刷新ListCollectionView将ComboBox中所选项的值设置为null
本文关键字：设置 null 选项 ListCollectionView ComboBox 刷新 | 更新日期: 2023-09-27 18:11:07
我有一个ListBox和两个ComboBox的视图。当我在ListBox中选择一个项目时，根据所选项目的属性值刷新ComboBox es的内容/值。在我的场景中，ListBox保存一个客户列表，第一个ComboBox保存一个国家列表。选中的项是客户的原产国。第二个ComboBox保存城市列表。所选城市为客户端的原籍城市。
第二个ComboBox的ItemsSource属性基于所有城市的ObservableCollection绑定到ListViewCollection。当国家ListBox中的选择发生变化时，我刷新过滤器以只显示属于所选国家的城市。
假设客户A来自新西兰奥克兰，客户B来自加拿大多伦多。当我选择A时，一切正常。第二个ComboBox只包含新西兰的城市，奥克兰被选中。现在我选择B，选择的国家现在是加拿大，城市列表中只包含加拿大城市，选择多伦多。如果我现在回到A，在国家中选择了新西兰，城市列表中只有新西兰的城市，没有选择奥克兰。
当我调试这个场景时，我注意到当我选择B时，对ListCollectionView.Refresh()的调用设置了客户端A上最初选择为null的城市的值(在调用Refresh时设置了一个断点，在模型上的城市设置器上设置了另一个断点，参见下面的代码)。
我猜 -虽然我不是100%确定-它正在发生，因为我在ComboBox的SelectedItem上有一个TwoWay绑定，当过滤器将列表更新到加拿大城市时，奥克兰消失了，此信息被发送回属性，然后更新到null。在某种程度上，这是有道理的。
我的问题是:我怎样才能避免这种情况的发生?当ItemsSource仅刷新时，我如何防止模型上的属性被更新?
下面是我的代码(它有点长，尽管我试图使它尽可能少的代码量，使问题可重现):
public class Country
{
public string Name { get; set; }
public IEnumerable<City> Cities { get; set; }
}
public class City
{
public string Name { get; set; }
public Country Country { get; set; }
}
public class ClientModel : NotifyPropertyChanged
{
#region Fields
private string name;
private Country country;
private City city;
#endregion
#region Properties
public string Name
{
get
{
return this.name;
}
set
{
this.name = value;
this.OnPropertyChange("Name");
}
}
public Country Country
{
get
{
return this.country;
}
set
{
this.country = value;
this.OnPropertyChange("Country");
}
}
public City City
{
get
{
return this.city;
}
set
{
this.city = value;
this.OnPropertyChange("City");
}
}
#endregion
}
public class ViewModel : NotifyPropertyChanged
{
#region Fields
private ObservableCollection<ClientModel> models;
private ObservableCollection<Country> countries;
private ObservableCollection<City> cities;
private ListCollectionView citiesView;
private ClientModel selectedClient;
#endregion
#region Constructors
public ViewModel(IEnumerable<ClientModel> models, IEnumerable<Country> countries, IEnumerable<City> cities)
{
this.Models = new ObservableCollection<ClientModel>(models);
this.Countries = new ObservableCollection<Country>(countries);
this.Cities = new ObservableCollection<City>(cities);
this.citiesView = (ListCollectionView)CollectionViewSource.GetDefaultView(this.cities);
this.citiesView.Filter = city => ((City)city).Country.Name == (this.SelectedClient != null ? this.SelectedClient.Country.Name : string.Empty);
this.CountryChangedCommand = new DelegateCommand(this.OnCountryChanged);
}
#endregion
#region Properties
public ObservableCollection<ClientModel> Models
{
get
{
return this.models;
}
set
{
this.models = value;
this.OnPropertyChange("Models");
}
}
public ObservableCollection<Country> Countries
{
get
{
return this.countries;
}
set
{
this.countries = value;
this.OnPropertyChange("Countries");
}
}
public ObservableCollection<City> Cities
{
get
{
return this.cities;
}
set
{
this.cities = value;
this.OnPropertyChange("Cities");
}
}
public ListCollectionView CitiesView
{
get
{
return this.citiesView;
}
}
public ClientModel SelectedClient
{
get
{
return this.selectedClient;
}
set
{
this.selectedClient = value;
this.OnPropertyChange("SelectedClient");
}
}
public ICommand CountryChangedCommand { get; private set; }
#endregion
#region Methods
private void OnCountryChanged(object obj)
{
this.CitiesView.Refresh();
}
#endregion
}
<Grid Grid.Column="0" DataContext="{Binding SelectedClient}">
<Grid.ColumnDefinitions>
<ColumnDefinition/>
<ColumnDefinition/>
</Grid.ColumnDefinitions>
<Grid.RowDefinitions>
<RowDefinition Height="25"/>
<RowDefinition Height="25"/>
</Grid.RowDefinitions>
<TextBlock Grid.Column="0" Grid.Row="0" Text="Country"/>
<local:ComboBox Grid.Column="1" Grid.Row="0" SelectedItem="{Binding Country}"
Command="{Binding DataContext.CountryChangedCommand, RelativeSource={RelativeSource AncestorType={x:Type local:MainWindow}}}"
ItemsSource="{Binding DataContext.Countries, RelativeSource={RelativeSource AncestorType={x:Type local:MainWindow}}}">
<local:ComboBox.ItemTemplate>
<DataTemplate>
<TextBlock Text="{Binding Name}"/>
</DataTemplate>
</local:ComboBox.ItemTemplate>
</local:ComboBox>
<TextBlock Grid.Column="0" Grid.Row="1" Text="City"/>
<ComboBox Grid.Column="1" Grid.Row="1" SelectedItem="{Binding City}"
ItemsSource="{Binding DataContext.CitiesView, RelativeSource={RelativeSource AncestorType={x:Type local:MainWindow}}}">
<ComboBox.ItemTemplate>
<DataTemplate>
<TextBlock Text="{Binding Name}"/>
