如何在IOS中对约束逐一进行动画处理？

Question

我有 6 个视图。我想一个一个地为约束设置动画，即，我只需要在第二个视图上的动画在第一个之后，然后在第二个第三个之后，依此类推。我已经在动画的完成处理程序中添加了代码，但它不起作用。所有约束的初始值在情节提要中设置为 300。我想把它一个一个改成0。现在，只有第一个动画在起作用。这就是我所做的。

layoutTopFirst.constant = 0.0;
    [UIView animateWithDuration:1.0 animations:^{
        [self.view layoutIfNeeded];
    } completion:^(BOOL finished) {
        self->layoutTopSecond.constant = 0.0;
        [UIView animateWithDuration:1.0 animations:^{
            [self.view layoutIfNeeded];
        } completion:^(BOOL finished) {
            self->layoutTopThird.constant = 0.0;
            [UIView animateWithDuration:1.0 animations:^{
                [self.view layoutIfNeeded];
            } completion:^(BOOL finished) {
                self->layoutTopFourth.constant = 0.0;
                [UIView animateWithDuration:1.0 animations:^{
                    [self.view layoutIfNeeded];
                } completion:^(BOOL finished) {
                    self->layoutTopFifth.constant = 0.0;
                    [UIView animateWithDuration:1.0 animations:^{
                        [self.view layoutIfNeeded];
                    } completion:^(BOOL finished) {
                        self->layoutTopSixth.constant = 0.0;
                        [UIView animateWithDuration:1.0 animations:^{
                            [self.view layoutIfNeeded];
                        } completion:^(BOOL finished) {
                            
                        }];
                    }];
                }];
            }];
        }];
    }];

如何一个接一个的做动画？

Answer 1

如果您显示所有代码（如何设置约束等）会有所帮助。

但是，这里有一个简单的例子。

它创建了 6 个标签，顶部约束为 100。点击“Do Anim”按钮将它们动画到顶部：0.0 ...再次点击以动画回 100：

#import "SequentialAnimViewController.h"

@interface SequentialAnimViewController () {
    NSMutableArray *views;
    NSMutableArray *topConstraints;
}
@end

@implementation SequentialAnimViewController

- (void)viewDidLoad {
    [super viewDidLoad];

    UIButton *button = [UIButton buttonWithType:UIButtonTypeSystem];
    [button addTarget:self action:@selector(animViews) forControlEvents:UIControlEventTouchUpInside];
    [button setTitle:@"Do Anim" forState:UIControlStateNormal];
    button.backgroundColor = [UIColor colorWithWhite:0.9 alpha:1.0];
    button.translatesAutoresizingMaskIntoConstraints = NO;
    [self.view addSubview:button];
    
    [button.centerXAnchor constraintEqualToAnchor:[self.view centerXAnchor]].active = YES;
    [button.centerYAnchor constraintEqualToAnchor:[self.view centerYAnchor]].active = YES;
    [button.widthAnchor constraintEqualToConstant:200.0].active = YES;

    views = [NSMutableArray new];
    topConstraints = [NSMutableArray new];
    
    CGFloat x = 40.0;
    CGFloat w = 40.0;

    UILayoutGuide *g = [self.view safeAreaLayoutGuide];

    for (int i = 0; i < 6; i++) {
        UILabel *v = [UILabel new];
        v.backgroundColor = [UIColor blueColor];
        v.textColor = [UIColor yellowColor];
        v.textAlignment = NSTextAlignmentCenter;
        v.text = [NSString stringWithFormat:@"%i", i];
        v.translatesAutoresizingMaskIntoConstraints = NO;

        [self.view addSubview:v];
        [v.widthAnchor constraintEqualToConstant:w].active = YES;
        [v.heightAnchor constraintEqualToConstant:w].active = YES;
        [v.leadingAnchor constraintEqualToAnchor:g.leadingAnchor constant:x].active = YES;

