向 UIPanGestureRecognizer 添加惯性

Question

我试图在屏幕上移动一个子视图，但我也想为对象添加惯性或动量。
我已经拥有的 UIPanGestureRecognizer 代码如下。

提前致谢。

UIPanGestureRecognizer *panGesture = [[UIPanGestureRecognizer alloc] initWithTarget:self       action:@selector(handlePan:)];
[self addGestureRecognizer:panGesture];

(void)handlePan:(UIPanGestureRecognizer *)recognizer
{

    CGPoint translation = [recognizer translationInView:self.superview];
    recognizer.view.center = CGPointMake(recognizer.view.center.x + translation.x,
                                     recognizer.view.center.y + translation.y);
    [recognizer setTranslation:CGPointMake(0, 0) inView:self.superview];

    if (recognizer.state == UIGestureRecognizerStateEnded) {
        [self.delegate card:self.tag movedTo:self.frame.origin];
    }
}

再次感谢。

Answer 1

看看RotationWheelAndDecelerationBehaviour。有一个示例说明如何对线性平移和旋转运动进行减速。诀窍是查看用户结束触摸并以小减速继续朝该方向前进时的速度。

Answer 2

好吧，我不是专业人士，但检查了多个答案后，我设法编写了自己的代码，我对此很满意。

请告诉我如何改进它以及我是否使用了任何不良做法。

- (IBAction)handlePan:(UIPanGestureRecognizer *)recognizer {

CGPoint translatedPoint = [recognizer translationInView:self.postViewContainer];
CGPoint velocity = [recognizer velocityInView:recognizer.view];

float bottomMargin = self.view.frame.size.height - containerViewHeight;
float topMargin = self.view.frame.size.height - scrollViewHeight;

if ([recognizer state] == UIGestureRecognizerStateChanged) {

    newYOrigin = self.postViewContainer.frame.origin.y + translatedPoint.y;

    if (newYOrigin <= bottomMargin  && newYOrigin >= topMargin) {
        self.postViewContainer.center = CGPointMake(self.postViewContainer.center.x, self.postViewContainer.center.y + translatedPoint.y);
    }
    [recognizer setTranslation:CGPointMake(0, 0) inView:self.postViewContainer];
}

if ([recognizer state] == UIGestureRecognizerStateEnded) {

    __block float newYAnimatedOrigin = self.postViewContainer.frame.origin.y + (velocity.y / 2.5);

    if (newYAnimatedOrigin <= bottomMargin && newYAnimatedOrigin >= topMargin) {
        [UIView animateWithDuration:1.2 delay:0
                            options:UIViewAnimationOptionCurveEaseOut
                         animations:^ {
                             self.postViewContainer.center = CGPointMake(self.postViewContainer.center.x, self.postViewContainer.center.y + (velocity.y / 2.5));
                         }
                         completion:^(BOOL finished) {
                             [self.postViewContainer setFrame:CGRectMake(0, newYAnimatedOrigin, self.view.frame.size.width, self.view.frame.size.height - newYAnimatedOrigin)];
                         }
         ];
    }
    else {
        [UIView animateWithDuration:0.6 delay:0
                            options:UIViewAnimationOptionCurveEaseOut
                         animations:^ {
                             if (newYAnimatedOrigin > bottomMargin) {
                                 self.postViewContainer.center = CGPointMake(self.postViewContainer.center.x, bottomMargin + self.postViewContainer.frame.size.height / 2);
                             }

                             if (newYAnimatedOrigin < topMargin) {
                                 self.postViewContainer.center = CGPointMake(self.postViewContainer.center.x, topMargin + self.postViewContainer.frame.size.height / 2);
                             }
                         }
                         completion:^(BOOL finished) {
                             if (newYAnimatedOrigin > bottomMargin)
                                 [self.postViewContainer setFrame:CGRectMake(0, bottomMargin, self.view.frame.size.width, scrollViewHeight)];

                             if (newYAnimatedOrigin < topMargin)
                                 [self.postViewContainer setFrame:CGRectMake(0, topMargin, self.view.frame.size.width, scrollViewHeight)];
                         }
         ];
    }
}

}

我使用了两种不同的动画，一种是默认惯性，另一种是当用户高速甩动 containerView 时。

它在 iOS 7 下运行良好。

Answer 3

我从公认答案的实施中获得灵感。这是 Swift 5.1 版本。

---

逻辑：

• 您需要计算角度随平移手势结束时的速度变化，并在无休止的计时器中继续旋转滚轮，直到速度因减速率而磨损。
• 在计时器的每次迭代中不断降低当前速度 有一些因素（比如，0.9）。
• 保持速度的下限 使计时器无效并完成减速过程。

