Flutter 中解析数据类型的使用指南

本指南介绍了flutter中的parse数据类型，使用来自 main dart 文件的示例。parse数据存储围绕parseobject展开，它包含json兼容数据的键值对，使其无模式。这意味着您可以存储任何数据，而无需提前定义模式。 您可以设置任何您想要的键值对，我们的后端将存储它们。 例如，假设您正在跟踪游戏的高分。一个单一的parse对象可以包含： 我们建议您 nameyourclasseslikethis 和 nameyourkeyslikethis 以增强代码的可读性和可维护性。 理解我们的应用程序 为了更好地理解back4app，让我们探索flutter应用程序中parse操作的代码示例，以及主要支持的数据类型。本指南不会解释任何flutter应用程序代码，因为主要关注点是将parse与flutter结合使用。 先决条件 要完成本教程，您需要： android studio https //developer android com/studio 或 安装 vs code （带有 插件 dart 和 flutter） 一个应用 创建 在 back4app 上 注意 请遵循 新解析应用教程 以了解如何在 back4app 上创建解析应用。 一个连接到 back4app 的 flutter 应用。 注意 请遵循 在 flutter 项目中安装 parse sdk 以创建一个连接到 back4app 的 flutter 项目。 一个运行 android 或 ios 的设备（或虚拟设备）。 1 使用 parse 对象 每个 parseobject 都有一个类名（例如，gamepoint），用于区分不同的数据类型。以下是如何创建和保存一个新的 parse 对象及其数据类型 字符串 , 整数 , 和 布尔值 final gamepoint = parseobject('gamepoint') set('score', 1337) set('playername', 'sean plott') set('cheatmode', false); await gamepoint save(); 查询新的 parse 对象并检索数据类型： final querybuilder\<parseobject> querygamepoints = querybuilder\<parseobject>(parseobject('gamepoint')); final parseresponse response = await querygamepoints query(); if (response success && response results != null) { for (var gamepoint in response results!) { final score = gamepoint get\<int>('score'); final playername = gamepoint get\<string>('playername'); final cheatmode = gamepoint get\<bool>('cheatmode'); } 2 计数器 您可以使用 set() 方法在 parseobject 中递增或递减整数字段。 然而，这并不有效，如果多个客户端试图更新同一个计数器，可能会导致问题。parse 提供了两种方法，可以自动递增和递减任何数字字段，以存储计数器类型的数据。 setincrement() setdecrement() 更新以递增一个计数器 int 值将被写为： final gamepoint = parseobject('gamepoint') objectid = 'yourobjectid' setincrement('intfield', 1); await gamepoint save(); 要递减： final gamepoint = parseobject('gamepoint') objectid = 'yourobjectid' setdecrement('intfield', 1); await gamepoint save(); 使用 setincrement() 和 setdecrement() 与 save() 调用允许您在更大的保存操作中更新一个值，在该操作中您可能会修改多个字段。这更好地避免了额外的网络请求。 3 列表 parse 提供了处理列表数据的方法，包括 setadd , setaddunique , setremove , 及其各自的 all 版本。 列表 \["a","b","c"] 3 1 setadd final gamepoint = parseobject('gamepoint') objectid = 'yourobjectid' setadd('liststringfield', 'd'); await gamepoint save(); 结果 \["a","b","c","d"] 3 2 setaddall final gamepoint = parseobject('gamepoint') objectid = 'yourobjectid' setaddall('liststringfield', \['e','f']); await gamepoint save(); 结果 \["a","b","c","d","e","f"] setaddall 不会添加重复元素，如果列表已经包含它们。 3 3 setaddunique final gamepoint = parseobject('gamepoint') objectid = 'yourobjectid' setaddunique('liststringfield', \['a', 'e', 'g']); await gamepoint save(); 结果 \["a","b","c","d","e","f","g"] 3 4 setremove final gamepoint = parseobject('gamepoint') objectid = 'yourobjectid' setremove('liststringfield', 'd'); await gamepoint save(); 结果 \["a","b","c","e","f","g"] 4 从 parseobject 中移除字段 您可以通过使用 unset 操作从对象中删除单个字段： final gamepoint = parseobject('gamepoint') objectid = 'yourobjectid' unset("liststringfield"); 5 文件 parsefile 让您在云中存储和检索应用程序文件。 下面是将本地图像文件上传到 back4app 的基本示例： // create parsefile object final parsefile = parsefile(file(image path)); final response = await parsefile save(); if (response success) { print('file uploaded successfully ${parsefile url}'); // save this file in an object final gamepoint = parseobject('gamepoint') set('title', 'post with an image') set('imagefile', parsefile); // saving the file as a field final postresponse = await gamepoint save(); } 此代码片段演示了如何检索图像文件： final query = querybuilder\<parseobject>(parseobject('gamepoint')); final response = await query query(); if (response success && response results != null) { for (var gamepoint in response results!) { parsefilebase? varfile = gamepoint get\<parsefilebase>('file'); if (varfile != null) { final fileurl = varfile url; print('game title image url $fileurl'); } else { print('no file found for this object '); } } } 从 parse server 5 2 3 开始，存在可能导致上传文件时出现错误的重大更改。请遵循 此指南 https //www back4app com/docs/platform/parse server version#o cil 来修复您可能遇到的任何上传问题。 稍后的指南将进一步讨论并展示如何 使用 parse 保存和显示文件 https //www back4app com/docs/flutter/parse sdk/flutter save file 6 地理坐标点 parse 允许您将现实世界的纬度和经度坐标与其 geopoint 数据类型的对象关联。将 parsegeopoint 添加到 parseobject 将使查询能够考虑对象与参考点的接近程度。 示例 // request permission here and get the current location the `position` object // create geopoint object final geopoint = parsegeopoint(latitude position latitude, longitude position longitude); // create an object with the geopoint final gamepoint = parseobject('gamepoint') set('name', 'current location') set('location', geopoint); // save the geopoint in a field final response = await gamepoint save(); 您可以在这个 main dart https //github com/templates back4app/flutter datatypes/blob/18c4c372eb49c1cd950eeaac355564134a5e70c4/lib/src/main dart 文件中找到保存地理坐标点位置的独立示例。 完整应用示例 此示例演示如何： 创建、删除和更新一个 gamepoint parse 对象。 处理各种数据类型，包括字符串、双精度浮点数、布尔值、文件、地理点、列表和日期。 在 ios 上，您需要授予模拟器必要的访问权限。 ios 提供了关于受保护资源的开发者指南。该指南中的示例应用程序将需要 位置 https //developer apple com/documentation/bundleresources/information property list/nslocationwheninuseusagedescription 和 照片 https //developer apple com/documentation/bundleresources/information property list/nsphotolibraryaddusagedescription 权限键才能正常工作。将这些键添加到 info plist 文件中，该文件位于 /ios/runner/info plist 如果您在网页上运行 flutter 应用程序，可以跳过上述步骤： import 'dart\ async'; import 'package\ flutter/material dart'; import 'package\ parse server sdk flutter/parse server sdk flutter dart'; import 'package\ image picker/image picker dart'; import 'package\ flutter/foundation dart'; import 'dart\ io'; void main() async { widgetsflutterbinding ensureinitialized(); const keyparseapplicationid = 'your application id'; const keyparseclientkey = 'your client key'; const keyparseserverurl = 'https //parseapi back4app com'; await parse() initialize( keyparseapplicationid, keyparseserverurl, clientkey keyparseclientkey, autosendsessionid true, debug true, ); runapp(const myapp()); } class myapp extends statelesswidget { const myapp({super key}); @override widget build(buildcontext context) { return materialapp( title 'datatypes', theme themedata( primaryswatch colors blue, ), home const myhomepage(), ); } } class myhomepage extends statefulwidget { const myhomepage({super key}); @override myhomepagestate createstate() => myhomepagestate(); } class myhomepagestate extends state\<myhomepage> { final texteditingcontroller stringcontroller = texteditingcontroller(); final texteditingcontroller doublecontroller = texteditingcontroller(); final texteditingcontroller liststringcontroller = texteditingcontroller(); final texteditingcontroller listintcontroller = texteditingcontroller(); final texteditingcontroller pointercontroller = texteditingcontroller(); final texteditingcontroller objectidcontroller = texteditingcontroller(); final texteditingcontroller uniquevaluecontroller = texteditingcontroller(); final texteditingcontroller removevaluecontroller = texteditingcontroller(); bool boolvalue = false; datetime selecteddate = datetime now(); final string responsemessage = ''; xfile? pickedfile; bool isloading = false; @override widget build(buildcontext context) { return scaffold( appbar appbar( title const text('datatypes'), ), body padding( padding const edgeinsets all(16 0), child singlechildscrollview( child column( crossaxisalignment crossaxisalignment start, children \<widget>\[ buildtextfield('string field', stringcontroller), const sizedbox(height 20), buildtextfield('double field', doublecontroller, isnumeric true), const sizedbox(height 20), buildswitch('bool field', boolvalue, (value) { setstate(() { boolvalue = value; }); }), const sizedbox(height 20), textbutton( onpressed () => selectdate(context), child text( 'select date ${ selecteddate tolocal()}' split(' ')\[0]), ), const sizedbox(height 20), buildtextfield( 'list string field (comma separated)', liststringcontroller), const sizedbox(height 20), buildtextfield( 'list int field (comma separated)', listintcontroller), const