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copied!<p>Here is a block of code I use to rotate an imageview by one finger.</p> <pre><code>private float mCenterX, mCenterY; private float direction = 0; private float sX, sY; private float startDirection=0; private void touchStart(float x, float y) { mCenterX = this.getWidth() / 2; mCenterY = this.getHeight() / 2; sX = x; sY = y; } private void touchMove(float x, float y) { // this calculate the angle the image rotate float angle = (float) angleBetween2Lines(mCenterX, mCenterY, sX, sY, x, y); direction = (float) Math.toDegrees(angle) * -1 + startDirection; this.invalidate(); } @Override protected void onDraw(Canvas canvas) { canvas.rotate(direction, mCenterX, mCenterY); super.onDraw(canvas); } @Override public boolean onTouchEvent(MotionEvent event) { float x = event.getX(); float y = event.getY(); switch (event.getAction()) { case MotionEvent.ACTION_DOWN: // record the start position of finger touchStart(x, y); break; case MotionEvent.ACTION_MOVE: // update image angle touchMove(x, y); break; case MotionEvent.ACTION_UP: startDirection = direction; break; } return true; } public double angleBetween2Lines(float centerX, float centerY, float x1, float y1, float x2, float y2) { double angle1 = Math.atan2(y1 - centerY, x1 - centerX); double angle2 = Math.atan2(y2 - centerY, x2 - centerX); return angle1 - angle2; } </code></pre> <p>Hope this help</p> <p>Edit: Basically, what the above code does is enable user to rotate an image, and the center of the image will not change. angleBetween2Line() is to calculate the degree that finger has moved in a circle whose center is the image's center.</p>

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