</DataTemplate>
</ComboBox.ItemTemplate>
</ComboBox>
</Grid>
<ListBox Grid.Column="1" ItemsSource="{Binding Models}" SelectedItem="{Binding SelectedClient}">
<ListBox.ItemTemplate>
<DataTemplate>
<TextBlock Text="{Binding Name}"/>
</DataTemplate>
</ListBox.ItemTemplate>
</ListBox>
</Grid>
如果它有任何帮助，这里也是我的自定义ComboBox的代码来处理国家选择的变化通知。
public class ComboBox : System.Windows.Controls.ComboBox, ICommandSource
{
#region Fields
public static readonly DependencyProperty CommandProperty = DependencyProperty.Register(
"Command",
typeof(ICommand),
typeof(ComboBox));
public static readonly DependencyProperty CommandParameterProperty = DependencyProperty.Register(
"CommandParameter",
typeof(object),
typeof(ComboBox));
public static readonly DependencyProperty CommandTargetProperty = DependencyProperty.Register(
"CommandTarget",
typeof(IInputElement),
typeof(ComboBox));
#endregion
#region Properties
public ICommand Command
{
get { return (ICommand)this.GetValue(CommandProperty); }
set { this.SetValue(CommandProperty, value); }
}
public object CommandParameter
{
get { return this.GetValue(CommandParameterProperty); }
set { this.SetValue(CommandParameterProperty, value); }
}
public IInputElement CommandTarget
{
get { return (IInputElement)this.GetValue(CommandTargetProperty); }
set { this.SetValue(CommandTargetProperty, value); }
}
#endregion
#region Methods
protected override void OnSelectionChanged(System.Windows.Controls.SelectionChangedEventArgs e)
{
base.OnSelectionChanged(e);
var command = this.Command;
var parameter = this.CommandParameter;
var target = this.CommandTarget;
var routedCommand = command as RoutedCommand;
if (routedCommand != null && routedCommand.CanExecute(parameter, target))
{
routedCommand.Execute(parameter, target);
}
else if (command != null && command.CanExecute(parameter))
{
command.Execute(parameter);
}
}
#endregion
}
Window的构造函数中创建并填充视图模型，如下所示:
public MainWindow()
{
InitializeComponent();
Country canada = new Country() { Name = "Canada" };
Country germany = new Country() { Name = "Germany" };
Country vietnam = new Country() { Name = "Vietnam" };
Country newZealand = new Country() { Name = "New Zealand" };
List<City> canadianCities = new List<City>
{
new City { Country = canada, Name = "Montréal" },
new City { Country = canada, Name = "Toronto" },
new City { Country = canada, Name = "Vancouver" }
};
canada.Cities = canadianCities;
List<City> germanCities = new List<City>
{
new City { Country = germany, Name = "Frankfurt" },
new City { Country = germany, Name = "Hamburg" },
new City { Country = germany, Name = "Düsseldorf" }
};
germany.Cities = germanCities;
List<City> vietnameseCities = new List<City>
{
new City { Country = vietnam, Name = "Ho Chi Minh City" },
new City { Country = vietnam, Name = "Da Nang" },
new City { Country = vietnam, Name = "Hue" }
};
vietnam.Cities = vietnameseCities;
List<City> newZealandCities = new List<City>
{
new City { Country = newZealand, Name = "Auckland" },
new City { Country = newZealand, Name = "Christchurch" },
new City { Country = newZealand, Name = "Invercargill" }
};
newZealand.Cities = newZealandCities;
ObservableCollection<ClientModel> models = new ObservableCollection<ClientModel>
{
new ClientModel { Name = "Bob", Country = newZealand, City = newZealandCities[0] },
new ClientModel { Name = "John", Country = canada, City = canadianCities[1] }
};
List<Country> countries = new List<Country>
{
canada, newZealand, vietnam, germany
};
List<City> cities = new List<City>();
cities.AddRange(canadianCities);
cities.AddRange(germanCities);
cities.AddRange(vietnameseCities);
cities.AddRange(newZealandCities);
ViewModel vm = new ViewModel(models, countries, cities);
this.DataContext = vm;
}
应该可以通过简单地复制/粘贴上述所有代码来重现问题。我用的是。net 4.0。
最后，我阅读了这篇文章(以及其他一些文章)，并试图将给出的建议应用到我的案例中，但没有成功。我想我做错了:
我也读了这个问题，但是如果我的ListBox变大了，我可能最终不得不明确地跟踪数百个项目，如果可能的话，我不想这样做。
您的模型有点冗余。你有国家列表，每个国家都有城市列表。然后组成城市的整体列表，当选择发生变化时更新。如果您将更改城市组合框的数据源，您将得到所需的行为:
<ComboBox Grid.Column="1" Grid.Row="1" SelectedItem="{Binding City}"
ItemsSource="{Binding Country.Cities}">
<ComboBox.ItemTemplate>
<DataTemplate>
<TextBlock Text="{Binding Name}"/>
</DataTemplate>
</ComboBox.ItemTemplate>
</ComboBox>
你猜对了为什么城市被设置为null
但是如果你想保持你的模型，就像你上面描述的那样，你应该改变方法调用的顺序。要做到这一点，你应该使用Application.Current.Dispatcher属性(你不需要改变上面提到的ComboBox):
private void OnCountryChanged()
{
var uiDispatcher = System.Windows.Application.Current.Dispatcher;
uiDispatcher.BeginInvoke(new Action(this.CitiesView.Refresh));
}