如何更改uiview的框架是在iOS中使用自動佈局？

Question

我在XIB中添加了1個視圖，它被設置爲自動佈局。但是當運行時，我想改變那個視圖的框架。我知道如果使用自動佈局，需要在我的代碼中設置translatesAutoresizingMaskIntoConstraints = YES。我這樣做，我該視圖中創建新的框架，但它顯示在控制檯的警告消息：

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) 
(
    "<NSIBPrototypingLayoutConstraint:0x16e4b750 'IB auto generated at build time for view with fixed frame' V:|-(0)-[UIView:0x16ed3c30] (Names: '|':UIView:0x16ee06b0)>", 
    "<NSAutoresizingMaskLayoutConstraint:0x16e19e30 h=-&- v=-&- UIView:0x16ed3c30.midY == UIView:0x16ee06b0.midY + 44>", 
    "<NSAutoresizingMaskLayoutConstraint:0x16e19e60 h=-&- v=-&- UIView:0x16ed3c30.height == UIView:0x16ee06b0.height>" 
) 

Will attempt to recover by breaking constraint 
<NSIBPrototypingLayoutConstraint:0x16e4b750 'IB auto generated at build time for view with fixed frame' V:|-(0)-[UIView:0x16ed3c30] (Names: '|':UIView:0x16ee06b0)> 

Break on objc_exception_throw to catch this in the debugger. 
The methods in the UIConstraintBasedLayoutDebugging category on UIView listed in <UIKit/UIView.h> may also be helpful. 

這是創造新的幀的代碼，我只想Y的原點等於0

self.leftView.frame= CGRectMake(0, 0, 40, self.view.frame.size.height); 

我該如何解決這個錯誤？請給點建議。非常感謝。

Answer 1

如果我理解你正確，我認爲你需要在你的類中使用存儲的NSLayoutConstraint變量，然後將約束的常量值更新爲0，以使你的UIView滑動到頂部。

此外，當你使用自動佈局，您通常設置：

myView.translateAutoResizingMaskIntoConstraint = NO; 

這是NO而不是YES。

因此，一個例子是這樣的：

@interface MyViewController() 
{ 
    NSLayoutConstraint *myViewTopConstraint; 
} 

@end 

@implementation MyViewController 

-(void)setupMyConstraintsMethod 
{ 
    ... 

    // --------------------------------------------------------------- 
    // This constraint here says "myView" top edge should be pinned 
    // to the top edge of the view controller's view but with an offset 
    // of 50 pixels. 
    // --------------------------------------------------------------- 
    NSLayoutConstraint *myViewTopConstraint = [NSLayoutConstraint constraintWithItem:self.myView attribute:NSLayoutAttributeTop relatedBy:NSLayoutRelationEqual toItem:self.view attribute:NSLayoutAttributeTop multiplier:1.0 constant:50.0]; 

    [self.view addConstraint:myViewTopConstraint]; 
} 

-(void)buttonPressed:(id)sender 
{ 
    // ------------------------------------------------------------ 
    // now you want myView's top edge to be at the top of your 
    // view controller's view, so you set the constant to 0 
    // ------------------------------------------------------------ 
    myViewTopConstraint.constant = 0; 

    // animates the sliding up of "myView" 
    [UIView animateWithDuration:0.5 animations:^{ 
     [self.view layoutIfNeeded]; 
    }]; 
} 

@end