在类内调用 start startActivityForResult

Question

我需要从课堂内部调用startActivityForResult，但我没有得到java.lang.NullPointerException。

文件：注册片段.java

public class SignUpFragment extends Fragment {
    ImageView imageView;

    private OnFragmentInteractionListener mListener;
    public SignUpFragment() {
        // Required empty public constructor
        Test test = new Test();
        test.getImageData();
    }
}

PS：Test.java不是Activity，它的类和我扩展了Activity以访问startActivityForResult

文件测试.java

public class Test extends Activity {
    public void getImageData() {
        Intent pickIntent = new Intent(Intent.ACTION_PICK, android.provider.MediaStore.Images.Media.EXTERNAL_CONTENT_URI);
        pickIntent.setType("image/*");
        startActivityForResult(pickIntent, 1);
    }
    @Override
    public void onActivityResult(int requestCode, int resultCode, Intent data) {
        super.onActivityResult(requestCode, resultCode, data);
        Log.d(“Reps”, ”Called”);
    }
}

更新：这是错误日志：

mozeh E/AndroidRuntime: FATAL EXCEPTION: main
     Process: com.example.moaaznash.userregistrationmozeh, PID: 28091
     java.lang.NullPointerException
         at android.app.Activity.startActivityForResult(Activity.java:3424)
         at android.app.Activity.startActivityForResult(Activity.java:3385)
         at com.example.moaaznash.mozehlibraryandroid.TestMozeh1.startPhotoLibs(TestMozeh1.java:52)
         at com.example.moaaznash.userregistrationmozeh.SignUpFragment$1.onClick(SignUpFragment.java:101)
         at android.view.View.performClick(View.java:4438)
         at android.view.View$PerformClick.run(View.java:18422)
         at android.os.Handler.handleCallback(Handler.java:733)
         at android.os.Handler.dispatchMessage(Handler.java:95)
         at android.os.Looper.loop(Looper.java:136)
         at android.app.ActivityThread.main(ActivityThread.java:5017)
         at java.lang.reflect.Method.invokeNative(Native Method)
         at java.lang.reflect.Method.invoke(Method.java:515)
         at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:779)
         at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:595)
         at dalvik.system.NativeStart.main(Native Method)
     [ 03-19 10:08:41.231  1615: 1809 D/         ]
     HostConnection::get() New Host Connection established 0xb990e140, tid 1809

Answer 1

我倾向于将getImageData((和onActivityResult放到包含Fragment的活动类中(例如，通过侦听器在Activity和Fragment之间进行通信(。

但下面是一个替代方案

public class SignUpFragment extends Fragment {
    private final int PICK_ID = 1;
    public SignUpFragment() {
        // Required empty public constructor
    }
    public static SignUpFragment newInstance() {
        SignUpFragment fragment = new SignUpFragment();
        Bundle args = new Bundle();
        fragment.setArguments(args);
        return fragment;
    }
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        getImageData();
    }
    @Override
    public void onActivityResult(int requestCode, int resultCode, Intent data) {
        super.onActivityResult(requestCode, resultCode, data);
        if (requestCode == PICK_ID && resultCode == Activity.RESULT_OK) {
            Log.d("TAG", "onActivityResult");
            if (data != null) {
                try {
                    InputStream inputStream = getActivity().getContentResolver().openInputStream(data.getData());
                    //...
                } catch (FileNotFoundException e) {
                    e.printStackTrace();
                }
            }
        }
    }
    public void getImageData(){
        Intent pickIntent = new Intent(Intent.ACTION_PICK, android.provider.MediaStore.Images.Media.EXTERNAL_CONTENT_URI);
        pickIntent.setType("image/*");
        startActivityForResult(pickIntent, PICK_ID);
    }
}

在您的活动中，只需放置这样的东西

    public class MainActivity extends AppCompatActivity {
        @Override
        protected void onCreate(Bundle savedInstanceState) {
            super.onCreate(savedInstanceState);
            setContentView(R.layout.activity_main);
            getSupportFragmentManager()
                     .beginTransaction()
                     .add(android.R.id.content, SignUpFragment.newInstance())
                     .commit();
        }
    }

Answer 2

您把 Activity 当作一个普通的 Java 类，而不是另一个 Activity。因此，当您调用 startActivityForResult(( 时，您会得到一个空指针异常，因为尚未调用活动的 onCreate((，这意味着其当前实例对于调用 startActivityForResult(( 无效。

Answer 3

public class Test extends Activity {
    public void getImageData() {
        Intent pickIntent = new Intent(Intent.ACTION_PICK, android.provider.MediaStore.Images.Media.EXTERNAL_CONTENT_URI);
        pickIntent.setType("image/*");
        if (pickIntent == 1) {
            startActivity(pickIntent);
        }
    }
    @Override
    public void onActivityResult(int requestCode, int resultCode, Intent data) {
        super.onActivityResult(requestCode, resultCode, data);
        Log.d(“Reps”,”Called”);
    }
}