How to Build a Backend for Xamarin?

introduction in this tutorial, you will learn how to build a backend for your xamarin mobile apps using back4app’s powerful features we will rely on the back4app rest api , graphql , and other web api options instead of using a dedicated sdk this approach keeps your mobile client lightweight and flexible, enabling you to connect to your data through simple http calls we will cover creating database models, applying security, handling authentication, and performing file operations by following these steps, you’ll see how to build a backend for xamarin quickly and securely you’ll also explore scheduling automated tasks and integrating webhooks to extend your xamarin app’s functionality, so you can focus on coding your ui instead of juggling server configurations once you’ve completed this guide, you will have a reusable template for building mobile apps that rely on back4app for their backend you will also understand how to apply access control lists (acls), write cloud code (if needed), and incorporate advanced workflows like live queries or cloud jobs in your final solution prerequisites to get the most out of this tutorial, make sure you have a back4app account sign up for free here https //www back4app com/ a new back4app project getting started with back4app https //www back4app com/docs/get started/new parse app xamarin development environment (visual studio or visual studio for mac) xamarin installation docs https //docs microsoft com/en us/xamarin/get started/installation/ basic knowledge of c# and xamarin (including how to make web api requests from a public class in c#) with these prerequisites ready, you’ll be set to follow along and connect your xamarin project to back4app step 1 – creating a new project on back4app and connecting create a back4app project in your back4app dashboard this is the foundation for your backend name your project (for example, “xamarin backend tutorial”) locate your app keys by going to the app’s “security & keys” section you’ll see the rest, graphql, or other keys you might use when making requests from your mobile client configure your xamarin project to make http requests instead of a parse sdk, you’ll use either httpclient , or any network library you prefer, to call your back4app app’s rest or graphql endpoints for example, you can store your application id and rest api key in a secure place or in a constants file public class back4appconstants { public const string appid = "your application id"; public const string restapikey = "your rest api key"; public const string serverurl = "https //parseapi back4app com"; } when calling the web api , always include these credentials in your request headers this ensures your requests are routed to the correct app with the required authorization step 2 – setting up the database 1\ creating a data model use the back4app dashboard to define your classes or let them be created dynamically on first request for instance, if you want a todo class, you can create it in the database section or on the fly via rest api calls curl x post \\ h "x parse application id your application id" \\ h "x parse rest api key your rest api key" \\ h "content type application/json" \\ d '{"title" "buy groceries", "iscompleted" false}' \\ https //parseapi back4app com/classes/todo 2\ creating a data model using the ai agent back4app provides an ai agent that can generate complete class structures open the ai agent in your back4app project describe your model (e g , “please create a new class named ‘todo’ with title and iscompleted fields ”) confirm to generate the schema automatically 3\ reading and writing data (rest) within your xamarin project, you can write a public class (for example, restclient ) that handles all requests to back4app using system net http; using system text; using newtonsoft json; public class restclient { private readonly httpclient client; public restclient() { client = new httpclient(); client defaultrequestheaders add("x parse application id", back4appconstants appid); client defaultrequestheaders add("x parse rest api key", back4appconstants restapikey); } public async task createtodoasync(string title, bool iscompleted) { var newtodo = new { title = title, iscompleted = iscompleted }; var content = new stringcontent(jsonconvert serializeobject(newtodo), encoding utf8, "application/json"); var response = await client postasync($"{back4appconstants serverurl}/classes/todo", content); // handle the response } public async task\<list\<todo>> gettodosasync() { var response = await client getasync($"{back4appconstants serverurl}/classes/todo"); var jsonstring = await response content readasstringasync(); // parse json into a c# model (todo) // return the result // return new list\<todo>(); // placeholder } } public class todo { public string objectid { get; set; } public string title { get; set; } public bool iscompleted { get; set; } } 4\ reading and writing data (graphql) for graphql queries, you can send requests to the back4app graphql endpoint curl x post \\ h "content type application/json" \\ h "x parse application id your application id" \\ h "x parse master key your master key" \\ \ data '{"query" "mutation { createtodo(input {fields {title \\"wash the car\\" iscompleted\ false}}){ todo{ objectid title }}}"}' \\ https //parseapi back4app com/graphql similarly, from xamarin, you could post a json body with your graphql string to https //parseapi back4app com/graphql 5\ working with live queries (optional) although you are using web api calls rather than the parse sdk, you can still enable live queries if you want real time data updates you would use specialized connections (websockets) to subscribe to class changes enable live queries from your app’s server settings in back4app, then use a compatible client library in xamarin, if available alternatively, you can build your own websocket solution or rely on polls if real time support is optional for your app step 3 – applying security with acls and clps 1\ overview of acls and clps back4app security includes class level permissions (clps) and access control lists (acls) clps define which users or roles can read/write to an entire class acls add per object security combine them to make sure only authorized users can manipulate your data 2\ setting up class level permissions open the database section on back4app select your class (like todo) go to class level permissions to set read/write rules you might only allow authenticated users to read or write this ensures that your mobile client must log in before reading data step 4 – writing cloud code