在 UIScrollView 上拖动图像

Question

当用户触摸UITableViewCell 上的图像时，会调用UIViewController。 它使用modalViewController 调用。 在这个modalViewController 上是一个UIScrollView，中间有另一个UIImageView，它使用NSDictionary（从UITableViewCell 传递）获取图像。

现在，我想要实现的是用户只能垂直拖动图像的能力，这样稍微拖动和释放就会导致图像以动画方式返回到中心。如果用户将其拖到极端，则整个UIScrollView 将被解除，用户返回UITableView。我使用了以下代码。这里的问题是，正如我的名字所暗示的那样，这段代码很粗糙。有没有一种不需要太多计算的优雅方法？

BOOL imageMoved=NO;

- (void) touchesMoved:(NSSet *)touches
        withEvent:(UIEvent *)event {
UITouch * touch = [touches anyObject];
CGPoint pos = [touch locationInView: [UIApplication sharedApplication].keyWindow];

CGRect imageRect = _photoImageView.frame;//_photoImageView object of UIImageView
CGFloat imageHeight = imageRect.size.height;//getting height of the image
CGFloat imageTop=240-imageHeight/2;
CGFloat imageBottom=imageTop+imageHeight;//setting boundaries for getting coordinates of touch.
// Touches that originate above imageTop and below imageBottom are ignored(until touch reaches UIImageView)

if (pos.y>50&&pos.y<430&&pos.y>=imageTop&&pos.y<=imageBottom){//extremes are defined as top and bottom 50 pixels.
    imagedMoved=YES;//BOOL variable to hold if the image was dragged or not
    NSLog(@"%f", pos.y);
    [UIView setAnimationDelay:0];

    [UIView animateWithDuration:0.4

                     animations:^{_photoImageView.frame=CGRectMake(0,pos.y-imageHeight/2,320,200);}

                     completion:^(BOOL finished){ }];
}
}

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

UITouch * touch = [touches anyObject];
CGPoint pos = [touch locationInView: [UIApplication sharedApplication].keyWindow];

if (pos.y>50&&pos.y<430){//if touch has NOT ended in the extreme 50 pixels vertically
    [UIView setAnimationDelay:0];//restoring UIImageView to original center with animation

    [UIView animateWithDuration:0.4

                     animations:^{_photoImageView.frame=CGRectMake(0,140,320,200);}

                     completion:^(BOOL finished){ }];
imagedMoved=NO;//prepare BOOL value for next touch event
}

else if(pos.y<50||pos.y>430)
    if(imagedMoved)
    [self.photoBrowser exit] ;//exit function(imported from UIScrollViewController) dismisses
                  //modalView using [self dismissViewControllerAnimated:YES completion:nil];
}

此处的所有代码都是对MWPhotoBrowser 中UITapView 的自定义副本的修改。

Answer 1

哟，这是一个更简单的方法，或多或少是亚历山德罗所说的一个例子。我没有找到屏幕顶部，但我给出了它的错觉。

BCViewController.h

#import <UIKit/UIKit.h>

@interface BCViewController : UIViewController <UIScrollViewDelegate>
@property (weak, nonatomic) IBOutlet UIScrollView *svScroller;
@property (weak, nonatomic) IBOutlet UIImageView *ivFish;

@end




#import "BCViewController.h"

@interface BCViewController (){
   UIPanGestureRecognizer *_panGestureRecognizer;
   CGPoint                 _fishOrigin;
}

@end

@implementation BCViewController

- (void)viewDidLoad
{
    [super viewDidLoad];
   self.svScroller.delegate = self;
   [self.svScroller setContentSize:self.view.frame.size];
   self.svScroller.translatesAutoresizingMaskIntoConstraints = NO;
   self.ivFish.userInteractionEnabled = YES;

   _panGestureRecognizer = [[UIPanGestureRecognizer alloc] initWithTarget:self action:@selector(handlePanFrom:)];
   [self.ivFish addGestureRecognizer:_panGestureRecognizer];

   _fishOrigin = self.ivFish.center;

   NSLog(@"center %f", self.ivFish.center.x);
}

- (void)didReceiveMemoryWarning
{
    [super didReceiveMemoryWarning];
    // Dispose of any resources that can be recreated.
}

-(void)handlePanFrom:(UIPanGestureRecognizer *)recognizer{
   // if you want it but not used
   CGPoint translation = [recognizer translationInView:recognizer.view];
   // if you want it but not used
   CGPoint velocity    = [recognizer velocityInView:recognizer.view];
   CGPoint tempPoint;


if (recognizer.state == UIGestureRecognizerStateBegan) {

} else if (recognizer.state == UIGestureRecognizerStateChanged) {
    tempPoint = [recognizer locationInView:self.view];

    self.ivFish.center = CGPointMake(175.5, tempPoint.y);

} else if (recognizer.state == UIGestureRecognizerStateEnded) {
    CGPoint tempPoint;
    tempPoint = [recognizer locationInView:self.view];

    if (tempPoint.y < 132) {
        [UIView animateWithDuration:.3 delay:0
                            options:UIViewAnimationOptionCurveEaseOut
                         animations:^ {
                             [self.navigationController popViewControllerAnimated:TRUE];
                         }
                         completion:NULL];
    } else {
        [UIView animateWithDuration:.3 delay:0
                            options:UIViewAnimationOptionCurveEaseOut
                         animations:^ {
                             self.ivFish.center = _fishOrigin;
                         }
                         completion:NULL];
    }
}
}