Joon

Android

Kotlin

Activity Result API: RegisterForActivityResult

Almost every Android developers have tried passing data and getting response between two activities. Before Result API released, we passed data on startActivityForResult and got responses on onActivityResult which is easy to nested and complicated as project goes by. Unlike onActivityResult, ActivityResultCallback of Result API get responses at each ActivityResultLauncher.

Let’s Dive into Code🌊

First of all, don’t forget to add this to your build.gradle.

implementation 'androidx.activity:activity-ktx:1.2.0'
implementation 'androidx.fragment:fragment-ktx:1.3.0'

registerForActivityResult() takes an ActivityResultContract and an ActivityResultCallback and returns an ActivityResultLauncher which you’ll use to launch the other activity. An ActivityResultContract defines the input type needed to produce a result along with the output type of the result.

class MainActivity : AppCompatActivity() {

    //'getContent' is an 'ActivityResultLauncher'
    val getContent = registerForActivityResult(ActivityResultContracts.GetContent()) { uri: Uri? ->
        // 'ActivityResultCallback': Handle the returned Uri    
    }

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)

        selectButton.setOnClickListener {
            // Pass in the mime type you'd like to allow the user to select
            // as the input
            getContent.launch("image/*")
            // This launch Image folder to get image uri
        }
    }
}

Internal Code😯

public static class GetContent extends ActivityResultContract<String, Uri> {

    @CallSuper
    @NonNull
    @Override
    public Intent createIntent(@NonNull Context context, @NonNull String input) {
        return new Intent(Intent.ACTION_GET_CONTENT)
                .addCategory(Intent.CATEGORY_OPENABLE)
                .setType(input);
    }

    @Nullable
    @Override
    public final SynchronousResult<Uri> getSynchronousResult(@NonNull Context context,
            @NonNull String input) {
        return null;
    }

    @Nullable
    @Override
    public final Uri parseResult(int resultCode, @Nullable Intent intent) {
        if (intent == null || resultCode != Activity.RESULT_OK) return null;
        return intent.getData();
    }
}

This is specific code of GetContent. createIntent() takes a Context and the input and constructs the Intent that will be used with startActivityForResult(). parseResult() produces the output from the given resultCode and the Intent. It still use internally resultCode, data of onActivityResult we used before.

Default Contracts. Just use it!🥴

We’ve looked at GetContent as a Contract. There are some standard activity call contracts, as provided by android.

CreateDocument
GetContent
GetMultipleContents
OpenDocument
OpenDocumentTree
OpenMultipleDocuments
PickContact
RequestMultiplePermissions
RequestPermission
StartActivityForResult
StartIntentSenderForResult
TakePicture
TakePicturePreview
TakeVideo

see detail description

Creating a Custom Contract📝

class PickRingtone : ActivityResultContract<Int, Uri?>() {
    override fun createIntent(context: Context, ringtoneType: Int) =
        Intent(RingtoneManager.ACTION_RINGTONE_PICKER).apply {
            putExtra(RingtoneManager.EXTRA_RINGTONE_TYPE, ringtoneType)
        }

    override fun parseResult(resultCode: Int, result: Intent?) : Uri? {
        if (resultCode != Activity.RESULT_OK) {
            return null
        }
        return result?.getParcelableExtra(RingtoneManager.EXTRA_RINGTONE_PICKED_URI)
    }
}

class MainActivity : AppCompatActivity() {

    val getRington = registerForActivityResult(PickRingtone()) {
        //handle the returned uri
    }

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)

        btn.setOnClickListener {
            getRington.launch(1)
        }
    }
}

If there’s a mistake, always welcome your opinion!

android 4
kotlin 2
progressBar 1
compose 1
editText 1

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