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:view1 attribute:NSLayoutAttributeTop relatedBy:NSLayoutRelationEqual toItem:superview attribute:NSLayoutAttributeTop multiplier:1.0 constant:padding.top], [NSLayoutConstraint constraintWithItem:view1 attribute:NSLayoutAttributeLeft relatedBy:NSLayoutRelationEqual toItem:superview attribute:NSLayoutAttributeLeft multiplier:1.0 constant:padding.left], [NSLayoutConstraint constraintWithItem:view1 attribute:NSLayoutAttributeBottom relatedBy:NSLayoutRelationEqual toItem:superview attribute:NSLayoutAttributeBottom multiplier:1.0 constant:-padding.bottom], [NSLayoutConstraint constraintWithItem:view1 attribute:NSLayoutAttributeRight relatedBy:NSLayoutRelationEqual toItem:superview attribute:NSLayoutAttributeRight multiplier:1 constant:-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44 make.top.equalTo(weakSelf.view.mas_top).with.offset(44); //距离左边30 make.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150 make.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44 make.top.equalTo(weakSelf.view.mas_top).with.offset(44); //距离左边30 make.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150 make.height.mas_equalTo(@150); }]; //地址:http://www.cnblogs.com/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。
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