虚拟方法错误和空指针异常错误

Question

我找不出为什么我不断收到错误。错误一直告诉我，我的日期是null，并且我将它设置为null，但我不是。我也在网上查看，并且我确实按照所有方向粘贴了代码，并且仍然没有运气。

protected void onCreate(Bundle savedInstanceState) { 
    super.onCreate(savedInstanceState); 
    setContentView(R.layout.activity_main); 

    mNavigationDrawerFragment = (NavigationDrawerFragment) 
      getSupportFragmentManager().findFragmentById(R.id.navigation_drawer); 
    mTitle = getTitle(); 

    // Set up the drawer. 
    mNavigationDrawerFragment.setUp(
      R.id.navigation_drawer, 
      (DrawerLayout) findViewById(R.id.drawer_layout)); 

    TextView date = (TextView) findViewById(R.id.textView); 
    String Date= DateFormat.getDateTimeInstance().format(new Date()); 
    date.setText(Date); 
} 

下面是schedule_layout

<TextView 
    android:layout_width="wrap_content" 
    android:layout_height="wrap_content" 
    android:text="DATE HERE" 
    android:id="@+id/date_text" 
    android:layout_below="@+id/textView" 
    android:layout_centerHorizontal="true" /> 

而且这里的XML文件是我的logcat

java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.nick.veronaremindersapp/com.example.nick.veronaremindersapp.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.TextView.setText(java.lang.CharSequence)' on a null object reference 
     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2339) 
     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2413) 
     at android.app.ActivityThread.access$800(ActivityThread.java:155) 
     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1317) 
     at android.os.Handler.dispatchMessage(Handler.java:102) 
     at android.os.Looper.loop(Looper.java:135) 
     at android.app.ActivityThread.main(ActivityThread.java:5343) 
     at java.lang.reflect.Method.invoke(Native Method) 
     at java.lang.reflect.Method.invoke(Method.java:372) 
     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:905) 
     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:700) 
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.TextView.setText(java.lang.CharSequence)' on a null object reference 
     at com.example.nick.veronaremindersapp.MainActivity.onCreate(MainActivity.java:61) 

Answer 1

，当你调用findViewById您没有使用正确的ID。在这里，您使用textView -

TextView date = (TextView) findViewById(R.id.textView); 

但在这里，你用date_text

android:id="@+id/date_text" 

更改一个或另一个这样两个ID相同。