Java类列表未从另一个类中的列表更新

Question

I do believe that answer should already be somewhere on so, but after some search I still cant figure out my problem..

public class cl1{   
private List<Map> world_map = new ArrayList<Map>();

public List<Map> returnmap(){
return world_map;
}

public void addtomap(float x, float y, int type){
Map tile = new Map();
tile.x = x;
tile.y = y;
tile.type = type;
world_map.add(tile);
}
}

Activity class:

protected void onCreate(Bundle savedInstanceState) {
    btn.setOnClickListener(new OnClickListener() {

        @Override
        public void onClick(View vw) {

            List<Map> map = new ArrayList<Map>();
            map = robot.returnmap();

            for(int i=0;i<map.size();i++){
                txt.setText(String.valueOf(i));
            }

            cl1.addtomap(x, y, 1);
            x++;
            y++;


        }

This works fine: I can add to cl1.world_map with my method from activity class, and I can also get values from world_map from my activity class.

I have another class:

protected List<Map> strap = new ArrayList<Map>();

@Override
protected void onDraw(Canvas canvas){
    super.onDraw(canvas);
    returnmap();
    canvas.drawText(String.valueOf(strap.size()), 100, 120, paint1);
}

private void returnmap(){
    strap = robot.returnmap();
}

Here I'm always getting value of 0, like the "List strap" would never update?

Answer 1

您的'robot'变量可能正在重新实例化，或者在两个类中甚至不是相同的实例，如果不是这种情况，请记住，在android中有很多事件可以让您重新获得片段或活动-实例化，您应该始终保存打算保留的状态