如何以编程方式创建布局约束

Question

我在通用应用程序的底部显示一个视图,并在我的视图中动态添加此视图.我希望每次都像iAd一样在底部显示这个视图.在两个方向.如何为此添加约束.请建议.

谢谢

Answer 1

要将视图固定到屏幕底部,您需要设置以下约束.

1. 关于父视图的主要约束 - X.
2. 关于父视图的尾随约束 - 宽度
3. 关于父视图的底部约束 - Y.
4. 高度约束附加到自我 - 高度.

让我们补充一下.

UIView *subView=bottomView;
UIView *parent=self.view;

subView.translatesAutoresizingMaskIntoConstraints = NO;

//Trailing    
NSLayoutConstraint *trailing =[NSLayoutConstraint
                                constraintWithItem:subView
                                attribute:NSLayoutAttributeTrailing
                                relatedBy:NSLayoutRelationEqual
                                toItem:parent   
                                attribute:NSLayoutAttributeTrailing
                                multiplier:1.0f
                                constant:0.f];

//Leading

NSLayoutConstraint *leading = [NSLayoutConstraint
                                   constraintWithItem:subView
                                   attribute:NSLayoutAttributeLeading
                                   relatedBy:NSLayoutRelationEqual
                                   toItem:parent
                                   attribute:NSLayoutAttributeLeading
                                   multiplier:1.0f
                                   constant:0.f];

//Bottom
NSLayoutConstraint *bottom =[NSLayoutConstraint
                                 constraintWithItem:subView
                                 attribute:NSLayoutAttributeBottom
                                 relatedBy:NSLayoutRelationEqual
                                 toItem:parent
                                 attribute:NSLayoutAttributeBottom
                                 multiplier:1.0f
                                 constant:0.f];

//Height to be fixed for SubView same as AdHeight
NSLayoutConstraint *height = [NSLayoutConstraint
                               constraintWithItem:subView
                               attribute:NSLayoutAttributeHeight
                               relatedBy:NSLayoutRelationEqual
                               toItem:nil
                               attribute:NSLayoutAttributeNotAnAttribute
                               multiplier:0
                               constant:ADHeight];

    //Add constraints to the Parent
    [parent addConstraint:trailing];
    [parent addConstraint:bottom];
    [parent addConstraint:leading];

    //Add height constraint to the subview, as subview owns it.
    [subView addConstraint:height];

希望这可以帮助.

干杯.

Answer 2

之前答案的小扩展名,因为addConstraint将来会被弃用.这是UI视图的扩展.将视图添加到层​​次结构后,请使用这些功能.

OBJC

@implementation UIView (Constraints)

-(void)addConstaintsToSuperviewWithLeftOffset:(CGFloat)leftOffset topOffset:(CGFloat)topOffset {

    self.translatesAutoresizingMaskIntoConstraints = false;

    [[NSLayoutConstraint constraintWithItem: self
                                  attribute: NSLayoutAttributeLeading
                                  relatedBy: NSLayoutRelationEqual
                                     toItem: self.superview
                                  attribute: NSLayoutAttributeLeading
                                 multiplier: 1
                                   constant: leftOffset] setActive:true];

    [[NSLayoutConstraint constraintWithItem: self
                                  attribute: NSLayoutAttributeTop
                                  relatedBy: NSLayoutRelationEqual
                                     toItem: self.superview
                                  attribute: NSLayoutAttributeTop
                                 multiplier: 1
                                   constant: topOffset] setActive:true];
}

-(void)addConstaintsWithWidth:(CGFloat)width height:(CGFloat)height {

    self.translatesAutoresizingMaskIntoConstraints = false;


    [[NSLayoutConstraint constraintWithItem: self
                                  attribute: NSLayoutAttributeWidth
                                  relatedBy: NSLayoutRelationEqual
                                     toItem: nil
                                  attribute: NSLayoutAttributeNotAnAttribute
                                 multiplier: 1
                                   constant: width] setActive:true];

