在iOS中按点偏移从中心移动图像

Posted 2023-03-16

【中文标题】在iOS中按点偏移从中心移动图像

【英文标题】：move image by point offset from center in iOS

【发布时间】：2013-01-19 06:47:21

【问题描述】：

我正在使用 UIPanGesture 在 iPhone 屏幕上移动图像。有些图像很小，当您在手指周围移动它们时，会遮挡您对图像本身的看法。我想在移动图像的同时设置图像的中心，以便图像中心实际上是触摸位置前面的 10 个点，而不是将其设置为触摸位置。

我测试了下面的内容，但很快意识到它反复从 Y 中减去 10，使图像离触摸位置越来越远，最终离开屏幕，而不是保持恒定的 10 点偏移。

我应该怎么做？

- (void) TestGestureMethod:(UIPanGestureRecognizer *) panGesture 
    CGPoint translation = [panGesture translationInView:self.view];
    switch (panGesture.state) 
    case UIGestureRecognizerStateBegan:
        [self.view bringSubviewToFront:testObject];
        break;
    case UIGestureRecognizerStateChanged:
        testObject.center = CGPointMake(testObject.center.x + translation.x,
                                        testObject.center.y + translation.y);
        testObject.center = CGPointMake(testObject.center.x, testObject.center.y - 10);
        break;
    case UIGestureRecognizerStateEnded:
        break;
    
    [panGesture setTranslation:CGPointZero inView:self.view];

【参考方案1】：

由于您不是翻译图像而是手动设置其中心，您是否考虑过使用 UIGestureRecognizer locationInView: 而不是 translationInView:？

你可以做这样的事情......

- (void)TestGestureMethod:(UIPanGestureRecognizer *)panGesture

    CGPoint location = [panGesture locationInView:self.view];

    switch (panGesture.state) 
        ...
        case UIGestureRecognizerStateChanged:
            testObject.center = CGPointMake(location.x, location.y - 10);
        break;
        ... 
    

这应该会导致图像中心始终位于触摸点下方 10 点处。

【讨论】：

有没有办法为第一次拖动时对象的突然移动设置动画？也许调整它的大小，或者添加一个弹簧动作？

【参考方案2】：

试试这个：

- (void) TestGestureMethod:(UIPanGestureRecognizer *) panGesture 
    CGPoint translation = [panGesture translationInView:self.view];
    switch (panGesture.state) 
    case UIGestureRecognizerStateBegan:
        [self.view bringSubviewToFront:testObject];
        testObject.center = CGPointMake(testObject.center.x, testObject.center.y - 10);
        break;
    case UIGestureRecognizerStateChanged:
        testObject.center = CGPointMake(testObject.center.x + translation.x,
                                        testObject.center.y + translation.y);

        break;
    case UIGestureRecognizerStateEnded:
        break;
    
    [panGesture setTranslation:CGPointZero inView:self.view];

【参考方案3】：

试试这个，这解决了你的问题：

- (void)handlePanGesture:(UIPanGestureRecognizer *)gestureRecognizer

    UIView *piece = [gestureRecognizer view];

    if ([gestureRecognizer state] == UIGestureRecognizerStateBegan || [gestureRecognizer state] == UIGestureRecognizerStateChanged) 
        CGPoint translation = [gestureRecognizer translationInView:[piece superview]];

        [piece setCenter:CGPointMake([piece center].x + translation.x, [piece center].y + translation.y)];
        [gestureRecognizer setTranslation:CGPointZero inView:[piece superview]];
    

希望对你有帮助。