UIControl 上的重定向拖动事件

Question

对于我正在开发的 iOS 应用程序，用户设备上的所有图像都显示在屏幕的一部分上。用户应该能够将这些图像拖到屏幕的另一部分，以将它们添加到将在记忆游戏中使用的图像集中。

这是一个屏幕截图，以防我的解释难以想象

当用户拖动图像时，我希望创建一个稍小的半透明版本的图像，他们将其拖到底部，但原始图像保留在那里。我可以很好地生成新图像，甚至可以指定一个移动新图像的目标。我遇到的问题是为了拖动新图像，用户必须将手指从屏幕上抬起并再次开始拖动。我希望新图像能够取代旧图像拖动事件。这是我现在的代码。

UIControl *mask =  [[UIControl alloc]initWithFrame:frame];
[mask addSubview:img];
[mask addTarget:self action:@selector(dragExited:withEvent:) forControlEvents:UIControlEventTouchDragExit];
[scrImages addSubview:mask];


-(IBAction)dragExited:(id)sender withEvent:(UIEvent*)event
{
    UIControl *control = sender;
    [control resignFirstResponder];
    UIImageView *img = [control.subviews objectAtIndex:0];
    CGPoint point = [[[event allTouches]anyObject]locationInView:self.view];
    UIControl *mask = [[UIControl alloc]initWithFrame:CGRectMake(0, 0, img.image.size.width, img.image.size.height)];
    mask.center = point;
    [mask addSubview:[[UIImageView alloc]initWithImage:img.image]];
    [mask addTarget:mask action:@selector(removeFromSuperview) forControlEvents:UIControlEventTouchUpInside];
    [self.view addSubview:mask];
    [mask addTarget:self action:@selector(thumbnailMoved:withEvent:) forControlEvents:UIControlEventTouchDragInside];
    [mask touchesMoved:nil withEvent:nil];
}

-(IBAction)thumbnailMoved:(id)sender withEvent:(UIEvent*)event
{
    UIControl *control = sender;
    CGPoint point = [[[event allTouches]anyObject]locationInView:self.view];
    control.center = point;
}

我尝试通过调用[mask touchesMoved:nil withEvent:nil]; 来启动拖动过程，但这似乎不起作用。有什么想法吗？

Answer 1

我将用另一种技术来回答这个问题，pan gestures。我没有使用你的技术，所以我不能和它说话，但我一直使用以下方法：

UIPanGestureRecognizer *pan;

pan = [[UIPanGestureRecognizer alloc] initWithTarget:self action:@selector(handlePanImage:)];
image01.userInteractionEnabled = YES;
[self.image01 addGestureRecognizer:pan];

pan = [[UIPanGestureRecognizer alloc] initWithTarget:self action:@selector(handlePanImage:)];
image02.userInteractionEnabled = YES;
[self.image02 addGestureRecognizer:pan];

然后我有处理程序：

- (void)handlePanImage:(UIPanGestureRecognizer *)sender
{
    static CGPoint originalCenter;
    static UIImageView *imageview;

    if (sender.state == UIGestureRecognizerStateBegan)
    {
        UIImageView *selectedImageView = (UIImageView *) sender.view;
        imageview = [[UIImageView alloc] initWithFrame:selectedImageView.frame];
        imageview.image = selectedImageView.image;
        imageview.alpha = 0.8;
        [sender.view.superview addSubview:imageview];

        originalCenter = imageview.center;
    }
    else if (sender.state == UIGestureRecognizerStateChanged)
    {
        CGPoint translation = [sender translationInView:sender.view.superview];

        imageview.center = CGPointMake(originalCenter.x + translation.x, originalCenter.y + translation.y);
    }
    else if (sender.state == UIGestureRecognizerStateEnded)
    {
        [imageview removeFromSuperview];
        imageview = nil;

        CGPoint translation = [sender translationInView:sender.view.superview];

        // do whatever you want to at the end, in this case, animating the moving
        // of the old image to the new location. perhaps you don't want to move your
        // old image, but leave it there, maybe you just want to change the alpha of
        // what you dragged back to 1.0 and snap it into place. Just do whatever you
        // want here. Note, in this latter scenario, if you want to be able to drag
        // the new image back out, you'll have to create a new pan gesture recognizer
        // for it.

        [UIView animateWithDuration:0.2 
                         animations:^{
                             sender.view.center = CGPointMake(originalCenter.x + translation.x, originalCenter.y + translation.y);;
                         }];
    }
    else if (sender.state == UIGestureRecognizerStateCancelled || sender.state == UIGestureRecognizerStateFailed)
    {
        [imageview removeFromSuperview];
        imageview = nil;
    }
}

您也可以，而不是为每个图像创建一个新的手势识别器，只需在父视图上创建一个，检测您结束的图像，然后继续。这可能看起来像：

UIPanGestureRecognizer *pan = [[UIPanGestureRecognizer alloc] initWithTarget:self action:@selector(handlePanSuperView:)];
[self.view addGestureRecognizer:pan];

然后：

- (void)handlePanSuperView:(UIPanGestureRecognizer *)sender
{
    static CGPoint originalCenter;
    static UIImageView *selectedImageView = nil;
    static UIImageView *draggedImageView = nil;

    if (sender.state == UIGestureRecognizerStateBegan)
    {
        selectedImageView = nil;
        CGPoint location = [sender locationInView:sender.view];
        for (UIImageView *imageview in _imageviews)
        {
            if (CGRectContainsPoint(imageview.frame, location))
                selectedImageView = imageview;
        }
        if (selectedImageView)
        {
            draggedImageView = [[UIImageView alloc] initWithFrame:selectedImageView.frame];
            draggedImageView.image = selectedImageView.image;
            draggedImageView.alpha = 0.8;
            [sender.view addSubview:draggedImageView];

            originalCenter = selectedImageView.center;
        }
    }
    else if (sender.state == UIGestureRecognizerStateChanged && selectedImageView)
    {
        CGPoint translation = [sender translationInView:sender.view];

        draggedImageView.center = CGPointMake(originalCenter.x + translation.x, originalCenter.y + translation.y);
    }
    else if (sender.state == UIGestureRecognizerStateEnded && selectedImageView)
    {
        [draggedImageView removeFromSuperview];
        draggedImageView = nil;

        CGPoint translation = [sender translationInView:sender.view];

        // do whatever you want to at the end, in this case, animating the moving of the old image

        [UIView animateWithDuration:0.2 
                         animations:^{
                             selectedImageView.center = CGPointMake(originalCenter.x + translation.x, originalCenter.y + translation.y);;
                         }];
    }
    else if ((sender.state == UIGestureRecognizerStateCancelled || sender.state == UIGestureRecognizerStateFailed) && selectedImageView)
    {
        [draggedImageView removeFromSuperview];
        draggedImageView = nil;
    }
}