ora se esegui un logout riuscito, vedrai un messaggio come questo mentre vieni reindirizzato alla userlogin userlogin schermata, che è la prima nella pila di navigazione collega il tuo userregistration userregistration a un pulsante di registrazione all'interno della userlogin userlogin schermata e ripeti lo stesso schema di reindirizzamento alla tua app homescreen homescreen ricorda di leggere la documentazione di react navigation react navigation per scoprire diverse opzioni di personalizzazione e controllare ogni aspetto della navigazione della tua app userlogin js 1 // 2&#x9; 3 export const userlogin = () => { 4 const navigation = usenavigation(); 5&#x9; 6 const \[username, setusername] = usestate(''); 7 const \[password, setpassword] = usestate(''); 8&#x9; 9 const douserlogin = async function () { 10 // note that these values come from state variables that we've declared before 11 const usernamevalue = username; 12 const passwordvalue = password; 13 return await parse user login(usernamevalue, passwordvalue) 14 then(async (loggedinuser) => { 15 // login returns the corresponding parseuser object 16 alert alert( 17 'success!', 18 `user ${loggedinuser get('username')} has successfully signed in!`, 19 ); 20 // to verify that this is in fact the current user, currentasync can be used 21 const currentuser parse user = await parse user currentasync(); 22 console log(loggedinuser === currentuser); 23 // navigation navigate takes the user to the screen named after the one 24 // passed as parameter 25 navigation navigate('home'); 26 return true; 27 }) 28 catch((error) => { 29 // error can be caused by wrong parameters or lack of internet connection 30 alert alert('error!', error message); 31 return false; 32 }); 33 }; 34&#x9; 35 return ( 36 \<view style={styles login wrapper}> 37 \<view style={styles form}> 38 \<textinput 39 style={styles form input} 40 value={username} 41 placeholder={'username'} 42 onchangetext={(text) => setusername(text)} 43 autocapitalize={'none'} 44 keyboardtype={'email address'} 45 /> 46 \<textinput 47 style={styles form input} 48 value={password} 49 placeholder={'password'} 50 securetextentry 51 onchangetext={(text) => setpassword(text)} 52 /> 53 \<touchableopacity onpress={() => douserlogin()}> 54 \<view style={styles button}> 55 \<text style={styles button label}>{'sign in'}\</text> 56 \</view> 57 \</touchableopacity> 58 \</view> 59 \<view style={styles login social}> 60 \<view style={styles login social separator}> 61 \<view style={styles login social separator line} /> 62 \<text style={styles login social separator text}>{'or'}\</text> 63 \<view style={styles login social separator line} /> 64 \</view> 65 \<view style={styles login social buttons}> 66 \<touchableopacity> 67 \<view 68 style={\[ 69 styles login social button, 70 styles login social facebook, 71 ]}> 72 \<image 73 style={styles login social icon} 74 source={require(' /assets/icon facebook png')} 75 /> 76 \</view> 77 \</touchableopacity> 78 \<touchableopacity> 79 \<view style={styles login social button}> 80 \<image 81 style={styles login social icon} 82 source={require(' /assets/icon google png')} 83 /> 84 \</view> 85 \</touchableopacity> 86 \<touchableopacity> 87 \<view style={styles login social button}> 88 \<image 89 style={styles login social icon} 90 source={require(' /assets/icon apple png')} 91 /> 92 \</view> 93 \</touchableopacity> 94 \</view> 95 \</view> 96 <> 97 \<touchableopacity onpress={() => navigation navigate('sign up')}> 98 \<text style={styles login footer text}> 99 {"don't have an account? "} 100 \<text style={styles login footer link}>{'sign up'}\</text> 101 \</text> 102 \</touchableopacity> 103 \</> 104 \</view> 105 ); 106 }; 107&#x9; 108 // userlogin tsx 1 // 2&#x9; 3 export const userlogin fc<{}> = ({}) reactelement => { 4 const navigation = usenavigation(); 5&#x9; 6 const \[username, setusername] = usestate(''); 7 const \[password, setpassword] = usestate(''); 8&#x9; 9 const douserlogin = async function () promise\<boolean> { 10 // note that these values come from state variables that we've declared before 11 const usernamevalue string = username; 12 const passwordvalue string = password; 13 return await parse user login(usernamevalue, passwordvalue) 14 then(async (loggedinuser parse user) => { 15 // login returns the corresponding parseuser object 16 alert alert( 17 'success!', 18 `user ${loggedinuser get('username')} has successfully signed in!