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
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
}