将ComboBox SelectedItem设置为不存在于ItemSource中的数据对象

Question

我有一个组合框，其SelectedItem和ItemSource属性绑定到viewmodel。 ItemSource中的对象对时间敏感，因为对象到期，我只能将集合中的活动项目设置为ItemSource。现在在某个点上，selectedItem对象可能不在ItemSource中。 我认为ItemSource的正常行为是只允许从ItemSource集合中选择对象，但在这种情况下，我确实想选择一个不再位于ItemSource中的对象。 我该如何实现这种行为？我会在这里发布一些代码来支持我的问题。

Window.xaml

<Window x:Class="ExpiredSelectedItem.MainWindow" 
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" 
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" 
    Title="MainWindow" Height="350" Width="525"> 
<Grid> 
    <ComboBox Height="23" 
       HorizontalAlignment="Left" 
       Margin="184,68,0,0" 
       Name="comboBox1" 
       VerticalAlignment="Top" 
       Width="120" 
       ItemsSource="{Binding CustomList}" 
       SelectedItem="{Binding ActiveItem}" 
       SelectedValue="Code" 
       SelectedValuePath="{Binding ActiveItem.Code}" 
       DisplayMemberPath="Code" 
       /> 
</Grid> 

Window.xaml.cs

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 ExpiredSelectedItem 
{ 
    /// <summary> 
    /// Interaction logic for MainWindow.xaml 
    /// </summary> 

public partial class MainWindow : Window 
{ 
    public MainWindow() 
    { 
     InitializeComponent(); 

     CustomList = new List<DomainObject>(); 

     CustomList.AddRange(new DomainObject[] { 
      new DomainObject() { Code = "A", IsActive =true}, 
      new DomainObject() { Code ="B", IsActive = true}, 
      new DomainObject() { Code = "C", IsActive =true}, 
     }); 

     ActiveItem = new DomainObject() { Code = "D", IsActive = false }; 

     this.DataContext = this; 
    } 


    public List<DomainObject> CustomList { get; set; } 

    public DomainObject ActiveItem { get; set; } 
} 

public class DomainObject 
{ 
    public string Code { get; set; } 
    public bool IsActive { get; set; } 

} 

}

即使我在选择代码隐藏，当代码d组合框加载第一个项目（A）被选中。预期的行为是应该在文本框中选择“D”，但打开下拉菜单时不应该有任何项目。

Answer 1

我不知道这是否会起到任何作用，但它确实看起来很可疑。尝试将其取出：

<ComboBox ... SelectedValue="Code" ... 

Answer 2

为了保持选择的项目时，它不是在列表中，你可以做到以下几点：

• 防止了ActiveItem从越来越设置为NULL;请参阅：if（value！= null）
• 清除组合框;请参阅：comboBox1.SelectedIndex = -1;
• 执行INotifyPropertyChanged（您可能已经这样做）

这些变化可能会导致您的代码弊大于利，但希望这可以让你开始。

这里是后台代码：

using System.Collections.Generic; 
using System.ComponentModel; 
using System.Windows; 

namespace ComboBoxSelectedItem 
{ 
    public partial class MainWindow : Window, INotifyPropertyChanged 
    { 
    public event PropertyChangedEventHandler PropertyChanged; 
    void Notify(string propName) 
    { 
     if (PropertyChanged != null) 
     { 
     PropertyChanged(this, new PropertyChangedEventArgs(propName)); 
     } 
    } 

    public MainWindow() 
    { 
     InitializeComponent(); 

     CustomList = new List<DomainObject>(); 

     CustomList.AddRange(new DomainObject[] { 
     new DomainObject() { Code = "A", IsActive =true}, 
     new DomainObject() { Code ="B", IsActive = true}, 
     new DomainObject() { Code = "C", IsActive =true}, 
     }); 

     this.DataContext = this; 
    } 

    public List<DomainObject> CustomList { get; set; } 

    private DomainObject _activeItem = new DomainObject() { Code = "D", IsActive = false }; 
    public DomainObject ActiveItem 
    { 
     get { return _activeItem; } 
     set 
     { 
     if (value != null) 
     { 
      _activeItem = value; 
     } 

     Notify("ActiveItem"); 
     } 
    } 

    private void Button_Click(object sender, RoutedEventArgs e) 
    { 
     ActiveItem = new DomainObject() { Code = "D", IsActive = false }; 
     comboBox1.SelectedIndex = -1; 
    } 
    } 
} 

这里是XAML：

<Window x:Class="ComboBoxSelectedItem.MainWindow" 
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" 
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" 
    Title="MainWindow" Height="350" Width="525"> 
    <Grid> 
    <Grid.RowDefinitions> 
     <RowDefinition/> 
     <RowDefinition/> 
     <RowDefinition/> 
    </Grid.RowDefinitions> 
    <ComboBox 
     Grid.Row="0" 
     Height="23" 
     HorizontalAlignment="Left" 
     Name="comboBox1" 
     VerticalAlignment="Top" 
     Width="120" 
     ItemsSource="{Binding CustomList}" 
     SelectedItem="{Binding ActiveItem}" 
     DisplayMemberPath="Code"/> 
    <TextBox 
     Grid.Row="1" 
     Text="{Binding Path=ActiveItem.Code, Mode=TwoWay}"/> 
    <Button 
     Grid.Row="2" 
     Content="D" 
     Click="Button_Click"/> 
    </Grid> 
</Window>