`, 19 ); 20 // to verify that this is in fact the current user, currentasync can be used 21 const currentuser parse user = await parse user currentasync(); 22 console log(loggedinuser === currentuser); 23 // navigation navigate takes the user to the screen named after the one 24 // passed as parameter 25 navigation navigate('home'); 26 return true; 27 }) 28 catch((error object) => { 29 // error can be caused by wrong parameters or lack of internet connection 30 alert alert('error!', error message); 31 return false; 32 }); 33 }; 34&#x9; 35 return ( 36 \<view style={styles login wrapper}> 37 \<view style={styles form}> 38 \<textinput 39 style={styles form input} 40 value={username} 41 placeholder={'username'} 42 onchangetext={(text) => setusername(text)} 43 autocapitalize={'none'} 44 keyboardtype={'email address'} 45 /> 46 \<textinput 47 style={styles form input} 48 value={password} 49 placeholder={'password'} 50 securetextentry 51 onchangetext={(text) => setpassword(text)} 52 /> 53 \<touchableopacity onpress={() => douserlogin()}> 54 \<view style={styles button}> 55 \<text style={styles button label}>{'sign in'}\</text> 56 \</view> 57 \</touchableopacity> 58 \</view> 59 \<view style={styles login social}> 60 \<view style={styles login social separator}> 61 \<view style={styles login social separator line} /> 62 \<text style={styles login social separator text}>{'or'}\</text> 63 \<view style={styles login social separator line} /> 64 \</view> 65 \<view style={styles login social buttons}> 66 \<touchableopacity> 67 \<view 68 style={\[ 69 styles login social button, 70 styles login social facebook, 71 ]}> 72 \<image 73 style={styles login social icon} 74 source={require(' /assets/icon facebook png')} 75 /> 76 \</view> 77 \</touchableopacity> 78 \<touchableopacity> 79 \<view style={styles login social button}> 80 \<image 81 style={styles login social icon} 82 source={require(' /assets/icon google png')} 83 /> 84 \</view> 85 \</touchableopacity> 86 \<touchableopacity> 87 \<view style={styles login social button}> 88 \<image 89 style={styles login social icon} 90 source={require(' /assets/icon apple png')} 91 /> 92 \</view> 93 \</touchableopacity> 94 \</view> 95 \</view> 96 <> 97 \<touchableopacity onpress={() => navigation navigate('sign up')}> 98 \<text style={styles login footer text}> 99 {"don't have an account? "} 100 \<text style={styles login footer link}>{'sign up'}\</text> 101 \</text> 102 \</touchableopacity> 103 \</> 104 \</view> 105 ); 106 }; 107&#x9; 108 // userregistration js 1 export const userregistration = () => { 2 const navigation = usenavigation(); 3&#x9; 4 const \[username, setusername] = usestate(''); 5 const \[password, setpassword] = usestate(''); 6&#x9; 7 const dousersignup = async function () { 8 // note that these values come from state variables that we've declared before 9 const usernamevalue = username; 10 const passwordvalue = password; 11 // since the signup method returns a promise, we need to call it using await 12 return await parse user signup(usernamevalue, passwordvalue) 13 then((createduser) => { 14 // parse user signup returns the already created parseuser object if successful 15 alert alert( 16 'success!', 17 `user ${createduser get('username')} was successfully created!`, 18 ); 19 // navigation navigate takes the user to the screen named after the one 20 // passed as parameter 21 navigation navigate('home'); 22 return true; 23 }) 24 catch((error) => { 25 // signup can fail if any parameter is blank or failed an uniqueness check on the server 26 alert alert('error!', error message); 27 return false; 28 }); 29 }; 30&#x9; 31 return ( 32 \<view style={styles login wrapper}> 33 \<view style={styles form}> 34 \<textinput 35 style={styles form input} 36 value={username} 37 placeholder={'username'} 38 onchangetext={(text) => setusername(text)} 39 autocapitalize={'none'} 40 keyboardtype={'email address'} 41 /> 42 \<textinput 43 style={styles form input} 44 value={password} 45 placeholder={'password'} 46 securetextentry 47 onchangetext={(text) => setpassword(text)} 48 /> 49 \<touchableopacity onpress={() => dousersignup()}> 50 \<view style={styles button}> 51 \<text style={styles button label}>{'sign up'}\</text> 52 \</view> 53 \</touchableopacity> 54 \</view> 55 \<view style={styles login social}> 56 \<view style={styles login social separator}> 57 \<view style={styles login social separator line} /> 58 \<text style={styles login social separator text}>{'or'}\</text> 59 \<view style={styles login social separator line} /> 60 \</view> 61 \<view style={styles login social buttons}> 62 \<touchableopacity> 63 \<view 64 style={\[ 65 styles login social button, 66 styles login social facebook, 67 ]}> 68 \<image 69 style={styles login social icon} 70 source={require(' /assets/icon facebook png')} 71 /> 72 \</view> 73 \</touchableopacity> 74 \<touchableopacity> 75 \<view style={styles login social button}> 76 \<image 77 style={styles login social icon} 78 source={require(' /assets/icon google png')} 79 /> 80 \</view> 81 \</touchableopacity> 82 \<touchableopacity> 83 \<view style={styles login social button}> 84 \<image 85 style={styles login social icon} 86 source={require(' /assets/icon apple png')} 87 /> 88 \</view> 89 \</touchableopacity> 90 \</view> 91 \</view> 92 <> 93 \<touchableopacity onpress={() => navigation navigate('login')}> 94 \<text style={styles login footer text}> 95 {'already have an account? '} 96 \<text style={styles login footer link}>{'log in'}\</text> 97 \</text> 98 \</touchableopacity> 99 \</> 100 \</view> 101 ); 102 }; 103&#x9; 104 // userregistration tsx 1 // 2&#x9; 3 export const userregistration fc<{}> = ({}) reactelement => { 4 const navigation = usenavigation(); 5&#x9; 6 const \[username, setusername] = usestate(''); 7 const \[password, setpassword] = usestate(''); 8&#x9; 9 const dousersignup = async function () promise\<boolean> { 10 // note that these values come from state variables that we've declared before 11 const usernamevalue string = username; 12 const passwordvalue string = password; 13 // since the signup method returns a promise, we need to call it using await 14 return await parse user signup(usernamevalue, passwordvalue) 15 then((createduser parse user) => { 16 // parse user signup returns the already created parseuser object if successful 17 alert alert( 18 'success!', 19 `user ${createduser get('username')} was successfully created!`, 20 ); 21 // navigation navigate takes the user to the screen named after the one 22 // passed as parameter 23 navigation navigate('home'); 24 return true; 25 }) 26 catch((error object) => { 27 // signup can fail if any parameter is blank or failed an uniqueness check on the server 28 alert alert('error!', error message); 29 return false; 30 }); 31 }; 32&#x9; 33 return ( 34 \<view style={styles login wrapper}> 35 \<view style={styles form}> 36 \<textinput 37 style={styles form input} 38 value={username} 39 placeholder={'username'} 40 onchangetext={(text) => setusername(text)} 41 autocapitalize={'none'} 42 keyboardtype={'email address'} 43 /> 44 \<textinput 45 style={styles form input} 46 value={password} 47 placeholder={'password'} 48 securetextentry 49 onchangetext={(text) => setpassword(text)} 50 /> 51 \<touchableopacity onpress={() => dousersignup()}> 52 \<view style={styles button}> 53 \<text style={styles button label}>{'sign up'}\</text> 54 \</view> 55 \</touchableopacity> 56 \</view> 57 \<view style={styles login social}> 58 \<view style={styles login social separator}> 59 \<view style={styles login social separator line} /> 60 \<text style={styles login social separator text}>{'or'}\</text> 61 \<view style={styles login social separator line} /> 62 \</view> 63 \<view style={styles login social buttons}> 64 \<touchableopacity> 65 \<view 66 style={\[ 67 styles login social button, 68 styles login social facebook, 69 ]}> 70 \<image 71 style={styles login social icon} 72 source={require(' /assets/icon facebook png')} 73 /> 74 \</view> 75 \</touchableopacity> 76 \<touchableopacity> 77 \<view style={styles login social button}> 78 \<image 79 style={styles login social icon} 80 source={require(' /assets/icon google png')} 81 /> 82 \</view> 83 \</touchableopacity> 84 \<touchableopacity> 85 \<view style={styles login social button}> 86 \<image 87 style={styles login social icon} 88 source={require(' /assets/icon apple png')} 89 /> 90 \</view> 91 \</touchableopacity> 92 \</view> 93 \</view> 94 <> 95 \<touchableopacity onpress={() => navigation navigate('login')}> 96 \<text style={styles login footer text}> 97 {'already have an account? '} 98 \<text style={styles login footer link}>{'log in'}\</text> 99 \</text> 100 \</touchableopacity> 101 \</> 102 \</view> 103 ); 104 }; 105&#x9; 106 // le tue schermate di accesso e registrazione ora dovrebbero apparire così conclusione alla fine di questa guida, hai imparato come accedere e disconnettere gli utenti di parse su react native e come navigare gli utenti attraverso la tua applicazione usando react navigation react navigation nella prossima guida, ti mostreremo come eseguire query utili sugli utenti