functions 1\ why cloud code cloud code allows you to run custom server side logic you can create business rules, validations, or triggers that run when data changes this reduces the risk of tampering since logic runs outside the mobile client 2\ example function and triggers below is a simplified sample of a cloud function in the main js file parse cloud define('helloxamarin', async (request) => { return 'hello from xamarin cloud code!'; }); parse cloud beforesave('todo', (request) => { const todo = request object; if (!todo get('title')) { throw 'title is required'; } }); 3\ deployment to deploy, you can use the back4app cli or the cloud code section in your dashboard once deployed, you can call your functions from xamarin via rest curl x post \\ h "x parse application id your app id" \\ h "x parse rest api key your rest api key" \\ h "content type application/json" \\ d '{}' \\ https //parseapi back4app com/functions/helloxamarin 4\ npm modules if you need extra libraries, install them via npm in your cloud code project folder after that, require them in your main js this approach is useful for calling third party apis from the server side step 5 – configuring authentication 1\ enable user authentication in back4app, the user class manages user credentials under app settings , you can enable user authentication, email verification, and password reset settings 2\ user sign up / log in (rest) from your xamarin project, you could write c# methods to handle sign up and login public async task signupuserasync(string username, string password, string email) { var user = new { username = username, password = password, email = email }; var content = new stringcontent(jsonconvert serializeobject(user), encoding utf8, "application/json"); var response = await client postasync($"{back4appconstants serverurl}/users", content); // parse response } public async task loginuserasync(string username, string password) { var loginendpoint = $"{back4appconstants serverurl}/login?username={username}\&password={password}"; var response = await client getasync(loginendpoint); // parse response } you can then store session tokens client side for future requests 3\ social login to integrate social logins (e g , google, facebook), consult the back4app social login docs https //www back4app com/docs/platform/sign in with apple each provider has its own oauth flow, which you can handle from your mobile client then, pass the returned tokens to back4app step 6 – handling file storage 1\ setting up file storage files can be uploaded by sending a post request with the file data in the body for instance, to store an image from your xamarin app, read the image into a byte array, then send curl x post \\ h "x parse application id your app id" \\ h "x parse rest api key your rest api key" \\ h "content type image/png" \\ \ data binary "@local image png" \\ https //parseapi back4app com/files/myimage png 2\ example upload with c# public async task\<string> uploadfileasync(byte\[] filedata, string filename) { var filecontent = new bytearraycontent(filedata); filecontent headers contenttype = new system net http headers mediatypeheadervalue("image/png"); var response = await client postasync($"{back4appconstants serverurl}/files/{filename}", filecontent); var jsonresponse = await response content readasstringasync(); // parse the response to get file url return "file url from response"; } 3\ security considerations to secure file uploads, go to your back4app server settings and adjust the file permissions for instance, you can only allow authenticated users to upload step 7 – email verification and password reset 1\ overview email verification ensures that users own the email they registered with password reset links allow them to regain access if they forget their passwords 2\ back4app dashboard configuration enable email verification under email settings edit the password reset template and set the “from” address you can also customize the email content to match your branding 3\ implementation once enabled, if a user signs up with an email, they will get a verification link password reset calls are made to the same base api with the user’s email to trigger a reset email step 8 – scheduling tasks with cloud jobs 1\ what cloud jobs do cloud jobs let you schedule routine tasks, such as cleaning old data or sending daily digest emails, all from the back4app platform 2\ example parse cloud job('cleanupoldtodos', async (request) => { const todo = parse object extend('todo'); const query = new parse query(todo); const now = new date(); const thirty days ago = new date(now 30 24 60 60 1000); query lessthan('createdat', thirty days ago); const oldtodos = await query find({ usemasterkey true }); await parse object destroyall(oldtodos, { usemasterkey true }); return `deleted ${oldtodos length} old items `; }); deploy the cloud code, then schedule the job under app settings > server settings > background jobs step 9 – integrating webhooks define a webhook on back4app by navigating to more > webhooks and clicking “add webhook ” provide the endpoint, such as https //your service com/webhook endpoint choose triggers, like “new object in todo class ” webhooks can notify third party services, so your xamarin app can remain lightweight while external systems handle extra logic or notifications step 10 – exploring the back4app admin panel the back4app admin app is a user friendly way to handle crud operations without writing queries enable it in app dashboard > more > admin app create an admin user, choose a subdomain, and log in this admin app is ideal for non technical team members who need to manage data but shouldn’t have direct database access conclusion you have just seen how to build a backend for xamarin using back4app apis you created secure classes, added clps and acls , handled authentication, and explored file uploads, scheduling tasks, and integrating with external services this approach ensures your mobile apps stay fast and flexible while leveraging the power of a hosted database and cloud environment next steps expand your xamarin application to handle more complex logic, caching, or advanced roles and permissions dive into advanced features , such as push notifications, or integrate real time data with live queries if you need collaborative updates visit the official back4app documentation for deeper guides on security, performance, and debugging create real world solutions by mixing third party apis (payment gateways, analytics, social media) with your back4app backend this combination can enhance your mobile client’s functionality and keep your code organized