WPF - MVVM - ComboBox SelectedItem

本文关键字：SelectedItem ComboBox MVVM WPF | 更新日期: 2023-09-27 18:37:28

我在后台ViewModel（INotifyPropertyChanged实现）和类Category，它只有一个类型string的属性。我的组合框选定项绑定到类别的实例。当我更改实例的值时，所选项未更新，组合框未更改。

编辑：代码

组合框：

<ComboBox x:Name="categoryComboBox" Grid.Column="1"  Grid.Row="3" Grid.ColumnSpan="2" 
          Margin="10" ItemsSource="{Binding Categories}"
          DisplayMemberPath="Name" SelectedValue="{Binding NodeCategory, Mode=TwoWay}"/>

财产：

private Category _NodeCategory;
public Category NodeCategory
{
    get
    {
        return _NodeCategory;
    }
    set
    {
        _NodeCategory = value;
        OnPropertyChanged("NodeCategory");
    }
}
[Serializable]
public class Category : INotifyPropertyChanged
{
    private string _Name;
    [XmlAttribute("Name")]
    public string Name
    {
        get
        {
            return _Name;
        }
        set
        {
            _Name = value;
            OnPropertyChanged("Name");
        }
    }
    public void OnPropertyChanged(string propertyName)
    {
        if (PropertyChanged != null)
        {
            PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
        }
    }
    [field:NonSerialized]
    public event PropertyChangedEventHandler PropertyChanged;
}

我正在尝试的是：当我设置

NodeCategory = some_list_of_other_objects.Category;

以使用适当的DisplayMemberPath Combobox中选择该项目

WPF - MVVM - ComboBox SelectedItem

您在此行中设置的类别 -

NodeCategory = some_list_of_other_objects.Category;

并且您的类别集合（ItemsSource="{Binding Categories}"）中的一个应该引用相同的对象。如果不是，那么SelectedItem将不起作用。

解决方案 1 -

你也可以尝试使用这样的SelectedValuePath——

<ComboBox x:Name="categoryComboBox" 
          ItemsSource="{Binding Categories}"
          DisplayMemberPath="Name" 
          SelectedValuePath="Name" 
          SelectedValue="{Binding NodeCategory, Mode=TwoWay}" />

在代码中，您可以执行以下操作 -

private string _NodeCategory;
public string NodeCategory
{
    get
    {
        return _NodeCategory;
    }
    set
    {
        _NodeCategory = value;
        OnPropertyChanged("NodeCategory");
    }
}

并像这样设置所选项目 -

NodeCategory = some_list_of_other_objects.Category.Name;

并像这样使用选定的值 -

Category selectedCategory = 
   some_list_of_other_objects.FirstOrDefault(cat=> cat.Name == NodeCategory);

或 

Category selectedCategory = 
   Categories.FirstOrDefault(cat=> cat.Name == NodeCategory);

解决方案 2 -

另一种可能的解决方案可能是——

NodeCategory = 
  Categories.FirstOrDefault(cat=> cat.Name == some_list_of_other_objects.Category.Name);

这样，您的 NodeCategory 属性将具有Categories集合中对象的引用，并且SelectedItem将起作用。

您的 XAML 需要进行一些修改，但我认为真正的问题在于您发布的代码，我认为它不能讲述完整的故事。对于初学者，组合框ItemSource绑定到名为"类别"的属性，但你不显示此属性的编码方式或NodeCategory属性最初如何与项目同步。

尝试使用以下代码，您将看到当用户更改组合框中的值时，所选项目保持同步。

XAML 

<Window x:Class="WpfApplication1.MainWindow"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    Title="MainWindow" Height="350" Width="525">
<StackPanel>
    <ComboBox x:Name="categoryComboBox"
              Grid.Column="1"
              Grid.Row="3"
              Grid.ColumnSpan="2"
              Margin="10"
              ItemsSource="{Binding Categories}"
              DisplayMemberPath="Name"
              SelectedItem="{Binding NodeCategory}" />
    <Label Content="{Binding NodeCategory.Name}" />
</StackPanel>

