主要还是使用 Masonry ，看另一篇文章，这里大致了解系统自动布局的方法，其实masonry 与系统的差不多。只是简化了代码量。
一般方法 添加约束
- 1 首先 需要对自动布局的 obj 设置：
self.leftView.translatesAutoresizingMaskIntoConstraints = NO;
- 2 添加约束，简单介绍，需要注意的挺多，不小心就会报错哦。
// 父视图 添加约束 ：方程式：
leftView 的 top = self.view 的 top （倍数1） + 100；
[self.view addConstraint:[NSLayoutConstraint constraintWithItem:self.leftView
attribute:NSLayoutAttributeTop
relatedBy:NSLayoutRelationEqual
toItem:self.view
attribute:NSLayoutAttributeTop
multiplier:1.
constant:100]];
- 3 对于 约束 存在优先级
NSLayoutConstraint *leftTop = [NSLayoutConstraint constraintWithItem:self.leftView
attribute:NSLayoutAttributeTop
relatedBy:NSLayoutRelationEqual
toItem:self.view
attribute:NSLayoutAttributeTop
multiplier:1.
constant:100];
leftTop.priority = UILayoutPriorityDefaultHigh;
- 3 举个例子:左右两个view 等高等宽，自动布局
self.leftView = [UIView new];
self.leftView.backgroundColor = [UIColor redColor];
[self.view addSubview:self.leftView];
self.rightView = [UIView new];
self.rightView.backgroundColor = [UIColor greenColor];
[self.view addSubview:self.rightView];
self.leftView.translatesAutoresizingMaskIntoConstraints = NO;
self.rightView.translatesAutoresizingMaskIntoConstraints = NO;
[self.view addConstraint:[NSLayoutConstraint constraintWithItem:self.leftView
attribute:NSLayoutAttributeTop
relatedBy:NSLayoutRelationEqual
toItem:self.view
attribute:NSLayoutAttributeTop
multiplier:1.
constant:100]];
// l 左 = s 左 + 20
[self.view addConstraint:[NSLayoutConstraint constraintWithItem:self.leftView
attribute:NSLayoutAttributeLeft
relatedBy:NSLayoutRelationEqual
toItem:self.view
attribute:NSLayoutAttributeLeft
multiplier:1.
constant:20]];
// l 高 = 200；
[self.view addConstraint:[NSLayoutConstraint constraintWithItem:self.leftView
attribute:NSLayoutAttributeHeight
relatedBy:NSLayoutRelationEqual
toItem:nil
attribute:NSLayoutAttributeHeight
multiplier:1.
constant:200]];
// r 上 = l 上
[self.view addConstraint:[NSLayoutConstraint constraintWithItem:self.rightView
attribute:NSLayoutAttributeTop
relatedBy:NSLayoutRelationEqual
toItem:self.leftView
attribute:NSLayoutAttributeTop
multiplier:1.
constant:0]];
// r 左 = l 右 + 20
[self.view addConstraint:[NSLayoutConstraint constraintWithItem:self.rightView
attribute:NSLayoutAttributeLeft
relatedBy:NSLayoutRelationEqual
toItem:self.leftView
attribute:NSLayoutAttributeRight
multiplier:1.
constant:20]];
// r 右 = s 右 - 20
[self.view addConstraint:[NSLayoutConstraint constraintWithItem:self.rightView
attribute:NSLayoutAttributeRight
relatedBy:NSLayoutRelationEqual
toItem:self.view
attribute:NSLayoutAttributeRight
multiplier:1.
constant:-20]];
// r 高 = l 高
[self.view addConstraint:[NSLayoutConstraint constraintWithItem:self.rightView
attribute:NSLayoutAttributeHeight
relatedBy:NSLayoutRelationEqual
toItem:self.leftView
attribute:NSLayoutAttributeHeight
multiplier:1.
constant:0]];
// r 宽 = l 宽
[self.view addConstraint:[NSLayoutConstraint constraintWithItem:self.rightView
attribute:NSLayoutAttributeWidth
relatedBy:NSLayoutRelationEqual
toItem:self.leftView
attribute:NSLayoutAttributeWidth
multiplier:1.0
constant:0]];
format 方式 添加约束
略坑 大概了解一点点
注意 obj 需要 [obj] 框起来，其他好像没什么要注意的，用起来没有上面的方便，主要是不熟练。
[self.view addConstraints:[NSLayoutConstraint constraintsWithVisualFormat:@"V:|-100-[leftView(==200)]" options:0 metrics:nil views:@{@"leftView":self.leftView,@"rightView":self.rightView}]];
[self.view addConstraints:[NSLayoutConstraint constraintsWithVisualFormat:@"V:|-100-[rightView(==200)]" options:0 metrics:nil views:@{@"leftView":self.leftView,@"rightView":self.rightView}]];
[self.view addConstraints:[NSLayoutConstraint constraintsWithVisualFormat:@"H:|-10-[leftView]-10-[rightView(==leftView)]-20-|" options:0 metrics:nil views:@{@"leftView":self.leftView,@"rightView":self.rightView}]];
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