Android How to Call Method From Another Class

Question

Right now I'm working on app that will draw line on onClick. I'm drawing line in LineView.java class and performing onClick method in MainActivity.java. To solve this problem I have checked similar questions. The first solution:

LineView.onDraw();

It gives me this error:

Multiple markers at this line
    - The method onDraw(Canvas) in the type LineView is not applicable for the 
     arguments ()
    - Suspicious method call; should probably call "draw" rather than "onDraw"

Also I tried to write in MainActivity:

LineView lineView = new LineView(null);
lineView.onDraw();

But it also gives an error:

Multiple markers at this line
    - The method onDraw(Canvas) in the type LineView is not applicable for the 
     arguments ()
    - Suspicious method call; should probably call "draw" rather than "onDraw"

Here's my LineView.java:

public class LineView extends View {
Paint paint = new Paint();
Point A;
Point B;
boolean draw = false;

public void onCreate(Bundle savedInstanceState) {

}

public LineView(Context context, AttributeSet attrs) {
  super(context, attrs);
  }

public LineView(Context context, AttributeSet attrs, int defstyle) {
super(context, attrs, defstyle );
  }


public LineView(Context context) {
super(context);
paint.setColor(Color.BLACK);
}

@Override
public void onDraw(Canvas canvas) {
    draw = MainActivity.draw;
    if(draw){
    //A = (getIntent().getParcelableExtra("PointA"));
    A = MainActivity.A;
    B = MainActivity.B;

    canvas.drawLine(A.x, A.y, B.x, B.y, paint);
    }
}

private Intent getIntent() {
    // TODO Auto-generated method stub
    return null;
}

}

My MainActivity.java onClick:

 @Override
       public void onClick(View v) {
           draw = true;
                       LineView.onDraw();
                     }
   });

Thanks in advance!

Answer 1

You are not supposed to call onDraw() on any View directly. Views draw themselves if they are visible and in the view hierarchy. If you need the view to draw itself because something has changed (like your A and B variables), then you should do something like this :

LineView.invalidate();

invalidate() tells the UI system that the view has changed and onDraw() should be called at some point in the near future (probably the next iteration of the UI thread).

I think your 'draw' variable is probably unnecessary. If you want to hide the view sometimes, then use setVisibility() instead.