masonry的奇葩

问题：

    约束警告：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:0x7fa1e4f39270 UIView:0x7fa1e5007170.left == UIView:0x7fa1e519a300.left + 10>",

    "<MASLayoutConstraint:0x7fa1e4f39ae0 UIView:0x7fa1e5007170.right == UIView:0x7fa1e519a300.right - 10>",

    "<NSLayoutConstraint:0x7fa1e25a2130 UIView:0x7fa1e519a300.width == 0>"

)

Will attempt to recover by breaking constraint 

<MASLayoutConstraint:0x7fa1e4f39ae0 UIView:0x7fa1e5007170.right == UIView:0x7fa1e519a300.right - 10>

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.

code：

-(UIView *)createFooterView{

    UIView * view = [[UIView alloc]initWithFrame:CGRectMake(0, 0, SCREEN_WIDTH, 50.f)];

    [view setBackgroundColor:[UIColor whiteColor]];

    UIView * lineView = [[UIView alloc]init];

    [view addSubview:lineView];

    [lineView makeConstraints:^(MASConstraintMaker *make) {

        make.centerY.equalTo(view.centerY);

        make.left.equalTo(view.left).offset(10);

        make.right.equalTo(view.right).offset(-10);                //此行与下行的比较 这么写不警告

//        make.width.equalTo(SCREEN_WIDTH -w 20);          //这么写  就有以上警告

        make.height.equalTo(1.f);

        

    }];

    [lineView setBackgroundColor:[CommUtls colorWithHexString:@"#cecece"]];

    UILabel * label = [[UILabel alloc]init];

    [view addSubview:label];

    [label setText:@"    已经到底部了    "];

    [label makeConstraints:^(MASConstraintMaker *make) {

        make.centerY.equalTo(lineView.centerY);

        make.centerX.equalTo(lineView.centerX);

    }];

    [label setFont:[UIFont systemFontOfSize:13.f]];

    [label setTextColor:[CommUtls colorWithHexString:@"0x666666"]];

    [label setBackgroundColor:[UIColor whiteColor]];

    

    return view;

}

总结：将一个view赋给另个View时 未知宽度 左右约束 产生警告 ，控制宽度便可