Question

I have DrawView. If I touch this view it draws small circles. I wont to draw circles but not to touch view – with help function “setPoints”. What I do:

package com.samples;
import ...

public class DrawView extends View {
    ArrayList<Point> points = new ArrayList<Point>();

    Paint paint = new Paint();

    private int pSize = 5;
    private int pColor = Color.BLACK;

    public DrawView(Context context, AttributeSet attrs) {

        super(context, attrs);

        setFocusable(true);
        setFocusableInTouchMode(true);

        this.setOnTouchListener(new View.OnTouchListener() {
            @Override
            public boolean onTouch(View v, MotionEvent event) {
                v.setOnTouchListener(this);
                    Point point = new Point();
                    point.x = event.getX();
                    point.y = event.getY();
                    points.add(point); 
                    invalidate();
                }
                return true;
            }
        });
        requestFocus();
    }

    @Override
    public void onDraw(Canvas canvas) { 
        for (Point point : points) {
            canvas.drawCircle(point.x, point.y, pSize, paint);
        }
    }

    public void setPoints(Float xP, Float yP)
    {
        Point point = new Point();
        point.x = xP;
        point.y = yP;
        points.add(point);
        postInvalidate();
    }
}

class Point {
    float x, y;

    @Override
    public String toString() {
        return x + ", " + y;
    }
}

Please tell me, how get canvas out setPoints function?

Update:
Wow, it’s really interesting problem. My DrawView contains in HorizontalScrollView. Because if I set in this DrawView right coordinates, no one knows where are drawable circles.

Answer 1

You can’t. The canvas is managed by the system and is passed to your onDraw(). I don’t understand why you’d need it outside of there. Just redeclare setPoints like this

public void setPoints(Canvas canvas, Float xP, Float Yp)

You can keep a cache of the previous drawings (or store the previous points)