为什么我得到类转换异常？安卓

Question

我正在开发一个应该加载图库并抓取图像并将其显示在图像视图中的 android 应用程序。我让它工作但从活动更改为片段以使用 ViewPager，从那时起它一直在崩溃。我相信这是因为我正在使用一种用于片段活动的方法。

public class Fragment_1 extends Fragment {
private static int RESULT_LOAD_IMAGE = 1;

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
        Bundle savedInstanceState) {
    // Inflate the layout for this fragment

    Button buttonLoadImage = (Button) getView().findViewById(
            R.id.buttonLoadPicture);
    buttonLoadImage.setOnClickListener(new View.OnClickListener() {

        @Override
        public void onClick(View arg0) {
            Log.v("ButtonPress: ", "Pressed");

            Intent i = new Intent(
                    Intent.ACTION_PICK,
                    android.provider.MediaStore.Images.Media.EXTERNAL_CONTENT_URI);
            Log.v("ButtonPress: ", "intent=" + i);

            startActivityForResult(i, RESULT_LOAD_IMAGE);
        }
    });
    return inflater.inflate(R.layout.fragment_1, container, false);

}

@Override
public void onActivityResult(int requestCode, int resultCode, Intent data) {
    super.onActivityResult(requestCode, resultCode, data);

    if (requestCode == RESULT_LOAD_IMAGE && resultCode == Activity.RESULT_OK    && null != data) {
        Uri selectedImage = data.getData();
        String[] filePathColumn = { MediaStore.Images.Media.DATA };

        Cursor cursor = getActivity().getContentResolver().query(selectedImage,
                filePathColumn, null, null, null);
        cursor.moveToFirst();

        int columnIndex = cursor.getColumnIndex(filePathColumn[0]);
        String picturePath = cursor.getString(columnIndex);
        cursor.close();

        ImageView imageView = (ImageView) getView().findViewById(R.id.imgView);
        imageView.setImageBitmap(BitmapFactory.decodeFile(picturePath));

    }

}

}

我收到的错误是：

05-05 22:17:59.214: E/AndroidRuntime(32610): FATAL EXCEPTION: main
05-05 22:17:59.214: E/AndroidRuntime(32610): Process: com.example.hashtagged, PID: 32610
05-05 22:17:59.214: E/AndroidRuntime(32610): java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.example.hashtagged/com.example.hashtagged.Fragment_1}: java.lang.ClassCastException: com.example.hashtagged.Fragment_1 cannot be cast to android.app.Activity
05-05 22:17:59.214: E/AndroidRuntime(32610):    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2131)
05-05 22:17:59.214: E/AndroidRuntime(32610):    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2265)
05-05 22:17:59.214: E/AndroidRuntime(32610):    at android.app.ActivityThread.access$800(ActivityThread.java:145)
05-05 22:17:59.214: E/AndroidRuntime(32610):    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1206)
05-05 22:17:59.214: E/AndroidRuntime(32610):    at android.os.Handler.dispatchMessage(Handler.java:102)
05-05 22:17:59.214: E/AndroidRuntime(32610):    at android.os.Looper.loop(Looper.java:136)
05-05 22:17:59.214: E/AndroidRuntime(32610):    at android.app.ActivityThread.main(ActivityThread.java:5142)
05-05 22:17:59.214: E/AndroidRuntime(32610):    at java.lang.reflect.Method.invokeNative(Native Method)
05-05 22:17:59.214: E/AndroidRuntime(32610):    at java.lang.reflect.Method.invoke(Method.java:515)
05-05 22:17:59.214: E/AndroidRuntime(32610):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:791)
05-05 22:17:59.214: E/AndroidRuntime(32610):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:607)
05-05 22:17:59.214: E/AndroidRuntime(32610):    at dalvik.system.NativeStart.main(Native Method)
05-05 22:17:59.214: E/AndroidRuntime(32610): Caused by: java.lang.ClassCastException: com.example.hashtagged.Fragment_1 cannot be cast to android.app.Activity
05-05 22:17:59.214: E/AndroidRuntime(32610):    at android.app.Instrumentation.newActivity(Instrumentation.java:1061)
05-05 22:17:59.214: E/AndroidRuntime(32610):    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2122)
05-05 22:17:59.214: E/AndroidRuntime(32610):    ... 11 more

Answer 1

尝试先在 OnCreateView 上为 View 充气，如下所示：

private Button mButtonLoadImage;

@Override public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
  View view = inflater.inflate(R.layout.fragment_1, container, false);
  mButtonLoadImage = (Button) view.findViewById(R.id.buttonLoadPicture);
  return view;
}

并在onViewCreated里面设置onClickListener：

@Override public void onViewCreated(View view, Bundle savedInstanceState) {
  super.onViewCreated(view, savedInstanceState);
  mButtonLoadImage.setOnClickListener(onClickLoad);
}

//Good practice
private View.OnClickListener onClickLoad = new View.OnClickListener() {
  @Override public void onClick(View view) {
    //TODO action here
  }
};

Answer 2

您正在 Fragment 类中使用活动类的 onActivityResult() 方法。这就是您收到此错误的原因。 onActivityResult 应该在片段类的活动类中定义，而不是在片段本身上。操作方法见此链接。here