Ios 以编程方式在UITableViewCell上设置约束

到目前为止，我一直在使用故事板来设置我的约束，但我正在尝试学习如何以编程方式进行操作。当前的问题是：

[self.view addConstraints:@[centreHorizontallyConstraint,centreVeryConstraint,lblheight,lblwidth]];

表格需要返回

cellForRowAt

中的单元格。在那里，我只需要添加一个UILabel元素，该元素将被约束到左上下和右上的锚定。表格单元格高度设置为自动，因为我不知道标签的大小。我的代码如下所示：

var uil = UILabel()

cell.addSubview(uil)
uil.leftAnchor.constraint(equalTo: cell.leftAnchor).isActive = true
uil.rightAnchor.constraint(equalTo: cell.rightAnchor).isActive = true
uil.topAnchor.constraint(equalTo: cell.topAnchor).isActive = true
uil.bottomAnchor.constraint(equalTo: cell.bottomAnchor).isActive = true
uil.numberOfLines = 0;
uil.text = "Some variable sized text that could be anything really";

[self.view addConstraints:@[centreHorizontallyConstraint,centreVeryConstraint,lblheight,lblwidth]];

如果我不给

ui标签一个框架，我什么也看不到。但是，如果我这样做，请使用以下内容：

UILabel(frame: CGRect(x: 0 , y: 0 , width: 100, height: 100)

[self.view addConstraints:@[centreHorizontallyConstraint,centreVeryConstraint,lblheight,lblwidth]];

然后，正如预期的那样，我看到了标签，但好像约束不适用

[self.view addConstraints:@[centreHorizontallyConstraint,centreVeryConstraint,lblheight,lblwidth]];

我错过了什么？约束是完全描述性的，难道还不够吗？
我认为您应该在应用约束之前添加这一行

uil.translatesAutoresizingMaskIntoConstraints = false

[self.view addConstraints:@[centreHorizontallyConstraint,centreVeryConstraint,lblheight,lblwidth]];

我认为您应该在应用约束之前添加这一行

uil.translatesAutoresizingMaskIntoConstraints = false

[self.view addConstraints:@[centreHorizontallyConstraint,centreVeryConstraint,lblheight,lblwidth]];

如果要动态添加视图，则需要设置
view.translatesAutoResizezingMaskintoConstraints=false

[self.view addConstraints:@[centreHorizontallyConstraint,centreVeryConstraint,lblheight,lblwidth]];

欲知详情

[self.view addConstraints:@[centreHorizontallyConstraint,centreVeryConstraint,lblheight,lblwidth]];

然后应用下面的约束，因为它将起作用

// align lbl from the left and right
cell.addConstraints(NSLayoutConstraint.constraintsWithVisualFormat("H:|-8-[view]-8-|", options: NSLayoutFormatOptions(rawValue: 0), metrics: nil, views: ["view": lbl]));

// align lbl from the top and bottom
cell.addConstraints(NSLayoutConstraint.constraintsWithVisualFormat("V:|-8-[view]-8-|", options: NSLayoutFormatOptions(rawValue: 0), metrics: nil, views: ["view": lbl]));

[self.view addConstraints:@[centreHorizontallyConstraint,centreVeryConstraint,lblheight,lblwidth]];

如果要动态添加视图，则需要设置
view.translatesAutoResizezingMaskintoConstraints=false

[self.view addConstraints:@[centreHorizontallyConstraint,centreVeryConstraint,lblheight,lblwidth]];

欲知详情

[self.view addConstraints:@[centreHorizontallyConstraint,centreVeryConstraint,lblheight,lblwidth]];

然后应用下面的约束，因为它将起作用

// align lbl from the left and right
cell.addConstraints(NSLayoutConstraint.constraintsWithVisualFormat("H:|-8-[view]-8-|", options: NSLayoutFormatOptions(rawValue: 0), metrics: nil, views: ["view": lbl]));

// align lbl from the top and bottom
cell.addConstraints(NSLayoutConstraint.constraintsWithVisualFormat("V:|-8-[view]-8-|", options: NSLayoutFormatOptions(rawValue: 0), metrics: nil, views: ["view": lbl]));

[self.view addConstraints:@[centreHorizontallyConstraint,centreVeryConstraint,lblheight,lblwidth]];

这里有一个工作代码片段，我已经在view controller中完成了，您可以对单元格执行同样的操作

 var uil:UILabel!

