Question

所以我在过去的几个小时里一直在努力解决这个问题并且在我认为没有办法解决我的问题之前进行搜索。基本上我正在尝试在Fragment扩展中使用Context而且它给了我错误我在这个要点中粘贴了完整的代码

从我在SO上发现的情况来看，当Context为null时会发生这种情况，但我不明白如何修复它。

logcat的：

> 06-18 10:20:08.972    5718-5718/com.aparosecurity.kblock W/dalvikvm﹕
> threadid=1: thread exiting with uncaught exception (group=0x41625898)
> 06-18 10:20:08.992    5718-5718/com.aparosecurity.kblock
> E/AndroidRuntime﹕ FATAL EXCEPTION: main
>     java.lang.NullPointerException
>             at com.aparosecurity.kblock.ImageFragment.onCreate(ImageFragment.java:77)
>             at android.support.v4.app.Fragment.performCreate(Fragment.java:1477)
>             at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:904)
>             at android.support.v4.app.FragmentManagerImpl.performPendingDeferredStart(FragmentManager.java:834)
>             at android.support.v4.app.Fragment.setUserVisibleHint(Fragment.java:841)
>             at android.support.v4.app.FragmentPagerAdapter.setPrimaryItem(FragmentPagerAdapter.java:130)
>             at android.support.v4.view.ViewPager.populate(ViewPager.java:1066)
>             at android.support.v4.view.ViewPager.populate(ViewPager.java:914)
>             at android.support.v4.view.ViewPager.onMeasure(ViewPager.java:1436)
>             at android.view.View.measure(View.java:15848)
>             at android.widget.LinearLayout.measureVertical(LinearLayout.java:847)
>             at android.widget.LinearLayout.onMeasure(LinearLayout.java:588)
>             at android.view.View.measure(View.java:15848)
>             at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5012)
>             at android.widget.FrameLayout.onMeasure(FrameLayout.java:310)
>             at android.view.View.measure(View.java:15848)
>             at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5012)
>             at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1404)
>             at android.widget.LinearLayout.measureVertical(LinearLayout.java:695)
>             at android.widget.LinearLayout.onMeasure(LinearLayout.java:588)
>             at android.view.View.measure(View.java:15848)
>             at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5012)
>             at android.widget.FrameLayout.onMeasure(FrameLayout.java:310)
>             at com.android.internal.policy.impl.PhoneWindow$DecorView.onMeasure(PhoneWindow.java:2189)
>             at android.view.View.measure(View.java:15848)
>             at android.view.ViewRootImpl.performMeasure(ViewRootImpl.java:1905)
>             at android.view.ViewRootImpl.measureHierarchy(ViewRootImpl.java:1104)
>             at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:1284)
>             at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:1004)
>             at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:5481)
>             at android.view.Choreographer$CallbackRecord.run(Choreographer.java:749)
>             at android.view.Choreographer.doCallbacks(Choreographer.java:562)
>             at android.view.Choreographer.doFrame(Choreographer.java:532)
>             at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:735)
>             at android.os.Handler.handleCallback(Handler.java:730)
>             at android.os.Handler.dispatchMessage(Handler.java:92)
>             at android.os.Looper.loop(Looper.java:137)
>             at android.app.ActivityThread.main(ActivityThread.java:5136)
>             at java.lang.reflect.Method.invokeNative(Native Method)
>             at java.lang.reflect.Method.invoke(Method.java:525)
>             at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:737)
>             at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
>             at dalvik.system.NativeStart.main(Native Method)

感谢任何帮助。

失败的特定行，使用mContext时会发生错误。

@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    fragVal = getArguments() != null ? getArguments().getInt("val") : 1;
    mHandler = new Handler();

    // Initializes a Bluetooth adapter.  For API level 18 and above, get a reference to
    // BluetoothAdapter through BluetoothManager.
    final BluetoothManager bluetoothManager =
            (BluetoothManager) mContext.getSystemService(Context.BLUETOOTH_SERVICE);
    mBluetoothAdapter = bluetoothManager.getAdapter();

}

Answer 1

您尚未初始化mContext并且它为空。在null引用上调用方法会导致NPE。

在片段中，使用getActivity()获取可用作Context的托管活动的引用。（警告：仅当附加到活动时。在onCreate()之后的onAttach()中工作。）

所以，替换

mContext.getSystemService()

与

getActivity().getSystemService()

低功耗蓝牙 - java.lang.NullPointerException

1 个答案: