WPF - MVVM - ComboBox SelectedItem

Question

我在后台和类Category有ViewModel （实现了INotifyPropertyChanged ），它只有一个string类型的属性。 我的ComboBox SelectedItem绑定到Category的实例。 当我更改实例的值时，SelectedItem没有被更新，并且Combobox没有被更改。

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}"/>

属性：

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;

使用适当的DisplayMemberPath在Combobox选择该项目

Answer 1

您在此行中设置的类别 -

NodeCategory = some_list_of_other_objects.Category;

您的Categories集合中存在的一个（ ItemsSource="{Binding Categories}" ）应该指向同一个对象。 如果它们不是那么SelectedItem将无法工作。

解决方案1 ​​ -

你也可以尝试像这样使用SelectedValuePath -

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

在代码中你可以做这样的事情 -

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

并设置这样的选定项目 -

NodeCategory = some_list_of_other_objects.Category.Name;

并使用这样的选定值 -

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

要么

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

---

解决方案2 -

另一个可能的解决方案是 -

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

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

Answer 2

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，我认为这些代码并不能完整地讲述。 对于初学者，您的组合框ItemSource绑定到名为Categories的属性，但您不显示此属性的编码方式或NodeCategory属性最初如何与项同步。

尝试使用以下代码，您将看到所选项目保持同步，因为用户更改了组合框中的值。

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;
}

Answer 3

从我的小例子：

注意：这只是设置一个字符串（或另一个列表中的类别），但基础知识应该在这里相同：

基本上这样做：

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Window的ViewModel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Item ViewModel

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");
        }
    }
}

Answer 4

如果组合框绑定对象类视图模型，而SelectionBoxItem发送对象（在SelectionChanged在后面的代码）已经不是那种类型，这意味着它仍然加载。

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