WPF - System.Windows.Controls.ComboBox

Over View

ComboBox 由一个 TextBox 一个 Button 和一个 Popup 组合而成；

 

Data Binding

当 data binding 到 ComboBox 时，如何显示数据，有如下选择：

<ComboBox Width="90" Margin="0,0,10,0"
          ItemsSource="{Binding MyList}"
          DisplayMemberPath="ID"
          SelectedItem="{Binding MySelected}"
          SelectedValuePath="ID"
          />

<ComboBox Width="90" Margin="0,0,10,0"
          ItemsSource="{Binding MyList}"
          SelectedItem="{Binding MySelected}"
          SelectedValuePath="ID"
          >
    <ComboBox.ItemTemplate>
        <DataTemplate>
            <TextBlock Text="{Binding ID}"/>
        </DataTemplate>
    </ComboBox.ItemTemplate>
</ComboBox>

其中 MyList 是一个 ObservableCollection<MyItem>:

public class MyItem
{
    public int ID { get; set; }
    public string Name { get; set; }
}

 

Command Binding

绑定一个 Command 到 ComboBox 的 SelectionChanged 事件，可以有如下选择：

1，delegate 函数调用

2，从ComboBox 派生新类，实现 ICommandSource

3，使用 Attached Property

 

public static class ItemSelectedBehavior 

public static class ItemSelectedBehavior
{
    public static DependencyProperty ItemSelectedProperty =
        DependencyProperty.RegisterAttached("ItemSelected",
            typeof(ICommand),
            typeof(ItemSelectedBehavior),
            new FrameworkPropertyMetadata(null, new PropertyChangedCallback(ItemSelectedBehavior.ItemSelectedChanged)));

    public static void SetItemSelected(DependencyObject target, ICommand value)
    {
        target.SetValue(ItemSelectedBehavior.ItemSelectedProperty, value);
    }

    private static void ItemSelectedChanged(DependencyObject target, DependencyPropertyChangedEventArgs e)
    {
        Selector element = target as Selector;

        if (element != null)
        {
            // If we're putting in a new command and there wasn't one already hook the event
            if ((e.NewValue != null) && (e.OldValue == null))
            {
                element.SelectionChanged += element_SelectionChanged;
            }
            // If we're clearing the command and it wasn't already null unhook the event
            else if ((e.NewValue == null) && (e.OldValue != null))
            {
                element.SelectionChanged -= element_SelectionChanged;
            }
        }
    }

    private static void element_SelectionChanged(object sender, System.Windows.Controls.SelectionChangedEventArgs e)
    {
        Selector element = sender as Selector;
        if (element != null)
        {
            ICommand command = (ICommand)element.GetValue(ItemSelectedBehavior.ItemSelectedProperty);
            command.Execute(element.SelectedItem);
        }
    }
}

 

<ComboBox ItemsSource="{Binding MyStringList}"
          local:ItemSelectedBehavior.ItemSelected="{Binding CmdSelectionChanged}"
          />

参考：http://johnllao.wordpress.com/2009/07/21/attached-property-sample/

 

属性 Text 和 属性 SelectedItem

 

Editable ComboBox

<ComboBox Grid.Row="1"
          ItemsSource="{Binding MyStringList}"
          SelectedItem="{Binding MySelectedString}"
          IsEditable="True"
          StaysOpenOnEdit="True"
          Text="{Binding EditingString}"
          />

Text 属性 binding 改变之前，会先改变 SelectedItem 的 binding。

 

如何响应 TextChanged 事件

最简单的方法：

<ComboBox TextBoxBase.TextChanged="theTextBox_TextChanged"
          IsEditable="True"                      
          />

另外的一个方法是，在 ComboBox 的 Loaded 事件里找到 TextBox，然后响应其事件。如何获得那个TextBox？