自动布局,约束和动画

Question

我们假设我有这个UIView:

有这些相对约束:

@property (strong, nonatomic) IBOutlet NSLayoutConstraint *leftMarginConstraint;
@property (strong, nonatomic) IBOutlet NSLayoutConstraint *topMarginConstraint;
@property (strong, nonatomic) IBOutlet NSLayoutConstraint *widthConstraint;
@property (strong, nonatomic) IBOutlet NSLayoutConstraint *heightConstraint;

好吧现在让我们假设当用户点击时UIButton按钮应该移动到视图的右下角.我们可以轻松地使用两个约束来定义按钮和底部布局指南之间的底部空间,以及从按钮和视图的右边缘定义右空间(尾随空间).

问题是UIButton已经有两个约束(左/上)和两个约束来定义它的宽度和高度,所以我们不能添加两个新约束,因为它们会与其他约束冲突.

动画场景的简单和常见情况,但它给我带来了一些问题.想法？

编辑

当用户点击时UIButton,我需要按钮:

1. 将其标题更改为"Second"
2. 等待1秒钟并移动到右下角(删除顶部和左侧边距约束并添加底部和右边距约束)
3. 将其标题改为"第三"
4. 等待1秒并移动到右上角(删除下边距约束并添加上边距约束)

我是否真的必须使用这个凌乱的代码？

@implementation ViewController
{
    NSLayoutConstraint *_topMarginConstraint;
    NSLayoutConstraint *_leftMarginConstraint;
    NSLayoutConstraint *_bottomMarginConstraint;
    NSLayoutConstraint *_rightMarginConstraint;
}

- (IBAction)buttonPressed:(id)sender
{
    UIButton *button = sender;

    // 1.
    [sender setTitle:@"Second" forState:UIControlStateNormal];

    // 2.
    double delayInSeconds = 1.0;
    dispatch_time_t popTime = dispatch_time(DISPATCH_TIME_NOW, delayInSeconds * NSEC_PER_SEC);
    dispatch_after(popTime, dispatch_get_main_queue(), ^(void) {
        [button removeConstraints:@[self.leftMarginConstraint, self.topMarginConstraint]];
        _bottomMarginConstraint = [NSLayoutConstraint constraintWithItem:self.view
                                                               attribute:NSLayoutAttributeBottom
                                                               relatedBy:0 toItem:button
                                                               attribute:NSLayoutAttributeBottom
                                                              multiplier:1
                                                                constant:20];
        [self.view addConstraint:_bottomMarginConstraint];

        _rightMarginConstraint = [NSLayoutConstraint constraintWithItem:self.view
                                                              attribute:NSLayoutAttributeRight
                                                              relatedBy:0 toItem:button
                                                              attribute:NSLayoutAttributeRight
                                                             multiplier:1
                                                               constant:20];
        [self.view addConstraint:_rightMarginConstraint];

        [UIView animateWithDuration:1 animations:^{
            [self.view layoutIfNeeded];
        } completion:^(BOOL finished) {
            // 3.
            [sender setTitle:@"Third" forState:UIControlStateNormal];

            // 4.
            double delayInSeconds = 1.0;
            dispatch_time_t popTime = dispatch_time(DISPATCH_TIME_NOW, delayInSeconds * NSEC_PER_SEC);
            dispatch_after(popTime, dispatch_get_main_queue(), ^(void) {
                [button removeConstraint:_bottomMarginConstraint];
                _topMarginConstraint = [NSLayoutConstraint constraintWithItem:self.view
                                                                       attribute:NSLayoutAttributeTop
                                                                       relatedBy:0 toItem:button
                                                                       attribute:NSLayoutAttributeTop
                                                                      multiplier:1
                                                                        constant:20];
                [UIView animateWithDuration:1 animations:^{
                    [self.view layoutIfNeeded];
                }];
            });
        }];
    });
}

严重？:d

Answer 1

删除左侧和顶部约束,添加底部和右侧约束,然后在动画块中调用layoutIfNeeded以设置新位置的动画.第二种方法中的代码move2可以嵌入到move1的完成块中,但是如果你将两个移动保持在不同的方法中,我发现它更容易阅读(它需要添加另一个属性,bottomCon):

- (IBAction)move1:(UIButton *)sender {
    [sender setTitle:@"Second" forState:UIControlStateNormal];
    [sender layoutIfNeeded];
    [self.view removeConstraints:@[self.leftCon,self.topCon]];
    self.bottomCon = [NSLayoutConstraint constraintWithItem:self.view attribute:NSLayoutAttributeBottom relatedBy:0 toItem:self.button attribute:NSLayoutAttributeBottom multiplier:1 constant:20];
    [self.view addConstraint:self.bottomCon];
    [self.view addConstraint:[NSLayoutConstraint constraintWithItem:self.view attribute:NSLayoutAttributeRight relatedBy:0 toItem:self.button attribute:NSLayoutAttributeRight multiplier:1 constant:20]];
    [UIView animateWithDuration:1 delay:1.0 options:0 animations:^{
        [self.view layoutIfNeeded];
    } completion:^(BOOL finished) {
        [sender setTitle:@"Third" forState:UIControlStateNormal];
        [self move2];
    }];
}

-(void)move2 {
    [self.view removeConstraint:self.bottomCon];
    [self.view addConstraint:[NSLayoutConstraint constraintWithItem:self.view attribute:NSLayoutAttributeTop relatedBy:0 toItem:self.button attribute:NSLayoutAttributeTop multiplier:1 constant:-20]];
    [UIView animateWithDuration:1 delay:1.0 options:0 animations:^{
        [self.view layoutIfNeeded];
    } completion:nil];
}