AutoLayout And Animation

1，在rootView中添加一个view，并设置约束，左、右、上，都设置与super的边距为20，高度为100。

2，编写代码控制

#import "ViewController.h"

@interface ViewController ()
@property (weak, nonatomic) IBOutlet UIView *animationView;

@property (nonatomic, assign) BOOL isForwadAnimation;
@end

@implementation ViewController

- (void)viewDidLoad {
    [super viewDidLoad];
    // Do any additional setup after loading the view, typically from a nib.
    self.isForwadAnimation = NO;
}

// 点击view时改变animationView约束中与Top的间距
- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event
{
    if(self.isForwadAnimation)
    {
        [self replaceTopConstrainOnView:self.animationView contant:20];
    }
    else
    {
        [self replaceTopConstrainOnView:self.animationView contant:200];
    }
    // 启动动画
    [self animateConstraints];
    self.isForwadAnimation = !self.isForwadAnimation;
}

// 改变约束的值
- (void)replaceTopConstrainOnView:(UIView *)view contant:(float)contant
{
    [self.view.constraints enumerateObjectsUsingBlock:^(NSLayoutConstraint *constraint, NSUInteger idx, BOOL *stop) {
        if(constraint.firstItem == view && constraint.firstAttribute == NSLayoutAttributeTop)
        {
            constraint.constant = contant;
        }
    }];
}

// 利用UIView的类方法做动画
- (void)animateConstraints
{
    [UIView animateWithDuration:2.0 animations:^{
        [self.view layoutIfNeeded];
    }];
}

 3,总结

// 如果约束是相对顶部的话就获取firstItem
// 如果约束是相对底部的话就获取secondItem