Question

我无法从我的Android服务类打印出简单的Toast消息：

 @Override
public void run() {
    handler.post(new Runnable() {
        @Override
        public void run() {
            Toast.makeText(context, "thread is running", Toast.LENGTH_LONG).show();
        }
    }); 
  }

此run方法位于实现Runnable类的Service内部，因此我使用的是handler.post，但是无法在内部run()方法中使用任何内容。我认为handler.post发布会有用，有什么不对？

其余代码和logcat打印输出在下面;

public class LotteryServer extends Service implements Runnable {

            Handler handler = new Handler();
            Context context = this;

            @Override
            public int onStartCommand(Intent intent, int flags, int startId){
                 super.onStartCommand(intent, startId, startId);
                 Toast.makeText(context, "My Service Started", Toast.LENGTH_LONG).show();
                 return START_STICKY;
            }

            @Override
            public IBinder onBind(Intent arg0) {
                 // TODO Auto-generated method stub
                 return null;
            }
            @Override   
            public void onDestroy() {
                super.onDestroy();
                Toast.makeText(context, "My Service Stopped", Toast.LENGTH_LONG).show();
            }
            @Override
            public void run() {
            handler.post(new Runnable() {
                     @Override
                     public void run() {
                          Toast.makeText(context, "thread is running",     Toast.LENGTH_LONG).show();
                     }
            }); 

    }
}

logcat的;

02-21 15:09:33.279: E/AndroidRuntime(24038): FATAL EXCEPTION: main
02-21 15:09:33.279: E/AndroidRuntime(24038): java.lang.NullPointerException
02-21 15:09:33.279: E/AndroidRuntime(24038): at android.content.ContextWrapper.getResources(ContextWrapper.java:81)
02-21 15:09:33.279: E/AndroidRuntime(24038):    at android.widget.Toast.<init>(Toast.java:92)
02-21 15:09:33.279: E/AndroidRuntime(24038):    at android.widget.Toast.makeText(Toast.java:233)
02-21 15:09:33.279: E/AndroidRuntime(24038):    at com.lottery.clientplayer.LotteryServer$1.run(LotteryServer.java:44)
02-21 15:09:33.279: E/AndroidRuntime(24038):    at android.os.Handler.handleCallback(Handler.java:605)
02-21 15:09:33.279: E/AndroidRuntime(24038):    at android.os.Handler.dispatchMessage(Handler.java:92)
02-21 15:09:33.279: E/AndroidRuntime(24038):    at android.os.Looper.loop(Looper.java:137)
02-21 15:09:33.279: E/AndroidRuntime(24038):    at android.app.ActivityThread.main(ActivityThread.java:4699)
02-21 15:09:33.279: E/AndroidRuntime(24038):    at java.lang.reflect.Method.invokeNative(Native Method)
02-21 15:09:33.279: E/AndroidRuntime(24038):    at java.lang.reflect.Method.invoke(Method.java:511)
02-21 15:09:33.279: E/AndroidRuntime(24038):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:790)
02-21 15:09:33.279: E/AndroidRuntime(24038):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:557)
02-21 15:09:33.279: E/AndroidRuntime(24038):    at dalvik.system.NativeStart.main(Native Method)

Answer 1

更改此

Toast.makeText(context, "thread is running", Toast.LENGTH_LONG).show();

到

Toast.makeText(LotteryServer.this, "thread is running", Toast.LENGTH_LONG).show();

Answer 2

Toast.makeText(context, "thread is running", Toast.LENGTH_LONG).show();

相反上下文使用getApplicationContext（）希望这可以工作..因为这将获得整个Context的scop。试试吧

Answer 3

使用runOnUIThread（Runnable）如果这不起作用，试试这个

Handler mHandler = new Handler();
final Runnable mUpdateResults = new Runnable() {
public void run() {
    Toast(this, message, duration).show();
}

new Thread() {
 public void run() {
    mHandler.post(mUpdateResults);
 }
}.start();

在新的线程中使用Handler的空指针异常在Service，Android中启动

3 个答案: