从asynctask调用活动方法

Question

I have two classes: Main - Activity and Second - AsyncTask . I want to fire mymethod on button click.

I have tried.

public class Second extends AsyncTask<Void, Void, Void> {

    Main main;

    @Override
    protected void onProgressUpdate(Void... values) {
    // TODO Auto-generated method stub
    super.onProgressUpdate(values);

    main = new Main(); //Wrong because is an Activity

    Button con = (Button)activity.findViewById(R.id.con);

    con.setOnClickListener(new View.OnClickListener() {

        @Override
        public void onClick(View v) {
             // TODO Auto-generated method stub
            main.mymethod(v);
        }
     });
   }
}

But it throws java.lang.IllegalStateException: System services not available to Activities before onCreate() .

Answer 1

It looks like you never set main to an instance so it is null .

You need to do something like

Main main = new Main();

In fact since you are referencing main from an inner class you also need to make main final so it can be referenced by the inner class:

final Main main = new Main();

Answer 2

Your asynctask class should be a private inner class of Main. This way you will be able to access everything you want from Main while in Second

The solution where you would pass the main Activity as param to Second would be a bad idea as the activity could be leaked as Second would still have a reference to Main while the system would want to destroy main.

Answer 3

If you really need to call your mymethod(View v) then write it within another separate class , better as static method , it will help you to use that method without taking instance of the class. You probably can't use the method of other Activity like you want because as it's a Activity so it must run onCreate before you can use it. Hope it helps.