iOS使用代码调整约束做动画效果时出现Unable to simultaneously satisfy constraints.

出现这个问题时, 首先应该仔细看错误, 去除多余的存在冲突的约束, 

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. (Note: If you're seeing NSAutoresizingMaskLayoutConstraints that you don't understand, refer to the documentation for the UIView property translatesAutoresizingMaskIntoConstraints) 
(
    "<NSLayoutConstraint:0x170097340 V:|-(0)-[UICollectionView:0x127981200]   (Names: '|':UIView:0x1275336e0 )>",
    "<NSLayoutConstraint:0x170095680 V:[UICollectionView:0x127981200]-(38)-|   (Names: '|':UIView:0x1275336e0 )>",
    "<NSLayoutConstraint:0x17009d830 V:[_UILayoutGuide:0x12753f2d0]-(0)-[UIView:0x1275336e0]>",
    "<NSLayoutConstraint:0x1700973e0 V:[UIView:0x1275336e0]-(416)-[_UILayoutGuide:0x12753f090]>",
    "<_UILayoutSupportConstraint:0x1742bda60 V:[_UILayoutGuide:0x12753f2d0(0)]>",
    "<_UILayoutSupportConstraint:0x1742b9560 V:|-(0)-[_UILayoutGuide:0x12753f2d0]   (Names: '|':UIView:0x1275ce900 )>",
    "<_UILayoutSupportConstraint:0x1742bdbe0 V:[_UILayoutGuide:0x12753f090(0)]>",
    "<_UILayoutSupportConstraint:0x1742bd9a0 _UILayoutGuide:0x12753f090.bottom == UIView:0x1275ce900.bottom>",
    "<NSLayoutConstraint:0x174284d80 'UIView-Encapsulated-Layout-Height' V:[UIView:0x1275ce900(416)]>"
)

Will attempt to recover by breaking constraint 
<NSLayoutConstraint:0x170095680 V:[UICollectionView:0x127981200]-(38)-|   (Names: '|':UIView:0x1275336e0 )>

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.

 

这些都做完了发现还是报错的话, 看一下代码里改变约束的顺序

- (void)updateViewConstraints {
    [super updateViewConstraints];
    //隐藏筛选框
    _siftTopCons.constant = -ScreenHeight+64;//顶部先上去
    _siftBottomCons.constant = ScreenHeight-64;//底部再上来

}

比如这个地方, 我让这个View整体往上移动一个屏幕高度, 使其隐藏, 那么应该先把顶部的约束设置完, 再设置底部, 同理, 当要显示的时候, 整个View往下移动一个屏幕高度, 就应该先设置底部的约束, 再设置顶部, 总之就是不要让整个View的大小在设置的过程中发生可能的 尺寸变小

　　　　　
　　　　
　　　　　_siftBottomCons.constant = 0;//底部先出来
        _siftTopCons.constant = 0;//顶部再向下
        
        [UIView animateWithDuration:0.27 animations:^{
            [self.view layoutIfNeeded];
        }];