重复添加constraint后警告Unable to simultaneously satisfy constraints.

[FaiChou]

code

[self.view addConstraints:[self.view1 constraintsSize:CGSizeMake(50, 30)]];
[self.view addConstraints:[self.view1 constraintsTopInContainer:10.0f]];
[self.view addConstraints:[self.view1 constraintsTopInContainer:20.0f]];

console

2016-09-02 19:53:50.192 FaiChouTest[3223:179657] 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. 
(
    "<NSLayoutConstraint:0x7faad0d452c0 UIView:0x7faad306b8f0.top == UIView:0x7faad3017670.top + 10>",
    "<NSLayoutConstraint:0x7faad0d2daf0 UIView:0x7faad306b8f0.top == UIView:0x7faad3017670.top + 20>"
)

Will attempt to recover by breaking constraint 
<NSLayoutConstraint:0x7faad0d2daf0 UIView:0x7faad306b8f0.top == UIView:0x7faad3017670.top + 20>

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.

这样会使得添加动画变得困难，我们需要手动移除原先的constraint，再添加之。
我们可以在原封装方法里添加判断。

[FaiChou]

Masonry里对于动画，格外添加了一个方法mas_updateConstraints。

I am new to autoLayout.