android - 尝试启动未注册的 ActivityResultLauncher

Question

有时我会收到这个 IllegalStateException，它说您必须确保在调用 launch() 之前注册了 ActivityResultLauncher。但是没有方法可以检查 ActivityResultLauncher 是否已注册。我该如何解决这个问题以及为什么会发生这种情况？另外，不清楚何时调用 unregister() 方法，有什么例子吗？

Answer 1

请注意在 onCreate 中注册您的 activityResultLauncher防止副作用的方法

public class MyActiviy extends AppCompatActivity {
    .
    .
    .

    private ActivityResultLauncher<Intent> myLauncher;

    @Override
    protected void onCreate(@Nullable Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        //some stuff

        // Register your launcher here
        myLauncher = registerForActivityResult(new ActivityResultContracts.StartActivityForResult(), result -> {
            if (result.getResultCode() == RESULT_OK && result.getData() != null) {
                Intent data = result.getData();
            }
        });
      
        findViewById(R.id.myButton).setOnClickListener(v -> {
            // call `launch` after user click on button or something like that
            Intent intent = new Intent(this, TargetActivity.class);
            myLauncher.launch(intent);
        });
    }

}

引用谷歌文档:

When using the ActivityResultRegistry APIs, it's strongly recommendedto use the APIs that take a LifecycleOwner, as the LifecycleOwnerautomatically removes your registered launcher when the Lifecycle isdestroyed. However, in cases where a LifecycleOwner is not available,each ActivityResultLauncher class allows you to manually callunregister() as an alternative.

看看 Here