@interface ViewController ()
//设置三个View
/**<#XXX#>*/
@property (nonatomic , strong) UIView * orangeView;
/**<#XXX#>*/
@property (nonatomic , strong) UIView * yellowView;
/**<#XXX#>*/
@property (nonatomic , strong) UIView * greenView;
@end
@implementation ViewController
- (void)viewDidLoad {
[super viewDidLoad];
// NSLog(@"测试工程");
// self.view.backgroundColor = UIColor.redColor;
self.orangeView = [[UIView alloc]init];
self.orangeView.backgroundColor = [UIColor orangeColor];
[self.view addSubview:self.orangeView];
UIView *yellowView = [[UIView alloc]init];
yellowView.backgroundColor = [UIColor yellowColor];
[self.view addSubview:yellowView];
self.yellowView = yellowView;
UIView *greenView = [[UIView alloc]init];
greenView.backgroundColor = [UIColor greenColor];
[self.view addSubview:greenView];
self.greenView = greenView;
//配置约束
[self setUpRestrain];
[self.orangeView removeFromSuperview];
// [self.yellowView removeFromSuperview];
[self.view setNeedsLayout];
}
//配置约束
-(void)setUpRestrain
{
__weak typeof( self) weakSelf = self;
//对于橙色View只需正常设置约束就好
[self.orangeView mas_makeConstraints:^(MASConstraintMaker *make) {
make.width.height.mas_equalTo(100);
make.left.equalTo(weakSelf.view).offset(20);
make.top.offset(50);
}];
// 黄色View只会发生一次变化，就多设一个优先级较低的约束就好
[self.yellowView mas_makeConstraints:^(MASConstraintMaker *make) {
make.width.height.mas_equalTo(100);
make.left.offset(20);
make.top.equalTo(weakSelf.orangeView.mas_bottom).offset(20);
//当橙色View消失后,黄色View缺少左边约束，所以给其加一个优先级更低的左边约束。当第一个左边约束失效后，这个约束就起作用了
make.top.equalTo(weakSelf.view).offset(50).priority(300);
}];
//同理绿色View的低级约束就得设置两个
[self.greenView mas_makeConstraints:^(MASConstraintMaker *make) {
make.width.height.mas_equalTo(100);
make.left.offset(20);
make.top.equalTo(weakSelf.yellowView.mas_bottom).offset(20).priority(379);
make.top.equalTo(weakSelf.orangeView.mas_bottom).offset(20).priority(300);
make.top.equalTo(weakSelf.view).offset(50).priority(200);
}];
}
