ObservableCollection中的SelectedItem

Question

我有:

<DataTemplate x:Name="_ComboBoxTemplate" x:Key="_ComboBoxTemplate">
    <StackPanel Orientation="Horizontal">
        <StackPanel>
            <StackPanel Orientation="Horizontal" HorizontalAlignment="Center">
                <TextBlock VerticalAlignment="Center" Text="{Binding}" FontSize="24"/>
            </StackPanel>
        </StackPanel>
    </StackPanel>
</DataTemplate>

<ComboBox x:Name="_criteria" ItemTemplate="{StaticResource _ComboBoxTemplate}" ItemsSource="{Binding}"/>

在后面的代码中:

this.DataContext = new string[] { "0", "1", "2", "3", "4", "5" };

我如何得到它使默认SelectedItem的ComboBox是5？

Answer 1

创建一个包含项目列表和所选项目的类:

public class ViewModel
{
    public string[] Items { get; set; }
    public string SelectedItem { get; set; }
}

在后面的代码中初始化它并将其设置为DataContext:

DataContext = new ViewModel
{
    Items = new string[] { "0", "1", "2", "3", "4", "5" },
    SelectedItem = "5"
}

现在将两个属性绑定到ComboBox:

<ComboBox x:Name="_criteria" 
          ItemTemplate="{StaticResource _ComboBoxTemplate}"
          ItemsSource="{Binding Items}"
          SelectedItem="{Binding SelectedItem}"/>

如果SelectedItem为该值设置双向绑定,DataContext则甚至会在用户更改时自动更新.

你为什么ObservableCollection在标题中提到？