    [[NSLayoutConstraint constraintWithItem: self
                                  attribute: NSLayoutAttributeHeight
                                  relatedBy: NSLayoutRelationEqual
                                     toItem: nil
                                  attribute: NSLayoutAttributeNotAnAttribute
                                 multiplier: 1
                                   constant: height] setActive:true];
}

@end

斯威夫特3

extension UIView {

    public func addConstaintsToSuperview(leftOffset: CGFloat, topOffset: CGFloat) {

        self.translatesAutoresizingMaskIntoConstraints = false

        NSLayoutConstraint(item: self,
                           attribute: .leading,
                           relatedBy: .equal,
                           toItem: self.superview,
                           attribute: .leading,
                           multiplier: 1,
                           constant: leftOffset).isActive = true

        NSLayoutConstraint(item: self,
                           attribute: .top,
                           relatedBy: .equal,
                           toItem: self.superview,
                           attribute: .top,
                           multiplier: 1,
                           constant: topOffset).isActive = true
    }

    public func addConstaints(height: CGFloat, width: CGFloat) {

        self.translatesAutoresizingMaskIntoConstraints = false

        NSLayoutConstraint(item: self,
                           attribute: .height,
                           relatedBy: .equal,
                           toItem: nil,
                           attribute: .notAnAttribute,
                           multiplier: 1,
                           constant: height).isActive = true


        NSLayoutConstraint(item: self,
                           attribute: .width,
                           relatedBy: .equal,
                           toItem: nil,
                           attribute: .notAnAttribute,
                           multiplier: 1,
                           constant: width).isActive = true
    }
}

Answer 3

此外,从iOS 9开始,它可以通过锚点完成:

斯威夫特3

extension UIView {

    func addConstaintsToSuperview(leadingOffset: CGFloat, topOffset: CGFloat) {

        guard superview != nil else {
            return
        }

        translatesAutoresizingMaskIntoConstraints = false

        leadingAnchor.constraint(equalTo: superview!.leadingAnchor,
                                 constant: leadingOffset).isActive = true

        topAnchor.constraint(equalTo: superview!.topAnchor,
                             constant: topOffset).isActive = true
    }

    func addConstaints(height: CGFloat, width: CGFloat) {

        heightAnchor.constraint(equalToConstant: height).isActive = true
        widthAnchor.constraint(equalToConstant: width).isActive = true
    }

}

OBJC类别

@implementation UIView (Constraints)

-(void)addConstaintsToSuperviewWithLeadingOffset:(CGFloat)leadingOffset topOffset:(CGFloat)topOffset
{
    if (self.superview == nil) {
        return;
    }

    self.translatesAutoresizingMaskIntoConstraints = false;

    [[self.leadingAnchor constraintEqualToAnchor:self.superview.leadingAnchor
                                        constant:leadingOffset] setActive:true];

    [[self.topAnchor constraintEqualToAnchor:self.superview.topAnchor
                                   constant:topOffset] setActive:true];
}

-(void)addConstaintsWithHeight:(CGFloat)height width:(CGFloat)width
{
    [[self.heightAnchor constraintEqualToConstant:height] setActive:true];
    [[self.widthAnchor constraintEqualToConstant:width] setActive:true];
}

@end

Answer 4

您可以像下面这样以编程方式使用自动布局约束

fileprivate func setupName(){
        let height = CGFloat(50)

        lblName.text = "Hello world"
        lblName.backgroundColor = .lightGray

        //Step 1
        lblName.translatesAutoresizingMaskIntoConstraints = false

        //Step 2
        self.view.addSubview(lblName)

        //Step 3
        NSLayoutConstraint.activate([

            lblName.leadingAnchor.constraint(equalTo: self.view.safeAreaLayoutGuide.leadingAnchor),
            lblName.trailingAnchor.constraint(equalTo: self.view.safeAreaLayoutGuide.trailingAnchor),
            lblName.topAnchor.constraint(equalTo: self.view.safeAreaLayoutGuide.bottomAnchor,constant: -height),
            lblName.bottomAnchor.constraint(equalTo: self.view.safeAreaLayoutGuide.bottomAnchor),
            ])

    }

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