将UIImageView / UIView拖到1轴上而没有view.center跳转到触摸位置（从视图上的任何位置拖动以在x轴上移动）

Question

I'm creating a draggable UIImageView much like the iPhone/iPod Touch's "Slide to Unlock" slider when the device is locked.

I can get the view to move smoothly along the x-axis by using: float newCenter = touchPoint.x;

But this doesn't take into account the offset of the touch from the center. It's simply moving the center point of the view to the touch point. I'm trying to move the view by dragging it from any point along the x-axis of the UIImageView.

Below, I tried calculating the newCenter within TouchesMoved but it fails to slide smoothly.

The code:

- (void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event {

    UITouch *touch = [touches anyObject];
    CGPoint touchPoint = [touch locationInView:self]; // self is a UIView

    CGRect sliderRect = sliderView.frame; // sliderView is a UIImageView

    if (CGRectContainsPoint(sliderRect, touchPoint)){

        float sliderHalfWidth = sliderView.frame.size.width / 2;
        float leftEdge = sliderView.center.x - sliderHalfWidth;
        float distanceToTouchFromEdge = touchPoint.x - leftEdge;

        float newCenter = (distanceToTouchFromEdge - sliderHalfWidth) + touchPoint.x; // <--- the math here is probably incorrect. I tried a few other formulas, none of which gave me the results I was looking for.
        //float newCenter = touchPoint.x;  <--- This slides smoothly but always centers view on touch-point (we want to drag from anywhere)

        NSLog(@"--------------");
        NSLog(@"sliderHalfWidth: %f", sliderHalfWidth);
        NSLog(@"sliderView.center.x: %f", sliderView.center.x);
        NSLog(@"leftEdge: %f", leftEdge);
        NSLog(@"distanceToTouchFromEdge: %f", distanceToTouchFromEdge);
        NSLog(@"touchPoint.x: %f", touchPoint.x);
        NSLog(@"newCenter: %f", newCenter);
        NSLog(@"--------------");

        sliderView.center = CGPointMake(newCenter, sliderView.frame.size.height/2);

    }
}

Any thoughts?

Answer 1

I ended up using a UISlider.

I found the post below, which is incredibly helpful if you're looking for the same solution.

It has a link to an xcode project with a fairly accurate recreation of Apple's native "Slide to Unlock" slider feature.

http://www.iphonedevsdk.com/forum/iphone-sdk-development/11470-there-way-i-can-use-slide-unlock-slider.html#post124686