简单的一触式“绘图视图”，但在触摸完成之前继续获得ACTION_CANCEL

Question

This has been driving me crazy.

I think I have everything in place but no matter what I do the touches seem to be cancelled before I lift my finger off the view. Even stranger I can draw long horizontal lines but vertical ones are always very short.

I am using a Samsung G SII 2.3.3 but building to 2.1

Ant ideas?

My sample code:

  package com.mycompany.myviews;

  import java.util.ArrayList;

  import android.content.Context;
  import android.graphics.Canvas;
  import android.graphics.Color;
  import android.graphics.Paint;
  import android.graphics.Path;
  import android.graphics.Point;
  import android.util.AttributeSet;
  import android.util.Log;
  import android.view.MotionEvent;
  import android.view.View;

  public class CustomView extends View
  {
    private ArrayList<DrawPoint> points = new ArrayList<DrawPoint>();

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

    public void addPoint(DrawPoint p)
    {
      points.add(p);
    }

      public boolean onTouchEvent (MotionEvent event)
      {
        DrawPoint p = new DrawPoint((int)event.getX(), (int)event.getY());

        switch(event.getAction())
        {
        case android.view.MotionEvent.ACTION_DOWN:
          p.start = true;
          break;

        case android.view.MotionEvent.ACTION_CANCEL:
          Log.d("TouchView", "On Touch cancelled.");
          break;
        }

        addPoint(p);
        invalidate();

        return true;
      }

    public void onDraw(Canvas c) 
    {
        super.onDraw(c);

        Path path = new Path();

        for (int i = 0; i < points.size(); i++)
        {
          DrawPoint currentPoint = points.get(i);
          if (currentPoint.start == true)
            path.moveTo(currentPoint.p.x, currentPoint.p.y);
          else
            path.lineTo(currentPoint.p.x, currentPoint.p.y);
        }

        Paint paint = new Paint();
        paint.setStyle(Paint.Style.STROKE);
        paint.setStrokeWidth(2);
        paint.setColor(Color.BLACK);
        c.drawPath(path, paint);
    }

    private class DrawPoint
    {
      public boolean start = false;
      public Point p;

      DrawPoint(int x, int y)
      {
        p = new Point(x, y);
      }
    }
  }

UPDATE: OK, I figured this out. Because this view is inside another View some of the touches are being intercepted by the parent or parents.

The solution I have found to be good enough for my needs is to add the following line into the case for ACTION_DOWN :

getParent().requestDisallowInterceptTouchEvent(true);

This then allows my view to get all touches.

Answer 1

The solution I have found to be good enough for my needs is to add the following line into the case for ACTION_DOWN :

getParent().requestDisallowInterceptTouchEvent(true);

This then allows my view to get all touches.

Answer 2

I edited my answer...

I found a finger-painting example in the Android Samples, and also a discussion about that example on stackoverflow. Hope this helps you out.

http://developer.android.com/resources/samples/ApiDemos/src/com/example/android/apis/graphics/FingerPaint.html

Android FingerPaint Example using Canvas, what is the offscreen Canvas?

My original post...

I don't have a solution, but did find a site that might give you some ideas on what you could do...

http://bestsiteinthemultiverse.com/2008/11/android-graphics-example/