invalidate里放着ONDRAW的方法，当调用I时，会自动更新图片

如果上次记录的位置在-1，那么就更新为现在的位置，更新后就不再为-1了，就不再变了

也就是说是保留第一次触碰到的位置

public class CustomView extends View {private int mLastX, mLastY;private boolean isDragging = false;public CustomView(Context context) {super(context);}@Overridepublic boolean onTouchEvent(MotionEvent event) {int action = event.getAction();int currX = (int) event.getX();int currY = (int) event.getY();switch (action) {case MotionEvent.ACTION_DOWN:if (event.getPointerCount() == 1) {isDragging = true;}mLastX = currX;mLastY = currY;break;case MotionEvent.ACTION_MOVE:if (isDragging) {int dx = currX - mLastX;int dy = currY - mLastY;// 拖拽int left = getLeft() + dx;int top = getTop() + dy;int right = getRight() + dx;int bottom = getBottom() + dy;layout(left, top, right, bottom);} else {int dx = currX - mLastX;int dy = currY - mLastY;// 拉伸ViewGroup.LayoutParams layoutParams = getLayoutParams();layoutParams.width += dx;layoutParams.height += dy;setLayoutParams(layoutParams);}mLastX = currX;mLastY = currY;break;case MotionEvent.ACTION_UP:isDragging = false;break;}return true;}
}

public class CustomView extends View {private int mLastX, mLastY;private boolean isDragging = false;private boolean isScaling = false;private float initialDistance;public CustomView(Context context) {super(context);}@Overridepublic boolean onTouchEvent(MotionEvent event) {int action = event.getAction();int currX = (int) event.getX();int currY = (int) event.getY();switch (action & MotionEvent.ACTION_MASK) {case MotionEvent.ACTION_DOWN:if (event.getPointerCount() == 1) {isDragging = true;}mLastX = currX;mLastY = currY;break;case MotionEvent.ACTION_POINTER_DOWN:if (event.getPointerCount() == 2) {isDragging = false;isScaling = true;initialDistance = getDistance(event);}break;case MotionEvent.ACTION_MOVE:if (isDragging) {int dx = currX - mLastX;int dy = currY - mLastY;// 拖拽int left = getLeft() + dx;int top = getTop() + dy;int right = getRight() + dx;int bottom = getBottom() + dy;layout(left, top, right, bottom);} else if (isScaling) {float currentDistance = getDistance(event);float scale = currentDistance / initialDistance;// 拉伸ViewGroup.LayoutParams layoutParams = getLayoutParams();layoutParams.width *= scale;layoutParams.height *= scale;setLayoutParams(layoutParams);}break;case MotionEvent.ACTION_POINTER_UP:if (event.getPointerCount() == 2) {isScaling = false;}break;case MotionEvent.ACTION_UP:isDragging = false;isScaling = false;break;}return true;}private float getDistance(MotionEvent event) {float dx = event.getX(0) - event.getX(1);float dy = event.getY(0) - event.getY(1);return (float) Math.sqrt(dx * dx + dy * dy);}
}