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在如今的iOS开发中，Autolayout已经是不得不使用了，而且是我们主动的去拥抱Autolayout。使用Autolayout最普遍的方式就是在xib或者storyboard中可视化的添加各种约束，这也是Autolayout入门需要掌握的，关于这部分内容，可以参考《iOS开发——Autolayout的实践与技巧》这篇博客。对于比较简单的App开发，可能使用可视化Autolayout也就足够了。但是如果UI布局稍微复杂多变一点，那么就不得不使用代码了。对于iOS原生的代码自动布局，真的是过于繁琐。所以这里就要来介绍目前广泛使用的第三方库Masonry的使用，入门非常的方便简单。也是一位合格的iOS开发者需要掌握的。博客案例代码上传至 https://github.com/chenyufeng1991/MasonryLearnDemo 。
（1）使用Cocoapods导入Masonry，对于如何使用Cocoapods，请参考《iOS包管理工具Cocoapods的安装与使用》这篇博客。Podfile文件如下：
platform:ios,‘8.0‘ pod ‘Masonry‘
Masonry中有三种添加约束的方法：
- (NSArray *)mas_makeConstraint:(void(^)(MASConstraintMaker *))block;
- (NSArray *)mas_updateConstraint:(void(^)(MASConstraintMaker *))block;
- (NSArray *)mas_remakeConstraint:(void(^)(MASConstraintMaker *))block;
mas_makeConstraint:只负责新增约束，初次设置约束使用；
mas_updateConstraint:更新block中出现的约束，如果找不到该约束，会新增约束。
mas_remakeConstraint:清除之前的所有约束，仅保留最新的约束。
（3）equalTo和mas_equalTo的区别
其实mas_equalTo是一个宏，源码中是这样定义的：
#define mas_equalTo(...) equalTo(MASBoxValue((__VA_ARGS__))) #define mas_greaterThanOrEqualTo(...) greaterThanOrEqualTo(MASBoxValue((__VA_ARGS__))) #define mas_lessThanOrEqualTo(...) lessThanOrEqualTo(MASBoxValue((__VA_ARGS__))) #define mas_offset(...) valueOffset(MASBoxValue((__VA_ARGS__)))
MAS_SHORTHAND宏：定义了MAS_SHORTHAND宏之后，就可以使用UIView,NSArray中不带mas_前缀的makeConstraint,updateConstraint,remakeConstraint方法，以及UIView中不带mas_前缀的Attribute。
MAS_SHORTHAND_GLOBALS:直接对equalTo传入基础类型，Masonry自动转化为NSValue对象。
（4）比例系数与常数系数
multipliedBy(0.5)可以用来设置比例系数。
Masonry有四种设置Constant的方法：
- (MASConstraint * (^)(MASEdgeInsets insets))insets; - (MASConstraint * (^)(CGSize offset))sizeOffset; - (MASConstraint * (^)(CGPoint offset))centerOffset; - (MASConstraint * (^)(CGFloat offset))offset;insets方法可以同时设置top,left,bottom,right，接收MASEdgeInsets类型，也就是UiEdgeInsets类型，使用UIEdgeInetMake方法设置。
sizeOffset方法设置width,height，接收CGSize类型，使用CGSizeMake方法设置。
centerOffset方法设置centerX(X轴中心),centerY（Y轴中心）。
offset方法可以设置所有的偏移常量。
（5）对于一个约束，实际表示的是不等或者相等关系：
aView.Leading = 1.0 * bView.Trailing + 10;
其中：
aView :Item1;
Leading:Attribute1;
= : Relationship;
1.0 :Multiplier
bView：Item2；
Trailing ：Attribute2;
10 :Constant;
（6）MASConstraintMaker提供了22种Attribute类型：
//第一类 @property (nonatomic, strong, readonly) MASConstraint *left; @property (nonatomic, strong, readonly) MASConstraint *top; @property (nonatomic, strong, readonly) MASConstraint *right; @property (nonatomic, strong, readonly) MASConstraint *bottom; @property (nonatomic, strong, readonly) MASConstraint *leading; @property (nonatomic, strong, readonly) MASConstraint *trailing; @property (nonatomic, strong, readonly) MASConstraint *width; @property (nonatomic, strong, readonly) MASConstraint *height; @property (nonatomic, strong, readonly) MASConstraint *centerX; @property (nonatomic, strong, readonly) MASConstraint *centerY; @property (nonatomic, strong, readonly) MASConstraint *baseline; //第二类 @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; //第三类 @property (nonatomic, strong, readonly) MASConstraint *edges; @property (nonatomic, strong, readonly) MASConstraint *size; @property (nonatomic, strong, readonly) MASConstraint *center;
第二类是边缘相关属性，向下支持到iOS8，由于版本要求比较高，所以用的比较少。
第三类是复合属性，edges(top,left,right,bottom),size(width,height),center(centerX,centerY).
