Question

我正在创建一个使用改造从API获取数据的应用。所以我写了一个从BrodcaseReceiver扩展的连接接收器类来检查互联网连接和互联网连接的任何变化。

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);
}}

MyApplication.java

    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NullPointer异常。

Answer 1

在您的广播接收器中，您需要初始化application类，如：

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

另外，请确保在manifest

中添加班级名称

Answer 2

您是否已将# BEGIN WordPress <IfModule mod_rewrite.c> RewriteEngine On RewriteBase / RewriteRule ^index\.php$ - [L] RewriteCond %{REQUEST_FILENAME} !-f RewriteCond %{REQUEST_FILENAME} !-d RewriteRule . /index.php [L] </IfModule> # END WordPress课程添加到MyApplication？看起来应该是这样的：

AndroidManifest.xml

连接接收器空指针异常错误

2 个答案: