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:
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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],
]];
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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:
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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);
}];
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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
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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);
}];
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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~
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/**
* 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;
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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:
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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);
}];
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3.子视图之间的位置设置:
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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);
}];
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4.链式写法，算是一个便利的写法:
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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);
}];
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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。