（7）扩展UIView中的Attribute:
@property (nonatomic, strong, readonly) MASViewAttribute *mas_left; @property (nonatomic, strong, readonly) MASViewAttribute *mas_top; @property (nonatomic, strong, readonly) MASViewAttribute *mas_right; @property (nonatomic, strong, readonly) MASViewAttribute *mas_bottom; @property (nonatomic, strong, readonly) MASViewAttribute *mas_leading; @property (nonatomic, strong, readonly) MASViewAttribute *mas_trailing; @property (nonatomic, strong, readonly) MASViewAttribute *mas_width; @property (nonatomic, strong, readonly) MASViewAttribute *mas_height; @property (nonatomic, strong, readonly) MASViewAttribute *mas_centerX; @property (nonatomic, strong, readonly) MASViewAttribute *mas_centerY; @property (nonatomic, strong, readonly) MASViewAttribute *mas_baseline; @property (nonatomic, strong, readonly) MASViewAttribute *(^mas_attribute)(NSLayoutAttribute attr); @property (nonatomic, strong, readonly) MASViewAttribute *mas_leftMargin; @property (nonatomic, strong, readonly) MASViewAttribute *mas_rightMargin; @property (nonatomic, strong, readonly) MASViewAttribute *mas_topMargin; @property (nonatomic, strong, readonly) MASViewAttribute *mas_bottomMargin; @property (nonatomic, strong, readonly) MASViewAttribute *mas_leadingMargin; @property (nonatomic, strong, readonly) MASViewAttribute *mas_trailingMargin; @property (nonatomic, strong, readonly) MASViewAttribute *mas_centerXWithinMargins; @property (nonatomic, strong, readonly) MASViewAttribute *mas_centerYWithinMargins;
（8）SHORTHAND简便写法：Masonry提供了不加mas_前缀的方法，只需要定义几个宏：
--- MAS_SHORTHAND :定义了MAS_SHORTHAND宏之后，就可以使用UIView,NSArray中不带mas_前缀的makeConstraint,updateConstraint,remakeConstraint，以及UiView中不带mas_前缀的Attribute。
--- MAS_SHORTHAND_GLOBALS ：直接对equalTo传入基础类型，Masonry自动转化为NSValue对象。
（9）with的使用
在Masonry的链式语法中，with可以对一个对象的多个属性进行连接，但也可以不用with.源码中的解释是：with是一个可选的语法属性，没有任何影响，但是能提高约束的可读性。
（10）小技巧
--- 如果等式两边的Attribute是一样的，可以省略等式右边的Attribute；
--- 如果是等于关系，并且右边的view是父view，equalTo也可以省略；
--- multipier默认为1时，可以不写；
--- offset默认为0时，可以不写；
--- 所以，如果不嫌麻烦的话，可以对所有的约束添加multipliedBy()和offset()，看起来也会清楚直观。
（11）mas_key属性的使用：
mas_key相当于View原生的tag属性一样，是为了区分不同的View的，mas_key标志的是字符串，更加方便直观。如果在遇到约束冲突打印Log时，使用Key标识后，会很容易找到冲突位置。我下面会通过一个例子来讲解。
（12）weakSelf的使用
对于block中self的循环引用问题，可以参考《iOS开发——Block引起循环引用的解决方案》这篇博客。Masonry的约束也是写在block中，所以我通过一个宏定义：
//定义宏，用于block #define WeakSelf(weakSelf) __weak __typeof(&*self)weakSelf = self;
在block之前定义：
WeakSelf(weakSelf);所以在block中就不使用self,而改用weakSelf即可。
（13）关于（8）中提到的两个宏定义，定义时的位置一定要在#import头文件之前，如下所示：
#define MAS_SHORTHAND #define MAS_SHORTHAND_GLOBALS #import "FirstViewController.h" #import "Masonry.h"
我下面通过几个小例子来作为Masonry的入门：
【1】绘制一个红色的View，在屏幕中上下左右居中，宽高为200：
//绘制一个红色的View
- (void)setRedView
{
WeakSelf(weakSelf);
self.redView = [[UIView alloc] init];
self.redView.backgroundColor = [UIColor redColor];
//在设置Autolayout之前，要将view添加到self.view上面
[self.view addSubview:self.redView];
[self.redView mas_makeConstraints:^(MASConstraintMaker *make) {
make.center.mas_equalTo(weakSelf.view);
make.size.mas_equalTo(CGSizeMake(200, 200));
}];
}注意：在对redView设置约束之前，一定要把它添加到self.view中！【2】在红色的View中绘制一个灰色的View，主要学习如何使用复合属性和单一属性设置四周边距：
//在红色的View中绘制一个灰色的View
- (void)setGrayViewEdgeInsetToRedView
{
WeakSelf(weakSelf);
self.grayView = [[UIView alloc] init];
self.grayView.backgroundColor = [UIColor grayColor];
[self.redView addSubview:self.grayView];
[self.grayView mas_makeConstraints:^(MASConstraintMaker *make) {
//可以使用符合属性设置
// make.edges.equalTo(weakSelf.redView).with.insets(UIEdgeInsetsMake(20, 20, 20, 20));
//上述代码也可以拆分为：
//可以使用with对同一条约束设置参数
// make.top.equalTo(weakSelf.redView).with.offset(20);
// make.left.equalTo(weakSelf.redView).with.offset(20);
// make.bottom.equalTo(weakSelf.redView).with.offset(-20);
// make.right.equalTo(weakSelf.redView).with.offset(-20);
// 也可以去掉with
make.top.equalTo(weakSelf.redView).offset(20);
make.left.equalTo(weakSelf.redView).offset(20);
make.bottom.equalTo(weakSelf.redView).offset(-20);
make.right.equalTo(weakSelf.redView).offset(-20);
}];
}【3】在灰色View里面绘制两个等宽等间距的View，设置左右边距，相互之间的边距为15,同时自动计算他们的宽度：
//在灰色View里面绘制两个等宽等间距的View,设置左右边距、相互之间边距为15
- (void)setTwoViewInGrayView
{
WeakSelf(weakSelf);
UIView *subView1 = [[UIView alloc] init];
UIView *subView2 = [[UIView alloc] init];
subView1.backgroundColor = [UIColor orangeColor];
subView2.backgroundColor = [UIColor blueColor];
[self.grayView addSubview:subView1];
[self.grayView addSubview:subView2];
[subView1 mas_makeConstraints:^(MASConstraintMaker *make) {
make.centerY.equalTo(weakSelf.grayView.mas_centerY);
make.left.equalTo(weakSelf.grayView.mas_left).with.offset(15);
make.right.equalTo(subView2.mas_left).with.offset(-15);
//设置subView1的高度为grayView高度的0.5.
make.height.equalTo(weakSelf.grayView).multipliedBy(0.5);
make.width.equalTo(subView2.mas_width);
}];
[subView2 mas_makeConstraints:^(MASConstraintMaker *make) {
make.centerY.equalTo(weakSelf.grayView.mas_centerY);
make.left.equalTo(subView1.mas_right).with.offset(15);
make.right.equalTo(weakSelf.grayView.mas_right).offset(-15);
make.height.equalTo(weakSelf.grayView).multipliedBy(0.5);
make.width.equalTo(subView1.mas_width);
}];
//以上的两个约束还有如下简化的写法
[subView1 mas_remakeConstraints:^(MASConstraintMaker *make) {
//设置subView1的centerY属性，如果后面的grayView的参数也是centerY的话，就可以省略
make.centerY.equalTo(weakSelf.grayView);
//因为默认也是想要和grayView的左边距对齐，所以可以省略mas_left;
make.left.equalTo(weakSelf.grayView).with.offset(15);
//下面的mas_left不能省略，因为前面的参数是right,当前后参数不一致时，不能省略后面的参数
make.right.equalTo(subView2.mas_left).with.offset(-15);
make.height.equalTo(weakSelf.grayView).multipliedBy(0.5);
//可以省略下面subView2的width参数
make.width.equalTo(subView2);
}];
[subView2 mas_remakeConstraints:^(MASConstraintMaker *make) {
make.centerY.equalTo(weakSelf.grayView);
make.left.equalTo(subView1.mas_right).with.offset(15);
make.right.equalTo(weakSelf.grayView).offset(-15);
make.height.equalTo(weakSelf.grayView).multipliedBy(0.5);
make.width.equalTo(subView1);
}];
}- (void)setMutiplierAndConstant
{
WeakSelf(weakSelf);
UIView *yellowView = [[UIView alloc] init];
yellowView.backgroundColor = [UIColor yellowColor];
[self.view addSubview:yellowView];
[yellowView mas_makeConstraints:^(MASConstraintMaker *make) {
make.width.equalTo(weakSelf.view.mas_width).offset(-10).multipliedBy(0.5);//根据公式，这里的-10就是constant.
