iOS开发 autoResizingMask使用

autoResizingMask 是UIView的一个属性，在一些简单的布局中，使用autoResizingMask，可以实现子控件相对于父控件的自动布局。

autoResizingMask 是UIViewAutoresizing 类型的，其定义为：

@property(nonatomic) UIViewAutoresizing autoresizingMask;    // simple resize. default is UIViewAutoresizingNone

UIViewAutoresizing 是一个枚举类型，默认是 UIViewAutoresizingNone,其可以取得值有：

typedef NS_OPTIONS(NSUInteger, UIViewAutoresizing) {
    UIViewAutoresizingNone                 = 0,
    UIViewAutoresizingFlexibleLeftMargin   = 1 << 0,
    UIViewAutoresizingFlexibleWidth        = 1 << 1,
    UIViewAutoresizingFlexibleRightMargin  = 1 << 2,
    UIViewAutoresizingFlexibleTopMargin    = 1 << 3,
    UIViewAutoresizingFlexibleHeight       = 1 << 4,
    UIViewAutoresizingFlexibleBottomMargin = 1 << 5
};

各属性解释：

UIViewAutoresizingNone	不会随父视图的改变而改变
UIViewAutoresizingFlexibleLeftMargin	自动调整view与父视图左边距，以保证右边距不变
UIViewAutoresizingFlexibleWidth	自动调整view的宽度，保证左边距和右边距不变
UIViewAutoresizingFlexibleRightMargin	自动调整view与父视图右边距，以保证左边距不变
UIViewAutoresizingFlexibleTopMargin	自动调整view与父视图上边距，以保证下边距不变
UIViewAutoresizingFlexibleHeight	自动调整view的高度，以保证上边距和下边距不变
UIViewAutoresizingFlexibleBottomMargin	自动调整view与父视图的下边距，以保证上边距不变

注意：autoResizingMask 既可以在代码中直接使用，也可以在UIStoryboard中使用。

一个代码中使用autoResizingMask的例子：

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions {
    
    self.window = [[UIWindow alloc] initWithFrame:[[UIScreen mainScreen] bounds]];
    UIViewController *viewController = [[UIViewController alloc] init];
    self.window.rootViewController = viewController;
    self.window.backgroundColor = [UIColor whiteColor];
    
    UIView *view = [[UIView alloc] initWithFrame:CGRectMake(20,100,200,100)];
    [view setBackgroundColor:[UIColor grayColor]];
    [self.window addSubview:view];
    
    UIButton *button = [[UIButton alloc] initWithFrame:CGRectMake(20,20,50,50)];
    [button setBackgroundColor:[UIColor whiteColor]];
    [view addSubview:button];
    //距离父视图右边距不变
    //button.autoresizingMask = UIViewAutoresizingFlexibleLeftMargin;
    //距离父视图的左边距不变
    //button.autoresizingMask = UIViewAutoresizingFlexibleRightMargin;
    //距离父视图的左右边距不变，button大小会调整
    //button.autoresizingMask = UIViewAutoresizingFlexibleWidth;
    //view.frame = CGRectMake(20,100,300,100);
    
    //距离父视图的下边距不变
    //button.autoresizingMask = UIViewAutoresizingFlexibleTopMargin;
    //距离父视图的上边距不变
    //button.autoresizingMask = UIViewAutoresizingFlexibleBottomMargin;
    //距离父视图的上下边距不变,button大小会调整
    button.autoresizingMask = UIViewAutoresizingFlexibleHeight;
    view.frame = CGRectMake(20,100,200,200);
    
    [self.window makeKeyAndVisible];
    return YES;
}

另外，autoResizingMask 可以组合使用。例如：

button.autoresizingMask = UIViewAutoresizingFlexibleBottomMargin | UIViewAutoresizingFlexibleLeftMargin;

表示的是，子控件相对于父控件的顶部和右侧的距离不变。