我在Activity中尝试启动Service，但出现“undefined intent constructor”的报错信息。
MyService.java代码如下：

public class MyService extends Service {

@Override
public IBinder onBind(Intent intent) {
    return null;
}

public static boolean isInstanceCreated() { 
      return instance != null; 
   }

@Override
public void onCreate() {
    Toast.makeText(this, "My Service Created", Toast.LENGTH_LONG).show();
    Log.d(TAG, "onCreate");

     instance = this;
}

@Override
public void onDestroy() {
    Toast.makeText(this, "My Service Stopped", Toast.LENGTH_LONG).show();
    Log.d(TAG, "onDestroy");
    instance = null;

}

@Override
public void onStart(Intent intent, int startid) {
            Toast.makeText(getBaseContext(), "Service started",Toast.LENGTH_SHORT).show();
    }


}

启动SampleService.java的代码如下：

  public class SampleService extends Activity{
@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.grid_activity);
    Intent myintent =new Intent(SampleService.this,MyService.this);//Error show here..
    startService(myintent);
      }
 }

在manifest file中设定service的初值如下：

<service android:enabled="true" android:name="com.MyApp.MyService" />

请大家帮我解决这个错误。

原问题：Error:undefined intent constructor when start service in android