使用自定义ItemTemplate时未设置组合框SelectedItem

Question

我有一个带有自定义ItemTemplate的组合框，它有一个绑定到该页面的ViewModel的CheckBox。

我试图做的是，每当ComboBox关闭时，将所选的ComboBox项设置为第一个选中的值，但该值不会相应地设置。

我缺了什么吗？

Xaml:

<ComboBox x:Name="myComboBox" ItemsSource="{Binding ComboBoxList}" SelectedItem="{Binding SelectedPerson, Mode=TwoWay}" HorizontalAlignment="Center" VerticalAlignment="Center" Height="50" Width="150">
<ComboBox.ItemTemplate>
<DataTemplate>
<CheckBox IsChecked="{Binding Path=IsChecked, Mode=TwoWay}" Content="{Binding}" Margin="0" />
</DataTemplate>
</ComboBox.ItemTemplate>
<interactivity:Interaction.Behaviors>
<core:DataTriggerBehavior Binding="{Binding IsDropDownOpen, ElementName=myComboBox}" ComparisonCondition="NotEqual" Value="True">
<core:InvokeCommandAction Command="{Binding DropDownClosedCommand}"/>
</core:DataTriggerBehavior>
</interactivity:Interaction.Behaviors>
</ComboBox>

视图模型：

public class MainViewModel : INotifyPropertyChanged
{
private string header;
public string Header
{
get { return header; }
set
{
header = value;
RaisePropertyChange(nameof(Header));
}
}
private Person selectedPerson;
public Person SelectedPerson
{
get { return selectedPerson; }
set { selectedPerson = value; RaisePropertyChange(nameof(SelectedPerson)); }
}

private ObservableCollection<Person> comboBoxList;
public ObservableCollection<Person> ComboBoxList
{
get { return comboBoxList; }
set { comboBoxList = value; }
}

public DelegateCommand DropDownClosedCommand { get; set; }
public MainViewModel()
{
Header = "My Header";
ComboBoxList = new ObservableCollection<Person> {
new Person() { Name = "Person 1", IsChecked = false },
new Person() { Name = "Person 2", IsChecked = false },
new Person() { Name = "Person 3", IsChecked = false },
new Person() { Name = "Person 4", IsChecked = false }
};
DropDownClosedCommand = new DelegateCommand(OnDropDownClosed);
}
public event PropertyChangedEventHandler PropertyChanged;
private void RaisePropertyChange(string propertyName)
{
PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
}
private void OnDropDownClosed(object e)
{
SelectedPerson = ComboBoxList.FirstOrDefault(x => x.IsChecked);
}
}
public class Person
{
public string Name { get; set; }
public bool IsChecked { get; set; }
public override string ToString()
{
return Name;
}
}

Answer 1

最后，我发现了阻止ComboBox设置SelectedItem的问题。这是因为SelectedPerson没有在UI线程上设置，所以我将代码封装在调度器中，它可以按预期工作。

代码：

CoreApplication.MainView.CoreWindow.Dispatcher.RunAsync(CoreDispatcherPriority.Normal,
() =>
{
SelectedPerson = ComboBoxList.FirstOrDefault(x => x.IsChecked);
});