编辑 1 - 根据问题更新更新答案。即添加对在启用/禁用高亮模式之间切换的支持。
EDIT 2 - 重组答案并添加更多细节。
选项 1：通过IsEnabled 启用/禁用视图单元
最简单的选择是使用IsEnabled 属性，它反过来启用/禁用背景闪光行为。这种方法的唯一缺点是它还会禁用子控件上的点击，即如果父视图单元的IsEnabled 是false，则不会触发点击事件/手势识别器。
例如：
XAML
<!-- Add name attribute to view-cell -->
<ViewCell x:Name="deselectCell" ..>
<Grid>
<Grid x:Name="deselectGridLink" ..
....
</ViewCell>
代码隐藏
private void SetPageDetails()
{
if (App.cardCountForSelectedCategories == 0)
{
deselectCell.IsEnabled = false; //disable background flash
...
}
else
{
deselectCell.IsEnabled = true;
...
}
}
建议 1 - 使用数据绑定和触发器
您可以使用触发器和数据绑定，而不是在代码隐藏中控制每个标签的可见性（视图模型将具有IsDeselectEnabled 属性）：
<ViewCell IsEnabled="{Binding IsDeselectEnabled}" Height="50">
<Label Margin="20,0,20,0" Style="{DynamicResource ListItemTextStyle}" HorizontalOptions="StartAndExpand" VerticalOptions="Center" Text="Deselect All">
<Label.Triggers>
<DataTrigger TargetType="Label" Binding="{Binding IsDeselectEnabled}" Value="true">
<Setter Property="TextColor" Value="Blue" />
</DataTrigger>
<DataTrigger TargetType="Label" Binding="{Binding IsDeselectEnabled}" Value="false">
<Setter Property="TextColor" Value="Silver" />
</DataTrigger>
</Label.Triggers>
</Label>
</ViewCell>
建议 2 - 使用以视图为源的触发器
<ViewCell x:Name="deselectCell" Height="50">
<Label Margin="20,0,20,0" Style="{DynamicResource ListItemTextStyle}" HorizontalOptions="StartAndExpand" VerticalOptions="Center" Text="Deselect All">
<Label.Triggers>
<DataTrigger TargetType="Label" Binding="{Binding IsEnabled, Source={x:Reference deselectCell}}" Value="true">
<Setter Property="TextColor" Value="Blue" />
</DataTrigger>
<DataTrigger TargetType="Label" Binding="{Binding IsEnabled, Source={x:Reference deselectCell}}" Value="false">
<Setter Property="TextColor" Value="Silver" />
</DataTrigger>
</Label.Triggers>
</Label>
</ViewCell>
选项 2：启用/禁用突出显示，但允许点击
要在切换ViewCell 的背景突出显示行为时允许点击，我们需要实现平台渲染器。
对于 iOS，我们可以使用 SelectionStyle 来切换此行为，而对于 android，我们可以使用 Clickable 属性。
共享控制：
public class CustomViewCell : ViewCell
{
public static readonly BindableProperty AllowHighlightProperty =
BindableProperty.Create(
"AllowHighlight", typeof(bool), typeof(CustomViewCell),
defaultValue: true);
public bool AllowHighlight
{
get { return (bool)GetValue(AllowHighlightProperty); }
set { SetValue(AllowHighlightProperty, value); }
}
}
iOS 渲染器：
[assembly: ExportRenderer(typeof(CustomViewCell), typeof(CustomViewCellRenderer))]
namespace SampleApp.iOS
{
public class CustomViewCellRenderer : ViewCellRenderer
{
UITableViewCell _nativeCell;
//get access to the associated forms-element and subscribe to property-changed
public override UITableViewCell GetCell(Cell item, UITableViewCell reusableCell, UITableView tv)
{
_nativeCell = base.GetCell(item, reusableCell, tv);
var formsCell = item as CustomViewCell;
if (formsCell != null)
{
formsCell.PropertyChanged -= OnPropertyChanged;
formsCell.PropertyChanged += OnPropertyChanged;
}
//and, update the style
SetStyle(formsCell);
return _nativeCell;
}
void OnPropertyChanged(object sender, PropertyChangedEventArgs e)
{
var formsCell = sender as CustomViewCell;
if (formsCell == null)
return;
//TODO: Trying to find a nicer and more robust way to dispose and unsubscribe :(
if (_nativeCell == null)
formsCell.PropertyChanged -= OnPropertyChanged;
if (e.PropertyName == CustomViewCell.AllowHighlightProperty.PropertyName)
{
SetStyle(formsCell);
}
}
private void SetStyle(CustomViewCell formsCell)
{
//added this code as sometimes on tap, the separator disappears, if style is updated before tap animation finishes
//https://stackoverflow.com/questions/25613117/how-do-you-prevent-uitableviewcellselectionstylenone-from-removing-cell-separato
Device.StartTimer(TimeSpan.FromMilliseconds(50), () => {
Device.BeginInvokeOnMainThread(() =>
{
if (formsCell.AllowHighlight)
_nativeCell.SelectionStyle = UITableViewCellSelectionStyle.Default;
else
_nativeCell.SelectionStyle = UITableViewCellSelectionStyle.None;
});
return false;
});
}
}
}
Android 渲染器：
[assembly: ExportRenderer(typeof(CustomViewCell), typeof(CustomViewCellRenderer))]
namespace SampleApp.Droid
{
public class CustomViewCellRenderer : ViewCellRenderer
{
Android.Views.View _nativeCell;
protected override Android.Views.View GetCellCore(Cell item, Android.Views.View convertView, Android.Views.ViewGroup parent, Android.Content.Context context)
{
_nativeCell = base.GetCellCore(item, convertView, parent, context);
SetStyle();
return _nativeCell;
}
// this one is simpler as the base class has a nice override-able method for our purpose - so we don't need to subscribe
protected override void OnCellPropertyChanged(object sender, System.ComponentModel.PropertyChangedEventArgs e)
{
base.OnCellPropertyChanged(sender, e);
if(e.PropertyName == CustomViewCell.AllowHighlightProperty.PropertyName)
{
SetStyle();
}
}
private void SetStyle()
{
var formsCell = Cell as CustomViewCell;
if (formsCell == null)
return;
_nativeCell.Clickable = !formsCell.AllowHighlight;
}
}
}
示例用法 1 - 通过数据绑定
<local:CustomViewCell AllowHighlight="{Binding IsHighlightEnabled}" ..>
<Grid>
<Grid x:Name="deselectGridLink" ..
