xcode 获取现有的 NSLayoutConstraint 宽度？

Getting an existing NSLayoutConstraint for the width?

提问by IluTov

I'm trying to animate a control in Cocoa with auto layout.

我正在尝试使用自动布局为 Cocoa 中的控件设置动画。

Now, I can set [[constraint animator] setConstant:newWidth];, which works. But how can I get the right constraint?

现在，我可以设置[[constraint animator] setConstant:newWidth];，这很有效。但是我怎样才能得到正确的约束呢？

With [self constraints]you can get all the constraints, and in this case I can just select constraints[0], but the order of the constraints may vary.

有了[self constraints]你可以得到所有的约束，在这种情况下我可以选择constraints[0]，但限制的顺序可能会有所不同。

How can I be certain I always have the right constraint? The constraints are set in Interface Builder. I have seen that you can add a IBOutlet to it, but it doesn't seem necessary.

我怎么能确定我总是有正确的约束？约束在 Interface Builder 中设置。我已经看到您可以向其添加 IBOutlet，但似乎没有必要。

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My solution

我的解决方案

Thanks, it worked great. I wrote a little category.

谢谢，效果很好。我写了一个小类。

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NSView+NSLayoutConstraintFilter.h

NSView+NSLayoutConstraintFilter.h

#import <Cocoa/Cocoa.h>

@interface NSView (NSLayoutConstraintFilter)
- (NSLayoutConstraint *)constraintForAttribute:(NSLayoutAttribute)attribute;
- (NSArray *)constaintsForAttribute:(NSLayoutAttribute)attribute;
@end

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NSView+NSLayoutConstraintFilter.m

NSView+NSLayoutConstraintFilter.m

#import "NSView+NSLayoutConstraintFilter.h"

@implementation NSView (NSLayoutConstraintFilter)

- (NSArray *)constaintsForAttribute:(NSLayoutAttribute)attribute {
    NSPredicate *predicate = [NSPredicate predicateWithFormat:@"firstAttribute = %d", attribute];
    NSArray *filteredArray = [[self constraints] filteredArrayUsingPredicate:predicate];

    return filteredArray;
}

- (NSLayoutConstraint *)constraintForAttribute:(NSLayoutAttribute)attribute {
    NSArray *constraints = [self constaintsForAttribute:attribute];

    if (constraints.count) {
        return constraints[0];
    }

    return nil;
}

@end

回答by Sunil Pandey

Every contraint has an attribute [constraint firstAttribute]It returns an enum NSLayoutAttribute

每个[constraint firstAttribute]约束都有一个属性它返回一个枚举 NSLayoutAttribute

typedef NS_ENUM(NSInteger, NSLayoutAttribute) {
    NSLayoutAttributeLeft = 1,
    NSLayoutAttributeRight,
    NSLayoutAttributeTop,
    NSLayoutAttributeBottom,
    NSLayoutAttributeLeading,
    NSLayoutAttributeTrailing,
    NSLayoutAttributeWidth,
    NSLayoutAttributeHeight,
    NSLayoutAttributeCenterX,
    NSLayoutAttributeCenterY,
    NSLayoutAttributeBaseline,

    NSLayoutAttributeNotAnAttribute = 0
};

so you can check NSLayoutAttributeWidth for width.

所以你可以检查 NSLayoutAttributeWidth 的宽度。

Sample code:

示例代码：

NSArray constraints = [self constraints];
NSPredicate *predicate = [NSPredicate predicateWithFormat:@"firstAttribute = %d", NSLayoutAttributeWidth];
NSArray *filteredArray = [constraints filteredArrayUsingPredicate:predicate];
if(filteredArray.count == 0){
      return nil;
}
NSLayoutConstraint *constraint =  [constraints objectAtIndex:0];

回答by longkai

Here is the swift 3 version tested on Xcode 8.2.1 and macOS 10.12.2.

这是在 Xcode 8.2.1 和 macOS 10.12.2 上测试的 swift 3 版本。

The code shows how to get a button's width and height constraints, but you could filter whatever you want from NSLayoutAttributeenum.

代码显示了如何获取按钮的宽度和高度约束，但您可以从NSLayoutAttribute枚举中过滤任何您想要的内容。

let cons = signInButton.constraints.filter {
    
/**
 * Utils when working with constraints
 */
extension NSLayoutConstraint{
    /**
     * Returns all constraints of kinds
     * EXAMPLE: NSLayoutConstraint.ofKind(rect.immediateConstraints, kinds: [.width,.height]) //width, height
     */
    static func ofKind(_ constraints:[NSLayoutConstraint],kinds:[NSLayoutAttribute]) -> [NSLayoutConstraint]{
        return kinds.map { kind in
            return constraints.filter { constraint in
                return constraint.firstAttribute == kind
            }
        }.flatMap({##代码##})//flattens 2d array to 1d array
    }
}
.firstAttribute == NSLayoutAttribute.width || ##代码##.firstAttribute == NSLayoutAttribute.height /// or other from `NSLayoutAttribute`
}
// do something with the constraints array, e.g.
NSLayoutConstraint.deactivate(cons)

回答by eonist

I wrote a reusable extension: (Swift 4.1)

我写了一个可重用的扩展：（Swift 4.1）

##代码##