java - 将数据从 DialogFragment 传递到 Activity 时出现 NullPointer

Question

我试图提示用户通过 DialogFragment 创建用户名。

当我显示对话框 fragment 时，我希望用户输入用户名，然后将该用户名传递回 Activity ，然后写入 Firebase:

对话框 fragment :

public class DisplayNameDialogFragment extends DialogFragment {

//TODO: Is this going to cause compile-time exception in these versions?
@TargetApi(Build.VERSION_CODES.ICE_CREAM_SANDWICH)
@Override
public Dialog onCreateDialog(Bundle savedInstanceState) {

    LayoutInflater inflater = getActivity().getLayoutInflater();
    View mView = inflater.inflate(R.layout.fragment_display_name_dialog, null);
    final EditText displayName = (EditText) mView.findViewById(R.id.display_name);
    AlertDialog.Builder builder = new AlertDialog.Builder(getActivity());
    builder.setTitle(R.string.DISPLAY_NAME_LABEL);
    builder.setView(mView);
    builder.setPositiveButton(R.string.dialog_done, new DialogInterface.OnClickListener() {
        @Override
        public void onClick(DialogInterface dialogInterface, int i) {
            String displayNameEntered = displayName.getText().toString();
                 listener.onFinishEditDialog(displayNameEntered);
        }
    });

    return builder.create();
}

public static interface EditNameDialogListener {
    public abstract void onFinishEditDialog(String inputText);
}

private EditNameDialogListener listener;

@Override
public void onAttach(Context context) {
    super.onAttach(context);
    try {
        this.listener = (EditNameDialogListener)getActivity();
    } catch (final ClassCastException e){
        throw new ClassCastException(getActivity().toString() + "must implement listener");
     }
   }
 }

接收 Activity :

public class SignupActivity extends AppCompatActivity implements DisplayNameDialogFragment.EditNameDialogListener{
private static final String TAG = "SignupActivity";

@Bind(R.id.input_email)
EditText _emailText;
@Bind(R.id.input_password)
EditText _passwordText;
@Bind(R.id.btn_signup)...........

@Override
public void onFinishEditDialog(String inputText) {
    FirebaseAuth auth = FirebaseAuth.getInstance();
    UserProfileChangeRequest m = new UserProfileChangeRequest.Builder()
            .setDisplayName(inputText).build();
    FirebaseUser user = auth.getCurrentUser();
    user.updateProfile(m);
    Log.v("INPUT_TEXT", user.getDisplayName());
    Toast.makeText(getApplicationContext(), inputText, Toast.LENGTH_LONG).show();
    Intent toHome = new Intent(SignupActivity.this, HomeActivity.class);
    startActivity(toHome);
      }
 }

我收到一个 NullPointer，但不确定原因:

java.lang.NullPointerException: println needs a message
                                                                         at android.util.Log.println_native(Native Method)
                                                                         at android.util.Log.v(Log.java:118)
                                                                         at com.troychuinard.fanpolls.SignupActivity.onFinishEditDialog(SignupActivity.java:367)
                                                                         at com.troychuinard.fanpolls.Fragment.DisplayNameDialogFragment$1.onClick(DisplayNameDialogFragment.java:39)
                                                                         at com.android.internal.app.AlertController$ButtonHandler.handleMessage(AlertController.java:163)
                                                                         at android.os.Handler.dispatchMessage(Handler.java:102)
                                                                         at android.os.Looper.loop(Looper.java:148)
                                                                         at android.app.ActivityThread.main(ActivityThread.java:5527)
                                                                         at java.lang.reflect.Method.invoke(Native Method)
                                                                         at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:730)
                                                                         at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:620)

Answer 1

改变

Log.v("INPUT_TEXT", user.getDisplayName());

至

Log.v("INPUT_TEXT", "" + user.getDisplayName());

错误java.lang.NullPointerException:println需要一条消息意味着您在Log中的消息必须!= null