Xamarin 自定义 UITableViewCell 在重用时重叠文本

Question

我正在使用 Monotouch.Dialog 框架为用户输入我的应用程序构建表单。我运行遇到一个奇怪的问题，即当我子 class UITableViewCell 时屏幕显示重叠的文本。当我说文本重叠时，我的意思是它看起来就像一个完整的单元格放在另一个单元格之上，而不仅仅是标签被推到一起或放错地方。

我在 Xamarin 网站上遵循了这个例子 here。

基本上我有这个 UITableViewCell class

public class SAFutureAdCell : UITableViewCell
{
    private UILabel issueAndSizeLabel, mailDateLabel, orderDateLabel, miscLabel, totalLabel;
    private UIImage monthlyImage, ccoImage;

    public SAFutureAdCell(IntPtr p) : base(p) 
    {
        init ();
    }
    public SAFutureAdCell(string resuseIdentifier) : base(UITableViewCellStyle.Default, resuseIdentifier)
    {
        init ();
    }
    public SAFutureAdCell(NSString cellKey): base(UITableViewCellStyle.Default, cellKey)
    {
        init ();
    }

    private void init()
    {
        issueAndSizeLabel = new UILabel() {
            TextColor = UIColor.Black,
            Font = UIFont.BoldSystemFontOfSize(15),
            BackgroundColor = UIColor.Clear,
            ShadowColor = UIColor.Clear,
            TextAlignment = UITextAlignment.Left,
            ClipsToBounds = true
        };

        mailDateLabel = new UILabel() {
            TextColor = UIColor.Black,
            Font = UIFont.BoldSystemFontOfSize(15),
            BackgroundColor = UIColor.Clear,
            ShadowColor = UIColor.Clear,
            TextAlignment = UITextAlignment.Left,
            ClipsToBounds = true
        };

        orderDateLabel = new UILabel() {
            TextColor = UIColor.Gray,
            Font = UIFont.SystemFontOfSize(13),
            BackgroundColor = UIColor.Clear,
            ShadowColor = UIColor.Clear,
            TextAlignment = UITextAlignment.Left,
            ClipsToBounds = true
        };

        miscLabel = new UILabel() {
            TextColor = UIColor.Gray,
            Font = UIFont.SystemFontOfSize(13),
            BackgroundColor = UIColor.Clear,
            ShadowColor = UIColor.Clear,
            TextAlignment = UITextAlignment.Right,
            ClipsToBounds = true
        };

        totalLabel = new UILabel() {
            TextColor = UIColor.Black,
            Font = UIFont.BoldSystemFontOfSize(15),
            BackgroundColor = UIColor.Clear,
            ShadowColor = UIColor.Clear,
            TextAlignment = UITextAlignment.Right,
            ClipsToBounds = true
        };

        monthlyImage = AppearanceManager.MonthlyIndicator; // small blue circle
        ccoImage = AppearanceManager.CcoIndicator; // small red circle
        ImageView.Image = monthlyImage;
        ImageView.ContentMode = UIViewContentMode.ScaleAspectFit;

        ContentView.AddSubviews(issueAndSizeLabel, mailDateLabel, orderDateLabel, miscLabel, totalLabel);

    }

    public override void LayoutSubviews()
    {
        base.LayoutSubviews();

        Accessory = UITableViewCellAccessory.DisclosureIndicator;

        var b = ContentView.Bounds;
        b.Width -= 30;
        var x = 24;

        issueAndSizeLabel.Frame = new RectangleF(x, 5, b.Width / 2, b.Height / 2 - 5).RoundFloats();
        mailDateLabel.Frame = new RectangleF(issueAndSizeLabel.Frame.Right, 5, b.Width / 4, b.Height / 2 - 5).RoundFloats();
        totalLabel.Frame = new RectangleF(mailDateLabel.Frame.Right, 5, b.Width / 4, b.Height / 2 - 5).RoundFloats();
        orderDateLabel.Frame = new RectangleF(x, b.Height / 2 + 5, b.Width / 3, b.Height / 2 - 10).RoundFloats();
        miscLabel.Frame = new RectangleF(totalLabel.Frame.Left, b.Height / 2 + 5, b.Width / 4, b.Height / 2 - 10).RoundFloats();
        ImageView.Frame = new RectangleF(5, 0, AppearanceManager.MonthlyIndicator.Size.Width, ContentView.Frame.Height);
    }

    public void Update(Ad ad)
    {
        issueAndSizeLabel.Text = string.Format("{0} - {1}", ad.IssueCode, ad.AdvertSize);
        mailDateLabel.Text = string.Format("Mail: {0}", ad.MailDate.ToShortDateString());
        orderDateLabel.Text = string.Format("Order: {0}", ad.OrderDate.ToShortDateString());
        miscLabel.Text = string.Format("Misc: {0}", ad.Misc.ToCurrency());
        totalLabel.Text = string.Format("Total: {0}", ad.Total.ToCurrency());

        if (ad.IsCCOPackage)
            ImageView.Image = ccoImage;
        else
            ImageView.Image = monthlyImage;

