使用 MVVM 处理 SelectedItem 事件的最简单方法是什么? [英] What is the easiest way to handle SelectedItem event with MVVM?

问题描述

在下面的代码中，当用户在组合框中选择客户时，客户名称将显示在文本框中.我在 ViewModel 上使用 ObservableCollection 属性填充 Combox 框，但如何处理 ViewModel 中的 SelectedItem 事件?

In the code below, when user selects Customer in the combobox, the customer's name is displayed in a textbox. I fill the Combox box with an ObservableCollection property on my ViewModel but how do I handle the SelectedItem event in my ViewModel?

使用代码隐藏很容易实现这一点，如下所示，但是我如何使用 MVVM 模式来实现这一点?

It's easy to implement this with code-behind as shown below, but how do I do this with the MVVM pattern?

我目前在我可以使用的基本 MVVM 模板中有 DelegateCommand 和 AttachedBehaviors，但我不知道如何在组合框选择一个新项目".

I currently have DelegateCommand and AttachedBehaviors in my basic MVVM template that I can use, but I can't figure out how to get them to fire when "combobox selects a new item".

查看:

<Window.Resources>
    <DataTemplate x:Key="CustomerTemplate">
        <StackPanel Orientation="Horizontal">
            <TextBlock Text="{Binding LastName}"/>
        </StackPanel>
    </DataTemplate>
</Window.Resources>

<DockPanel LastChildFill="False" Margin="10">
    <ComboBox 
        x:Name="CustomerList"
        ItemTemplate="{StaticResource CustomerTemplate}"
        HorizontalAlignment="Left"
        DockPanel.Dock="Top" 
        Width="200"
        SelectionChanged="CustomerSelected"
        ItemsSource="{Binding Customers}"/>

    <TextBlock x:Name="CurrentlySelectedCustomer"/>
</DockPanel>

背后的代码:

private void CustomerSelected(object sender, System.Windows.Controls.SelectionChangedEventArgs e)
{
    Customer customer = (Customer)CustomerList.SelectedItem;
    CurrentlySelectedCustomer.Text = String.Format("{0} {1}", customer.FirstName, customer.LastName);
}

推荐答案

您应该能够将 ViewModel 中的属性绑定到组合框的 SelectedItem 属性.如果您将其设置为双向绑定，您将在 SelectedItem 更改时收到通知，因为它将触发属性上的 set 方法.

You should be able to bind a property in you ViewModel to the SelectedItem property of the combobox. If you set this up as two way binding you will be notified when the SelectedItem is changed because it will trigger the set method on the property.

视图模型:

public ObservableCollection Customers
{
   get { return _customers; }
   set
   {
       if (_customers != value)
       {
           _customers = value;
           OnPropertyChanged("Customers");
       }
   }
}

public Customer SelectedCustomer
{
   get { return _selectedCustomer; }
   set
   {
       if (_selectedCustomer != value)
       {
           _selectedCustomer= value;
           LastName= value.LastName;
           OnPropertyChanged("SelectedCustomer");
       }
   }
}

public Customer LastName
{
   get { return _lastName; }
   set
   {
       if (_lastName!= value)
       {
           _lastName= value;
           OnPropertyChanged("LastName");
       }
   }
}

XML:

<DockPanel LastChildFill="False" Margin="10">
    <ComboBox 
        x:Name="CustomerList"
        ItemTemplate="{StaticResource CustomerTemplate}"
        HorizontalAlignment="Left"
        DockPanel.Dock="Top" 
        Width="200"
        SelectedItem="{Binding SelectedCustomer, Mode=TwoWay}"
        ItemsSource="{Binding Customers}"/>

    <TextBlock x:Name="CurrentlySelectedCustomer"
               Text="{Binding LastName}"/>
</DockPanel>

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