Xcode是不讓視圖保持水平居中

好吧我有這個奇怪的問題（因爲我從來沒有見過像這樣的任何錯誤），我有一個Textfield在我看來，我擴大其動畫寬度雙方（拖尾和先行），但問題是這樣的它只是從一個側面擴展（或尾隨或領導）Xcode是不讓視圖保持水平居中

我的代碼：

視圖控制器類

@IBOutlet var constraint1: NSLayoutConstraint! // textfield's leading constraint 
@IBOutlet var constraint2: NSLayoutConstraint! // textfield's trailing constraint 

    viewDidload(){........} 

    @IBAction func editingBegin(sender: AnyObject) { 

    fullnameTextField.layer.cornerRadius = 0 
    fullnameTextField.clipsToBounds = false 
    self.constraint2.constant = -16 // here i'm expanding the width by setting constant of my Textfield 
    self.constraint1.constant = -16 
    UIView.animateWithDuration(duration) { 
     self.fullnameTextField.layoutIfNeeded() 
    } 
}

我的NSLog錯誤：

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:0x155e77fb0 UITextField:0x155d85e40.trailing == UIView:0x155e46800.trailingMargin>", 
    "<NSLayoutConstraint:0x1546b02b0 UITextField:0x155d85e40.leading == UIView:0x155e46800.leadingMargin - 16>", 
    "<NSLayoutConstraint:0x1546447e0 UITextField:0x155d85e40.centerX == UIView:0x155e46800.centerX>" 
) 

Will attempt to recover by breaking constraint 
<NSLayoutConstraint:0x1546447e0 UITextField:0x155d85e40.centerX == UIView:0x155e46800.centerX> 

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.

這裏是我的故事板在那裏我設置的限制