无法对EditText字段（Android）进行setText（）-NullPointerException[重复]

Question

当我尝试对EditText进行setText（）时，我总是得到这个错误，我看不出哪里出错了。我想了解这个错误背后的逻辑。我敢肯定这是件小事情，但它现在真的困扰着我。

01-25 10:20:44.267 143 25-14325/com.example.gregsquibbs.greg_squibbs_todoapp3 E/androidruntime：致命异常：main process:com.example.gregsquibbs.gregsquibbs.greg_squibbs_todoapp3,pid:14325 java.lang.runtimeexception：无法启动活动ComponentInfo{在Android.app.activitythread.performLaunchActivity（activitythread.java:2817)在Android.app.activitythread.handlelaunchActivity（activitythread.java:2892)在Android.app.activitythread.-Wrap11（未知源：0）在Android.app.activitythread.$h.handleMessage（activitythread.java:1593)在Android.os.handler.dispatchMessage（handler.java:105)在(activitythread.java:6541)位于java.lang.reflect.method.inv在com.android.internal.os.zygote$methodandargscaller.run(zygoteinit.main(zygoteinit.java:767)处的oke（本机方法），原因是:java.lang.nullpointerException：试图在squibbs_todoapp3.editTodo.editTodoActivity.onCreate（editTodoActivity.java:41)在Android.app.activity.performCreate（activity.java:6975)在Android.app.instrumentation.CallActivityonCreate（instrumentation.java:1213)在Android.app.activityThread.performLaunchActivity（activityThread.java:2770)在Android.app.activityThread.handleLaunchActivity（在Android.app.activitythread.-Wrap11（未知来源：0） 在Android.app.activitythread$h.handleMessage(activitythread.java:1593) 在Android.os.handler.DispatchMessage(Handler.java:105) 在Android.os.looper.loop(looper.java:164) 在Android.app.activitythread.main（activitythread.java:6541) 在java.lang.reflect.Method.invoke（本机方法） 在com.android.internal.os.zygote$methodandargscaller.run(zygote.java:240)在com.android.internal.os.zygoteinit.main(zygoteinit.java:767)

这就是我创建etMessage并使用setText（）的地方

public class EditTodoFragment extends Fragment implements EditTodoContract.View {

private EditTodoContract.Presenter presenter;
private EditText etMessage;


public EditTodoFragment() {
    // Required empty public constructor
}

@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);

}

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
                         Bundle savedInstanceState) {

    View view = inflater.inflate(R.layout.edit_todo_fragment, container, false);

    System.out.println("Step 2 - Fragment check");
    etMessage = (EditText) view.findViewById(R.id.etMessage);


    return view;
}

public void setPresenter(EditTodoContract.Presenter todoPresenter) {
    this.presenter = todoPresenter;
}

public String getMessage() {
    String message = etMessage.getText().toString();
    return message;
}

public void setMessage(String message) {
    etMessage.setText(message);
}

}

下面是XML文件

<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context="com.example.gregsquibbs.greg_squibbs_todoapp3.EditTodo.EditTodoActivity">


<EditText
    android:id="@+id/etMessage"
    android:layout_width="match_parent"
    android:layout_height="300dp"
    android:layout_marginBottom="10dp"
    android:layout_marginLeft="10dp"
    android:layout_marginRight="10dp"
    android:layout_marginTop="10dp"
    android:background="@drawable/rect"
    android:ems="10"
    android:gravity="top"
    android:inputType="textShortMessage" />

<Button
    android:id="@+id/bSave"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:text="Save"
    android:layout_marginLeft="10dp"
    android:layout_marginRight="10dp"
    android:layout_marginTop="10dp"
    android:layout_marginBottom="10dp"
    android:onClick="saveButtonClicked"
    android:layout_gravity="center_horizontal|bottom"


    />

public class EditTodoActivity extends AppCompatActivity {
private String message;
private int position;
private EditTodoFragment editTodoFragment;
private EditTodoPresenter editTodoPresenter;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.edit_todo_activity);

    System.out.println("Step 1");

    FragmentManager fm = getSupportFragmentManager();
    Fragment fragment = fm.findFragmentById(R.id.contentFrameContainer);

    if (fragment == null){
        editTodoFragment = new EditTodoFragment();
        fm.beginTransaction()
                .add(R.id.contentFrameContainer, editTodoFragment)
                .commit();
        editTodoPresenter = new EditTodoPresenter(editTodoFragment);
    }


    message = getIntent().getStringExtra(IntentConstants.INTENT_MESSAGE_DATA);
    position = getIntent().getIntExtra(IntentConstants.INTENT_ITEM_POSITION, -1);
    editTodoFragment.setMessage(message);

}

public void saveButtonClicked(View v) {
    if(editTodoFragment.getMessage().equals("")) {
    } else {
        String changedMessage = (editTodoFragment.getMessage());
        Intent intent = new Intent();
        intent.putExtra(IntentConstants.INTENT_CHANGED_MESSAGE, changedMessage);
        intent.putExtra(IntentConstants.INTENT_ITEM_POSITION, position);
        finish();
    }
}

        etMessage = (EditText) view.findViewById(R.id.messageField);

我不知道这是否与此事有关。

Answer 1

错误可能是您在edit_todo_fragment之外的其他文件中定义了etmessage。这就是为什么您没有得到编译错误，因为对etmessage的引用存在，但它不存在于膨胀的视图中，因此您得到了NPE。