如何更新CALayer的約束條件？

我有一個CATextLayer，我希望能夠在我的視圖中垂直對齊。我可以設置一個約束來將它對齊到視圖的頂部，中間或底部;但我希望能夠讓用戶即時改變這一點。當我建立了我的CATextLayer，我用這個約束對齊，中間：如何更新CALayer的約束條件？

[textLayer addConstraint: [CAConstraint constraintWithAttribute:kCAConstraintMidY 
       relativeTo:@"superlayer" 
      attribute:kCAConstraintMidY]];

這工作得很好，但如果我想更新的層，將其調整到視圖頂部我嘗試：

[textLayer addConstraint: [CAConstraint constraintWithAttribute:kCAConstraintMaxY  
       relativeTo:@"superlayer" 
      attribute:kCAConstraintMaxY]];

當我添加新約束時，它不會與頂部對齊，而是越過視圖頂部，您只能看到它的一部分。它看起來像試圖應用這兩個約束。沒有removeConstraint，如果我在我的類上定義一個CAConstraint變量，並且在將它添加到CATextLayer後更新該變量，似乎會發生同樣的事情。我是否需要每次都重新創建CATextLayer？

來源

2009-09-04 Austin

看起來最好的方法是使用CATextLayer的setConstraints方法，並在需要更改垂直對齊時替換所有約束。這是我的代碼現在的樣子：

// Define the constraints for the class in the .h 

@interface LayerView : NSView { 

    CATextLayer *textLayer; 

    CAConstraint *verticalConstraint; 
    CAConstraint *horizontalConstraint; 
    CAConstraint *widthConstraint; 

} 

- (IBAction)alignTextToTop:(id)sender; 

@end 

@implementation LayerView 

- (id)initWithFrame:(NSRect)frameRect 
{ 
    id view = [super initWithFrame:frameRect]; 

    horizontalConstraint = [CAConstraint constraintWithAttribute:kCAConstraintMidX relativeTo:@"superlayer" attribute:kCAConstraintMidX]; 

    widthConstraint = [CAConstraint constraintWithAttribute:kCAConstraintWidth relativeTo:@"superlayer" attribute:kCAConstraintWidth]; 

    verticalConstraint = [CAConstraint constraintWithAttribute:kCAConstraintMidY relativeTo:@"superlayer" attribute:kCAConstraintMidY]; 

    [textLayer setConstraints:[NSArray arrayWithObjects:verticalConstraint, horizontalConstraint, widthConstraint, nil]]; 

    return view; 
} 

// Update the constraints using setConstraints 
- (IBAction)alignTextToTop:(id)sender 
{ 
    verticalConstraint = [CAConstraint constraintWithAttribute:kCAConstraintMaxY relativeTo:@"superlayer" attribute:kCAConstraintMaxY]; 

    [textLayer setConstraints:[NSArray arrayWithObjects:verticalConstraint, horizontalConstraint, widthConstraint, nil]]; 
} 

@end

來源

2009-09-07 00:08:05 Austin

如何更新CALayer的約束條件？

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