        [topConstraints addObject:[v.topAnchor constraintEqualToAnchor:g.topAnchor constant:100.0]];
        [views addObject:v];

        x += w + 8;
    }
    
    [NSLayoutConstraint activateConstraints:topConstraints];
}

-(void)animViews {
    __block int i = 0;
    __block CGFloat newConstant = ((NSLayoutConstraint *)self->topConstraints[0]).constant == 0.0 ? 100.0 : 0.0;
    ((NSLayoutConstraint *)self->topConstraints[i++]).constant = newConstant;
    [UIView animateWithDuration:1.0 animations:^{
        [self.view layoutIfNeeded];
    } completion:^(BOOL finished) {
        ((NSLayoutConstraint *)self->topConstraints[i++]).constant = newConstant;
        [UIView animateWithDuration:1.0 animations:^{
            [self.view layoutIfNeeded];
        } completion:^(BOOL finished) {
            ((NSLayoutConstraint *)self->topConstraints[i++]).constant = newConstant;
            [UIView animateWithDuration:1.0 animations:^{
                [self.view layoutIfNeeded];
            } completion:^(BOOL finished) {
                ((NSLayoutConstraint *)self->topConstraints[i++]).constant = newConstant;
                [UIView animateWithDuration:1.0 animations:^{
                    [self.view layoutIfNeeded];
                } completion:^(BOOL finished) {
                    ((NSLayoutConstraint *)self->topConstraints[i++]).constant = newConstant;
                    [UIView animateWithDuration:1.0 animations:^{
                        [self.view layoutIfNeeded];
                    } completion:^(BOOL finished) {
                        ((NSLayoutConstraint *)self->topConstraints[i++]).constant = newConstant;
                        [UIView animateWithDuration:1.0 animations:^{
                            [self.view layoutIfNeeded];
                        } completion:^(BOOL finished) {
                            NSLog(@"All Done!");
                        }];
                    }];
                }];
            }];
        }];
    }];
}
@end

Answer 2

如果只有第一个动画，请确保

• 您的其他五个约束引用都指向不同的垂直约束...例如，如果它们是 nil，您将看不到任何更改；
• 他们都是isActive；
• 没有任何其他约束阻止更新的常量产生更改。

---

对于它的价值，您可以考虑使用关键帧动画消除完成处理程序的塔，例如

CGFloat relativeDuration = 1.0 / 6.0;

[UIView animateKeyframesWithDuration:6 delay:0 options:kNilOptions animations:^{
    [UIView addKeyframeWithRelativeStartTime:0 relativeDuration:relativeDuration animations:^{
        self.topConstraint1.constant = 0;
        [self.view layoutIfNeeded];
    }];

    [UIView addKeyframeWithRelativeStartTime:1.0 * relativeDuration relativeDuration:relativeDuration animations:^{
        self.topConstraint2.constant = 0;
        [self.view layoutIfNeeded];
    }];

    [UIView addKeyframeWithRelativeStartTime:2.0 * relativeDuration relativeDuration:relativeDuration animations:^{
        self.topConstraint3.constant = 0;
        [self.view layoutIfNeeded];
    }];

    [UIView addKeyframeWithRelativeStartTime:3.0 * relativeDuration relativeDuration:relativeDuration animations:^{
        self.topConstraint4.constant = 0;
        [self.view layoutIfNeeded];
    }];

    [UIView addKeyframeWithRelativeStartTime:4.0 * relativeDuration relativeDuration:relativeDuration animations:^{
        self.topConstraint5.constant = 0;
        [self.view layoutIfNeeded];
    }];

    [UIView addKeyframeWithRelativeStartTime:5.0 * relativeDuration relativeDuration:relativeDuration animations:^{
        self.topConstraint6.constant = 0;
        [self.view layoutIfNeeded];
    }];
} completion:nil];

或者，更简单：

NSArray <NSLayoutConstraint *> *constraints = @[self.topConstraint1, self.topConstraint2, self.topConstraint3, self.topConstraint4, self.topConstraint5, self.topConstraint6];

CGFloat relativeDuration = 1.0 / (CGFloat) constraints.count;

[UIView animateKeyframesWithDuration:totalDuration delay:0 options:kNilOptions animations:^{
    for (NSInteger i = 0; i < constraints.count; i++) {
        [UIView addKeyframeWithRelativeStartTime: ((CGFloat) i) * relativeDuration relativeDuration:relativeDuration animations:^{
            constraints[i].constant = 0;
            [self.view layoutIfNeeded];
        }];
    }
} completion:nil];

产生：