IOS 使用Masonry+UITableViewCell布局时

代码适配，Masonry一般是首选的。项目中tableview使用最多，那么肯定少不了自定义的cell和view，这就牵涉到控件的布局。

使用过Masonry的都知道，有的时候控制台会输出很多警告，但是布局是正常的，这是为什么呢？

[LayoutConstraints] Unable to simultaneously satisfy constraints.
    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:0x6040004a8d60 ShopLabel:0x7fafc74af500.right == UITableViewCellContentView:0x7fafc7601430.right - 10>,
    <MASLayoutConstraint:0x6040004b6440 ShopLabel:0x7fafc74af500.width == 80>,
    <MASLayoutConstraint:0x6040004b72e0 ShopLabel:0x7fafc76c4e00.left == UITableViewCellContentView:0x7fafc7601430.left + 10>,
    <MASLayoutConstraint:0x6040004b7d60 ShopLabel:0x7fafc76c4e00.right == ShopLabel:0x7fafc74af500.left - 10>,
    <MASLayoutConstraint:0x6040006a7a40 ShopLabel:0x7fafc74b27e0.left == UITableViewCellContentView:0x7fafc7601430.left + 10>,
    <MASLayoutConstraint:0x6040006a6ea0 ShopLabel:0x7fafc74b27e0.width == 53.5705>,
    <MASLayoutConstraint:0x6040006a6180 ShopLabel:0x7fafc74b2ac0.left == ShopLabel:0x7fafc74b27e0.right>,
    <MASLayoutConstraint:0x6040006a66c0 ShopLabel:0x7fafc74b2ac0.right == UITableViewCellContentView:0x7fafc7601430.right - 10>,
    <MASLayoutConstraint:0x6000006ab1c0 ShopLabel:0x7fafc74b2ac0.left == ShopLabel:0x7fafc74b2ac0.right>,
)

Will attempt to recover by breaking constraint 
<MASLayoutConstraint:0x6000006ab1c0 ShopLabel:0x7fafc74b2ac0.left == ShopLabel:0x7fafc74b2ac0.right>

Make a symbolic breakpoint at UIViewAlertForUnsatisfiableConstraints to catch this in the debugger.
The methods in the UIConstraintBasedLayoutDebugging category on UIView listed in <UIKit/UIView.h> may also be helpful.

从输出的信息可以知道，有的控件的约束明显重复了设置，所以指出了是哪个控件，重复设置了哪些约束等等。。。。

Masonry可以设置约束的优先级，优先级分为priorityHigh,priorityMedium,priorityLow(高，中等，低)三个等级。优先级默认为中等，所以当我们对某一个控件的约束条件重复后，会打印警告信息，告诉我们应该去修复它们。

既然知道了警告的产生原因，那么解决办法有两种：
1.找到该控件，修改它的相关约束，以消除警告信息。
2.将控件的约束优先级置为高级，那么就算约束重复了也不会有警告。这也是最简单省事的办法。

处理方法：

[self.labelTitle mas_makeConstraints:^(MASConstraintMaker *make) {
        make.top.mas_equalTo(self.contentView.mas_top).offset(0);
        make.left.mas_equalTo(self.contentView.mas_left).offset(25);
        make.right.mas_equalTo(self.contentView.mas_right).offset(0);
        make.bottom.mas_equalTo(self.contentView.mas_bottom).offset(0).priorityHigh(1000);
        make.height.equalTo(@(25));
    }];