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How to cancel requests using Retrofit in Kotlin Android

How to cancel requests using Retrofit in Kotlin Android.

Here's a step-by-step tutorial on how to cancel requests using Retrofit in Kotlin for Android.

Step 1: Setup Retrofit​

First, you need to set up Retrofit in your Android project. You can add the Retrofit dependency to your build.gradle file:

implementation 'com.squareup.retrofit2:retrofit:2.9.0'
implementation 'com.squareup.retrofit2:converter-gson:2.9.0'

Step 2: Create the API Interface​

Next, create an interface that defines your API endpoints and request methods. For example, let's create an interface called ApiService:

interface ApiService {
    @GET("users")
    fun getUsers(): Call<List<User>>
}

Step 3: Create a Retrofit Instance​

Create a singleton instance of Retrofit in your project. You can create a class called ApiClient:

object ApiClient {
    private const val BASE_URL = "https://api.example.com/"
    private var retrofit: Retrofit? = null

    fun getClient(): Retrofit {
        if (retrofit == null) {
            retrofit = Retrofit.Builder()
                .baseUrl(BASE_URL)
                .addConverterFactory(GsonConverterFactory.create())
                .build()
        }
        return retrofit!!
    }
}

Step 4: Make API Requests​

To make API requests, you can create a function that uses the Retrofit instance and the API interface. For example, let's create a function that fetches a list of users:

fun fetchUsers() {
    val apiService = ApiClient.getClient().create(ApiService::class.java)
    val call = apiService.getUsers()

    call.enqueue(object : Callback<List<User>> {
        override fun onResponse(call: Call<List<User>>, response: Response<List<User>>) {
            if (response.isSuccessful) {
                val users = response.body()
                // Handle the response
            } else {
                // Handle error
            }
        }

        override fun onFailure(call: Call<List<User>>, t: Throwable) {
            // Handle failure
        }
    })
}

Step 5: Cancel Requests​

To cancel a request, you need to keep a reference to the Call object returned by Retrofit. You can then call the cancel() method on the Call object to cancel the request. Here's an example:

private var call: Call<List<User>>? = null

fun fetchUsers() {
    val apiService = ApiClient.getClient().create(ApiService::class.java)
    call = apiService.getUsers()

    call?.enqueue(object : Callback<List<User>> {
        override fun onResponse(call: Call<List<User>>, response: Response<List<User>>) {
            if (response.isSuccessful) {
                val users = response.body()
                // Handle the response
            } else {
                // Handle error
            }
        }

        override fun onFailure(call: Call<List<User>>, t: Throwable) {
            // Handle failure
        }
    })
}

fun cancelRequest() {
    call?.cancel()
}

In this example, the fetchUsers() function saves the Call object to the call variable. The cancelRequest() function can be called to cancel the request by calling the cancel() method on the call variable.

That's it! You now know how to cancel requests using Retrofit in Kotlin for Android.