如何为基于 ItemsControl 的控件（如 ListView 或 DataGrid）定义空 DataTemplate

Question

ListView 等 ASP.NET 控件允许通过设置 ListView.EmptyDataTemplate 属性，当数据源为空时将渲染此模板。

如何在 WPF 中（最好仅使用 XAML）对 执行相同操作基于 ItemsControl 的控件，例如 ListView 和 DataGrid ？因此，我想显示我的自定义 DataTemplate，以防 ItemsSource 为空。

Answer 1

有一个 100% xaml 解决方案利用“HasItems”依赖属性。

<ItemsControl>
    <ItemsControl.ItemTemplate>
        <DataTemplate>
            <TextBlock Text="{Binding Description}"/>
        </DataTemplate>
    </ItemsControl.ItemTemplate>
    <ItemsControl.Style>
        <Style TargetType="ItemsControl">
            <Style.Triggers>
                <Trigger Property="HasItems" Value="false">
                        <Setter Property="Template">
                            <Setter.Value>
                                <ControlTemplate>
                                    <TextBlock Text="This Control is empty"/>
                                </ControlTemplate>
                            </Setter.Value>
                        </Setter>
                </Trigger>
            </Style.Triggers>
        </Style>
    </ItemsControl.Style>
</ItemsControl>

Answer 2

您可以使用基于 DataTrigger 设置 Template 属性

，例如，

在资源中：

<ControlTemplate x:Key="EmptyListBoxTemplate">
     <TextBlock Text="Items count == 0" />
</ControlTemplate>

控制本身：

<ListBox ItemsSource="{Binding SomeCollection}">
    <ListBox.Style>
        <Style TargetType="{x:Type ListBox}">
            <Style.Triggers>
                <DataTrigger Value="{x:Null}" Binding="{Binding DataContext.SomeCollection, RelativeSource={RelativeSource Self}}">
                    <Setter Property="Template" Value="{StaticResource EmptyListBoxTemplate}" />
                </DataTrigger>
                <DataTrigger Value="0" Binding="{Binding DataContext.SomeCollection.Count, RelativeSource={RelativeSource Self}}">
                    <Setter Property="Template" Value="{StaticResource EmptyListBoxTemplate}" />
                </DataTrigger>
            </Style.Triggers>
        </Style>
    </ListBox.Style>
</ListBox>

可能有一种更简单的方法来进行绑定，但我现在没有编译器来弄清楚它会是什么:)

Answer 3

您可以使用 DataTemplate 选择器来执行此操作。

http://msdn.microsoft.com/en-us /library/system.windows.controls.datatemplateselector.aspx

更新1

代码：

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Data;
using System.Windows.Documents;
using System.Windows.Input;
using System.Windows.Media;
using System.Windows.Media.Imaging;
using System.Windows.Navigation;
using System.Windows.Shapes;

namespace EmptyRowsTemplate
{
    /// <summary>
    /// Interaction logic for MainWindow.xaml
    /// </summary>
    public partial class MainWindow : Window
    {
        public MainWindow()
        {
            InitializeComponent();

            this.Loaded += (o, e) => 
            {
                this.l.ItemsSource = new List<string>(3)
                {
                    "A",
                    null,
                    "B"
                };
            };
        }
    }

    public class TemplateManager : DependencyObject
    {
        public static readonly DependencyProperty BlankDataTemplateProperty =
            DependencyProperty.RegisterAttached("BlankDataTemplate",
            typeof(DataTemplate),
            typeof(TemplateManager),
            new PropertyMetadata(new PropertyChangedCallback((o, e) => 
            {
                ((ItemsControl)o).ItemTemplateSelector = new BlankDataTemplateSelector();
            })));

        public static void SetBlankDataTemplate(DependencyObject o, DataTemplate e)
        {
            o.SetValue(TemplateManager.BlankDataTemplateProperty, e);
        }

        public static DataTemplate GetBlankDataTemplate(DependencyObject o)
        {
            return (DataTemplate)o.GetValue(TemplateManager.BlankDataTemplateProperty);
        }

        private class BlankDataTemplateSelector : DataTemplateSelector
        {
            public BlankDataTemplateSelector()
                : base()
            {
            }

            public override DataTemplate SelectTemplate(object item, DependencyObject container)
            {
                ItemsControl itemControl =
                    (ItemsControl)ItemsControl.ItemsControlFromItemContainer(ItemsControl.ContainerFromElement(null, container));

                if (item == null)
                {
                    return TemplateManager.GetBlankDataTemplate(itemControl);
                }
                else
                {
                    return base.SelectTemplate(item, container);
                }

            }
        }
    }
}

---

Markup

---

<Window x:Class="EmptyRowsTemplate.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:local="clr-namespace:EmptyRowsTemplate"
        Title="MainWindow" Height="350" Width="525">
    <Grid>
        <ListBox x:Name="l">
            <local:TemplateManager.BlankDataTemplate>
                <DataTemplate>
                    <Button Background="Red">No Data!</Button>
                </DataTemplate>
            </local:TemplateManager.BlankDataTemplate>
        </ListBox>
    </Grid>
</Window>

---