拖放对象并将其返回到原始位置

Question

我正在尝试拖动图像并在释放后让它返回到原来的位置。到目前为止，我可以通过使用以下代码将图像创建为按钮来拖动图像：（如该问题的答案所示：Basic Drag and Drop in iOS）

UIButton *button = [UIButton buttonWithType:UIButtonTypeCustom];
[button addTarget:self action:@selector(imageTouch:withEvent:) forControlEvents:UIControlEventTouchDown];
[button addTarget:self action:@selector(imageMoved:withEvent:) forControlEvents:UIControlEventTouchDragInside];
[button setImage:[UIImage imageNamed:@"vehicle.png"] forState:UIControlStateNormal];
[self.view addSubview:button];

后来我定义：

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

释放后如何让它回到原来的位置？，对于初学者，我将保存每个图像应该返回的位置，但是，无论如何都要指示 UIImage 从它的当前位置移动并转移到另一个？，或任何其他替代解决方案？

Answer 1

UIGestureRecognizer 被 Apple 推荐用于最近的 iOS。您不仅可以将它用于 UIButton，还可以用于 UIView（尤其是在您的情况下为 UIImageView）等。所以我想推荐它。

在界面中：

@interface TestDragViewController : UIViewController {
    IBOutlet UIImageView *dragImage;
    CGPoint originalCenter;
}

在 viewDidLoad 中，请记得启用 userInteraction：

- (void)viewDidLoad {
    [super viewDidLoad];


    UIPanGestureRecognizer *panGesture = [[UIPanGestureRecognizer alloc] initWithTarget:self 
                                                                                 action:@selector(dragGesture:)];
    [dragImage addGestureRecognizer:panGesture];
    [dragImage setUserInteractionEnabled:YES];
}

在它的选择器中，我只是设置了动画来可视化返回效果：

#pragma mark -
#pragma mark UIPanGestureRecognizer selector
- (void) dragGesture:(UIPanGestureRecognizer *) panGesture{
    CGPoint translation = [panGesture translationInView:self.view];

    switch (panGesture.state) {
        case UIGestureRecognizerStateBegan:{
            originalCenter = dragImage.center;
        }
            break;
        case UIGestureRecognizerStateChanged:{
            dragImage.center = CGPointMake(dragImage.center.x + translation.x,
                                           dragImage.center.y + translation.y);
        }
            break;
        case UIGestureRecognizerStateEnded:{            
            [UIView animateWithDuration:kImageReturnTime 
                             animations:^{
                                 dragImage.center = originalCenter;
                             }
                             completion:^(BOOL finished){
                                 NSLog(@"Returned");
                             }];
        }
            break;
        default:
            break;
    }

    [panGesture setTranslation:CGPointZero inView:self.view];
}

干杯，

汤米

Answer 2

全局定义 CGPoint，或在 .h 文件中。

  CGPoint point;          

      UIButton *button = [UIButton buttonWithType:UIButtonTypeCustom];
      [button addTarget:self action:@selector(imageTouch:withEvent:)forControlEvents:UIControlEventTouchDown];
      [button addTarget:self action:@selector(imageMoved:withEvent:) forControlEvents:UIControlEventTouchDragInside];
      [button setImage:[UIImage imageNamed:@"vehicle.png"] forState:UIControlStateNormal];
      [self.view addSubview:button];

后来我定义：

- (IBAction) imageMoved:(UIButton*) sender withEvent:(UIEvent *) event
 {
point = [[[event allTouches] anyObject] locationInView:self.view];
UIControl *control = sender;
control.center = point;
 [sender addTarget:self action:@selector(touches:withEvent:) forControlEvents:UIControlEventTouchUpInside];
}

-(void)touches:(UIButton *)button withEvent:(UIEvent *)event {

[UIView animateWithDuration:0.1 delay:0 options:UIViewAnimationOptionCurveEaseOut | UIViewAnimationOptionAllowUserInteraction animations:^{
     button.center = point;

 } completion:^(BOOL finished){
     if (finished) {
    // do anything yu want
   }

效果很棒，因为我在我的项目中使用它！

Answer 3

如何在 UIControlEventTouchUpInside 上调用选择器，然后在选择器中，只需将按钮的框架设置为新的 x 和 y 坐标（您保存的坐标）。

Answer 4

在我在您所指的线程中链接到的解决方案中，我创建了一个通用拖放管理器，该管理器负责将拖动的对象返回到原始位置（如果在已知拖放区之外释放）。目前解决方案中没有动画，但您可以结合上面提出的一些想法。

看看generic drag and drop solution in iOS的一些方法

Answer 5

你知道吗，我昨天刚在做这个，所以这里有一点额外的动画：

- (void)previewImageTouchUpInside:(UIButton*)aButton {
    if (!previewImageDragged) {
        [self selectPreviewImage:aButton];
        return;
}

    previewImageDragged = NO;

    // If user drag photo a little and then release, we'll still treat it as a tap
    //  instead of drag
    if ((originalPositionOfButton.x - aButton.center.x) * 
      (originalPositionOfButton.x - aButton.center.x) + 
      (originalPositionOfButton.y - aButton.center.y) * 
      (originalPositionOfButton.y - aButton.center.y) < 10) {
        aButton.center = originalPositionOfButton;
        [self selectPreviewImage:aButton];
        return;
    }

    [UIView animateWithDuration:0.5
        delay:0
        options:UIViewAnimationOptionCurveEaseOut |
        UIViewAnimationOptionAllowUserInteraction animations:^{
        aButton.center = originalPositionOfButton;
    } completion:nil];
}



- (void)previewImageDraggedInside:(UIButton*)aButton event:(UIEvent*)event {
    if (!previewImageDragged) {
        originalPositionOfButton = aButton.center;
        [self.view bringSubviewToFront:aButton];
        [self.view bringSubviewToFront:[self.view viewWithTag:CHOOSE_PHOTO_BUTTON_TAG]];
    }

    UITouch* touch = [[event allTouches] anyObject];

    previewImageDragged = YES;
    aButton.center = CGPointMake(aButton.center.x+[touch locationInView:self.view].x-
        [touch previousLocationInView:self.view].x, 
        aButton.center.y+[touch locationInView:self.view].y-
        [touch previousLocationInView:self.view].y);
}

它仍然有一些神奇的数字，我没有重命名函数和变量以适合您的示例，但应该很清楚。我在这里也做了缩进，因为我没有在我的代码中手动打断长行。