编辑1 - 根据问题的更新,更新了答案。即添加支持在高亮启用/禁用模式之间切换。
编辑2 - 重新构建答案并添加更多细节。
选项1:通过IsEnabled
启用/禁用视图单元格
最简单的选项是使用IsEnabled属性,从而启用/禁用背景闪烁行为。这种方法的唯一缺点是它也会禁用子控件上的点击,即如果父视图单元格的IsEnabled
为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>
代码后置
private void SetPageDetails()
{
if (App.cardCountForSelectedCategories == 0)
{
deselectCell.IsEnabled = false;
...
}
else
{
deselectCell.IsEnabled = true;
...
}
}
建议1 - 使用数据绑定和触发器
不要在代码后台控制每个标签的可见性,可以使用以下方式进行绑定和触发器(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>
建议二 - 使用触发器作为源与视图配合使用。
<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>
Option-2: 启用/禁用高亮,但允许轻触
为了在切换ViewCell
的背景高亮行为时允许轻触,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,则可以使用Clickable属性。
共享控件:
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;
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;
}
SetStyle(formsCell);
return _nativeCell;
}
void OnPropertyChanged(object sender, PropertyChangedEventArgs e)
{
var formsCell = sender as CustomViewCell;
if (formsCell == null)
return;
if (_nativeCell == null)
formsCell.PropertyChanged -= OnPropertyChanged;
if (e.PropertyName == CustomViewCell.AllowHighlightProperty.PropertyName)
{
SetStyle(formsCell);
}
}
private void SetStyle(CustomViewCell formsCell)
{
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;
}
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 - 通过代码后台
XAML
<!-- Add name attribute to view-cell -->
<local:CustomViewCell x:Name="deselectCell" ..>
<Grid>
<Grid x:Name="deselectGridLink" ..
...
</local:CustomViewCell>
代码后台
private void SetPageDetails()
{
if (App.cardCountForSelectedCategories == 0)
{
deselectCell.AllowHighlight= false;
...
}
else
{
deselectCell.AllowHighlight= true;
...
}
}
选项3:禁用所有项的高亮和选择
这特别适用于ListView
。 更新后的问题现在指定单元格是TableView
的一部分,因此此选项在当前问题上下文中不再有效。
您需要实现平台渲染器以禁用高亮颜色,并将ItemTapped
处理程序添加到ListView
以通过始终将SelectedItem
设置为null来禁用选择。使用的参考资料:
- 禁用高亮项
- 禁用选择
代码
要开始,请创建自定义视图单元格:
public class NoSelectViewCell : ViewCell { }
将iOS渲染器实现为:
[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;
}
}
}
将Android渲染器实现为:
[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="" x:Name="deselectLink" HorizontalOptions="StartAndExpand" VerticalOptions="Center" Text="Deselect All" />
</Grid>
<Grid x:Name="deselectGridLabel" VerticalOptions="CenterAndExpand" Padding="20, 0">
<Label TextColor="Silver" Style="" x:Name="deselectLabel" HorizontalOptions="StartAndExpand" VerticalOptions="Center" Text="Deselect All" />
</Grid>
</Grid>
</local:NoSelectViewCell>
</DataTemplate>
</ListView.ItemTemplate>
</ListView>
代码后台
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
}