原因：java.lang.NullPointerException MainActivity.onPostCreate

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04-03 10:19:34.572    2189-2189/com.techexpert4u.duaaadhkaar E/AndroidRuntime﹕ FATAL EXCEPTION: main
    Process: com.techexpert4u.duaaadhkaar, PID: 2189
    java.lang.RuntimeException: Unable to start activity ComponentInfo{com.techexpert4u.duaaadhkaar/com.techexpert4u.duaaadhkaar.MainActivity}: java.lang.NullPointerException
            at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2195)
            at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2245)
            at android.app.ActivityThread.access$800(ActivityThread.java:135)
            at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1196)
            at android.os.Handler.dispatchMessage(Handler.java:102)
            at android.os.Looper.loop(Looper.java:136)
            at android.app.ActivityThread.main(ActivityThread.java:5017)
            at java.lang.reflect.Method.invokeNative(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:515)
            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:779)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:595)
            at dalvik.system.NativeStart.main(Native Method)
     Caused by: java.lang.NullPointerException
            at com.techexpert4u.duaaadhkaar.MainActivity.onPostCreate(MainActivity.java:936)
            at android.app.Instrumentation.callActivityOnPostCreate(Instrumentation.java:1150)
            at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2178)
            at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2245)
            at android.app.ActivityThread.access$800(ActivityThread.java:135)
            at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1196)
            at android.os.Handler.dispatchMessage(Handler.java:102)
            at android.os.Looper.loop(Looper.java:136)
            at android.app.ActivityThread.main(ActivityThread.java:5017)
            at java.lang.reflect.Method.invokeNative(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:515)
            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:779)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:595)
            at dalvik.system.NativeStart.main(Native Method)

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给定该源和堆栈跟踪，显然mDrawerToggle为null。

null mDrawerToggle字段似乎应该在initializeDrawer代码中初始化，但没有证据表明您调用过该方法

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在onCreate中调用initializeDrawer，或者在尝试使用mDrawerToggle之前，确保它发生在任何代码路径中。

@Solaiman如果您遵循堆栈跟踪，您将在第936行看到它。您如何初始化mDrawerToggle对象？我初始化了，但仍然有问题。我把代码贴在下面，很抱歉，我不明白你的意思，因为我是编程新手。你能再解释一下吗？提前谢谢。你的意思是我需要把它放在OnCreate中吗？你从来没有调用initializeDrawer，所以你从来没有完成它想要做的初始化。在onCreate中调用它确实是第一个想到的想法，但是要知道什么是最好的，需要更多地了解您的程序。

@Override
protected void onPostCreate(Bundle savedInstanceState) {
    super.onPostCreate(savedInstanceState);
    // Sync the toggle state after onRestoreInstanceState has occurred.
    mDrawerToggle.syncState();
}