Xamarin Forms Listview：通过检查OnTapped事件来取消选择所选项目

Question

当我第二次单击它时，将可以取消选择我的项目。 当我点击一个项目时，背景颜色变为蓝色。 我希望当我第二次点击列表中的同一项目时背景变为默认颜色。 您可以在这里找到我的代码，但是它不起作用。

XAML

<StackLayout Margin="5,0,5,0" HorizontalOptions="FillAndExpand" VerticalOptions="CenterAndExpand">
    <Frame Style="{StaticResource StandardFrameStyle}" HorizontalOptions="FillAndExpand" VerticalOptions="FillAndExpand">
      <ListView x:Name="lst_pickList" ItemSelected="OnItemSelected" ItemTapped="OnItemTapped" ItemsSource="{Binding PickList}" HasUnevenRows="True" Style="{StaticResource StandardListViewStyle}">
        <ListView.ItemTemplate>
          <DataTemplate>
            <ViewCell>
              <ViewCell.View>
                <Grid x:Name="grd_pickList" HorizontalOptions="FillAndExpand" VerticalOptions="FillAndExpand" >
                  <Grid.RowDefinitions>
                    <RowDefinition Height="Auto" />
                    <RowDefinition Height="Auto" />
                  </Grid.RowDefinitions>
                  <Grid.ColumnDefinitions>
                    <ColumnDefinition Width="*" />
                    <ColumnDefinition Width="*" />
                    <ColumnDefinition Width="*" />
                    <ColumnDefinition Width="*" />
                  </Grid.ColumnDefinitions>

                  <Label x:Name="lbl_comment" Text="Comment:" FontAttributes="Bold" Grid.Row="0" Grid.Column="0" VerticalTextAlignment="Center" Style="{StaticResource StandardLabelStyle}" />
                  <Label x:Name="lbl_itemNo" Text="ItemNo:" FontAttributes="Bold" Grid.Row="0" Grid.Column="2" VerticalTextAlignment="Center" Style="{StaticResource StandardLabelStyle}" />
                  <Label x:Name="lbl_description" Text="Description:" FontAttributes="Bold" Grid.Row="1" Grid.Column="0" VerticalTextAlignment="Center" Style="{StaticResource StandardLabelStyle}" />
                  <Label x:Name="lbl_restant" Text="Restant:" FontAttributes="Bold" Grid.Row="1" Grid.Column="2" VerticalTextAlignment="Center" Style="{StaticResource StandardLabelStyle}" />

                  <Label x:Name="lbl_comment_binding" Text="{Binding Comment}" Grid.Row="0" Grid.Column="1" VerticalTextAlignment="Center" Style="{StaticResource StandardLabelStyle}" />
                  <Label x:Name="lbl_itemNo_binding" Text="{Binding ItemNo}" Grid.Row="0" Grid.Column="3" VerticalTextAlignment="Center" Style="{StaticResource StandardLabelStyle}" />
                  <Label x:Name="lbl_description_binding" Text="{Binding Description}" Grid.Row="1" Grid.Column="1" VerticalTextAlignment="Center" Style="{StaticResource StandardLabelStyle}" />
                  <Label x:Name="lbl_restant_binding" Text="{Binding Restant}" Grid.Row="1" Grid.Column="3" VerticalTextAlignment="Center" Style="{StaticResource StandardLabelStyle}" />
                </Grid>
              </ViewCell.View>
            </ViewCell>
          </DataTemplate>
        </ListView.ItemTemplate>
      </ListView>
    </Frame>
  </StackLayout>

代码隐藏

public void OnItemTapped(object sender, ItemTappedEventArgs args)
    {
        var newSelectedPick = args.Item as Pick;

        if(selectedPick != null && selectedPick.Id == newSelectedPick.Id)
        {
            lst_pickList.SelectedItem = null;
        }
        else
        {
            selectedPick = newSelectedPick;
        }
    }

Answer 1

在名为IsSelected的Pick对象上创建一个boolean属性，然后将其grd_pickList的BackgroundColor与转换器Bind 。

即：

// XAML中

<ListView.Resources>
  <ResourceDictionary>
    <local:BgConverter x:Key="BgConverter"/>
  </ResourceDictionary>
</ListView.Resources>

<Grid x:Name="grd_pickList" HorizontalOptions="FillAndExpand" VerticalOptions="FillAndExpand" BackgroundColor="{Binding IsSelected,Converter={StaticResource BgConverter}}" >

//转换器

class BgConverter : IValueConverter
{

    public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
    {
        if (value is bool &&(bool)value)
            return Color.Blue;
         else
            return Color.White;
    }

    public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
    {
        throw new NotSupportedException();
    }
}

//Xaml.cs

public void OnItemTapped(object sender, ItemTappedEventArgs args)
{
    var itm = args.Item as Pick;
    itm.IsSelected = !itm.IsSelected;
}

重要提示 ：请务必IsSelected属性触发OnPropertyChanged事件。