- (void)viewDidLoad {
    [super viewDidLoad];
    
    //防止block的循环引用
    __weak typeof(self)weakself = self;
//  __weak typeof(self)weakself = self;
    
    UIView *bgview = [[UIView alloc] init];
    
    bgview.backgroundColor = [UIColor redColor];
    
    [self.view addSubview:bgview];
    //注意： 添加约束前必须要把view添加到视图上
#if 0
    //使用mas——makeConstraints添加约束
    [bgview mas_makeConstraints:^(MASConstraintMaker *make) {
        make.center.equalTo(weakself.view);
        make.size.mas_equalTo(CGSizeMake(200, 200));
    }];
#endif

#if 0
    //不想固定视图的宽高，让这个视图的大小由父视图与自己的间距控制
    [bgview mas_makeConstraints:^(MASConstraintMaker *make) {
        make.center.equalTo(weakself.view);
        make.edges.mas_offset(UIEdgeInsetsMake(10, 10, 10, 10));
    }];
    
#endif


    //单独的设置子视图与父视图某个方向的间距
    //以一个子视图必定在父视图里头的思路想，top，left设定值得时候都是正数，bottom，right，都是负数
    [bgview mas_makeConstraints:^(MASConstraintMaker *make) {
        make.top.equalTo(weakself.view).with.offset(20);
        make.left.equalTo(weakself.view).with.offset(10);
        make.bottom.equalTo(weakself.view).with.offset(-10);
        make.right.equalTo(weakself.view).with.offset(-10);
    }];
    

    
    //多个视图
    UIView *view1 = [[UIView alloc] init];
    view1.backgroundColor = [UIColor greenColor];
    [bgview addSubview:view1];
    
    [view1 mas_makeConstraints:^(MASConstraintMaker *make) {
        make.centerX.equalTo(bgview);
        make.size.mas_equalTo(CGSizeMake(200, 200));
        make.top.equalTo(bgview).with.offset(20);//控制视图与俯视图间距
    }];
    
    UIView *view2 = [[UIView alloc] init];
    view2.backgroundColor = [UIColor blueColor];
    [bgview addSubview:view2];
    
    [view2 mas_makeConstraints:^(MASConstraintMaker *make) {
        make.size.mas_equalTo(CGSizeMake(100, 100));
        make.top.equalTo(view1.mas_bottom).with.offset(20);
        make.centerX.equalTo(bgview);
//        make.left.equalTo(bgview.mas_left).with.offset(100);//这一句代码，会改变视图的width，因为同时要满足，centerx，与leftoffset(20)
    }];
   
    // Do any additional setup after loading the view, typically from a nib.
}