自动布局

• 代码

- (void)viewDidLoad
{
    [super viewDidLoad];
    
    UIButton * button = [UIButton buttonWithType:UIButtonTypeRoundedRect];
    [button setTitle:@"哈哈哈" forState:UIControlStateNormal];
    [self.view addSubview:button];

    //1.  关闭autoresize自动翻译
    button.translatesAutoresizingMaskIntoConstraints = NO;

    //2.  构建约束
    NSDictionary * map = NSDictionaryOfVariableBindings(button);
    NSString * format = @"|-10-[button]-10-|";
    NSArray * constains1 = 
    [NSLayoutConstraint constraintsWithVisualFormat:format
                                            options:0
                                            metrics:nil
                                              views:map];
    //3.  约束加入视图
    [self.view addConstraints:constains1];
    [self.view addConstraints:[NSLayoutConstraint constraintsWithVisualFormat:@"V:|-10-[button(==20)]" options:0 metrics:nil views:map]];


    UIButton * button1 = [UIButton buttonWithType:UIButtonTypeRoundedRect];
    [button1 setTitle:@"左按钮" forState:UIControlStateNormal];
    [self.view addSubview:button1];
    
    UIButton * button2 = [UIButton buttonWithType:UIButtonTypeRoundedRect];
    [button2 setTitle:@"右按钮" forState:UIControlStateNormal];
    [self.view addSubview:button2];
    
    //1.
    button1.translatesAutoresizingMaskIntoConstraints = NO;
    button2.translatesAutoresizingMaskIntoConstraints = NO;
    
    //2.
    
    NSDictionary * views = NSDictionaryOfVariableBindings(button1,button2);
    NSArray * horizontal =
    [NSLayoutConstraint constraintsWithVisualFormat:
     @"|-10-[button1]-10-[button2(==button1)]-10-|"
                                            options:
     NSLayoutFormatAlignAllCenterY
                                            metrics:nil
                                              views:views];
    
    [self.view addConstraints:horizontal];
    
    NSArray * bottom =
    [NSLayoutConstraint constraintsWithVisualFormat:
     @"V:[button1]-10-|"
                                            options:0
                                            metrics:nil
                                              views:views];
    
    [self.view addConstraints:bottom];
    
    
    
}

• IB

　　　　在Interface Builder中，右下角的3个按钮用于设置自动布局。