ios - 检测用户触摸移动方向？

Question

我使用 UIBezierPath 绘制了字母 A。它具有三个方向来演示用户将如何绘制此字母表。有什么方法可以检查用户触摸移动是否在同一方向？

Answer 1

我推荐一个 UIPanGestureRecognizer。它将为您提供当前位置、从起点开始的平移和当前速度。如果您跟踪速度，您就会知道它是否与之前的速度匹配。

可以使用-[UIBezierPath containsPoint:]判断手势是否还在A内。

像这样:

- (void)panRecognizerFired:(UIPanGestureRecognizer *)panRecognizer {
    switch (panRecognizer.state) {
        case UIGestureRecognizerStatePossible:
        {
            // ignore it until it changes to UIGestureRecognizerStateBegan
            return;
        }
        case UIGestureRecognizerStateBegan:
        {
            // handle gesture start here

            // change this to a break if you want a beginning touch to be processed
            // the same as a movement
            return;
        }
        case UIGestureRecognizerStateEnded:
        {
            // handle gesture end here - clean up and undo whatever happened
            // in UIGestureRecognizerStateBegan, show a new controller or something, etc

            // change this to a break if you want an ending touch to be processed
            // the same as a movement
            return;
        }
        case UIGestureRecognizerStateFailed:
        case UIGestureRecognizerStateCancelled:
        {
            // abort! undo everything here
            return;
        }
        default:
            // it moved! break to process that movement
            break;
    }

    CGPoint location = [panRecognizer locationInView:self.theViewThatHasTheLetterAInIt];
    CGPoint translation = [panRecognizer translationInView:self.theViewThatHasTheLetterAInIt];
    CGPoint velocity = [panRecognizer velocityInView:self.theViewThatHasTheLetterAInIt];

    BOOL isLocationInsidePath = [self.letterABezierPath containsPoint:location];

    // make decisions based on isLocationInsidePath and velocity here...
}

为了确保这个手势只允许在正确的数字附近开始，使 self 符合 UIGestureRecognizerDelegate 协议(protocol)并设置 self.panGestureRecognizer.delegate = self。然后你可以用这个限制起始位置:

- (BOOL)gestureRecognizerShouldBegin:(UIGestureRecognizer *)gestureRecognizer {
    if (gestureRecognizer == self.panGestureRecognizer) {
        CGPoint location = [gestureRecognizer locationInView:self.theViewThatHasTheLetterAInIt];

        // implement this property to return the center of the 1, 2, or 3 circle
        CGPoint targetCenter = self.currentTargetCenter;

        CGFloat distanceX = location.x - targetCenter.x;
        CGFloat distanceY = location.y - targetCenter.y;
        CGFloat distanceDiagonalSquared = (distanceX * distanceX) + (distanceY * distanceY);

        const CGFloat maxDistance = 20.f;

        return (distanceDiagonalSquared <= maxDistance * maxDistance);
    }

    return YES;
}