如何在 androidx.fragment.app.Fragment 中使用 registerForActivityResult？

Question

 ActivityResultLauncher<Intent> launcherImportFileSelection = requireActivity().registerForActivityResult(...

如果将上述代码放在onCreate(Bundle savedInstanceState)中，会抛出如下异常：

Exception: LifecycleOwner MyActivity@868498a is attempting to register while current state is RESUMED. LifecycleOwners must call register before they are STARTED.

如果放在构造函数中或者作为声明，requireActivity()会抛出如下异常：

java.lang.reflect.InvocationTargetException
        at java.lang.reflect.Constructor.newInstance0(Native Method)
        at java.lang.reflect.Constructor.newInstance(Constructor.java:343)
2021-04-17 15:15:41.948 27930-27930/net.biyee.onvifer E/AndroidRuntime:     at androidx.fragment.app.Fragment.instantiate(Fragment.java:613)
            ... 42 more
     Caused by: java.lang.IllegalStateException: Fragment MyFragment{fba6d22} (e0d1f006-996d-4051-9839-4575a92e33dd) not attached to an activity.
        at androidx.fragment.app.Fragment.requireActivity(Fragment.java:928)

我在 build.gradle 中有以下内容：

implementation 'androidx.fragment:fragment:1.3.2'

有人可以提供这方面的提示吗？

更新：

问题已解决。请参阅我与@CommonsWare的交流。

Answer 1

您需要在

onCreate()

方法之外设置一个注册调用，此外您还需要将

registerForActivityResult()

变量作为片段类的属性。 （仅适用于

Activity

而不是

Fragment

！）

为KOTLIN注册调用示例：

val getContent = registerForActivityResult(GetContent()) { uri: Uri? ->
// Handle the returned Uri

}

注册调用JAVA的例子：

// GetContent creates an ActivityResultLauncher<String> to allow you to pass
// in the mime type you'd like to allow the user to select
ActivityResultLauncher<String> mGetContent = registerForActivityResult(new GetContent(),
    new ActivityResultCallback<Uri>() {
        @Override
        public void onActivityResult(Uri uri) {
            // Handle the returned Uri
        }
});

此文档将帮助您理解和实践。干杯:)

Answer 2

如Receive an activity result in a separate class,

片段类实现 ActivityResultCaller 接口让 你使用 registerForActivityResult() APIs

所以你可以像在活动中一样使用它：

public class YourFragment extends Fragment {

    private final ActivityResultLauncher<input_type> mActivityResultLauncher = 
            registerForActivityResult(<your_contract>, <your_callback>);

    @Override
    public void onCreate(@Nullable Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        // just don't register here
        ...
    }

    // call this when needed (e.g. user presses a button)
    private void launchActivityForResult() {
        mActivityResultLauncher.launch(<input>);
    }

}