关于Autolayout和Masonry自动布局的几个坑

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)

(...........)


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.

(lldb) po [[UIWindow keyWindow] _autolayoutTrace]

UIWindow:0x7f9481c93360
|   •UIView:0x7f9481c9d680
|   |   *UIView:0x7f9481c9d990- AMBIGUOUS LAYOUT for UIView:0x7f9481c9d990.minX{id: 13}, UIView:0x7f9481c9d990.minY{id: 16}
|   |   *_UILayoutGuide:0x7f9481c9e160- AMBIGUOUS LAYOUT for _UILayoutGuide:0x7f9481c9e160.minY{id: 17}
|   |   *_UILayoutGuide:0x7f9481c9ebb0- AMBIGUOUS LAYOUT for _UILayoutGuide:0x7f9481c9ebb0.minY{id: 27}

(lldb) po 0x7f9481c9d990
<UIView: 0x7f9481c9d990; frame = (0 0; 768 359); autoresize = RM+BM; layer = <CALayer: 0x7fc82d338960>>

(lldb) expr ((UIView *)0x174197010).backgroundColor = [UIColor redColor]
(UICachedDeviceRGBColor *) $4 = 0x0000000174469cc0

//重写updateViewConstraints方法，进行约束的更新
- (void)updateViewConstraints {
    [self.growingButton mas_updateConstraints:^(MASConstraintMaker *make) {
        make.center.mas_equalTo(self.view);
        
        // 初始宽、高为100，优先级最低
        make.width.height.mas_equalTo(100 * self.scacle).priorityLow();
        // 最大放大到整个view
        make.width.height.lessThanOrEqualTo(self.view);
    }];
    [super updateViewConstraints];
}


// 通知需要更新约束，但是不立即执行
[self setNeedsUpdateConstraints];
// 立即更新约束，以执行动态变换
// update constraints now so we can animate the change
[self updateConstraintsIfNeeded];
// 执行动画效果, 设置动画时间
[UIView animateWithDuration:0.2 animations:^{
   [self layoutIfNeeded];
}];

self.button = ({
   UIButton *button = [[UIButton alloc] init];
   button.backgroundColor = [UIColor orangeColor];
   [self.view addSubview:button];
   [button mas_makeConstraints:^(MASConstraintMaker *make) {
       make.centerX.equalTo(self.view);
       make.width.height.equalTo(@100);
       make.top.equalTo(self.blueView.mas_bottom).with.offset(20);
   }];
   @weakify(self);
   [[button rac_signalForControlEvents:UIControlEventTouchUpInside] subscribeNext:^(id x) {
       
       @strongify(self);
       [self.blueView mas_remakeConstraints:^(MASConstraintMaker *make) {
        //这里进行大小状态的判断
           if (!self.isBigger) {
               make.top.bottom.left.right.equalTo(self.view).with.insets(UIEdgeInsetsMake(50, 50, 200, 50));
           } else {
               make.center.equalTo(self.view);
               make.width.height.equalTo(@200);
           }
       }];
       [UIView animateWithDuration:0.25f animations:^{
           [self.view layoutIfNeeded];
       }];
       
       self.isBigger = !self.isBigger;
   }];
   button;
});

//首先设置scrollview的约束
[_scrollView mas_makeConstraints:^(MASConstraintMaker *make) {
		make.edges.equalTo(self.view); // self.view一样大小
}];
//然后设置contentView的约束
_contentView.backgroundColor = [UIColor greenColor];
   [_contentView mas_makeConstraints:^(MASConstraintMaker *make) {
		make.edges.equalTo(_scrollView); // 大小   = _scrollView
       make.width.equalTo(_scrollView); // width  = _scrollView
}];
    
UIView *lastView;
CGFloat height = 25;

//添加子视图，并且设置子试图的约束，注意top的约束由上一个子视图决定
for (int i = 0; i < 10; i++) {
	UIView *view = [[UIView alloc]init];
	view.backgroundColor = [self randomColor];
	[_contentView addSubview:view];
   
   [view mas_makeConstraints:^(MASConstraintMaker *make) {
		make.top.equalTo(lastView ? lastView.mas_bottom : @0); // 第一个View top = 0;
		make.left.equalTo(@0); // left 0
		make.width.equalTo(_contentView); // width = _contentView;
		make.height.equalTo(@(height)); // height = height
   }];

   height += 25;
   lastView = view;
}

[_contentView mas_makeConstraints:^(MASConstraintMaker *make) {
	make.bottom.equalTo(lastView); // bottom =  lastView
}];