Java 连接接收器空指针异常错误

我正在制作一个应用程序，它使用改型从API获取数据。因此，我编写了一个从BrodcaseReceiver扩展而来的connectivity receiver类，用于检查internet连接以及internet连接的任何更改

我得到的错误是

    03-03 15:26:32.387 5547-5547/com.sriramr.movies E/AndroidRuntime: FATAL EXCEPTION: main
                                                              Process: com.sriramr.movies, PID: 5547
                                                              java.lang.RuntimeException: Unable to start activity ComponentInfo{com.sriramr.movies/com.sriramr.movies.activity.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'android.content.Context com.sriramr.movies.MyApplication.getApplicationContext()' on a null object reference
                                                                  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2665)
                                                                  at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2726)
                                                                  at android.app.ActivityThread.-wrap12(ActivityThread.java)
                                                                  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1477)
                                                                  at android.os.Handler.dispatchMessage(Handler.java:102)
                                                                  at android.os.Looper.loop(Looper.java:154)
                                                                  at android.app.ActivityThread.main(ActivityThread.java:6119)
                                                                  at java.lang.reflect.Method.invoke(Native Method)
                                                                  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:886)
                                                                  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:776)
                                                               Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'android.content.Context com.sriramr.movies.MyApplication.getApplicationContext()' on a null object reference
                                                                  at com.sriramr.movies.ConnectivityReceiver.isConnected(ConnectivityReceiver.java:33)
                                                                  at com.sriramr.movies.activity.MainActivity.checkConnetion(MainActivity.java:64)
                                                                  at com.sriramr.movies.activity.MainActivity.onCreate(MainActivity.java:52)
                                                                  at android.app.Activity.performCreate(Activity.java:6679)
                                                                  at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1118)
                                                                  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2618)
                                                                  at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2726) 
                                                                  at android.app.ActivityThread.-wrap12(ActivityThread.java) 
                                                                  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1477) 
                                                                  at android.os.Handler.dispatchMessage(Handler.java:102) 
                                                                  at android.os.Looper.loop(Looper.java:154) 
                                                                  at android.app.ActivityThread.main(ActivityThread.java:6119) 
                                                                  at java.lang.reflect.Method.invoke(Native Method) 
                                                                  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:886) 
                                                                  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:776) 

ConnectivityReceiver.java

public class ConnectivityReceiver extends BroadcastReceiver {

public static ConnectivityReceiverListener connectivityReceiverListener;

public ConnectivityReceiver() {
    super();
}

@Override
public void onReceive(Context context, Intent arg1) {
    ConnectivityManager cm = (ConnectivityManager) context
            .getSystemService(Context.CONNECTIVITY_SERVICE);
    NetworkInfo activeNetwork = cm.getActiveNetworkInfo();
    boolean isConnected = activeNetwork != null
            && activeNetwork.isConnectedOrConnecting();

    if (connectivityReceiverListener != null) {
        connectivityReceiverListener.onNetworkConnectionChanged(isConnected);
    }
}

public static boolean isConnected() {
    ConnectivityManager cm = (ConnectivityManager) MyApplication.getInstance().getApplicationContext()
            .getSystemService(Context.CONNECTIVITY_SERVICE);
    NetworkInfo activeNetwork = cm.getActiveNetworkInfo();
    return activeNetwork != null
            && activeNetwork.isConnectedOrConnecting();
}


public interface ConnectivityReceiverListener {
    void onNetworkConnectionChanged(boolean isConnected);
}}

    public class MyApplication extends Application {

private static MyApplication mInstance;

@Override
public void onCreate() {
    super.onCreate();

    mInstance = this;
}

public static synchronized MyApplication getInstance() {
    return mInstance;
}

public void setConnectivityListener(ConnectivityReceiver.ConnectivityReceiverListener listener) {
    ConnectivityReceiver.connectivityReceiverListener = listener;
}}

MyApplication.java

public class ConnectivityReceiver extends BroadcastReceiver {

public static ConnectivityReceiverListener connectivityReceiverListener;

public ConnectivityReceiver() {
    super();
}

@Override
public void onReceive(Context context, Intent arg1) {
    ConnectivityManager cm = (ConnectivityManager) context
            .getSystemService(Context.CONNECTIVITY_SERVICE);
    NetworkInfo activeNetwork = cm.getActiveNetworkInfo();
    boolean isConnected = activeNetwork != null
            && activeNetwork.isConnectedOrConnecting();

    if (connectivityReceiverListener != null) {
        connectivityReceiverListener.onNetworkConnectionChanged(isConnected);
    }
}

public static boolean isConnected() {
    ConnectivityManager cm = (ConnectivityManager) MyApplication.getInstance().getApplicationContext()
            .getSystemService(Context.CONNECTIVITY_SERVICE);
    NetworkInfo activeNetwork = cm.getActiveNetworkInfo();
    return activeNetwork != null
            && activeNetwork.isConnectedOrConnecting();
}


public interface ConnectivityReceiverListener {
    void onNetworkConnectionChanged(boolean isConnected);
}}

    public class MyApplication extends Application {

private static MyApplication mInstance;

@Override
public void onCreate() {
    super.onCreate();

    mInstance = this;
}

public static synchronized MyApplication getInstance() {
    return mInstance;
}

public void setConnectivityListener(ConnectivityReceiver.ConnectivityReceiverListener listener) {
    ConnectivityReceiver.connectivityReceiverListener = listener;
}}

---

我知道这是一个空指针异常。

您是否已将

MyApplication

类添加到

AndroidManifest.xml

中？它应该是这样的：

<application
        android:name="[PATH_TO_MyApplication]"
        android:allowBackup="true"
        android:icon="@drawable/icn_app"
        android:label="@string/app_name"
        android:supportsRtl="true"
        android:theme="@style/AppTheme">

---

在您的广播接收器中，您需要初始化您的

应用程序

类，如：

 @Override
 public void onReceive(final Context context, Intent intent) {
   MyApplication mApplication = ((MyApplication)context.getApplicationContext());
 }

---

还要确保在

清单中添加类名

显然

mInstance

为

null

，因为

MyApplication

从未使用过。。。在

MyApplication

中读取

Application

类文档

onCreate

是否调用过？调用onCreate。是 啊