    override func viewDidLoad() {
        super.viewDidLoad()
        self.uil = UILabel()
        self.uil?.translatesAutoresizingMaskIntoConstraints = false
        self.uil?.backgroundColor = UIColor.red
        self.uil?.text = "label text"
        self.uil.addSubview(self.uil!)
        self.uil?.leadingAnchor.constraint(equalTo: view.leadingAnchor, constant:10).isActive = true
        self.uil?.topAnchor.constraint(equalTo: view.topAnchor, constant:50).isActive = true
        self.uil?.trailingAnchor.constraint(equalTo: view.trailingAnchor, constant:-10).isActive = true
        self.uil?.heightAnchor.constraint(equalToConstant: 20.0).isActive = true


    }

[self.view addConstraints:@[centreHorizontallyConstraint,centreVeryConstraint,lblheight,lblwidth]];

这里有一个工作代码片段，我已经在view controller中完成了，您可以对单元格执行同样的操作

 var uil:UILabel!

    override func viewDidLoad() {
        super.viewDidLoad()
        self.uil = UILabel()
        self.uil?.translatesAutoresizingMaskIntoConstraints = false
        self.uil?.backgroundColor = UIColor.red
        self.uil?.text = "label text"
        self.uil.addSubview(self.uil!)
        self.uil?.leadingAnchor.constraint(equalTo: view.leadingAnchor, constant:10).isActive = true
        self.uil?.topAnchor.constraint(equalTo: view.topAnchor, constant:50).isActive = true
        self.uil?.trailingAnchor.constraint(equalTo: view.trailingAnchor, constant:-10).isActive = true
        self.uil?.heightAnchor.constraint(equalToConstant: 20.0).isActive = true


    }

[self.view addConstraints:@[centreHorizontallyConstraint,centreVeryConstraint,lblheight,lblwidth]];

下面是一个如何应用约束的示例。我将以标签为例

UILabel *lb1;
lb1 =[[UILabel alloc]init];
self.view addSubview:lb1];

lb1.translatesAutoresizingMaskIntoConstraints = NO;

[self.view addConstraints:@[centreHorizontallyConstraint,centreVeryConstraint,lblheight,lblwidth]];

//水平约束

NSLayoutConstraint *centreHorizontallyConstraint = [NSLayoutConstraint constraintWithItem:lb1 attribute:NSLayoutAttributeCenterX relatedBy:NSLayoutRelationEqual toItem:self.view attribute:NSLayoutAttributeCenterX multiplier:1 constant:0];

NSLayoutConstraint *centreVeryConstraint = [NSLayoutConstraint constraintWithItem:lb1 attribute:NSLayoutAttributeCenterY relatedBy:NSLayoutRelationEqual toItem:self.view attribute:NSLayoutAttributeCenterY multiplier:1 constant:0];

NSLayoutConstraint * lblheight = [NSLayoutConstraint constraintWithItem:lb1 attribute:NSLayoutAttributeHeight relatedBy:NSLayoutRelationEqual toItem:nil attribute:NSLayoutAttributeNotAnAttribute multiplier:1.0 constant:30];

NSLayoutConstraint * lblwidth = [NSLayoutConstraint constraintWithItem:lb1 attribute:NSLayoutAttributeWidth relatedBy:NSLayoutRelationEqual toItem:nil attribute:NSLayoutAttributeNotAnAttribute multiplier:1.0 constant:80];

[self.view addConstraints:@[centreHorizontallyConstraint,centreVeryConstraint,lblheight,lblwidth]];

//垂直约束

NSLayoutConstraint *centreHorizontallyConstraint = [NSLayoutConstraint constraintWithItem:lb1 attribute:NSLayoutAttributeCenterX relatedBy:NSLayoutRelationEqual toItem:self.view attribute:NSLayoutAttributeCenterX multiplier:1 constant:0];

NSLayoutConstraint *centreVeryConstraint = [NSLayoutConstraint constraintWithItem:lb1 attribute:NSLayoutAttributeCenterY relatedBy:NSLayoutRelationEqual toItem:self.view attribute:NSLayoutAttributeCenterY multiplier:1 constant:0];

NSLayoutConstraint * lblheight = [NSLayoutConstraint constraintWithItem:lb1 attribute:NSLayoutAttributeHeight relatedBy:NSLayoutRelationEqual toItem:nil attribute:NSLayoutAttributeNotAnAttribute multiplier:1.0 constant:30];

