擴展應用實例導致程序崩潰

Question

我跟着這個例子：

http://www.intridea.com/blog/2011/5/24/how-to-use-application-object-of-android

好像它的過程中MyApplication當 singleton = thisonCreate()崩潰。從MainActivity

public class MyApplication extends Application { 

@Override 
public void onConfigurationChanged(Configuration newConfig) { 
    super.onConfigurationChanged(newConfig); 
} 
private static MyApplication singleton; 

@Override 
public void onCreate() { 
    super.onCreate(); 
    Log.v("MyApplication", "Hi from my application"); 
    singleton = this; 
    Log.v("MyApplication", "End onCreat of myApplicatoin"); 

} 
@Override 
public void onLowMemory() { 
    super.onLowMemory(); 
} 

@Override 
public void onTerminate() { 
    super.onTerminate(); 
} 

public MyApplication getInstance(){ 
    return singleton; 
} 
public boolean isNetworkAvailable() { 
    return true; 
} 


} 

代碼：

MyApplication mApplication = (MyApplication) getApplicationContext(); 

這裏是logcat的消息：

11-23 16:43:01.398: V/MyApplication(30957): Hi from my application 
11-23 16:43:01.398: E/AndroidRuntime(30957): FATAL EXCEPTION: main 
11-23 16:43:01.398: E/AndroidRuntime(30957): java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.jimmyc.fall12.OpenClass/com.jimmyc.fall12.OpenClass.MainInterface}: java.lang.NullPointerException 
11-23 16:43:01.398: E/AndroidRuntime(30957): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2106) 
11-23 16:43:01.398: E/AndroidRuntime(30957): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2230) 
11-23 16:43:01.398: E/AndroidRuntime(30957): at android.app.ActivityThread.access$600(ActivityThread.java:141) 
11-23 16:43:01.398: E/AndroidRuntime(30957): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1234) 
11-23 16:43:01.398: E/AndroidRuntime(30957): at android.os.Handler.dispatchMessage(Handler.java:99) 
11-23 16:43:01.398: E/AndroidRuntime(30957): at android.os.Looper.loop(Looper.java:137) 
11-23 16:43:01.398: E/AndroidRuntime(30957): at android.app.ActivityThread.main(ActivityThread.java:5039) 
11-23 16:43:01.398: E/AndroidRuntime(30957): at java.lang.reflect.Method.invokeNative(Native Method) 
11-23 16:43:01.398: E/AndroidRuntime(30957): at java.lang.reflect.Method.invoke(Method.java:511) 
11-23 16:43:01.398: E/AndroidRuntime(30957): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:793) 
11-23 16:43:01.398: E/AndroidRuntime(30957): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:560) 
11-23 16:43:01.398: E/AndroidRuntime(30957): at dalvik.system.NativeStart.main(Native Method) 
11-23 16:43:01.398: E/AndroidRuntime(30957): Caused by: java.lang.NullPointerException 
11-23 16:43:01.398: E/AndroidRuntime(30957): at android.content.ContextWrapper.getApplicationContext(ContextWrapper.java:109) 
11-23 16:43:01.398: E/AndroidRuntime(30957): at com.jimmyc.fall12.OpenClass.MainInterface.<init>(MainInterface.java:75) 
11-23 16:43:01.398: E/AndroidRuntime(30957): at java.lang.Class.newInstanceImpl(Native Method) 
11-23 16:43:01.398: E/AndroidRuntime(30957): at java.lang.Class.newInstance(Class.java:1319) 
11-23 16:43:01.398: E/AndroidRuntime(30957): at android.app.Instrumentation.newActivity(Instrumentation.java:1054) 
11-23 16:43:01.398: E/AndroidRuntime(30957): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2097) 
> 11-23 16:43:01.398: E/AndroidRuntime(30957): ... 11 more 

任何想法？

線74，75，MainInterface 76

74：////////////////訪問全局函數

75：所有MyApplication mApplication =（ MyApplication）getApplicationContext（）;

76：//

Answer 1

需要初始化mApplication在onCreate()：

MyApplication mApplication; 

public void onCreate(Bundle savedInstanceState) { 
    ... 
    mApplication = (MyApplication) getApplicationContext();