WPF-當itemsource更改時，無法設置組合框selectedIndex

Question

我有一個顯示項目列表的組合框。 顯示的項目列表由一組單選按鈕確定。 我將單擊事件附加到單選按鈕，並嘗試在組合框上設置新的項源。 我希望selectedItem默認為0，而不是-1。

我究竟做錯了什么？

<Grid>
    <ComboBox Name="cb_Test" />
    <RadioButton Content="List 1" Name="radioButton1" Click="radioButton1_Click" />
    <RadioButton Content="List 2" Name="radioButton2" Click="radioButton2_Click" />
</Grid>

public partial class MainWindow : Window
{
    List<string> list1 = new List<string>() { "list 1", "list 1", "list 1" };
    List<string> list2 = new List<string>() { "list 2", "list 2", "list 2" };
    ComboBoxViewModel viewModel = new ComboBoxViewModel();

    public MainWindow()
    {
        InitializeComponent();
        this.DataContext = viewModel;
        cb_Test.ItemsSource = list1;
    }

    private void radioButton1_Click(object sender, RoutedEventArgs e)
    {
        cb_Test.ItemsSource = list1;
        viewModel.SelectedIndex = 0;
    }

    private void radioButton2_Click(object sender, RoutedEventArgs e)
    {
        cb_Test.ItemsSource = list2;
        viewModel.SelectedIndex = 0;
    }
}

public class ComboBoxViewModel : INotifyPropertyChanged
{
    private int selectedIndex;
    public event PropertyChangedEventHandler PropertyChanged;

    public int SelectedIndex
    {
        get { return selectedIndex; }
        set
        {
            if (selectedIndex != value)
            {
                selectedIndex = value;
                NotifyPropertyChanged("SelectedIndex");
            }
        }
    }

    private void NotifyPropertyChanged(string controlName)
    {
        if (PropertyChanged != null)
        {
            PropertyChanged(this, new PropertyChangedEventArgs(controlName));
        }
    }
}

Answer 1

您的XAML中沒有對ComboBoxViewModel視圖模型的任何數據綁定，至少提供了一個。 我認為這就是問題所在。

Answer 2

您需要將組合框綁定到VM。

public partial class MainWindow : Window
{
    List<string> list1 = new List<string>() { "list 1", "list 1", "list 1" };
    List<string> list2 = new List<string>() { "list 2", "list 2", "list 2" };
    ComboBoxViewModel viewModel = new ComboBoxViewModel();

    public MainWindow()
    {
        InitializeComponent();
        cb_Test.DataContext = viewModel;
    }

    private void radioButton1_Click(object sender, RoutedEventArgs e)
    {
        viewModel.ItemsSource = list1;
        viewModel.SelectedIndex = 0;
    }

    private void radioButton2_Click(object sender, RoutedEventArgs e)
    {
        viewModel.ItemsSource = list2;
        viewModel.SelectedIndex = 0;
    }
}

在XAML中

<Grid>
    <ComboBox Name="cb_Test"
              ItemsSource="{Binding ItemsSourse}"
              SelectedIndex="{Binding SelectedIndex}"/>
    <RadioButton Content="List 1" Name="radioButton1" Click="radioButton1_Click" />
    <RadioButton Content="List 2" Name="radioButton2" Click="radioButton2_Click" />
</Grid>

更好的設計是移動代碼viewModel.ItemsSource = list1; viewModel.SelectedIndex = 0; viewModel.ItemsSource = list1; viewModel.SelectedIndex = 0; 虛擬機本身。

Answer 3

同意提格倫。 無論這是什么，都需要將ComboBoxViewModel分配為Window / Page / Control的DataContext，並且需要在xaml的ComboBox的聲明中綁定SelectedIndex。 由於需要綁定，因此還應該將List集合移動到具有SelectedIndex的一個ViewModel，並將ComboBox ItemsSource綁定到ViewModel中的一個屬性，該屬性可以在某些條件下設置。