一、引子

　　学完了可视化编程的Xib和Storyboard，LZ对它们的感受就是的就是UI控件创建直接拖拽，尺寸适配加约束，Storyboard的页面跳转逻辑清晰可见，比起代码布局节省了很多的工作量。但是LZ相信还是很多人喜欢用纯代码来编写一个程序的（LZ就是一个，用代码写出来东西的成就感很足！），所以今天在这里给喜爱纯代码编程的程序猿们介绍一下纯代码约束布局的工具——Masonry。

　　二、Masonry介绍

　　Masonry源码下载地址：https://github.com/SoleMY/Masonry

　　Masonry是一个轻量级的布局框架 拥有自己的描述语法 采用更优雅的链式语法封装自动布局 简洁明了 并具有高可读性 而且同时支持 iOS 和 Max OS X。

　　Masonry支持的属性：

/// 左侧
@property (nonatomic, strong, readonly) MASConstraint *left;
/// 上侧
@property (nonatomic, strong, readonly) MASConstraint *top;
/// 右侧
@property (nonatomic, strong, readonly) MASConstraint *right;
/// 下侧
@property (nonatomic, strong, readonly) MASConstraint *bottom;
/// 首部
@property (nonatomic, strong, readonly) MASConstraint *leading;
/// 底部
@property (nonatomic, strong, readonly) MASConstraint *trailing;
/// 宽
@property (nonatomic, strong, readonly) MASConstraint *width;
/// 高
@property (nonatomic, strong, readonly) MASConstraint *height;
/// 横向中点
@property (nonatomic, strong, readonly) MASConstraint *centerX;
/// 纵向中点
@property (nonatomic, strong, readonly) MASConstraint *centerY;
/// 文本基线
@property (nonatomic, strong, readonly) MASConstraint *baseline;

// 在Masonry的源码中我们可以看到他们对应的NSLayoutAttribute的属性对应如下
- (MASConstraint *)left {
    return [self addConstraintWithLayoutAttribute:NSLayoutAttributeLeft];
}

- (MASConstraint *)top {
    return [self addConstraintWithLayoutAttribute:NSLayoutAttributeTop];
}

- (MASConstraint *)right {
    return [self addConstraintWithLayoutAttribute:NSLayoutAttributeRight];
}

- (MASConstraint *)bottom {
    return [self addConstraintWithLayoutAttribute:NSLayoutAttributeBottom];
}

- (MASConstraint *)leading {
    return [self addConstraintWithLayoutAttribute:NSLayoutAttributeLeading];
}

- (MASConstraint *)trailing {
    return [self addConstraintWithLayoutAttribute:NSLayoutAttributeTrailing];
}

- (MASConstraint *)width {
    return [self addConstraintWithLayoutAttribute:NSLayoutAttributeWidth];
}

- (MASConstraint *)height {
    return [self addConstraintWithLayoutAttribute:NSLayoutAttributeHeight];
}

- (MASConstraint *)centerX {
    return [self addConstraintWithLayoutAttribute:NSLayoutAttributeCenterX];
}

- (MASConstraint *)centerY {
    return [self addConstraintWithLayoutAttribute:NSLayoutAttributeCenterY];
}

- (MASConstraint *)baseline {
    return [self addConstraintWithLayoutAttribute:NSLayoutAttributeBaseline];
}

　　iOS8之后Masonry新出了几个属性：

/// 距离边框的距离，等同于选中Storyboard的Constrain to margins后加约束
@property (nonatomic, strong, readonly) MASConstraint *leftMargin;
@property (nonatomic, strong, readonly) MASConstraint *rightMargin;
@property (nonatomic, strong, readonly) MASConstraint *topMargin;
@property (nonatomic, strong, readonly) MASConstraint *bottomMargin;
@property (nonatomic, strong, readonly) MASConstraint *leadingMargin;
@property (nonatomic, strong, readonly) MASConstraint *trailingMargin;
@property (nonatomic, strong, readonly) MASConstraint *centerXWithinMargins;
@property (nonatomic, strong, readonly) MASConstraint *centerYWithinMargins;

- (MASConstraint *)leftMargin {
    return [self addConstraintWithLayoutAttribute:NSLayoutAttributeLeftMargin];
}

- (MASConstraint *)rightMargin {
    retur