我正在尝试检查实现ConnectivityReceiver.ConnectivityReceiverListener的片段中的互联网连接。守则如下
ConnectivityReceiver.java
import android.content.BroadcastReceiver;
import android.content.Context;
import android.content.Intent;
import android.net.ConnectivityManager;
import android.net.NetworkInfo;
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
import android.app.Application;
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;
}
}
片段活动有代码
@Override
public void onResume() {
super.onResume();
// register connection status listener
MyApplication.getInstance().setConnectivityListener(this);
}
我已经改变了＃34;这个＆＃34; getactivity（）并尝试过。它没有产生任何结果。我使用它时的堆栈跟踪如下
E/AndroidRuntime: FATAL EXCEPTION: main
Process: highski.developers.cflash, PID: 26183
java.lang.RuntimeException: Unable to resume activity {highski.developers.cflash/highski.developers.cflash.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'void highski.developers.cflash.connection_check.MyApplication.setConnectivityListener(highski.developers.cflash.connection_check.ConnectivityReceiver$ConnectivityReceiverListener)' on a null object reference
at android.app.ActivityThread.performResumeActivity(ActivityThread.java:2986)
at android.app.ActivityThread.handleResumeActivity(ActivityThread.java:3017)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2392)
at android.app.ActivityThread.access$800(ActivityThread.java:151)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1303)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:135)
at android.app.ActivityThread.main(ActivityThread.java:5254)
at java.lang.reflect.Method.invoke(Native Method)
at java.lang.reflect.Method.invoke(Method.java:372)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:903)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:698)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void highski.developers.cflash.connection_check.MyApplication.setConnectivityListener(highski.developers.cflash.connection_check.ConnectivityReceiver$ConnectivityReceiverListener)' on a null object reference
at highski.developers.cflash.fragments.HomeFragment.onResume(HomeFragment.java:362)
at android.support.v4.app.Fragment.performResume(Fragment.java:2020)
at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1107)
at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1252)
at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1234)
at android.support.v4.app.FragmentManagerImpl.dispatchResume(FragmentManager.java:2056)
at android.support.v4.app.FragmentController.dispatchResume(FragmentController.java:196)
at android.support.v4.app.FragmentActivity.onResumeFragments(FragmentActivity.java:504)
at android.support.v4.app.FragmentActivity.onPostResume(FragmentActivity.java:493)
at android.support.v7.app.AppCompatActivity.onPostResume(AppCompatActivity.java:178)
at android.app.Activity.performResume(Activity.java:6089)
at android.app.ActivityThread.performResumeActivity(ActivityThread.java:2975)
at android.app.ActivityThread.handleResumeActivity(ActivityThread.java:3017)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2392)
at android.app.ActivityThread.access$800(ActivityThread.java:151)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1303)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:135)
at android.app.ActivityThread.main(ActivityThread.java:5254)
at java.lang.reflect.Method.invoke(Native Method)
at java.lang.reflect.Method.invoke(Method.java:372)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:903)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:698)
请让我知道错误是什么以及如何解决。
答案 0 :(得分：3)
首先检查getInstance方法是否返回null，如果是，则检查Android Manifest。
你的清单应该包含类似的内容：
SELECT t.Name,
p.[Value],
MIN(t.[Timestamp]) as EarliestTimestamp ,
MAX(t.[Timestamp]) as LatestTimestamp
FROM Table1 t
OUTER APPLY (SELECT TOP 1 * FROM Table1 WHERE t.Name = Name ORDER BY [Timestamp] DESC) p
GROUP BY t.Name, p.[Value]
答案 1 :(得分：0)
必须是您的应用程序未在清单中声明，添加它。
和两个建议： 首先，connectivityReceiverListener是静态的，你注册它，记得unRegister它，否则它会泄漏内存。 其次，你的get实例是复杂而低效的，不需要使用synchronized方法！只需使用MyApplication.sIntance（声明公开）。