在UIControl上重定向拖动事件

Question

对于我正在处理的iOS应用，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动到屏幕的另一部分，以将它们添加到将在记忆游戏中使用的图像集中。

这是一个截图，以防我的解释难以想象

当用户拖动图像时，我想要发生的是一个略小的半透明版本的图像被创建，他们向下拖动到底部，但原始图像保持在那里。我可以很好地生成新图像，甚至可以分配一个移动新图像的目标。我遇到的问题是为了拖动用户必须将手指从屏幕上抬起并再次开始拖动的新图像。我希望新图像能够将旧图像拖动事件。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pan gestures来回答这个问题。我不使用你的技术，所以我不能说话，但我一直使用以下内容：

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];

然后我有了处理程序：

- (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，检测您所覆盖的图像，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;
    }
}