在WPF（Windows Presentation Foundation）中，实现一个筛选下拉多选控件可以极大地提升用户体验，尤其是在需要用户从大量选项中进行多选的场景中。本文将详细介绍如何基于WPF实现一个具备筛选功能的下拉多选控件。
首先，我们需要明确控件的功能需求：
为了实现上述功能，我们可以将控件分为以下几个部分：
首先，我们需要创建一个自定义控件，继承自UserControl。
<UserControl x:Class="MultiSelectComboBox.MultiSelectComboBox"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
mc:Ignorable="d"
d:DesignHeight="300" d:DesignWidth="400">
<Grid>
<ComboBox x:Name="comboBox" IsEditable="True" IsReadOnly="True" StaysOpenOnEdit="True">
<ComboBox.Template>
<ControlTemplate TargetType="ComboBox">
<Grid>
<ToggleButton x:Name="ToggleButton"
Template="{StaticResource ComboBoxToggleButton}"
Grid.Column="2"
Focusable="false"
IsChecked="{Binding Path=IsDropDownOpen, Mode=TwoWay, RelativeSource={RelativeSource TemplatedParent}}"
ClickMode="Press">
</ToggleButton>
<ContentPresenter x:Name="ContentSite"
IsHitTestVisible="False"
Content="{TemplateBinding SelectionBoxItem}"
ContentTemplate="{TemplateBinding SelectionBoxItemTemplate}"
ContentTemplateSelector="{TemplateBinding ItemTemplateSelector}"
Margin="3,3,23,3"
VerticalAlignment="Center"
HorizontalAlignment="Left" />
<TextBox x:Name="PART_EditableTextBox"
Style="{x:Null}"
Template="{StaticResource ComboBoxTextBox}"
HorizontalAlignment="Left"
VerticalAlignment="Center"
Margin="3,3,23,3"
Focusable="True"
Background="Transparent"
Visibility="Hidden"
IsReadOnly="{TemplateBinding IsReadOnly}" />
<Popup x:Name="Popup"
Placement="Bottom"
IsOpen="{TemplateBinding IsDropDownOpen}"
AllowsTransparency="True"
Focusable="False"
PopupAnimation="Slide">
<Grid x:Name="DropDown"
SnapsToDevicePixels="True"
MinWidth="{TemplateBinding ActualWidth}"
MaxHeight="{TemplateBinding MaxDropDownHeight}">
<Border x:Name="DropDownBorder"
Background="{StaticResource WindowBackgroundBrush}"
BorderBrush="{StaticResource SolidBorderBrush}"
BorderThickness="1" />
<ScrollViewer Margin="4,6,4,6" SnapsToDevicePixels="True">
<StackPanel IsItemsHost="True" KeyboardNavigation.DirectionalNavigation="Contained" />
</ScrollViewer>
</Grid>
</Popup>
</Grid>
</ControlTemplate>
</ComboBox.Template>
<ComboBox.ItemTemplate>
<DataTemplate>
<CheckBox Content="{Binding}" IsChecked="{Binding IsSelected, Mode=TwoWay}" />
</DataTemplate>
</ComboBox.ItemTemplate>
</ComboBox>
</Grid>
</UserControl>
在代码后台，我们需要实现筛选功能。我们可以通过监听TextBox的TextChanged事件来实现。
public partial class MultiSelectComboBox : UserControl
{
public MultiSelectComboBox()
{
InitializeComponent();
comboBox.ItemsSource = GetItems();
comboBox.AddHandler(TextBox.TextChangedEvent, new TextChangedEventHandler(OnTextChanged));
}
private void OnTextChanged(object sender, TextChangedEventArgs e)
{
var textBox = e.OriginalSource as TextBox;
if (textBox != null)
{
var filterText = textBox.Text;
comboBox.ItemsSource = GetItems().Where(item => item.Contains(filterText)).ToList();
}
}
private List<string> GetItems()
{
// 返回所有选项
return new List<string> { "选项1", "选项2", "选项3", "选项4", "选项5" };
}
}
为了实现多选功能，我们需要在CheckBox的IsChecked属性与数据源之间建立绑定。我们可以使用ObservableCollection来存储选项，并为每个选项添加一个IsSelected属性。
public class SelectableItem
{
public string Name { get; set; }
public bool IsSelected { get; set; }
}
public partial class MultiSelectComboBox : UserControl
{
public ObservableCollection<SelectableItem> Items { get; set; }
public MultiSelectComboBox()
{
InitializeComponent();
Items = new ObservableCollection<SelectableItem>
{
new SelectableItem { Name = "选项1", IsSelected = false },
new SelectableItem { Name = "选项2", IsSelected = false },
new SelectableItem { Name = "选项3", IsSelected = false },
new SelectableItem { Name = "选项4", IsSelected = false },
new SelectableItem { Name = "选项5", IsSelected = false }
};
comboBox.ItemsSource = Items;
comboBox.AddHandler(TextBox.TextChangedEvent, new TextChangedEventHandler(OnTextChanged));
}
private void OnTextChanged(object sender, TextChangedEventArgs e)
{
var textBox = e.OriginalSource as TextBox;
if (textBox != null)
{
var filterText = textBox.Text;
comboBox.ItemsSource = Items.Where(item => item.Name.Contains(filterText)).ToList();
}
}
}
最后，我们需要在TextBox中显示已选项。我们可以通过绑定TextBox的Text属性来实现。
public partial class MultiSelectComboBox : UserControl
{
public ObservableCollection<SelectableItem> Items { get; set; }
public MultiSelectComboBox()
{
InitializeComponent();
Items = new ObservableCollection<SelectableItem>
{
new SelectableItem { Name = "选项1", IsSelected = false },
new SelectableItem { Name = "选项2", IsSelected = false },
new SelectableItem { Name = "选项3", IsSelected = false },
new SelectableItem { Name = "选项4", IsSelected = false },
new SelectableItem { Name = "选项5", IsSelected = false }
};
comboBox.ItemsSource = Items;
comboBox.AddHandler(TextBox.TextChangedEvent, new TextChangedEventHandler(OnTextChanged));
comboBox.SelectionChanged += ComboBox_SelectionChanged;
}
private void ComboBox_SelectionChanged(object sender, SelectionChangedEventArgs e)
{
var selectedItems = Items.Where(item => item.IsSelected).Select(item => item.Name);
comboBox.Text = string.Join(", ", selectedItems);
}
private void OnTextChanged(object sender, TextChangedEventArgs e)
{
var textBox = e.OriginalSource as TextBox;
if (textBox != null)
{
var filterText = textBox.Text;
comboBox.ItemsSource = Items.Where(item => item.Name.Contains(filterText)).ToList();
}
}
}
通过以上步骤，我们实现了一个基于WPF的筛选下拉多选控件。该控件具备筛选、多选和显示已选项的功能，能够有效提升用户体验。在实际开发中，可以根据具体需求进一步优化和扩展该控件的功能。
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