Masonry研究1 View+MASAddtions

View+MASAddtions

使用Masonry主要用到的是UIView+MASAddtions的分类，这里面最主要的几个类如下

1. 常用的类

• MASViewAttribute 保存某个属性的类
• MASConstraintMaker 用于设置约束

这里一个很有意思的知识点，就是并没有直接写成UIView的分类，因为Masonry同事适配iOS、OSX，这样定义一个宏就可以一份代码不用区分具体是什么环境了

2、 MASUtilities.h 知识点1

#if TARGET_OS_IPHONE || TARGET_OS_TV

    #import <UIKit/UIKit.h>
    #define MAS_VIEW UIView
    #define MAS_VIEW_CONTROLLER UIViewController
    #define MASEdgeInsets UIEdgeInsets

    typedef UILayoutPriority MASLayoutPriority;
    static const MASLayoutPriority MASLayoutPriorityRequired = UILayoutPriorityRequired;
    static const MASLayoutPriority MASLayoutPriorityDefaultHigh = UILayoutPriorityDefaultHigh;
    static const MASLayoutPriority MASLayoutPriorityDefaultMedium = 500;
    static const MASLayoutPriority MASLayoutPriorityDefaultLow = UILayoutPriorityDefaultLow;
    static const MASLayoutPriority MASLayoutPriorityFittingSizeLevel = UILayoutPriorityFittingSizeLevel;

#elif TARGET_OS_MAC

    #import <AppKit/AppKit.h>
    #define MAS_VIEW NSView
    #define MASEdgeInsets NSEdgeInsets

    typedef NSLayoutPriority MASLayoutPriority;
    static const MASLayoutPriority MASLayoutPriorityRequired = NSLayoutPriorityRequired;
    static const MASLayoutPriority MASLayoutPriorityDefaultHigh = NSLayoutPriorityDefaultHigh;
    static const MASLayoutPriority MASLayoutPriorityDragThatCanResizeWindow = NSLayoutPriorityDragThatCanResizeWindow;
    static const MASLayoutPriority MASLayoutPriorityDefaultMedium = 501;
    static const MASLayoutPriority MASLayoutPriorityWindowSizeStayPut = NSLayoutPriorityWindowSizeStayPut;
    static const MASLayoutPriority MASLayoutPriorityDragThatCannotResizeWindow = NSLayoutPriorityDragThatCannotResizeWindow;
    static const MASLayoutPriority MASLayoutPriorityDefaultLow = NSLayoutPriorityDefaultLow;
    static const MASLayoutPriority MASLayoutPriorityFittingSizeCompression = NSLayoutPriorityFittingSizeCompression;

#endif

3、 获取布局属性，直接用MASViewAttribute得到

#pragma mark - NSLayoutAttribute properties

- (MASViewAttribute *)mas_left {
    return [[MASViewAttribute alloc] initWithView:self layoutAttribute:NSLayoutAttributeLeft];
}

4、获取两个类最近的共同父类，使用了一个2层递归遍历,思路是用第一个View，也就是当前View的每一个父类（包含第一个类自己）与第二个View的所有父类（包括第二个类自己）进行比较，这样只要有相等的则是共同的父类，复杂度为n*m
不知道具体效率怎么样

#pragma mark - heirachy

- (instancetype)mas_closestCommonSuperview:(MAS_VIEW *)view {
    MAS_VIEW *closestCommonSuperview = nil;

    MAS_VIEW *secondViewSuperview = view;
    while (!closestCommonSuperview && secondViewSuperview) {
        MAS_VIEW *firstViewSuperview = self;
        while (!closestCommonSuperview && firstViewSuperview) {
            if (secondViewSuperview == firstViewSuperview) {
                closestCommonSuperview = secondViewSuperview;
            }
            firstViewSuperview = firstViewSuperview.superview;
        }
        secondViewSuperview = secondViewSuperview.superview;
    }
    return closestCommonSuperview;
}

5、 添加约束的过程就是以下几个过程

• 设置不响应Autoresizing
• 创建一个MASConstraintMaker实例
• 通过block把约束保存到MASConstraintMaker里
• 然后调用MASConstraintMaker的install方法把约束加到View上并返回一个数组
• 修改就是给maker添加一个updateExisting=YES，重置就是给removeExisting=YES，默认设置时这两个属性都是NO
• 返回的数组是所有添加的MASContriaints

- (NSArray *)mas_makeConstraints:(void(^)(MASConstraintMaker *))block {
    self.translatesAutoresizingMaskIntoConstraints = NO;
    MASConstraintMaker *constraintMaker = [[MASConstraintMaker alloc] initWithView:self];
    block(constraintMaker);
    return [constraintMaker install];
}