registerForActivityResult 使用用途是監聽Activity結果。
以下是使用樣例
//需要傳遞Request用于解析Intent和解析上個Activity返回的結果
val launchdata = registerForActivityResult<PickVisualMediaRequest, Uri?>(ActivityResultContracts.PickVisualMedia()) {println("it $it")
}
//傳入啟動的Activity信息，來啟動Activity
launchdata.launch(PickVisualMediaRequest(mediaType = ActivityResultContracts.PickVisualMedia.ImageOnly))
實現原理分析：
首先四注冊流程
//其中mActivityResultRegistry是final變量
public final <I, O> ActivityResultLauncher<I> registerForActivityResult(@NonNull ActivityResultContract<I, O> contract,@NonNull ActivityResultCallback<O> callback) {return registerForActivityResult(contract, mActivityResultRegistry, callback);
}
public final <I, O> ActivityResultLauncher<I> register(@NonNull final String key,@NonNull final LifecycleOwner lifecycleOwner,@NonNull final ActivityResultContract<I, O> contract,@NonNull final ActivityResultCallback<O> callback) {Lifecycle lifecycle = lifecycleOwner.getLifecycle();if (lifecycle.getCurrentState().isAtLeast(Lifecycle.State.STARTED)) {throw new IllegalStateException("LifecycleOwner " + lifecycleOwner + " is "+ "attempting to register while current state is "+ lifecycle.getCurrentState() + ". LifecycleOwners must call register before "+ "they are STARTED.");}//將
)
)
