NSLayoutConstraint动画在iOS 10-11上的发行

Question

我正在尝试为视图实现显示/隐藏动画。其想法是调整视图的高度约束大小，并让它的superview与它一起调整大小。为此，我添加了视图的高度约束，并将其底部约束固定到superview的底部(因此我不需要指定superview的高度约束)

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在iOS 9上，它按预期工作：

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这种情况发生在iOS 10-11上：

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动画代码：

#import "ViewController.h"

@interface ViewController ()
{
    BOOL _hideFlag;
    CGFloat _redViewHeight;
}

@property (strong, nonatomic) IBOutlet UIView *containerView;
@property (strong, nonatomic) IBOutlet UIButton *toggleButton;
@property (strong, nonatomic) IBOutlet UIView *redView;
@property (strong, nonatomic) IBOutlet NSLayoutConstraint *redViewHeightConstraint;

@end

@implementation ViewController

- (void)viewDidLoad {
    [super viewDidLoad];
    [_toggleButton addTarget:self action:@selector(toggle:) forControlEvents:UIControlEventTouchUpInside];
    _redViewHeight = _redViewHeightConstraint.constant;
}

- (void)toggle:(UIButton *)sender
{
    _hideFlag = !_hideFlag;
    [_containerView layoutIfNeeded];

    [UIView animateWithDuration:0.2 animations:^{
        _redViewHeightConstraint.constant = _hideFlag ? 0 : _redViewHeight;
        [_containerView layoutIfNeeded];
    }];
}

@end

编辑

多亏了库尔迪普。强调一下:重点是至少在受影响的上层视图的层次结构中调用layoutIfNeeded。因此，在我的例子中，由于containerView的高度也在变化，我不得不在containerView的superview上调用layoutIfNeeded。

Answer 1

试一试它在iOS 9,10,11中工作

目标C

- (IBAction)btnChangeTapped:(UIButton *)sender {
    sender.selected =! sender.selected;

    if (sender.selected) {
        [self.view layoutIfNeeded];
        [UIView animateWithDuration:1.0 animations:^{
            self.constraintHeightOfView.constant = 100.0; // as per your require
            [self.view layoutIfNeeded];
        }];
    }
    else {
        [self.view layoutIfNeeded];
        [UIView animateWithDuration:1.0 animations:^{
            self.constraintHeightOfView.constant = 350.0; // Back to Normal
            [self.view layoutIfNeeded];
        }];
    }
}

Swift 5.0

@IBAction func btnChangeTapped(_ sender: UIButton) {
    sender.isSelected = !sender.isSelected

    if sender.isSelected {
        self.view.layoutIfNeeded()
        UIView.animate(withDuration: 1.0, animations: {
            self.constraintHeightOfView.constant = 100.0 // as per your require
            self.view.layoutIfNeeded()
        })
    } else {
        self.view.layoutIfNeeded()
        UIView.animate(withDuration: 1.0, animations: {
            self.constraintHeightOfView.constant = 350.0 // Back to Normal
            self.view.layoutIfNeeded()
        })
    }
}