如何使用 AutoLayout 以编程方式创建自定义 UITableViewCell

Question

我正在尝试实现一个 UITableView，它的行为类似于 twitter 客户端的时间线。现在我只是试图在 UITableViewCell 中获取两个标签。正如this Stack Overflow answer 所推荐的那样，我为每个布局使用了不同的reuseIdentifier。我的布局很简单，由一个标签或两个标签组成。最终我将调整 UITableViewCells 的高度，但首先我需要让单元格填充内容。

如果我用initWithFrame: 设置它们的框架，我可以得到标签，所以显示出来，但是约束没有被实现。

• 问题：是什么阻止了标签和约束的出现？我在 UITableViewCell 的实现中显然遗漏了一些东西，但我不知道它是什么。

• 第二个问题：我是否为viewDidLoad 中的每个reuseIdentifier 正确注册了UITableViewCell 类？

这可能会让人觉得很困难，但 Interface Builder 让我感到困惑，我想在代码中完成这一切。

下面是名为 TVTCell.h 的自定义 UITableViewCell 的代码：

static NSString * const kCellIDTitle = @"CellWithTitle";
static NSString * const kCellIDTitleMain = @"CellWithTitleMain";

@interface TVTCell : UITableViewCell
{
    NSString *reuseID;
}

@property (nonatomic, strong) UILabel *nameLabel;
@property (nonatomic, strong) UILabel *mainLabel;

@end

还有 TVTCell.m：

- (id)initWithStyle:(UITableViewCellStyle)style reuseIdentifier:(NSString *)reuseIdentifier
{
    self = [super initWithStyle:style reuseIdentifier:reuseIdentifier];
    if (self) {
        reuseID = reuseIdentifier;

        nameLabel = [[UILabel alloc] init];
        [nameLabel setTextColor:[UIColor blackColor]];
        [nameLabel setBackgroundColor:[UIColor colorWithHue:32 saturation:100 brightness:63 alpha:1]];
        [nameLabel setFont:[UIFont fontWithName:@"HelveticaNeue" size:18.0f]];
        [nameLabel setTranslatesAutoresizingMaskIntoConstraints:NO];
        [self.contentView addSubview:nameLabel];

        mainLabel = [[UILabel alloc] init];
        [mainLabel setTextColor:[UIColor blackColor]];
        [mainLabel setBackgroundColor:[UIColor colorWithHue:66 saturation:100 brightness:63 alpha:1]];
        [mainLabel setFont:[UIFont fontWithName:@"HelveticaNeue" size:18.0f]];
        [mainLabel setTranslatesAutoresizingMaskIntoConstraints:NO];
        [self.contentView addSubview:mainLabel];

        [self.contentView setTranslatesAutoresizingMaskIntoConstraints:NO];

    }
    return self;
}


- (void)updateConstraints
{
    [super updateConstraints];

    NSDictionary *views = NSDictionaryOfVariableBindings(nameLabel, mainLabel);
    if (reuseID == kCellIDTitle) {
        NSArray *constraints = [NSLayoutConstraint constraintsWithVisualFormat:@"H:|[nameLabel]|"
                                                options: NSLayoutFormatAlignAllCenterX
                                                metrics:nil
                                                  views:views];
        [self.contentView addConstraints:constraints];
        constraints = [NSLayoutConstraint constraintsWithVisualFormat:@"V:|[nameLabel]|"
                                                              options: NSLayoutFormatAlignAllCenterX
                                                              metrics:nil
                                                                views:views];
        [self.contentView addConstraints:constraints];
    }
    if (reuseID == kCellIDTitleMain) {
        NSArray *constraints = [NSLayoutConstraint constraintsWithVisualFormat:@"H:|[nameLabel]|"
                                                                       options: NSLayoutFormatAlignAllCenterX
                                                                       metrics:nil
                                                                         views:views];
        [self.contentView addConstraints:constraints];

        constraints = [NSLayoutConstraint constraintsWithVisualFormat:@"H:|[mainLabel]|"
                                                                       options: NSLayoutFormatAlignAllCenterX
                                                                       metrics:nil
                                                                         views:views];
        [self.contentView addConstraints:constraints];

        constraints = [NSLayoutConstraint constraintsWithVisualFormat:@"V:|[nameLabel][mainLabel]|"
                                                              options: NSLayoutFormatAlignAllLeft
                                                              metrics:nil
                                                                views:views];
        [self.contentView addConstraints:constraints];