---

用于计算减速度的主函数：

// deceleration behaviour constants (change these for different deceleration rates)
private let timerDuration = 0.025
private let decelerationSmoothness = 0.9
private let velocityToAngleConversion = 0.0025

private func animateWithInertia(velocity: Double) {
    _ = Timer.scheduledTimer(withTimeInterval: self.timerDuration, repeats: true) { [weak self] timer in
        guard let this = self else {
            return
        }
        let concernedVelocity = this.currentVelocity == 0.0 ? velocity : this.currentVelocity
        let newVelocity = concernedVelocity * this.decelerationSmoothness
        this.currentVelocity = newVelocity
        var angleTraversed = newVelocity * this.velocityToAngleConversion * this.maximumRotationAngleInCircle
        if !this.isClockwiseRotation {
            angleTraversed *= -1
        }
        // exit condition
        if newVelocity < 0.1 {
            timer.invalidate()
            this.currentVelocity = 0.0
        } else {
            this.traverseAngularDistance(angle: angleTraversed)
        }
    }
}

---

handlePanGesture 函数中包含上述函数的辅助函数、扩展和用法的完整工作代码。

// deceleration behaviour constants (change these for different deceleration rates)
private let timerDuration = 0.025
private let decelerationSmoothness = 0.9
private let velocityToAngleConversion = 0.0025

private let maximumRotationAngleInCircle = 360.0

private var currentRotationDegrees: Double = 0.0 {
    didSet {
        if self.currentRotationDegrees > self.maximumRotationAngleInCircle {
            self.currentRotationDegrees = 0
        }
        if self.currentRotationDegrees < -self.maximumRotationAngleInCircle {
            self.currentRotationDegrees = 0
        }
    }
}
private var previousLocation = CGPoint.zero
private var currentLocation = CGPoint.zero
private var velocity: Double {
    let xFactor = self.currentLocation.x - self.previousLocation.x
    let yFactor = self.currentLocation.y - self.previousLocation.y
    return Double(sqrt((xFactor * xFactor) + (yFactor * yFactor)))
}

private var currentVelocity = 0.0
private var isClockwiseRotation = false

@objc private func handlePanGesture(panGesture: UIPanGestureRecognizer) {
    let location = panGesture.location(in: self)

    if let rotation = panGesture.rotation {
        self.isClockwiseRotation = rotation > 0
        let angle = Double(rotation).degrees
        self.currentRotationDegrees += angle
        self.rotate(angle: angle)
    }

    switch panGesture.state {
    case .began, .changed:
        self.previousLocation = location
    case .ended:
        self.currentLocation = location
        self.animateWithInertia(velocity: self.velocity)
    default:
        print("Fatal State")
    }
}

private func animateWithInertia(velocity: Double) {
    _ = Timer.scheduledTimer(withTimeInterval: self.timerDuration, repeats: true) { [weak self] timer in
        guard let this = self else {
            return
        }
        let concernedVelocity = this.currentVelocity == 0.0 ? velocity : this.currentVelocity
        let newVelocity = concernedVelocity * this.decelerationSmoothness
        this.currentVelocity = newVelocity
        var angleTraversed = newVelocity * this.velocityToAngleConversion * this.maximumRotationAngleInCircle
        if !this.isClockwiseRotation {
            angleTraversed *= -1
        }
        if newVelocity < 0.1 {
            timer.invalidate()
            this.currentVelocity = 0.0
            this.selectAtIndexPath(indexPath: this.nearestIndexPath, shouldTransformToIdentity: true)
        } else {
            this.traverseAngularDistance(angle: angleTraversed)
        }
    }
}

private func traverseAngularDistance(angle: Double) {
    // keep the angle in -360.0 to 360.0 range
    let times = Double(Int(angle / self.maximumRotationAngleInCircle))
    var newAngle = angle - times * self.maximumRotationAngleInCircle
    if newAngle < -self.maximumRotationAngleInCircle {
        newAngle += self.maximumRotationAngleInCircle
    }
    self.currentRotationDegrees += newAngle
    self.rotate(angle: newAngle)
}

上面代码中使用的扩展：

extension UIView {
    func rotate(angle: Double) {
        self.transform = self.transform.rotated(by: CGFloat(angle.radians))
    }
}

extension Double {
    var radians: Double {
        return (self * Double.pi)/180
    }

    var degrees: Double {
        return (self * 180)/Double.pi
    }
}