Question

我无法弄清楚为什么我会一直收到错误。这些错误一直告诉我，我的约会时间为null而且我将其设置为null，但我不是。{我也看过网上，我已经完全粘贴了代码，并遵循了所有方向，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);
}

以下是schedule_layout

的XML文件

<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" />

这是我的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

拨打findViewById时，您没有使用正确的ID。在这里使用textView -

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

但是你在这里使用date_text

android:id="@+id/date_text"

更改一个或另一个，以便两个ID都相同。

虚方法错误和NullPointerException错误

1 个答案: