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registerForActivityResult 使用用途是监听Activity结果。

以下是使用样例

//需要传递Request用于解析Intent和解析上个Activity返回的结果
val launchdata = registerForActivityResult<PickVisualMediaRequest, Uri?>(ActivityResultContracts.PickVisualMedia()) {println("it $it")
}
//传入启动的Activity信息，来启动Activity
launchdata.launch(PickVisualMediaRequest(mediaType = ActivityResultContracts.PickVisualMedia.ImageOnly))

实现原理分析：

首先四注册流程

//其中mActivityResultRegistry是final变量

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.");}//将