NSLayoutConstraint * lblwidth = [NSLayoutConstraint constraintWithItem:lb1 attribute:NSLayoutAttributeWidth relatedBy:NSLayoutRelationEqual toItem:nil attribute:NSLayoutAttributeNotAnAttribute multiplier:1.0 constant:80];

[self.view addConstraints:@[centreHorizontallyConstraint,centreVeryConstraint,lblheight,lblwidth]];

//高度限制

NSLayoutConstraint *centreHorizontallyConstraint = [NSLayoutConstraint constraintWithItem:lb1 attribute:NSLayoutAttributeCenterX relatedBy:NSLayoutRelationEqual toItem:self.view attribute:NSLayoutAttributeCenterX multiplier:1 constant:0];

NSLayoutConstraint *centreVeryConstraint = [NSLayoutConstraint constraintWithItem:lb1 attribute:NSLayoutAttributeCenterY relatedBy:NSLayoutRelationEqual toItem:self.view attribute:NSLayoutAttributeCenterY multiplier:1 constant:0];

NSLayoutConstraint * lblheight = [NSLayoutConstraint constraintWithItem:lb1 attribute:NSLayoutAttributeHeight relatedBy:NSLayoutRelationEqual toItem:nil attribute:NSLayoutAttributeNotAnAttribute multiplier:1.0 constant:30];

NSLayoutConstraint * lblwidth = [NSLayoutConstraint constraintWithItem:lb1 attribute:NSLayoutAttributeWidth relatedBy:NSLayoutRelationEqual toItem:nil attribute:NSLayoutAttributeNotAnAttribute multiplier:1.0 constant:80];

[self.view addConstraints:@[centreHorizontallyConstraint,centreVeryConstraint,lblheight,lblwidth]];

//宽度限制

NSLayoutConstraint *centreHorizontallyConstraint = [NSLayoutConstraint constraintWithItem:lb1 attribute:NSLayoutAttributeCenterX relatedBy:NSLayoutRelationEqual toItem:self.view attribute:NSLayoutAttributeCenterX multiplier:1 constant:0];

NSLayoutConstraint *centreVeryConstraint = [NSLayoutConstraint constraintWithItem:lb1 attribute:NSLayoutAttributeCenterY relatedBy:NSLayoutRelationEqual toItem:self.view attribute:NSLayoutAttributeCenterY multiplier:1 constant:0];

NSLayoutConstraint * lblheight = [NSLayoutConstraint constraintWithItem:lb1 attribute:NSLayoutAttributeHeight relatedBy:NSLayoutRelationEqual toItem:nil attribute:NSLayoutAttributeNotAnAttribute multiplier:1.0 constant:30];

NSLayoutConstraint * lblwidth = [NSLayoutConstraint constraintWithItem:lb1 attribute:NSLayoutAttributeWidth relatedBy:NSLayoutRelationEqual toItem:nil attribute:NSLayoutAttributeNotAnAttribute multiplier:1.0 constant:80];

[self.view addConstraints:@[centreHorizontallyConstraint,centreVeryConstraint,lblheight,lblwidth]];

//添加约束

[self.view addConstraints:@[centreHorizontallyConstraint,centreVeryConstraint,lblheight,lblwidth]];

下面是一个如何应用约束的示例。我将以标签为例

UILabel *lb1;
lb1 =[[UILabel alloc]init];
self.view addSubview:lb1];

lb1.translatesAutoresizingMaskIntoConstraints = NO;

[self.view addConstraints:@[centreHorizontallyConstraint,centreVeryConstraint,lblheight,lblwidth]];

//水平约束

NSLayoutConstraint *centreHorizontallyConstraint = [NSLayoutConstraint constraintWithItem:lb1 attribute:NSLayoutAttributeCenterX relatedBy:NSLayoutRelationEqual toItem:self.view attribute:NSLayoutAttributeCenterX multiplier:1 constant:0];

NSLayoutConstraint *centreVeryConstraint = [NSLayoutConstraint constraintWithItem:lb1 attribute:NSLayoutAttributeCenterY relatedBy:NSLayoutRelationEqual toItem:self.view attribute:NSLayoutAttributeCenterY multiplier:1 constant:0];

NSLayoutConstraint * lblheight = [NSLayoutConstraint constraintWithItem:lb1 attribute:NSLayoutAttributeHeight relatedBy:NSLayoutRelationEqual toItem:nil attribute:NSLayoutAttributeNotAnAttribute multiplier:1.0 constant:30];