        ImageView.Alpha = (ad.IsMonthlyBilling || ad.IsCCOPackage) ? 1f : 0f;
    }
}

此元素使用此单元格。

public class SAFutureAdDetailElement : Element, IElementSizing
{
    public SAFutureAdDetailElement(Ad ad, NSAction tapped) : base("FutureAdDetail")
    {
        this.ad = ad;
        Tapped += tapped;
    }

    public SAFutureAdDetailElement(Ad ad) : base("FutureAdDetail")
    {
        this.ad = ad;
    }

    private static NSString cellKey = new NSString("SAFutureAdDetailElement");
    protected override NSString CellKey
    {
        get
        {
            return cellKey;
        }
    }

    public override UITableViewCell GetCell(UITableView tv)
    {
        var cell = tv.DequeueReusableCell (cellKey) as SAFutureAdCell;
        if (cell == null) {
            cell = new SAFutureAdCell(cellKey);
        }

        cell.Update (ad);

        return cell;
    }

    public override void Selected(DialogViewController dvc, UITableView tableView, NSIndexPath path)
    {
        if (Tapped != null)
            Tapped ();

        tableView.DeselectRow (path, true);
    }

    public float GetHeight(UITableView tableView, NSIndexPath indexPath)
    {
        return cellHeight;
    }

    private Ad ad;
    public event NSAction Tapped;

    private int cellHeight = 60;
}

像这样将这些元素的集合添加到 MTD 部分

Section CreateOnPageSection()
{
    var onPageSection = new Section ("Future On Page Ads");
    onPageSection.AddAll (
        from ad in orderInfo.AdsFuture
        where !Settings.offPageAdSizes.Contains (ad.AdvertSizeID)
        select new SAFutureAdDetailElement (
            ad, 
            () => {
                NavigationController.PushViewController (new FutureAdDetailController (customer.CustID, ad, this), true);
            }
        )
    );
    return onPageSection;
 }

然后将其作为 DialogViewController 的一部分添加到 RootElement。根元素添加了 3 个其他部分，所有部分都包含自定义元素，这些元素具有自己的自定义 UITableViewCells，它们都非常相似。它们的主要区别在于标签的位置和标签中的数据。

文本不会重叠，直到发生滚动或直到您将视图推到 NavigationController 上然后弹回到该视图。通常也很难在较新的 iPad 上重现（此应用程序仅限 iPad）。此问题在较早的 iPad 2s 上发生得更频繁。有时我可以在我的 Air 上实现它，但在那台机器上实现它要困难得多。

这是重叠文本的屏幕截图。

IOS UITableViewCell Overlapping Text

Answer 1

这一定是电池没有被正确地重新使用的情况。所以我的直觉是改变 GetCell 方法就可以完成这项工作。

public override UITableViewCell GetCell(UITableView tv)
{
    var cell = tv.DequeueReusableCell (cellKey);// as SAFutureAdCell;
    if (cell == null) {
        cell = new SAFutureAdCell(cellKey);
    }
    else
        {
            cell.Element = this;
        }

    cell.Update (ad);

    return cell;
}

您可以尝试像这样更改 GetCell 方法吗？它可能会修复它...

Answer 2

好的，所以我找到了我自己的问题的答案。看起来 LayoutSubviews 如何处理单元格回收存在问题。基本上我所做的是摆脱自定义单元格并将所有显示登录移动到自定义元素中的 GetCell 方法中。元素 class 看起来像这样。

public class SAFutureAdDetailElement : Element, IElementSizing
{
    public SAFutureAdDetailElement(Ad ad, NSAction tapped) : base("FutureAdDetail")
    {
        this.ad = ad;
        Tapped += tapped;
    }

    public SAFutureAdDetailElement(Ad ad) : base("FutureAdDetail")
    {
        this.ad = ad;
    }

    private static NSString cellKey = new NSString("SAFutureAdDetailElement");
    protected override NSString CellKey
    {
        get
        {
            return cellKey;
        }
    }

    public override UITableViewCell GetCell(UITableView tv)
    {
        var cell = tv.DequeueReusableCell (cellKey);
        if (cell == null) {
            cell = new UITableViewCell (UITableViewCellStyle.Default, cellKey);

            cell.IndentationLevel = 0;
            var x = 24;
            var contentWidth = tv.Bounds.Width - 30 - x;
            var issueAndSizeLabel = new UILabel (new RectangleF (x, 5, contentWidth / 2, cellHeight / 2 - 5).RoundFloats ()) {
                TextColor = UIColor.Black,
                Font = UIFont.BoldSystemFontOfSize (15),
                BackgroundColor = UIColor.Clear,
                ShadowColor = UIColor.Clear,
                TextAlignment = UITextAlignment.Left,
                ClipsToBounds = true,
                Text = string.Format ("{0} - {1}", ad.IssueCode, ad.AdvertSize)
            };