代码隐藏

public partial class MainWindow : Window, INotifyPropertyChanged
{
    private ObservableCollection<Category> _categories = new ObservableCollection<Category>
    {
        new Category { Name = "Squares"},
        new Category { Name = "Triangles"},
        new Category { Name = "Circles"},
    };
    public MainWindow()
    {
        InitializeComponent();
        NodeCategory = _categories.First();
        this.DataContext = this;
    }
    public IEnumerable<Category> Categories
    {
        get { return _categories; }
    }
    private Category _NodeCategory;
    public Category NodeCategory
    {
        get
        {
            return _NodeCategory;
        }
        set
        {
            _NodeCategory = value;
            OnPropertyChanged("NodeCategory");
        }
    }
    public void OnPropertyChanged(string propertyName)
    {
        if (PropertyChanged != null)
        {
            PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
        }
    }
    public event PropertyChangedEventHandler PropertyChanged;
}
[Serializable]
public class Category : INotifyPropertyChanged
{
    private string _Name;
    [XmlAttribute("Name")]
    public string Name
    {
        get
        {
            return _Name;
        }
        set
        {
            _Name = value;
            OnPropertyChanged("Name");
        }
    }
    public void OnPropertyChanged(string propertyName)
    {
        if (PropertyChanged != null)
        {
            PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
        }
    }
    [field: NonSerialized]
    public event PropertyChangedEventHandler PropertyChanged;
}

从我的小例子来看：

注意：这只是设置一个字符串（或其他列表中的类别），但这里的基础知识应该相同：

基本上这是完成的：

private void button1_Click(object sender, RoutedEventArgs e)
{
    (this.DataContext as ComboBoxSampleViewModel).SelectCategory("Categorie 4");
}

这是我的 XAML： 

<Grid>
    <ComboBox Height="23" HorizontalAlignment="Left" Margin="76,59,0,0"   
              Name="comboBox1" VerticalAlignment="Top" Width="120" 
              ItemsSource="{Binding List.Categories}" 
              DisplayMemberPath="Name" 
              SelectedValue="{Binding NodeCategory, Mode=TwoWay}" />
    <Button Content="Button" Height="27" HorizontalAlignment="Left" 
            Margin="76,110,0,0" Name="button1" VerticalAlignment="Top" 
            Width="120" Click="button1_Click" />
</Grid>

并在窗口的视图中

class ComboBoxSampleViewModel : INotifyPropertyChanged
{
    public event PropertyChangedEventHandler PropertyChanged;
    private void NotifyPropertyChanged(string info)
    {
        if (PropertyChanged != null)
        {
            PropertyChanged(this, new PropertyChangedEventArgs(info));
        }
    }
    public CategoryList List { get; set; }
    public ComboBoxSampleViewModel()
    {
        this.List = new CategoryList();
        NodeCategory = List.Selected;
    }
    private ComboBoxSampleItemViewModel nodeCategory;
    public ComboBoxSampleItemViewModel NodeCategory
    {
        get
        {
            return nodeCategory;
        }
        set
        {
            nodeCategory = value;
            NotifyPropertyChanged("NodeCategory");
        }
    }
    internal void SelectCategory(string p)
    {
        this.List.SelectByName(p);
        this.NodeCategory = this.List.Selected;
    }
}

在这个小班的帮助下：

public class CategoryList
{
    public ObservableCollection<ComboBoxSampleItemViewModel> Categories { get; set; }
    public ComboBoxSampleItemViewModel Selected { get; set; }
    public CategoryList()
    {
        Categories = new ObservableCollection<ComboBoxSampleItemViewModel>();
        var cat1 = new ComboBoxSampleItemViewModel() { Name = "Categorie 1" };
        var cat2 = new ComboBoxSampleItemViewModel() { Name = "Categorie 2" };
        var cat3 = new ComboBoxSampleItemViewModel() { Name = "Categorie 3" };
        var cat4 = new ComboBoxSampleItemViewModel() { Name = "Categorie 4" };
        Categories.Add(cat1);
        Categories.Add(cat2);
        Categories.Add(cat3);
        Categories.Add(cat4);
        this.Selected = cat3;
    }
    internal void SelectByName(string p)
    {
        this.Selected = this.Categories.Where(s => s.Name.Equals(p)).FirstOrDefault();
    }
}

而这个项目视图模型

public class ComboBoxSampleItemViewModel : INotifyPropertyChanged
{
    public event PropertyChangedEventHandler PropertyChanged;
    private void NotifyPropertyChanged(string info)
    {
        if (PropertyChanged != null)
        {
            PropertyChanged(this, new PropertyChangedEventArgs(info));
        }
    }
    private string name;
    public string Name 
    { 
        get
        {
            return name;
        }
        set
        {
            name = value;
            NotifyPropertyChanged("Name");
        }
    }
}

如果 Combobox 绑定到视图模型的对象类，而发送方对象的SelectionBoxItem（在代码隐藏的SelectionChanged中）没有该类型，则意味着它仍在加载。

ComboBox combo = sender as ComboBox;
if (combo.SelectionBoxItem.GetType() == typeof(BindedClass))
{
            // Not loading
}
相关文章：