iOS（Xamarin Forms）中的高度按钮在文本标签换行时不调整大小（我想要动态大小）

Question

我在 Xamarin.Forms 中有一个这样的 ListView：

        this.listView = new ListView();
        this.listView.HasUnevenRows = true;
        var dataTemplate = new DataTemplate(() =>
        {
            return new ViewCell { View = new CustomButtonTemplate()};
        });
        this.listView.ItemTemplate = dataTemplate;

CustomButtonTemplate.xaml

<local:CustomButton
        Margin="6"
        Padding="0"
        HeightRequest="-1"
        WidthRequest="-1"
        Style="{StaticResource Title_LabelStyle}"
        Text="{Binding DisplayText}" />

---

我也有一个按钮渲染器，但不起作用（没有 HeightRequest、WidthRequest、Padding 也不起作用）：

[assembly: ExportRenderer(typeof(CustomButton), typeof(CustomButtonMultilineRenderer))]

namespace SGUK.ClassAction.IOS.Renderers
{
    public class CustomButtonMultilineRenderer : ButtonRenderer
    {
        public CustomButtonMultilineRenderer()
        {
        }

        protected override void OnElementChanged(ElementChangedEventArgs<Xamarin.Forms.Button> e)
        {
            base.OnElementChanged(e);

            if (this.Control != null)
            {
                this.Control.TitleLabel.LineBreakMode = UILineBreakMode.WordWrap;
                this.Control.TitleEdgeInsets = new UIEdgeInsets(0, 10, 0, 10);
                this.Control.TitleLabel.TextAlignment = UITextAlignment.Center;
                this.Control.HorizontalAlignment = UIControlContentHorizontalAlignment.Center;
            }
        }
    }
}

（使用 MaterialButtonRenderer 也不起作用）

Answer 1

如果不使用自定义渲染器，HasUnevenRows=true 的自动高度在 iOS 上可以正常工作。如果使用自定义渲染器，则由渲染器设置单元格的高度，您必须在自定义渲染器中的GetHeightForRow方法中计算自己的行高。

[assembly: ExportRenderer(typeof(ListView), typeof(MyLVRenderer))]
namespace App79.iOS
{
public class MyLVRenderer : ListViewRenderer
    {
        //UITableViewSource originalSource;

        protected override void OnElementChanged(ElementChangedEventArgs<ListView> e)
        {
            base.OnElementChanged(e);

            UITableViewSource originalSource = (UIKit.UITableViewSource)Control.Source;
            Control.Source = new MyLVSource(originalSource, e.NewElement);

        }
    }

    public class MyLVSource : UITableViewSource
    {
        UITableViewSource originalSource;

        ListView myListView;


        public MyLVSource(UITableViewSource origSource, ListView myListV)
        {
            originalSource = origSource;
            myListView = myListV;
        }

        public override nint RowsInSection(UITableView tableview, nint section)
        {
            return originalSource.RowsInSection(tableview, section);
        }

        public override UITableViewCell GetCell(UITableView tableView, NSIndexPath indexPath)
        {
            return originalSource.GetCell(tableView, indexPath);
        }

        public override nfloat GetHeightForFooter(UITableView tableView, nint section)
        {
            return originalSource.GetHeightForFooter(tableView, section);
        }

        public override nfloat GetHeightForRow(UITableView tableView, NSIndexPath indexPath)
        {
            nfloat origHeight = originalSource.GetHeightForRow(tableView, indexPath);

            // calculate your own row height here

            ObservableCollection<Employee> employees = myListView.ItemsSource as ObservableCollection<Employee>;

            string displayName = employees[indexPath.Row].DisplayName;

            nfloat height = MeasureTextSize(displayName,UIScreen.MainScreen.Bounds.Size.Width-50,UIFont.SystemFontSize,null);

            return height;
        }

        public nfloat MeasureTextSize(string text, double width, double fontSize, string fontName = null)
        {
            var nsText = new NSString(text);
            var boundSize = new SizeF((float)width, float.MaxValue);
            var options = NSStringDrawingOptions.UsesFontLeading | NSStringDrawingOptions.UsesLineFragmentOrigin;

            if (fontName == null)
            {
                fontName = "HelveticaNeue";
            }

            var attributes = new UIStringAttributes
            {
                Font = UIFont.FromName(fontName, (float)fontSize)
            };

            var sizeF = nsText.GetBoundingRect(boundSize, options, attributes, null).Size;

            //return new Xamarin.Forms.Size((double)sizeF.Width, (double)sizeF.Height);
            return sizeF.Height + 5;
        }
    }
}

结果如下：

我上传了一个示例here，您可以查看。