            var mailDateLabel = new UILabel (new RectangleF (issueAndSizeLabel.Frame.Right, 5, contentWidth / 4, cellHeight / 2 - 5).RoundFloats ()) {
                TextColor = UIColor.Black,
                Font = UIFont.BoldSystemFontOfSize (15),
                BackgroundColor = UIColor.Clear,
                ShadowColor = UIColor.Clear,
                TextAlignment = UITextAlignment.Left,
                ClipsToBounds = true,
                Text = string.Format ("Mail: {0}", ad.MailDate.ToShortDateString ())
            };

            var orderDateLabel = new UILabel (new RectangleF (x, cellHeight / 2 + 5, contentWidth / 3, cellHeight / 2 - 10).RoundFloats ()) {
                TextColor = UIColor.Gray,
                Font = UIFont.SystemFontOfSize (13),
                BackgroundColor = UIColor.Clear,
                ShadowColor = UIColor.Clear,
                TextAlignment = UITextAlignment.Left,
                ClipsToBounds = true,
                Text = string.Format ("Order: {0}", ad.OrderDate.ToShortDateString ())
            };

            var totalLabel = new UILabel (new RectangleF (mailDateLabel.Frame.Right, 5, contentWidth / 4, cellHeight / 2 - 5).RoundFloats ()) {
                TextColor = UIColor.Black,
                Font = UIFont.BoldSystemFontOfSize (15),
                BackgroundColor = UIColor.Clear,
                ShadowColor = UIColor.Clear,
                TextAlignment = UITextAlignment.Right,
                ClipsToBounds = true,
                Text = string.Format ("Total: {0}", ad.Total.ToCurrency ())
            };

            var miscLabel = new UILabel (new RectangleF (totalLabel.Frame.Left, cellHeight / 2 + 5, contentWidth / 4, cellHeight / 2 - 10).RoundFloats ()) {
                TextColor = UIColor.Gray,
                Font = UIFont.SystemFontOfSize (13),
                BackgroundColor = UIColor.Clear,
                ShadowColor = UIColor.Clear,
                TextAlignment = UITextAlignment.Right,
                ClipsToBounds = true,
                Text = string.Format ("Misc: {0}", ad.Misc.ToCurrency ())
            };

            var indicator = new UIImageView (new RectangleF (5, 0, AppearanceManager.MonthlyIndicator.Size.Width, cellHeight));
            indicator.ContentMode = UIViewContentMode.ScaleAspectFit;
            if (ad.IsCCOPackage) {
                indicator.Image = AppearanceManager.CcoIndicator;
            } else if (ad.IsMonthlyBilling) {
                indicator.Image = AppearanceManager.MonthlyIndicator;
            }

            cell.Accessory = UITableViewCellAccessory.DisclosureIndicator;

            cell.ContentView.AddSubviews (indicator, issueAndSizeLabel, mailDateLabel, orderDateLabel, miscLabel, totalLabel);
        }

        ((UILabel)cell.ContentView.Subviews[1]).Text = string.Format("{0} - {1}", ad.IssueCode, ad.AdvertSize);
        ((UILabel)cell.ContentView.Subviews[2]).Text = string.Format("Mail: {0}", ad.MailDate.ToShortDateString());
        ((UILabel)cell.ContentView.Subviews[3]).Text = string.Format("Order: {0}", ad.OrderDate.ToShortDateString());
        ((UILabel)cell.ContentView.Subviews[4]).Text = string.Format("Misc: {0}", ad.Misc.ToCurrency());
        ((UILabel)cell.ContentView.Subviews[5]).Text = string.Format("Total: {0}", ad.Total.ToCurrency());
        if (ad.IsCCOPackage) {
            ((UIImageView)cell.ContentView.Subviews [0]).Image = AppearanceManager.CcoIndicator;
        } else if (ad.IsMonthlyBilling) {
            ((UIImageView)cell.ContentView.Subviews [0]).Image = AppearanceManager.MonthlyIndicator;
        } else {
            ((UIImageView)cell.ContentView.Subviews [0]).Image = null;
        }
        return cell;
    }

    public override void Selected(DialogViewController dvc, UITableView tableView, NSIndexPath path)
    {
        if (Tapped != null)
            Tapped ();

        tableView.DeselectRow (path, true);
    }

    public float GetHeight(UITableView tableView, NSIndexPath indexPath)
    {
        return cellHeight;
    }

    private Ad ad;
    public event NSAction Tapped;

    private int cellHeight = 60;
}

我唯一不喜欢的是更新单元格值有点痛苦，因为我必须从 UIView 数组中获取 UILabel 并将它们转换为像这样 ((UILabel)cell.ContentView.Subviews[1])，祝你好运，跟踪哪个 UILabel 是哪个，因为你现在不能使用变量名来引用 UILabel。是的，我确实尝试将标签设为元素的私有成员，并尝试以这种方式更新它们，但没有用。

Xamarin 自定义 UITableViewCell 在重用时重叠文本

Xamarin custom UITableViewCell overlapping text on reuse

c#

xamarin.ios

ios

monotouch.dialog

xamarin