关于Android中的活动上下文和处理程序

Question

I am testing some stuff with handlers , and i came accross the following issue, the design og the classes itself i guess makes not much sense (passing the context of the activity to the constructor of the other class , which in turns extends Thread ), but i think it could be useful from the "academic" point of view.

so i have two class - the first one is activity , and the second one extends Thread , with the idea that the second class will pass some data to the activity , and i made a constructor which will take both the handlers from the activity and the context of that activity

PS. I found out that the Issue actually appears only when i try to pass the Location object parameters , edited the code:

the Activity part :

public class MainActivity extends Activity {





public static final String content="Asega kvo stava";
public static final Integer kom=2;
 Context m;


 private Handler nok;
 Location loc;

 String TAG="TAG";
@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);


    nok=new Handler() {

     public void handleMessage(Message msg)


    {





         Log.d(TAG, "msg: " + msg);
         Bundle m=msg.getData();




        }



    };


        new locac(nok,this).start();

and here is the other class

public class  locac   extends Thread implements LocationListener{

public static Context Ctx;
private final Handler nok; 
      LocationManager norm;

public static String moi="manag.GPS_PROVIDER";


public locac (Handler h, Context k){


    nok=h;
    Ctx=k;


}


.....

public void run ()


{
    norm=(LocationManager)Ctx.getSystemService(Ctx.LOCATION_SERVICE);
    norm.requestLocationUpdates(norm.GPS_PROVIDER, 0, 0, this);
    Location oko=norm.getLastKnownLocation(norm.GPS_PROVIDER);


          int lato=(int)oko.getLatitude();


  Message message=new Message();
              Bundle bok=new Bundle();


        int beta=145;

          bok.putInt("tok",lato);
          bok.putInt("toke",beta);
          message.setData(bok);
         nok.sendMessage(message)   ;
  }

now if i try to compile that one , it gives me the following message

  java.lang.RuntimeException: Can't create handler inside thread that has not called 
  Looper.prepare()
at android.os.Handler.<init>(Handler.java:197)
at android.os.Handler.<init>(Handler.java:111)

if i remove the context part of the Constructor of the Locac, and leave it just

public locac (Handler h){


    nok=h;

}

and then just initialize it with - new locac(nok).start(); in the Activity class , then it works fine i can't figure why calling the context within the thread class gives the Looper message , a more detailed explanation will be greatly appreciated (for learning purposes also)

Answer 1

just in case anyone is interested , it turned out that the source of the problem was the requestLocationUpdates , which invokes the LocationListener object , which in turn calls the OnChangedLocation to get the updates

if we look at the LocationManager.java

public void onLocationChanged(Location location) {
        Message msg = Message.obtain();
        msg.what = TYPE_LOCATION_CHANGED;
        msg.obj = location;
        mListenerHandler.sendMessage(msg);
    }

which means the onLocationChanged calls the mListenerHandler and therefore the looper message..

Answer 2

If you replace in your MainActivity new locac(nok,this).start(); with new locac(nok,MainActivity.this); you will not get the error, because when you use you are referring to the Thread Object and not the object. And you cannot pass a Thread Object into a Thread