sizedbox(height 20), buildtextfield('pointer field (object id)', pointercontroller), const sizedbox(height 20), buildimagepicker(), const sizedbox(height 20), elevatedbutton( onpressed savedata, child const text('save'), ), const sizedbox(height 20), elevatedbutton( onpressed () async { await deletedata( objectidcontroller text); // await dummyfunction(); }, child const text('delete'), ), const sizedbox(height 20), buildtextfield( 'object id to delete or update', objectidcontroller), elevatedbutton( onpressed () async { await updatedata( objectidcontroller text); }, child const text('update'), ), const sizedbox(height 20), buildincrementdecrementbuttons(), const sizedbox(height 20), buildlistoperations(), const sizedbox(height 20), text( responsemessage), ], ), ), ), ); } widget buildtextfield(string label, texteditingcontroller controller, {bool isnumeric = false}) { return textfield( controller controller, keyboardtype isnumeric ? textinputtype number textinputtype text, decoration inputdecoration( border const outlineinputborder(), labeltext label, ), ); } widget buildswitch(string label, bool value, function(bool) onchanged) { return switchlisttile( title text(label), value value, onchanged onchanged, ); } widget buildimagepicker() { return gesturedetector( child pickedfile != null ? container( width 250, height 250, decoration boxdecoration(border border all(color colors blue)), child kisweb ? image network(pickedfile! path) image file(file(pickedfile! path)), ) container( width 250, height 250, decoration boxdecoration(border border all(color colors blue)), child const center( child text('click here to pick image from gamepoint')), ), ontap () async { final picker = imagepicker(); xfile? image = (await picker pickimage(source imagesource gallery)); if (image != null) { setstate(() { pickedfile = image; }); } }, ); } widget buildincrementdecrementbuttons() { return row( mainaxisalignment mainaxisalignment spacebetween, children \[ expanded( child elevatedbutton( onpressed () async { await incrementfield( objectidcontroller text); }, child const text('+ double'), ), ), const sizedbox(width 10), // adding some space between buttons expanded( child elevatedbutton( onpressed () async { await decrementfield( objectidcontroller text); }, child const text(' double'), ), ), ], ); } widget buildlistoperations() { return column( children \[ buildtextfield('unique value to add', uniquevaluecontroller), elevatedbutton( onpressed () async { await adduniquetolist( objectidcontroller text, uniquevaluecontroller text); }, child const text('add unique'), ), const sizedbox(height 20), buildtextfield('value to remove', removevaluecontroller), elevatedbutton( onpressed () async { await removefromlist( objectidcontroller text, removevaluecontroller text); }, child const text('remove'), ), ], ); } future\<void> savedata() async { //parse values string stringvalue = stringcontroller text; list\<string> liststringvalue = liststringcontroller text isnotempty ? liststringcontroller text split(',') // split by comma map((e) => e trim()) // remove any surrounding whitespace from each element tolist() \[]; list\<int> listtintvalue = listintcontroller text isnotempty ? listintcontroller text split(',') // split by comma map( (e) => int parse(e trim())) // convert each string to an integer tolist() \[]; double? doublevalue; if ( doublecontroller text isnotempty) { doublevalue = double parse( doublecontroller text); } bool boolvalue = boolvalue; datetime selecteddate = selecteddate; final gamepoint = parseobject('gamepoint') set('bool', boolvalue) set('date', selecteddate); if (stringvalue isnotempty) gamepoint set('string', stringvalue); if (doublevalue != null) gamepoint set('double', doublevalue); if (liststringvalue isnotempty) { gamepoint setaddall('liststring', liststringvalue); } if (listtintvalue isnotempty) gamepoint setaddall('listint', listtintvalue); if ( pointercontroller text isnotempty) { gamepoint set('pointer', parsepointer( pointercontroller text)); } if (pickedfile != null) { setstate(() { isloading = true; }); parsefilebase? parsefile; if (kisweb) { parsefile = parsewebfile(await pickedfile! readasbytes(), name 'file jpg'); } else { parsefile = parsefile(file(pickedfile! path)); } await parsefile save(); gamepoint set('file', parsefile); } var apiresponse = await gamepoint save(); if (apiresponse success && apiresponse results != null) { setstate(() { isloading = false; pickedfile = null; }); scaffoldmessenger of(context) removecurrentsnackbar() showsnackbar(const snackbar( content text( 'file saved successfully on back4app', style textstyle(color colors white), ), duration duration(seconds 3), backgroundcolor colors blue, )); } else { print("this is your request error ${apiresponse error}"); } } future\<void> updatedata(string objectid) async { final gamepoint = parseobject('gamepoint') objectid = objectid; // update fields with new values if ( stringcontroller text isnotempty) { gamepoint set('string', stringcontroller text); } if ( doublecontroller text isnotempty) { gamepoint set('double', double parse( doublecontroller text)); } gamepoint set('bool', boolvalue); gamepoint set('date', selecteddate); if ( liststringcontroller text isnotempty) { list\<string> liststringvalue = liststringcontroller text split(',') map((e) => e trim()) tolist(); gamepoint setaddall('liststring', liststringvalue); } if ( listintcontroller text isnotempty) { list\<int> listintvalue = listintcontroller text split(',') map((e) => int parse(e trim())) tolist(); gamepoint setaddunique('listint', listintvalue); } if ( pointercontroller text isnotempty) { gamepoint set('pointer', parsepointer( pointercontroller text)); } if (pickedfile != null) { parsefilebase? parsefile; if (kisweb) { parsefile = parsewebfile(await pickedfile! readasbytes(), name 'file jpg'); } else { parsefile = parsefile(file(pickedfile! path)); } await parsefile save(); gamepoint set('file', parsefile); } // save the updated object var response = await gamepoint save(); if (response success) { scaffoldmessenger of(context) showsnackbar( const snackbar(content text('data updated successfully!')), ); } else { scaffoldmessenger of(context) showsnackbar( snackbar( content text('error updating data ${response error! message}')), ); } } future\<void> incrementfield(string objectid) async { final gamepoint = parseobject('gamepoint') objectid = objectid setincrement('double', 1); await gamepoint save(); } future\<void> decrementfield(string objectid) async { final gamepoint = parseobject('gamepoint') objectid = objectid setdecrement('double', 1); await gamepoint save(); } future\<void> adduniquetolist(string objectid, string value) async { final gamepoint = parseobject('gamepoint') objectid = objectid setaddunique('liststring', value); await gamepoint save(); } future\<void> removefromlist(string objectid, string value) async { final gamepoint = parseobject('gamepoint') objectid = objectid setremove('liststring', value); await gamepoint save(); } future\<void> selectdate(buildcontext context) async { final datetime? picked = await showdatepicker( context context, initialdate selecteddate, firstdate datetime(2000), lastdate datetime(2101), ); if (picked != null && picked != selecteddate) { setstate(() { selecteddate = picked; }); } } future\<void> deletedata(string objectid) async { // delete data logic final parseobject = parseobject('gamepoint') objectid = objectid unset("liststring"); await parseobject save(); } // convert pointer field to a suitable format parseobject parsepointer(string objectid) { // there should be an existing game class with objects final pointer = parseobject('game') objectid = objectid; return pointer; } } 这段代码在flutter中初始化parse sdk，设置主应用程序，并显示一个带有标题的简单主页。 结论 在本指南中，您了解了parseobjects和parse提供的各种数据类型。您还学习了如何处理将数据类型保存到和从您的back4app后端检索的操作。