来自服务类本身的startService()

Question

我尝试从服务的类启动一个Android服务.这样做的原因是为了实现一些平台独立性.

这样做我在android.content.ContextWrapper.startService(ContextWrapper.java:326)上得到一个NullPointerException.平台目标是2.1-update1,有什么建议吗？

请参阅下面的代码(我保留了导入以节省一些空间)

/* GUI: HelloAndroid.java */
package com.example.helloandroid;

public class HelloAndroid extends Activity {
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);

        // that works!
        startService(new Intent("com.example.helloandroid.UnusualService"));

        // stop the service works of course, too
        stopService(new Intent("com.example.helloandroid.UnusualService"));

        // unusual start does not work:
        UnusualService myService = new UnusualService();
        myService.startService();
    }
}

/* Service: UnusualService.java */
package com.example.helloandroid;

public class UnusualService extends Service {    
    @Override
    public void onCreate() {
        Toast.makeText(this, R.string.service_started, Toast.LENGTH_SHORT).show();
    }

    @Override
    public void onDestroy() {
        Toast.makeText(this, R.string.service_stopped, Toast.LENGTH_SHORT).show();
    }

    @Override
    public IBinder onBind(Intent intent) {
        return null; // make something here when the rest works 
    }

    public void startService() {
        // folowing line will cause the NullPointerException
        startService(new Intent("com.example.helloandroid.UnusualService"));
    }

    public void stopService() {
        stopSelf();
    }
}

Answer 1

当然 - 您新创建的服务没有对​​上下文的引用,因此上下文是null因此系统会抛出一个NullPointerException.请记住:不要使用自己创建服务new- 系统会为您执行此操作!