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：

1. 可以给控件添加left/right/top/bottom/size/height/width/insert约束；
2. 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；
3. 可以通过view.mas_bottom获得view的某个约束；
4. 在约束的block中，使用make来给当前控件添加约束。