Xamarin.Forms 中ListView 修改選中效果

在Xamarin.Forms中ListView是非常常用的控件之一，ListView有一個默認的選中效果，顏色和自己的App很不搭，怎么辦呢？

1. 在很多時候，ListView在使用中不需要選中，更多情況下，只是點擊一下而已，那么我們可以將其SelectMode設置為None。

<ListView 
    BackgroundColor="Transparent"
    temsSource="{Binding PasswordList}" 
    RowHeight="96" Margin="12"  SelectionMode="None"
    ItemTapped="ListView_ItemTapped" SeparatorVisibility="None"
    SeparatorColor="Transparent"/>    

2. 如果需要修改選中效果顏色怎么處理呢？

首先，自定義ExtendedViewCell繼承ViewCell；

　　

public class ExtendedViewCell : ViewCell
  {
    public static readonly BindableProperty SelectedBackgroundColorProperty =
        BindableProperty.Create("SelectedBackgroundColor", 
                                typeof(Color), 
                                typeof(ExtendedViewCell), 
                                Color.Default);

    public Color SelectedBackgroundColor
    {
      get { return (Color)GetValue(SelectedBackgroundColorProperty); }
      set { SetValue(SelectedBackgroundColorProperty, value); }
    }
  }

然后，根據各個平台為ExtendedViewCell提供一個Renderer（ExtendedViewCellRenderer）；

Android:

[assembly: ExportRenderer(typeof(ExtendedViewCell), typeof(ExtendedViewCellRenderer))]
namespace Deom.Droid.CustomRenderers
{
  public class ExtendedViewCellRenderer : ViewCellRenderer
  {

    private Android.Views.View _cellCore;
    private Drawable _unselectedBackground;
    private bool _selected;

    protected override Android.Views.View GetCellCore(Cell item, 
                                                      Android.Views.View convertView, 
                                                      ViewGroup parent, 
                                                      Context context)
    {
      _cellCore = base.GetCellCore(item, convertView, parent, context);

      _selected = false;
      _unselectedBackground = _cellCore.Background;

      return _cellCore;
    }

    protected override void OnCellPropertyChanged(object sender, PropertyChangedEventArgs args)
    {
      base.OnCellPropertyChanged(sender, args);

      if (args.PropertyName == "IsSelected")
      {
        _selected = !_selected;

        if (_selected)
        {
          var extendedViewCell = sender as ExtendedViewCell;
          _cellCore.SetBackgroundColor(extendedViewCell.SelectedBackgroundColor.ToAndroid());
        }
        else
        {
          _cellCore.SetBackground(_unselectedBackground);
        }
      }
    }
  }

}

iOS:

[assembly: ExportRenderer(typeof(ExtendedViewCell), typeof(ExtendedViewCellRenderer))]
namespace Demo.iOS.CustomRenderers
{
  public class ExtendedViewCellRenderer : ViewCellRenderer
  {
    public override UITableViewCell GetCell(Cell item, UITableViewCell reusableCell, UITableView tv)
    {
      var cell = base.GetCell(item, reusableCell, tv);
      var view = item as ExtendedViewCell;
      cell.SelectedBackgroundView = new UIView
      {
        BackgroundColor = view.SelectedBackgroundColor.ToUIColor(),
      };

      return cell;
    }

  }
}

這樣就能修改選中效果啦。