Loki

Code X 轴中心对齐，相当于确定了 X 值，给定控件的宽度，然后进行约束，相等

 
    UIImageView *iconImg = [[UIImageView alloc] init];
    iconImg.backgroundColor = [UIColor clearColor];
    [iconImg setImage:[UIImage imageNamed:@"icon"]];
    [self.view addSubview:iconImg];
    
    [iconImg mas_makeConstraints:^(MASConstraintMaker *make) {
       
        make.top.equalTo(weakSelf.view).offset(100);
        make.width.equalTo(@70);
        make.height.equalTo(iconImg.mas_width);
        make.centerX.mas_equalTo(self.view.mas_centerX);
        
    }];