...
</local:CustomViewCell>
示例用法 2 - 通过代码隐藏
XAML
<!-- Add name attribute to view-cell -->
<local:CustomViewCell x:Name="deselectCell" ..>
<Grid>
<Grid x:Name="deselectGridLink" ..
...
</local:CustomViewCell>
代码隐藏
private void SetPageDetails()
{
if (App.cardCountForSelectedCategories == 0)
{
deselectCell.AllowHighlight= false; //disable background flash
...
}
else
{
deselectCell.AllowHighlight= true;
...
}
}
Option-3：禁用突出显示，选择所有项目
这尤其适用于ListView。 更新后的问题现在指定单元格是TableView 的一部分，因此该选项在当前问题上下文中不再有效。
您将需要实现平台渲染器以禁用突出显示颜色，并将ItemTapped 处理程序添加到ListView 以通过将SelectedItem 始终设置为空来禁用选择。参考文献：
- Disable highlight item
- Disable selection
代码
首先，创建一个自定义视图单元：
public class NoSelectViewCell : ViewCell { }
实现iOS渲染器为：
[assembly: ExportRenderer(typeof(NoSelectViewCell), typeof(NoSelectViewCellRenderer))]
namespace SampleApp.iOS
{
public class NoSelectViewCellRenderer : ViewCellRenderer
{
public override UITableViewCell GetCell(Cell item, UITableViewCell reusableCell, UITableView tv)
{
var nativeCell = base.GetCell(item, reusableCell, tv);
nativeCell.SelectionStyle = UITableViewCellSelectionStyle.None;
return nativeCell;
}
}
}
实现android渲染器为：
[assembly: ExportRenderer(typeof(NoSelectViewCell), typeof(NoSelectViewCellRenderer))]
namespace SampleApp.Droid
{
public class NoSelectViewCellRenderer : ViewCellRenderer
{
protected override Android.Views.View GetCellCore(Cell item, Android.Views.View convertView, Android.Views.ViewGroup parent, Android.Content.Context context)
{
var cell = base.GetCellCore(item, convertView, parent, context);
cell.Focusable = false;
cell.FocusableInTouchMode = false;
var listView = parent as Android.Widget.ListView;
if (listView != null)
{
listView.SetSelector(Android.Resource.Color.Transparent);
listView.CacheColorHint = Xamarin.Forms.Color.Transparent.ToAndroid();
}
return cell;
}
}
}
示例用法：
XAML
<ListView ItemTapped="Handle_ItemTapped">
<ListView.ItemTemplate>
<DataTemplate>
<local:NoSelectViewCell Height="50">
<Grid>
<Grid x:Name="deselectGridLink" VerticalOptions="CenterAndExpand" Padding="20, 0">
<Label TextColor="Blue" Style="{DynamicResource ListItemTextStyle}" x:Name="deselectLink" HorizontalOptions="StartAndExpand" VerticalOptions="Center" Text="Deselect All" />
</Grid>
<Grid x:Name="deselectGridLabel" VerticalOptions="CenterAndExpand" Padding="20, 0">
<Label TextColor="Silver" Style="{DynamicResource ListItemTextStyle}" x:Name="deselectLabel" HorizontalOptions="StartAndExpand" VerticalOptions="Center" Text="Deselect All" />
</Grid>
</Grid>
</local:NoSelectViewCell>
</DataTemplate>
</ListView.ItemTemplate>
</ListView>
代码隐藏
void Handle_ItemTapped(object sender, Xamarin.Forms.ItemTappedEventArgs e)
{
// don't do anything if we just de-selected the row
if (e.Item == null) return;
// do something with e.SelectedItem
((ListView)sender).SelectedItem = null; // de-select the row
}