Question

我需要从课堂内拨打require，但我没有startActivityForResult。

文件：SignUpFragment.java

java.lang.NullPointerException

P.S：public class SignUpFragment extends Fragment { ImageView imageView; private OnFragmentInteractionListener mListener; public SignUpFragment() { // Required empty public constructor Test test = new Test(); test.getImageData(); } }不是Test.java，其类和我扩展Activity以访问Activity

文件Test.java

startActivityForResult

更新：这是错误日志：

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”);
    }

}

Answer 1

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”);
    }
}

Answer 2

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

但下面是另一种选择

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，只需输入类似的内容

    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 3

您将Activity视为普通Java类，而不是像其他Activity一样。因此，当您调用startActivityForResult（）时，您会得到一个nullpointerexception，因为尚未调用Activity的onCreate（），这意味着它的当前实例对于调用startActivityForResult（）无效。

在类中调用start startActivityForResult

3 个答案: