C# WPF 组合框选择第一项

Question

晚安，

我希望我的组合框选择其中的第一项。我正在使用 C# 和 WPF。我从数据集中读取数据。填充组合框：

DataTable sitesTable = clGast.SelectAll().Tables[0];
cbGastid.ItemsSource = sitesTable.DefaultView;

组合框 XAML 代码：

<ComboBox 
   Name="cbGastid" 
   ItemsSource="{Binding}" 
   DisplayMemberPath="Description" 
   SelectedItem="{Binding Path=id}"
   IsSynchronizedWithCurrentItem="True" />

如果我尝试：

cbGastid.SelectedIndex = 0; 

它不起作用。

Answer 1

试试这个，而不是 SelectedIndex

cbGastid.SelectedItem = sitesTable.DefaultView.[0][0]; // Assuming you have items here.

或者在Xaml中设置

<ComboBox 
        Name="cbGastid" 
        ItemsSource="{Binding}" 
        DisplayMemberPath="Description" 
        SelectedItem="{Binding Path=id}"
        IsSynchronizedWithCurrentItem="True"
        SelectedIndex="0" />

Answer 2

用这个更新你的XAML：

<ComboBox 
        Name="cbGastid" 
        ItemsSource="{Binding}" 
        DisplayMemberPath="Description" 
        SelectedItem="{Binding Path=id}"
        IsSynchronizedWithCurrentItem="True"
        SelectedIndex="0" />  // Add me!

Answer 3

试试这个，

从 de C# 代码中删除以下行：

cbGastid.ItemsSource = sitesTable.DefaultView; 

并添加：

cbGastid.DataContext = sitesTable.DefaultView

Answer 4

试试这个..

    int selectedIndex = 0;
    cbGastid.SelectedItem = cbGastid.Items.GetItemAt(selectedIndex);

XAML 代码：

    <ComboBox 
        Name="cbGastid" 
        ItemsSource="{Binding}" 
        DisplayMemberPath="Description" 
        SelectedItem="{Binding Path=id}"
        IsSynchronizedWithCurrentItem="True" />

Answer 5

如果我在我的 VM 中添加一个 SelectedIndex 属性并在 xaml.这是对 ItemSource 和 SelectedItem 的补充。这样 SelectedIndex 默认为 0，我得到了我想要的。

    public List<string> ItemSource { get; } = new List<string> { "Item1", "Item2", "Item3" };
    public int TheSelectedIndex { get; set; }

    string _theSelectedItem = null;
    public string TheSelectedItem
    {
        get { return this._theSelectedItem; }
        set
        {
            this._theSelectedItem = value;
            this.RaisePropertyChangedEvent("TheSelectedItem"); 
        } 
    }

以及在xaml中的正确绑定；

    <ComboBox MaxHeight="25"  Margin="5,5,5,0" 
      ItemsSource="{Binding ItemSource}" 
      SelectedItem="{Binding TheSelectedItem, Mode=TwoWay}"
      SelectedIndex="{Binding TheSelectedIndex}" />

Answer 6

使用此代码更新您的 XAML：

<ComboBox 
   Name="cbGastid" 
   ItemsSource="{Binding}" 
   DisplayMemberPath="Description" 
   SelectedItem="{Binding Path=id, UpdateSourceTrigger=PropertyChanged, Mode=OneWayToSource}"
   IsSynchronizedWithCurrentItem="True" />

希望它有效:)

Answer 7

让我分享我的解决方案，经过多次试验后对我有用。 这是我的组合框：

        <ComboBox   
                Name="fruitComboBox"
                ItemsSource="{Binding Fruits}"
                SelectedIndex="0"
                SelectedValue="{Binding ComboSelectedValue}"
                IsSynchronizedWithCurrentItem="True">

        <i:Interaction.Triggers>
            <i:EventTrigger EventName="SelectionChanged">
                <i:InvokeCommandAction Command="{Binding displayFruitName}"         
                                       CommandParameter="{Binding SelectedValue, ElementName=fruitComboBox}"/>
            </i:EventTrigger>
            <i:EventTrigger EventName="Loaded">
                <i:InvokeCommandAction Command="{Binding displayFruitName}"         
                                       CommandParameter="{Binding SelectedValue, ElementName=fruitComboBox}"/>
            </i:EventTrigger>
        </i:Interaction.Triggers> 
       
        </ComboBox>

就我而言，每次在组合框中选择新项目或更新项目源时，我都必须调用一个命令。但是，在更新项目源时，未选择零索引处的元素。那么，我做了什么？我补充说：

IsSynchronizedWithCurrentItem="True"

在组合框属性中。它对我有用。

我的 ViewModel 中的一些代码如下：

    /// item source for comboBox
    private List<string> fruits = new List<string>();
    public List<string> Fruits
    {
        get { return fruits; }
        set 
        {
            fruits = value;
            OnPropertyChanged();
            ComboSelectedValue = value[0];
        }
    }

    // property to which SelectedValue property of comboxBox is bound.
    private string comboselectedValue;
    public string ComboSelectedValue
    {
        get { return comboselectedValue; }
        set 
        { 
            comboselectedValue = value;
            OnPropertyChanged();
        }
    }

您可以参考此 stackoverflow link 和 msdn link 以进一步了解 IsSynchronizedWithCurrentItem="True"

希望对您有所帮助！ :)

Answer 8

这对我有用...给定一个具有一对多关系的 Authors 和 Books 表。 XAML 如下所示：

<ComboBox DisplayMemberPath="AuthorName" ItemsSource="{Binding Authors}" Name="ComboBoxAuthors"
              SelectedItem="{Binding SelectedAuthor}"
              IsSynchronizedWithCurrentItem="True" Grid.Row="0" Grid.Column="0"/>
<ComboBox DisplayMemberPath="BookTitle" ItemsSource="{Binding Books}" Name="ComboBoxBooks"
              SelectedItem="{Binding SelectedBook}"
              IsSynchronizedWithCurrentItem="True" Grid.Row="0" Grid.Column="1" />

然后我的 ViewModel 看起来像这样：

enter public class MainViewModel : INotifyPropertyChanged
{
    public event PropertyChangedEventHandler PropertyChanged;
    private void NotifyPropertyChanged(String propertyName = "")
    {
        PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
    }

    BooksEntities ctx = new BooksEntities();
    List<Author> _authors;
    List<Book> _books;
    Author _selectedAuthor;
    Book _selectedBook;


    public MainViewModel()
    {
        FillAuthors();
    }

    public List<Author> Authors
    {
        get { return _authors; }
        set
        {
            _authors = value;
            NotifyPropertyChanged();
            if (_authors.Count > 0) SelectedAuthor = _authors[0]; // <--- DO THIS
        }
    }

    public Author SelectedAuthor
    {
        get { return _selectedAuthor; }
        set
        {
            _selectedAuthor = value;
            FillBooks();
            NotifyPropertyChanged();
        }
    }

    public List<Book> Books
    {
        get { return _books; }
        set
        {
            _books = value;
            NotifyPropertyChanged();
            if (_books.Count > 0) SelectedBook = _books[0]; // <--- DO THIS
        }
    }

    public Book SelectedBook
    {
        get { return _selectedBook; }
        set
        {
            _selectedBook = value;
            NotifyPropertyChanged();
        }
    }

    #region Private Functions

    private void FillAuthors()
    {
        var q = (from a in ctx.Authors select a).ToList();
        this.Authors = q;
    }

    private void FillBooks()
    {
        Author author = this.SelectedAuthor;

        var q = (from b in ctx.Books
                 orderby b.BookTitle
                 where b.AuthorId == author.Id
                 select b).ToList();
        this.Books = q;
    }

    #endregion
}

查看 ViewModel 类的 Authors 和 Books 属性。一旦它们被设置，通常的 PropertyChanged 事件就会被引发并且 SelectedAuthor / SelectedBook 被设置为第一项。

希望这会有所帮助。