Question

I have this class:
My problem:

public class Example extends Activity implements OnClickListener{
    DrawView view1;
    Canvas canvas = new Canvas();

    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);   
        view1 = new DrawView(this);
        setContentView(view1);
    }


    @Override
    public boolean onTouchEvent(MotionEvent event) {
    int x = (int) event.getX();
    int y = (int) event.getY();

    switch (event.getAction()) {
        case MotionEvent.ACTION_DOWN:
            view1.setFirstCoord(x, y);
            break;
        case MotionEvent.ACTION_MOVE:
            break;
        case MotionEvent.ACTION_UP:
            view1.setSecondCoord(x, y);
            view1.dispatchDraw(canvas);
            break;
        }
    return true;
    }

    public class DrawView extends LinearLayout {
        private Paint paint = new Paint();
        public int x1, x2;
        public int y1, y2;

        public DrawView(Context c){
            super(c);           
            LayoutInflater inflater = (LayoutInflater) c.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
            addView(inflater.inflate(R.layout.union, null));

            x1 = 0;
            x2 = 0;
            y1 = 0;
            y2 = 0;

            paint.setColor(Color.BLACK);
            paint.setAntiAlias(true);
            paint.setDither(true);
            paint.setStyle(Paint.Style.STROKE);
            paint.setStrokeJoin(Paint.Join.ROUND);
            paint.setStrokeWidth(10);        
        }

        @Override
        public void dispatchDraw(Canvas canvas) {
            super.dispatchDraw(canvas);
            canvas.drawLine(0, 50, 900,2000 , paint);//WORKS
            canvas.drawLine((int) x1, (int) y1,(int) x2,(int) y2, paint);//NO WORKS
        }

        public void setFirstCoord(int e, int f){
            x1 = e;
            y1 = f;
        }

        public void setSecondCoord(int e, int f){
            x2 = e;
            y2 = f;
        }
    }
}

When the next line is executed I see the “example” line on the screem:

canvas.drawLine(0, 50, 900,2000 , paint);

But when the following line “is executed” is not painted any straight line. Why???

canvas.drawLine((int) x1, (int) y1,(int) x2,(int) y2, paint);

I also tried with:

canvas.drawLine(x1, y1, x2, y2, paint);

But, obviously, the results are the same.

I also tried with executed a onDraw() method but any line is painted because onDraw paint under de “UI” (under the content of the layout .xml file)

I hope found somebody who can help me. I think the solution can very easy but I’m going crazy trying things without finding the solution.

Thanks!!!

The solution:

public class Example extends Activity implements OnClickListener{
    DrawView view1;
    Canvas canvas = new Canvas();

    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);   
        view1 = new DrawView(this);
        setContentView(view1);
        view1.setOnClickListener(this);
    }

    public class DrawView extends LinearLayout {
        private Paint paint = new Paint();
        public int x1, x2;
        public int y1, y2;

        public DrawView(Context c){
            super(c);           
            LayoutInflater inflater = (LayoutInflater) c.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
            addView(inflater.inflate(R.layout.union, null));

            x1 = 0;
            x2 = 0;
            y1 = 0;
            y2 = 0;

            paint.setColor(Color.BLACK);
            paint.setAntiAlias(true);
            paint.setDither(true);
            paint.setStyle(Paint.Style.STROKE);
            paint.setStrokeJoin(Paint.Join.ROUND);
            paint.setStrokeWidth(10);        
        }

        public boolean onTouchEvent(MotionEvent event) {
        int x = (int) event.getX();
        int y = (int) event.getY();

        switch (event.getAction()) {
        case MotionEvent.ACTION_DOWN:
            view1.setFirstCoord(x, y);
            break;
        case MotionEvent.ACTION_MOVE:
            break;
        case MotionEvent.ACTION_UP:
            view1.setSecondCoord(x, y);
            view1.onDraw(canvas);
            view1.postInvalidate();
            break;
        }
        return true;
        }

        public void setFirstCoord(int e, int f){
            x1 = e;
            y1 = f;
        }

        public void setSecondCoord(int e, int f){
            x2 = e;
            y2 = f;
        }

        public void onDraw(Canvas canvas){
        canvas.drawLine((int) x1, (int) y1,(int) x2,(int) y2, paint);
    }
    }
}

THANKS AGAIN for your help and your attention. It’s a pleasure!!!

Answer 1

Instead of putting your drawing code in dispatch draw, try putting it in onDraw.

Then modify your onTouch method to look like this:

@Override
public boolean onTouchEvent(MotionEvent event) {
  int x = (int) event.getX();
  int y = (int) event.getY();
  switch (event.getAction()) {
    case MotionEvent.ACTION_DOWN:
    view1.setFirstCoord(x, y);
    break;
    case MotionEvent.ACTION_MOVE:
    break;
    case MotionEvent.ACTION_UP:
    view1.setSecondCoord(x, y);
    view1.postInvalidate();
    break;
  }
   return true;
}