iphone - iPhone-惯性拖动

Question

我有一个用户必须在屏幕上拖动的对象。这是一个常规的UIImageView。当前，可以拖动图像，但是在释放图像时，它会停在手指抬起图像的位置。我想要的是创造动量，这样我就可以给图像带来冲动，并且它会滚动直到它反弹到屏幕边缘为止。

我不想像添加物理库之类的东西那么复杂。我想将其保持在最低限度。

我怎么做？你们能指出我一些指导或正确的方向吗？

谢谢。

Answer 1

在不使用任何物理库的情况下执行此操作的一种方法是:

首先在您的类中创建4个实例变量，如下所示:

CFTimeInterval startTime;
CGPoint startPoint;
CGPoint oldPoint;
BOOL imageViewTouched;

在您的 - (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event方法中要有以下代码:

- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event
{
    UITouch *touch = [[event allTouched] anyObject];
    // Test to see if the touched view is your image view. If not just return.
    if (touch.view != <#yourImageView#>) {
        return;
    }

    startPoint = [touch locationInView:self.view];
    oldPoint = startPoint;
    startTime = CACurrentMediaTime();
    imageViewTouched = YES;
}

对于 - (void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event，请执行以下操作:

- (void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event
{
    // Fingers were moved on the screen but your image view was not touched in the beginning
    if (!imageViewTouched) {
        return;
    }

    UITouch *touch = [[event allTouches] anyObject];
    CGPoint newPoint = [touch locationInView:self.view];

    <#yourImageView#>.frame = CGRectOffset(<#yourImageView#>.frame, newPoint.x - oldPoint.x, newPoint.y - oldPoint.y);
    oldPoint = newPoint;
}

现在为 - (void)touchesEnded:(NSSet *)touches withEvent:(UIEvent *)event尝试以下操作:

- (void)touchesEnded:(NSSet *)touches withEvent:(UIEvent *)event
{
    // Fingers were removed from the screen but your image view was not touched in the beginning
    if (!imageViewTouched) {
        return;
    }

    imageViewTouched = NO;

    UITouch *touch = [[event allTouches] anyObject];
    CGPoint endPoint = [touch locationInView:self.view];
    CFTimeInterval endTime = CACurrentMediaTime();

    CFTimeInterval timeDifference = endTime - startTime;

    // You may play with this value until you get your desired effect
    CGFloat maxSpeed = 80;

    CGFloat deltaX = 0;
    CGFloat deltaY = 0;

    if (timeDifference < 0.35) {
        deltaX = (endPoint.x - startPoint.x) / (timeDifference * 10);
        deltaY = (endPoint.y - startPoint.y) / (timeDifference * 10);
    }

    if      (deltaX > maxSpeed)         { deltaX =  maxSpeed; }
    else if (deltaX < -maxSpeed)        { deltaX = -maxSpeed; }
    else if (deltaX > -5 && deltaX < 5) { deltaX = 0; }

    if      (deltaY > maxSpeed)         { deltaY =  maxSpeed; }
    else if (deltaY < -maxSpeed)        { deltaY = -maxSpeed; }
    else if (deltaY > -5 && deltaY < 5) { deltaY = 0; }

    [UIView begginAnimations:nil context:nil];
    [UIView setAnimationDuration:0.5f];
    [UIView setAnimationCurve:UIViewAnimationCurveEaseOut];

    <#yourImageView#>.frame = CGRectOffset(<#yourImageView#>.frame, deltaX, deltaY);

    [UIView commitAnimations];
}

请让我知道这是否有意义和/或对您有用。干杯!