        [self.contentView addConstraint:[NSLayoutConstraint constraintWithItem:nameLabel
                                     attribute:NSLayoutAttributeHeight
                                     relatedBy:NSLayoutRelationEqual
                                        toItem:nil
                                     attribute:NSLayoutAttributeNotAnAttribute
                                    multiplier:0.0
                                      constant:44.0]];
        [self.contentView addConstraint:[NSLayoutConstraint constraintWithItem:nameLabel
                                                                     attribute:NSLayoutAttributeWidth
                                                                     relatedBy:NSLayoutRelationEqual
                                                                        toItem:self.contentView
                                                                     attribute:NSLayoutAttributeNotAnAttribute
                                                                    multiplier:0.0
                                                                      constant:1]];
    }
}

抱歉，代码太多了。这是我的 UITableView 的tableView:cellForRowAtIndexPath:

- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
    if (indexPath.row == 0 || indexPath.row == 2 || indexPath.row == 3) {
        TVTCell *cell = [tableView dequeueReusableCellWithIdentifier:kCellIDTitle forIndexPath:indexPath];

        [[cell nameLabel] setText:[nameArray objectAtIndex:indexPath.row]];

        return cell;
    } else if (indexPath.row == 1 || indexPath.row == 4 || indexPath.row == 5) {
        TVTCell *cell = [tableView dequeueReusableCellWithIdentifier:kCellIDTitleMain forIndexPath:indexPath];

        [[cell nameLabel] setText:[nameArray objectAtIndex:indexPath.row]];
        [[cell mainLabel] setText:[dataArray objectAtIndex:indexPath.row]];

        return cell;
    } else
    {
        UITableViewCell *badCell = [[UITableViewCell alloc] init];
        NSLog(@"Warning! returning a cell that shouldnt be here");
        badCell.textLabel.text = @"Warning!";
        return badCell;
    }
}

最后，UITableView 的 viewDidLoad 方法：

- (void)viewDidLoad
{
    [super viewDidLoad];

    [[self tableView] registerClass:[TVTCell class] forCellReuseIdentifier:kCellIDTitle];
    [[self tableView] registerClass:[TVTCell class] forCellReuseIdentifier:kCellIDTitleMain];
}

Answer 1

您可以在 swift 4 中使用自动布局以编程方式创建 UITableViewCell，如下所示。这不是您在问题中指定的上述问题的解决方案，它是更通用的实现如何使用自动布局以编程方式快速创建 Tableview 单元格：

class ViewController: UITableViewController {

override func viewDidLoad() {
   super.viewDidLoad()
   tableView.register(CustomCell2.self, forCellReuseIdentifier: "cell")
}

override func numberOfSections(in tableView: UITableView) -> Int {
  return 1
}
override func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
  return 2
}

override func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
  guard let cell = tableView.dequeueReusableCell(withIdentifier: "cell") as? CustomCell2 else { return UITableViewCell() }
  cell.model = CellModel(labelString: "set constriant by code")
  return cell
  }  
  }

定义模型：

struct CellModel {
  let labelString : String
 }

定义自定义单元格：

class CustomCell2 : UITableViewCell {
private let label : UILabel = {
    let label = UILabel()
    label.translatesAutoresizingMaskIntoConstraints = false // enable auto layout
    label.backgroundColor = .green // to visualize the background of label
    label.textAlignment = .center // center text alignment
    return label
}()

private func addLabel() {
    addSubview(label)
    NSLayoutConstraint.activate([
        // label width is 70% of cell width 
        label.widthAnchor.constraint(equalTo: widthAnchor, multiplier: 0.7),
        // label is horizontally center of cell
        label.centerXAnchor.constraint(equalTo: centerXAnchor)
    ])
}

var model : CellModel? {
    didSet {
        label.text = model?.labelString ?? ""
    }
}

