关于iOS布局自动iPhone6之后就是AutoLayOut，AutoLayOut固然非常好用，不过有时候我们需要在页面手动进行页面布局，VFL算是一种选择，而且VFL不复杂，理解起来很容易，实际开发中用的特别熟还好，要是第一次看估计要花点功夫才能搞定。Masonry算是VFL的简化版，用的人比较多，之前项目中用过一次，对手动写页面的开发来说算是福利。

基础知识

首先我们看一个常见的问题将一个子View放在的UIViewController的某个位置，通过设置边距来实现，效果如下:

如果通过VFL我们代码会是这样的:

UIView *superview = self.view;UIView *view1 = [[UIView alloc] init];view1.translatesAutoresizingMaskIntoConstraints = NO;view1.backgroundColor = [UIColor redColor];[superview addSubview:view1];UIEdgeInsets padding = UIEdgeInsetsMake(200, 50, 200, 50);[superview addConstraints:@[//约束[NSLayoutConstraint constraintWithItem:view1attribute:NSLayoutAttributeToprelatedBy:NSLayoutRelationEqualtoItem:superviewattribute:NSLayoutAttributeTopmultiplier:1.0constant:padding.top],[NSLayoutConstraint constraintWithItem:view1attribute:NSLayoutAttributeLeftrelatedBy:NSLayoutRelationEqualtoItem:superviewattribute:NSLayoutAttributeLeftmultiplier:1.0constant:padding.left],[NSLayoutConstraint constraintWithItem:view1attribute:NSLayoutAttributeBottomrelatedBy:NSLayoutRelationEqualtoItem:superviewattribute:NSLayoutAttributeBottommultiplier:1.0constant:-padding.bottom],[NSLayoutConstraint constraintWithItem:view1attribute:NSLayoutAttributeRightrelatedBy:NSLayoutRelationEqualtoItem:superviewattribute:NSLayoutAttributeRightmultiplier:1constant:-padding.right],]];

只是简单的设置了一个边距，如果视图的关系比较复杂，维护起来会是一个很痛苦的事情，我们看一下Masonry是如何实现的，导入Masonry.h头文件，约束的代码:

UIView *childView=[UIView new];[childView setBackgroundColor:[UIColor redColor]];//先将子View加入在父视图中[self.view addSubview:childView];__weak typeof(self) weakSelf = self;UIEdgeInsets padding = UIEdgeInsetsMake(200, 50, 200, 50);[childView mas_makeConstraints:^(MASConstraintMaker *make) {make.edges.equalTo(weakSelf.view).with.insets(padding);}];

通过mas_makeConstraints设置边距有种鸟枪换炮的感觉，我们即将开启一段新的旅程，可以紧接着看下面比较实用的功能~

实用知识

1.View设置大小

UIView *childView=[UIView new];[childView setBackgroundColor:[UIColor redColor]];//先将子View加入在父视图中[self.view addSubview:childView];__weak typeof(self) weakSelf = self;[childView mas_makeConstraints:^(MASConstraintMaker *make) {//设置大小make.size.mas_equalTo(CGSizeMake(100, 100));//居中make.center.equalTo(weakSelf.view);}];

效果如下:

　　

这里友情其实一个小内容，目前我们设置约束都是通过mas_makeConstraints用来创建约束,mas_updateConstraints用来更新约束，mas_remakeConstraints重置约束，清除之前的约束，保留最新的约束,如果想深入解释下，可以阅读下面的英文解释~

/*** Creates a MASConstraintMaker with the callee view.* Any constraints defined are added to the view or the appropriate superview once the block has finished executing** @param block scope within which you can build up the constraints which you wish to apply to the view.** @return Array of created MASConstraints*/- (NSArray *)mas_makeConstraints:(void(^)(MASConstraintMaker *make))block;/*** Creates a MASConstraintMaker with the callee view.* Any constraints defined are added to the view or the appropriate superview once the block has finished executing.* If an existing constraint exists then it will be updated instead.** @param block scope within which you can build up the constraints which you wish to apply to the view.** @return Array of created/updated MASConstraints*/- (NSArray *)mas_updateConstraints:(void(^)(MASConstraintMaker *make))block;/*** Creates a MASConstraintMaker with the callee view.* Any constraints defined are added to the view or the appropriate superview once the block has finished executing.* All constraints previously installed for the view will be removed.** @param block scope within which you can build up the constraints which you wish to apply to the view.** @return Array of created/updated MASConstraints*/- (NSArray *)mas_remakeConstraints:(void(^)(MASConstraintMaker *make))block;

2.设置高度，这里设置左右边距，因此不设置宽度，如果想单独设置width可参考高度的设置方式:

UIView *childView=[UIView new];[childView setBackgroundColor:[UIColor greenColor]];//先将子View加入在父视图中[self.view addSubview:childView];__weak typeof(self) weakSelf = self;[childView mas_makeConstraints:^(MASConstraintMaker *make) {//距离顶部44make.top.equalTo(weakSelf.view.mas_top).with.offset(44);//距离左边30make.left.equalTo(weakSelf.view.mas_left).with.offset(30);//距离右边30，注意是负数make.right.equalTo(weakSelf.view.mas_right).with.offset(-30);//高度150make.height.mas_equalTo(@150);}];

3.子视图之间的位置设置:

UIView *childView=[UIView new];[childView setBackgroundColor:[UIColor greenColor]];//先将子View加入在父视图中[self.view addSubview:childView];__weak typeof(self) weakSelf = self;[childView mas_makeConstraints:^(MASConstraintMaker *make) {//距离顶部44make.top.equalTo(weakSelf.view.mas_top).with.offset(44);//距离左边30make.left.equalTo(weakSelf.view.mas_left).with.offset(30);//距离右边30，注意是负数make.right.equalTo(weakSelf.view.mas_right).with.offset(-30);//高度150make.height.mas_equalTo(@150);}];//地址:http:///xiaofeixiang/UIView *nextView=[UIView new];[nextView setBackgroundColor:[UIColor redColor]];[self.view addSubview:nextView];[nextView mas_makeConstraints:^(MASConstraintMaker *make) {make.top.equalTo(childView.mas_bottom).with.offset(30);make.right.equalTo(childView.mas_right).with.offset(-30);make.width.mas_equalTo(@100);make.height.mas_equalTo(@100);}];

4.链式写法，算是一个便利的写法:

UIView *childView=[UIView new];[childView setBackgroundColor:[UIColor greenColor]];//先将子View加入在父视图中[self.view addSubview:childView];__weak typeof(self) weakSelf = self;[childView mas_makeConstraints:^(MASConstraintMaker *make) {make.top.and.left.mas_equalTo(weakSelf.view).with.offset(100);make.bottom.and.right.mas_equalTo(weakSelf.view).with.offset(-100);//第二种写法更简单，相对于就是父视图// make.top.and.left.mas_equalTo(100);// make.bottom.and.right.mas_equalTo(-100);}];UILabel *label=[UILabel new];[label setText:@"博客园-FlyElephant"];[label setTextColor:[UIColor redColor]];[label setTextAlignment:NSTextAlignmentCenter];[self.view addSubview:label];[label mas_makeConstraints:^(MASConstraintMaker *make) {make.left.mas_equalTo(weakSelf.view).with.offset(10);make.height.mas_equalTo(20);make.right.mas_equalTo(weakSelf.view).with.offset(-10);make.bottom.mas_equalTo(weakSelf.view).with.offset(-50);}];

　网上关于Masonry的教程很多，给的例子的也很多，这几种情况基本上满足了开发中的需求，不会有太多的出入，算是一个简易版的教程，Masonry的中属性和iOS中的属性是有对应的关系，不过因为很简单，基本上没怎么看，下图是一个对照关系:

总结：

可以给控件添加left/right/top/bottom/size/height/width/insert约束；

库提供了三个方法，mas_makeConstraints添加约束，mas_updateConstraints修改约束，mas_remakeConstraints清除以前约束并添加新约束；

可以通过view.mas_bottom获得view的某个约束；

在约束的block中，使用make来给当前控件添加约束。