Teleport the image in the touched position in canv

问题:

I have tried t create a simple canvas but the image does't appear in the touched position moves only when I drag, I want also that teleports in the touched position if the user clicks a point of the screen

My code

   public class CustomView extends View {

        Bitmap mBmp;
        Random mRnd;
        Paint mPaint;

        private static final int INVALID_POINTER_ID = -1;

        private float mPosX;
        private float mPosY;

        private float mLastTouchX;
        private float mLastTouchY;
        private int mActivePointerId = INVALID_POINTER_ID;

        private ScaleGestureDetector mScaleDetector;
        private float mScaleFactor = 1.f;

        int w, h, bw, bh;
        int px = -1, py = -1;

        public CustomView(Context context) {
            this(context, null, 0);
            mBmp = BitmapFactory.decodeResource(context.getResources(),
                    R.drawable.icon);
            mScaleDetector = new ScaleGestureDetector(context, new ScaleListener());

        }

        public CustomView(Context context, AttributeSet attrs, int defStyle) {
            super(context, attrs, defStyle);
            mScaleDetector = new ScaleGestureDetector(context, new ScaleListener());
        }

        public CustomView(Context context, AttributeSet attrs) {
            super(context, attrs, 0);
            mScaleDetector = new ScaleGestureDetector(context, new ScaleListener());

            mBmp = BitmapFactory.decodeResource(context.getResources(),
                    R.drawable.icon); 
            bw = mBmp.getWidth(); 
            bh = mBmp.getHeight();
            mPaint = new Paint(); 
            mPaint.setColor(Color.CYAN);
            mPaint.setAntiAlias(true);
            mRnd = new Random();

        }

        @Override
        protected void onDraw(Canvas canvas) {
            super.onDraw(canvas);

            canvas.save();
            Log.d("DEBUG", "X: " + mPosX + " Y: " + mPosY);
            canvas.translate(mPosX, mPosY);
            canvas.scale(mScaleFactor, mScaleFactor);

            if (px == -1 && py == -1) { 
                px = w / 2 - bw / 2; 
                py = h / 2 - bh / 2; 
            }

            canvas.drawCircle(px + (bw / 2), py + (bh / 2), 70, mPaint); 
            canvas.drawBitmap(mBmp, px, py, null); 

            canvas.restore();

        }

        public void updatePosition() {
            px = mRnd.nextInt(w - bw);
            py = mRnd.nextInt(h - bh);
            invalidate();
        }

        @Override
        protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
            w = MeasureSpec.getSize(widthMeasureSpec);
            h = MeasureSpec.getSize(heightMeasureSpec);
            setMeasuredDimension(w, h);
        }

        @Override
        public boolean onTouchEvent(MotionEvent ev) {
            mScaleDetector.onTouchEvent(ev);

            final int action = ev.getAction();
            switch (action & MotionEvent.ACTION_MASK) {
            case MotionEvent.ACTION_DOWN: {
                final float x = ev.getX();
                final float y = ev.getY();

                mLastTouchX = x;
                mLastTouchY = y;
                mActivePointerId = ev.getPointerId(0);
                break;
            }

            case MotionEvent.ACTION_MOVE: {
                final int pointerIndex = ev.findPointerIndex(mActivePointerId);
                final float x = ev.getX(pointerIndex);
                final float y = ev.getY(pointerIndex);

                if (!mScaleDetector.isInProgress()) {
                    final float dx = x - mLastTouchX;
                    final float dy = y - mLastTouchY;

                    mPosX += dx;
                    mPosY += dy;

                    invalidate();
                }

                mLastTouchX = x;
                mLastTouchY = y;

                break;
            }

            case MotionEvent.ACTION_UP: {
                mActivePointerId = INVALID_POINTER_ID;
                break;
            }

            case MotionEvent.ACTION_CANCEL: {
                mActivePointerId = INVALID_POINTER_ID;
                break;
            }

            case MotionEvent.ACTION_POINTER_UP: {
                final int pointerIndex = (ev.getAction() & MotionEvent.ACTION_POINTER_INDEX_MASK) >> MotionEvent.ACTION_POINTER_INDEX_SHIFT;
                final int pointerId = ev.getPointerId(pointerIndex);
                if (pointerId == mActivePointerId) {
                    final int newPointerIndex = pointerIndex == 0 ? 1 : 0;
                    mLastTouchX = ev.getX(newPointerIndex);
                    mLastTouchY = ev.getY(newPointerIndex);
                    mActivePointerId = ev.getPointerId(newPointerIndex);
                }
                break;
            }
            }

            return true;
        }

        private class ScaleListener extends
                ScaleGestureDetector.SimpleOnScaleGestureListener {
            @Override
            public boolean onScale(ScaleGestureDetector detector) {
                mScaleFactor *= detector.getScaleFactor();

                // Don't let the object get too small or too large.
                mScaleFactor = Math.max(0.1f, Math.min(mScaleFactor, 10.0f));

                invalidate();
                return true;
            }
        }

    }

Could someone help me? Thanks

回答1:

Don't forget to call invalidate(); so your canvas redraws in your ACTION_DOWN case statement. Also it looks like you should be setting the following in ACTION_DOWN.

                mPosX = mLastTouchX;
                mPosY = mLastTouchY;