// Init 
override init(style: UITableViewCellStyle, reuseIdentifier: String?) {
    super.init(style: style, reuseIdentifier: reuseIdentifier)
    addLabel()
}

required init?(coder aDecoder: NSCoder) {
    fatalError("init(coder:) has not been implemented")
}
}

This is the output of above program.

This is the actual project, you can check out.

Answer 2

您的代码有几个问题。首先，我想你会发现，如果你做一些记录，updateConstraints 永远不会被调用。我会将所有代码放在 init 方法中。此外，您的约束中有几处错误。不需要将高度设置为 44 的约束，因为您已经将标签固定到单元格的到和底部。我不知道你想用最后一个做什么，看起来这会使 nameLabel 宽 1 点。此外，您不应该将内容视图的 translatesAutoresizingMaskIntoConstraints 设置为 NO，这会导致奇怪的效果。所以这是我认为你想要的代码：

- (id)initWithStyle:(UITableViewCellStyle)style reuseIdentifier:(NSString *)reuseIdentifier {
    self = [super initWithStyle:style reuseIdentifier:reuseIdentifier];
    if (self) {
        reuseID = reuseIdentifier;

        nameLabel = [[UILabel alloc] init];
        [nameLabel setTextColor:[UIColor blackColor]];
        [nameLabel setBackgroundColor:[UIColor colorWithHue:32 saturation:100 brightness:63 alpha:1]];
        [nameLabel setFont:[UIFont fontWithName:@"HelveticaNeue" size:18.0f]];
        [nameLabel setTranslatesAutoresizingMaskIntoConstraints:NO];
        [self.contentView addSubview:nameLabel];

        mainLabel = [[UILabel alloc] init];
        [mainLabel setTextColor:[UIColor blackColor]];
        [mainLabel setBackgroundColor:[UIColor colorWithHue:66 saturation:100 brightness:63 alpha:1]];
        [mainLabel setFont:[UIFont fontWithName:@"HelveticaNeue" size:18.0f]];
        [mainLabel setTranslatesAutoresizingMaskIntoConstraints:NO];
        [self.contentView addSubview:mainLabel];

        NSDictionary *views = NSDictionaryOfVariableBindings(nameLabel, mainLabel);
        if (reuseID == kCellIDTitle) {
            NSArray *constraints = [NSLayoutConstraint constraintsWithVisualFormat:@"H:|[nameLabel]|"
                                                                           options: 0
                                                                           metrics:nil
                                                                             views:views];
            [self.contentView addConstraints:constraints];
            constraints = [NSLayoutConstraint constraintsWithVisualFormat:@"V:|[nameLabel]|"
                                                                  options: 0
                                                                  metrics:nil
                                                                    views:views];
            [self.contentView addConstraints:constraints];
        }
        if (reuseID == kCellIDTitleMain) {
            NSArray *constraints = [NSLayoutConstraint constraintsWithVisualFormat:@"H:|[nameLabel]|"
                                                                           options:0
                                                                           metrics:nil
                                                                             views:views];
            [self.contentView addConstraints:constraints];

            constraints = [NSLayoutConstraint constraintsWithVisualFormat:@"H:|[mainLabel]|"
                                                                  options: 0
                                                                  metrics:nil
                                                                    views:views];
            [self.contentView addConstraints:constraints];

            constraints = [NSLayoutConstraint constraintsWithVisualFormat:@"V:|[nameLabel][mainLabel(==nameLabel)]|"
                                                                  options: 0
                                                                  metrics:nil
                                                                    views:views];
            [self.contentView addConstraints:constraints];

        }
    }
    return self;
}