Xamarin.iOS中CollectionViewCell无法显示数据，求代码排查

项目内其他CollectionView均正常工作，但当前这个CollectionView的Cell始终无法显示数据。能看到Cell边框、尺寸符合预期，调试时确认数据已赋值给Label，Cell数量与数据源字符串列表数量一致，就是看不到文本内容。

PhoneNumberCell代码 #

public partial class PhoneNumberCell : UICollectionViewCell
{
    public static readonly NSString Key = new NSString("PhoneNumberCell");

    UILabel lblPhoneNumberInfo = new UILabel();

    [Export("initWithFrame:")]
    public PhoneNumberCell(CGRect frame) : base(frame)
    {
        // 之前遇到过数据不显示的情况，所以设置了frame和文字颜色，但这里没用，删掉也还是看不到文本
        lblPhoneNumberInfo.Frame = new CGRect(0,0,ContentView.Frame.Width, 26f);
        lblPhoneNumberInfo.TextColor = UIColor.Black;
        // 能看到Cell的边框
        ContentView.Layer.BorderColor = UIColor.LightGray.CGColor;
        ContentView.Layer.BorderWidth = 2.0f;
        ContentView.BackgroundColor = UIColor.White;
        ContentView.Transform = CGAffineTransform.MakeScale(0.8f, 0.8f);
    }

    public void SetData(string pPhoneNumberInfo)
    {
        lblPhoneNumberInfo.Text = pPhoneNumberInfo;
    }

    protected PhoneNumberCell(IntPtr handle) : base(handle)
    {
        // 注意：这个构造方法不能包含初始化逻辑
    }
}

XIB文件内容 #

<?xml version="1.0" encoding="UTF-8" standalone="no"?>
<document type="com.apple.InterfaceBuilder3.CocoaTouch.XIB" version="3.0" toolsVersion="6211" systemVersion="14A298i" targetRuntime="iOS.CocoaTouch" propertyAccessControl="none" useAutolayout="YES" useTraitCollections="YES">
  <dependencies>
    <plugIn identifier="com.apple.InterfaceBuilder.IBCocoaTouchPlugin" version="7026.1" />
  </dependencies>
  <objects>
    <placeholder placeholderIdentifier="IBFilesOwner" id="-1" userLabel="File's Owner" />
    <placeholder placeholderIdentifier="IBFirstResponder" id="-2" customClass="UIResponder" />
    <collectionViewCell opaque="NO" clipsSubviews="YES" multipleTouchEnabled="YES" contentMode="center" customClass="PhoneNumberCell" id="cZE-iV-UFb">
      <rect key="frame" x="0.0" y="0.0" width="50" height="50" />
      <autoresizingMask key="autoresizingMask" flexibleMaxX="YES" flexibleMinY="YES" />
      <view key="contentView" opaque="NO" clipsSubviews="YES" multipleTouchEnabled="YES" contentMode="center">
        <rect key="frame" x="0.0" y="0.0" width="50" height="50" />
        <autoresizingMask key="autoresizingMask" />
        <color key="backgroundColor" white="0.0" alpha="0.0" colorSpace="calibratedWhite" />
      </view>
    </collectionViewCell>
  </objects>
</document>

数据源代码（PhoneNumberSource） #

public class PhoneNumberSource : UICollectionViewSource
{
    public IList<string> PhoneNumbers;
    public override nint NumberOfSections(UICollectionView collectionView)
    {
        return 1;
    }
    public override nint GetItemsCount(UICollectionView collectionView, nint section)
    {
        return PhoneNumbers.Count;
    }

    public PhoneNumberSource(IList<string> pPhoneNumbers)
    {
        PhoneNumbers = pPhoneNumbers;
    }
    public override UICollectionViewCell GetCell(UICollectionView collectionView, NSIndexPath indexPath)
    {
        var phoneNumberCell = (PhoneNumberCell)collectionView.DequeueReusableCell(PhoneNumberCell.Key, indexPath);
        string phoneinfo = PhoneNumbers[indexPath.Row];
        phoneNumberCell.SetData(phoneinfo);
        return phoneNumberCell;
    }
}

CollectionView布局代码 #

PhoneNumberList.CollectionViewLayout = new UICollectionViewFlowLayout()
{
    ItemSize = new CGSize((float)UIScreen.MainScreen.Bounds.Size.Width, 26f),
    HeaderReferenceSize = new CGSize(25, 25),
    SectionInset = new UIEdgeInsets(0, 0, 0, 0),
    ScrollDirection = UICollectionViewScrollDirection.Vertical,
    MinimumInteritemSpacing = 0, // 单元格间最小间距
    MinimumLineSpacing = 0,
};

问题根源与解决方法 #

核心问题 #

你创建的lblPhoneNumberInfo标签没有添加到Cell的ContentView上，所以即使赋值了文本，也不会在界面上显示。

修复步骤 #

在PhoneNumberCell的initWithFrame:构造方法里，添加一行代码将Label添加到ContentView：

ContentView.AddSubview(lblPhoneNumberInfo);

修改后的构造方法：

[Export("initWithFrame:")]
public PhoneNumberCell(CGRect frame) : base(frame)
{
    lblPhoneNumberInfo.Frame = new CGRect(0,0,ContentView.Frame.Width, 26f);
    lblPhoneNumberInfo.TextColor = UIColor.Black;
    // 添加这行代码
    ContentView.AddSubview(lblPhoneNumberInfo);
    
    ContentView.Layer.BorderColor = UIColor.LightGray.CGColor;
    ContentView.Layer.BorderWidth = 2.0f;
    ContentView.BackgroundColor = UIColor.White;
    ContentView.Transform = CGAffineTransform.MakeScale(0.8f, 0.8f);
}

补充优化建议 #

1. Cell注册方式统一：你同时使用了XIB和代码创建Cell，需确保注册方式正确。如果用XIB，在CollectionView初始化时调用RegisterNibForCell；如果纯代码创建，调用RegisterClassForCell，两种方式不要混用，避免初始化逻辑不执行。
2. 改用AutoLayout适配：ContentView.Frame.Width在initWithFrame:里可能未正确计算，建议用AutoLayout约束设置Label布局，适配不同尺寸：

lblPhoneNumberInfo.TranslatesAutoresizingMaskIntoConstraints = false;
ContentView.AddSubview(lblPhoneNumberInfo);
NSLayoutConstraint.ActivateConstraints(new[]
{
    lblPhoneNumberInfo.LeadingAnchor.ConstraintEqualTo(ContentView.LeadingAnchor),
    lblPhoneNumberInfo.TrailingAnchor.ConstraintEqualTo(ContentView.TrailingAnchor),
    lblPhoneNumberInfo.TopAnchor.ConstraintEqualTo(ContentView.TopAnchor),
    lblPhoneNumberInfo.HeightAnchor.ConstraintEqualTo(26)
});

内容的提问来源于stack exchange，提问作者Prescott Chartier