NSLayoutConstraint * lblwidth = [NSLayoutConstraint constraintWithItem:lb1 attribute:NSLayoutAttributeWidth relatedBy:NSLayoutRelationEqual toItem:nil attribute:NSLayoutAttributeNotAnAttribute multiplier:1.0 constant:80];

[self.view addConstraints:@[centreHorizontallyConstraint,centreVeryConstraint,lblheight,lblwidth]];

//垂直约束

NSLayoutConstraint *centreHorizontallyConstraint = [NSLayoutConstraint constraintWithItem:lb1 attribute:NSLayoutAttributeCenterX relatedBy:NSLayoutRelationEqual toItem:self.view attribute:NSLayoutAttributeCenterX multiplier:1 constant:0];

NSLayoutConstraint *centreVeryConstraint = [NSLayoutConstraint constraintWithItem:lb1 attribute:NSLayoutAttributeCenterY relatedBy:NSLayoutRelationEqual toItem:self.view attribute:NSLayoutAttributeCenterY multiplier:1 constant:0];

NSLayoutConstraint * lblheight = [NSLayoutConstraint constraintWithItem:lb1 attribute:NSLayoutAttributeHeight relatedBy:NSLayoutRelationEqual toItem:nil attribute:NSLayoutAttributeNotAnAttribute multiplier:1.0 constant:30];

NSLayoutConstraint * lblwidth = [NSLayoutConstraint constraintWithItem:lb1 attribute:NSLayoutAttributeWidth relatedBy:NSLayoutRelationEqual toItem:nil attribute:NSLayoutAttributeNotAnAttribute multiplier:1.0 constant:80];

[self.view addConstraints:@[centreHorizontallyConstraint,centreVeryConstraint,lblheight,lblwidth]];

//高度限制

NSLayoutConstraint *centreHorizontallyConstraint = [NSLayoutConstraint constraintWithItem:lb1 attribute:NSLayoutAttributeCenterX relatedBy:NSLayoutRelationEqual toItem:self.view attribute:NSLayoutAttributeCenterX multiplier:1 constant:0];

NSLayoutConstraint *centreVeryConstraint = [NSLayoutConstraint constraintWithItem:lb1 attribute:NSLayoutAttributeCenterY relatedBy:NSLayoutRelationEqual toItem:self.view attribute:NSLayoutAttributeCenterY multiplier:1 constant:0];

NSLayoutConstraint * lblheight = [NSLayoutConstraint constraintWithItem:lb1 attribute:NSLayoutAttributeHeight relatedBy:NSLayoutRelationEqual toItem:nil attribute:NSLayoutAttributeNotAnAttribute multiplier:1.0 constant:30];

NSLayoutConstraint * lblwidth = [NSLayoutConstraint constraintWithItem:lb1 attribute:NSLayoutAttributeWidth relatedBy:NSLayoutRelationEqual toItem:nil attribute:NSLayoutAttributeNotAnAttribute multiplier:1.0 constant:80];

[self.view addConstraints:@[centreHorizontallyConstraint,centreVeryConstraint,lblheight,lblwidth]];

//宽度限制

NSLayoutConstraint *centreHorizontallyConstraint = [NSLayoutConstraint constraintWithItem:lb1 attribute:NSLayoutAttributeCenterX relatedBy:NSLayoutRelationEqual toItem:self.view attribute:NSLayoutAttributeCenterX multiplier:1 constant:0];

NSLayoutConstraint *centreVeryConstraint = [NSLayoutConstraint constraintWithItem:lb1 attribute:NSLayoutAttributeCenterY relatedBy:NSLayoutRelationEqual toItem:self.view attribute:NSLayoutAttributeCenterY multiplier:1 constant:0];

NSLayoutConstraint * lblheight = [NSLayoutConstraint constraintWithItem:lb1 attribute:NSLayoutAttributeHeight relatedBy:NSLayoutRelationEqual toItem:nil attribute:NSLayoutAttributeNotAnAttribute multiplier:1.0 constant:30];

NSLayoutConstraint * lblwidth = [NSLayoutConstraint constraintWithItem:lb1 attribute:NSLayoutAttributeWidth relatedBy:NSLayoutRelationEqual toItem:nil attribute:NSLayoutAttributeNotAnAttribute multiplier:1.0 constant:80];

[self.view addConstraints:@[centreHorizontallyConstraint,centreVeryConstraint,lblheight,lblwidth]];

//添加约束

[self.view addConstraints:@[centreHorizontallyConstraint,centreVeryConstraint,lblheight,lblwidth]];