make.height.equalTo(weakSelf.view.mas_height).multipliedBy(0.2).offset(0);
make.top.equalTo(weakSelf.redView.mas_bottom).multipliedBy(1).offset(0);
make.left.equalTo(weakSelf.view.mas_left).multipliedBy(1).offset(10);
}];
}- (void)setViewWithKey
{
UIView *firstView = [[UIView alloc] init];
firstView.backgroundColor = [UIColor blackColor];
[self.view addSubview:firstView];
//这里使用mas_key参数
self.view.mas_key = @"self.view";
firstView.mas_key = @"firstView";
//写一个冲突的约束
[firstView mas_makeConstraints:^(MASConstraintMaker *make) {
make.size.mas_equalTo(CGSizeMake(100, 100));
make.left.offset(10);
make.right.offset(-10);
}];
}Probably at least one of the constraints in the following list is one you don‘t want. Try this: (1) look at each constraint and try to figure out which you don‘t expect; (2) find the code that added the unwanted constraint or constraints and fix it. ( "<MASLayoutConstraint:0x7fef6a6a5d80 UIView:0x7fef6a4289d0.width == 100>", "<MASLayoutConstraint:0x7fef6a7161a0 UIView:0x7fef6a4289d0.left == UIView:0x7fef6a40b970.left + 10>", "<MASLayoutConstraint:0x7fef6a7145e0 UIView:0x7fef6a4289d0.right == UIView:0x7fef6a40b970.right - 10>", "<NSLayoutConstraint:0x7fef6a7ade60 UIView:0x7fef6a40b970.width == 320>" ) Will attempt to recover by breaking constraint <MASLayoutConstraint:0x7fef6a6a5d80 UIView:0x7fef6a4289d0.width == 100>
当设置mas_key后，输入如下：
Probably at least one of the constraints in the following list is one you don‘t want. Try this: (1) look at each constraint and try to figure out which you don‘t expect; (2) find the code that added the unwanted constraint or constraints and fix it. ( "<MASLayoutConstraint:0x7fbf23e3b0b0 UIView:firstView.width == 100>", "<MASLayoutConstraint:0x7fbf23e58410 UIView:firstView.left == UIView:self.view.left + 10>", "<MASLayoutConstraint:0x7fbf23e588d0 UIView:firstView.right == UIView:self.view.right - 10>", "<NSLayoutConstraint:0x7fbf23e5a610 UIView:self.view.width == 320>" ) Will attempt to recover by breaking constraint <MASLayoutConstraint:0x7fbf23e3b0b0 UIView:firstView.width == 100>
【6】使用上述（8）谈到的两个宏，使用Masonry时可以省略mas_前缀，下面的代码是去掉了mas_前缀的，也可以成功编译运行：
- (void)useShorthand
{
UIView *firstView = [[UIView alloc] init];
firstView.backgroundColor = [UIColor blackColor];
[self.view addSubview:firstView];
self.view.mas_key = @"self.view";
firstView.mas_key = @"firstView";
//写一个冲突的约束
[firstView makeConstraints:^(MASConstraintMaker *make) {
make.size.equalTo(CGSizeMake(100, 100));
make.left.offset(10);
make.right.offset(-10);
}];
}
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原文地址：http://blog.csdn.net/chenyufeng1991/article/details/51429788
