Question

我的应用中有以下代码：

String[] filelist = APP.getContext().filelist();  

...

public class APP extends Application {
    static Context theContext;

    public void onCreate() {
        super.onCreate();
        theContext = this;
    }

    public static Context getContext() {
        Log.v("APP", "APP.getContext() called.");
        return theContext;
    }
}

无论我如何重写此代码，方法Context.filelist()都会返回NullPointerException。为什么会这样做？

我可以确认VERBOSE登录getContext()会显示。

logcat的：

D/AndroidRuntime(  342): >>>>>> AndroidRuntime START com.android.internal.os.RuntimeInit <<<<<<
D/AndroidRuntime(  342): CheckJNI is ON
D/AndroidRuntime(  342): Calling main entry com.android.commands.am.Am
I/ActivityManager(   83): Starting: Intent { act=android.intent.action.MAIN cat=[android.intent.category.LAUNCHER] flg=0x10000000 cmp=com.gobernador/.TopPage } from pid 342
I/ActivityManager(   83): Start proc com.gobernador for activity com.gobernador/.TopPage: pid=350 uid=10036 gids={3002}
D/AndroidRuntime(  342): Shutting down VM
D/dalvikvm(  342): GC_CONCURRENT freed 102K, 69% free 319K/1024K, external 0K/0K, paused 1ms+1ms
D/dalvikvm(  342): Debugger has detached; object registry had 1 entries
I/AndroidRuntime(  342): NOTE: attach of thread 'Binder Thread #3' failed
W/dalvikvm(  350): Exception Ljava/lang/NullPointerException; thrown while initializing Lcom/gobernador/APP;
W/dalvikvm(  350): Class init failed in newInstance call (Lcom/gobernador/APP;)
D/AndroidRuntime(  350): Shutting down VM
W/dalvikvm(  350): threadid=1: thread exiting with uncaught exception (group=0x40015560)
I/ARMAssembler(   83): generated scanline__00000177:03515104_00001002_00000000 [ 87 ipp] (110 ins) at [0x444ea6f0:0x444ea8a8] in 1886492 ns
E/AndroidRuntime(  350): FATAL EXCEPTION: main
E/AndroidRuntime(  350): java.lang.ExceptionInInitializerError
E/AndroidRuntime(  350):    at java.lang.Class.newInstanceImpl(Native Method)
E/AndroidRuntime(  350):    at java.lang.Class.newInstance(Class.java:1409)
E/AndroidRuntime(  350):    at android.app.Instrumentation.newApplication(Instrumentation.java:957)
E/AndroidRuntime(  350):    at android.app.Instrumentation.newApplication(Instrumentation.java:942)
E/AndroidRuntime(  350):    at android.app.LoadedApk.makeApplication(LoadedApk.java:461)
E/AndroidRuntime(  350):    at android.app.ActivityThread.handleBindApplication(ActivityThread.java:3260)
E/AndroidRuntime(  350):    at android.app.ActivityThread.access$2200(ActivityThread.java:117)
E/AndroidRuntime(  350):    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:969)
E/AndroidRuntime(  350):    at android.os.Handler.dispatchMessage(Handler.java:99)
E/AndroidRuntime(  350):    at android.os.Looper.loop(Looper.java:123)
E/AndroidRuntime(  350):    at android.app.ActivityThread.main(ActivityThread.java:3683)
E/AndroidRuntime(  350):    at java.lang.reflect.Method.invokeNative(Native Method)
E/AndroidRuntime(  350):    at java.lang.reflect.Method.invoke(Method.java:507)
E/AndroidRuntime(  350):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:839)
E/AndroidRuntime(  350):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:597)
E/AndroidRuntime(  350):    at dalvik.system.NativeStart.main(Native Method)
E/AndroidRuntime(  350): Caused by: java.lang.NullPointerException
E/AndroidRuntime(  350):    at com.gobernador.ReaderWriter.<init>(ReaderWriter.java:20)
E/AndroidRuntime(  350):    at com.gobernador.APP.<clinit>(APP.java:11)
E/AndroidRuntime(  350):    ... 16 more
W/ActivityManager(   83):   Force finishing activity com.gobernador/.TopPage

每次接受的答案：我写的代码不正常。我将构造函数（包含上面的行）移动到theContext = this;之后的行。

Answer 1

“new String [9]”没用。你可以这样写：

final String[] filelist = APP.getContext().filelist();

但它无法解决您的问题。问题是“APP”为空或“APP.getContext（）”返回null

Answer 2

在实例化类之前，

theContext未初始化，因此在此之前它将为null。

使getContext()方法非静态，并从该类的实例中调用它

一种方式是致电

((APP)(this.getApplication())).getContext().filelist()

来自您应用程序中的另一个活动。

Filelist抛出NullPointerException

2 个答案: