Activity上的NullPointerException onCreate

我收到这个错误，我不知道为什么。这个相同的代码以前工作;该问题在某个时间点更新后开始出现。Activity上的NullPointerException onCreate

堆栈跟踪：

E/AndroidRuntime: FATAL EXCEPTION: main 
Process: com.domain.appname, PID: 17964 
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.domain.appname/com.domain.appname.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'void com.domain.appname.NavigationDrawerFragment.setUp(int, android.support.v4.widget.DrawerLayout)' on a null object reference 
    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2379) 
    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2441) 
    at android.app.ActivityThread.access$800(ActivityThread.java:162) 
    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1349) 
    at android.os.Handler.dispatchMessage(Handler.java:102) 
    at android.os.Looper.loop(Looper.java:135) 
    at android.app.ActivityThread.main(ActivityThread.java:5431) 
    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:914) 
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:707) 
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void com.domain.appname.NavigationDrawerFragment.setUp(int, android.support.v4.widget.DrawerLayout)' on a null object reference 
    at com.domain.appname.MainActivity.onCreate(MainActivity.java:40) 
    at android.app.Activity.performCreate(Activity.java:6056) 
    at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1106) 
    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2332) 
    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2441)  
    at android.app.ActivityThread.access$800(ActivityThread.java:162)  
    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1349)  
    at android.os.Handler.dispatchMessage(Handler.java:102)  
    at android.os.Looper.loop(Looper.java:135)  
    at android.app.ActivityThread.main(ActivityThread.java:5431)  
    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:914)  
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:707)

下面是MainActivity.java违规代码：

... 

@Override 
protected void onCreate(Bundle savedInstanceState) { 
    super.onCreate(savedInstanceState); 
    if (BuildConfig.DEBUG){ Log.d(TAG, "Created in debug mode"); } 

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

    // Set up the drawer. 
    Log.d(TAG, "Setting up drawer"); 
    mNavigationDrawerFragment.setUp(// Line 40 
     R.id.navigation_drawer, 
     (DrawerLayout) findViewById(R.id.drawer_layout) 
    ); 

...

我发现了两个，似乎有类似的问题的问题。（这里的the first和the second）第一个看起来不相关，第二个没有答案。

我很困惑。 drawer_layout和navigation_drawer做不是扔“符号未解决”的错误。就像我说的，这一切都用于工作...

来源

2016-07-16 Keith

你永远不会打电话给Activity.setContentView(int)。这应该是这样的：

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

    // Rest. 
}

来源

2016-07-16 22:09:24 natario

是的，看起来我添加了'在调试模式下创建'，我放弃了重要的行。我希望这可以帮助别人（所以我可以感觉不那么愚蠢）。 – Keith

Activity上的NullPointerException onCreate

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