如何解决WPF数据绑定-我缺少什么？
| 我试图通过一个简单的示例来掌握WPF数据绑定的概念，但似乎我还没有完全理解所有的要点。 该示例是级联下拉菜单之一； XAML如下：<Window x:Class=\"CascadingDropDown.MainWindow\"
xmlns=\"http://schemas.microsoft.com/winfx/2006/xaml/presentation\"
xmlns:x=\"http://schemas.microsoft.com/winfx/2006/xaml\"
Title=\"MainWindow\" Height=\"496\" Width=\"949\" Loaded=\"Window_Loaded\">
<Grid>
<ComboBox Name=\"comboBox1\" ItemsSource=\"{Binding}\" DisplayMemberPath=\"Key\" SelectionChanged=\"comboBox1_SelectionChanged\" />
<ComboBox Name=\"comboBox2\" ItemsSource=\"{Binding}\" DisplayMemberPath=\"Name\" />
</Grid>
</Window>
public partial class MainWindow : Window
{
private ObservableCollection<ItemA> m_lstItemAContext = new ObservableCollection<ItemA>();
private ObservableCollection<ItemB> m_lstItemBContext = new ObservableCollection<ItemB>();
private IEnumerable<ItemB> m_lstAllItemB = null;
public MainWindow()
{
InitializeComponent();
this.comboBox1.DataContext = m_lstItemAContext;
this.comboBox2.DataContext = m_lstItemBContext;
}
private void Window_Loaded(object sender,RoutedEventArgs e)
{
var lstItemA = new List<ItemA>() { new ItemA(\"aaa\"),new ItemA(\"bbb\"),new ItemA(\"ccc\") };
var lstItemB = new List<ItemB>() { new ItemB(\"aaa\",\"a11\"),new ItemB(\"aaa\",\"a22\"),new ItemB(\"bbb\",\"b11\"),\"b22\") };
initPicklists(lstItemA,lstItemB);
}
private void initPicklists(IEnumerable<ItemA> lstItemA,IEnumerable<ItemB> lstItemB)
{
this.m_lstAllItemB = lstItemB;
this.m_lstItemAContext.Clear();
lstItemA.ToList().ForEach(a => this.m_lstItemAContext.Add(a));
}
#region Control event handlers
private void comboBox1_SelectionChanged(object sender,SelectionChangedEventArgs e)
{
ComboBox ddlSender = (ComboBox)sender;
ItemA itemaSelected = (ItemA)ddlSender.SelectedItem;
var lstNewItemB = this.m_lstAllItemB.Where(b => b.KeyA == itemaSelected.Key);
this.m_lstItemBContext.Clear();
lstNewItemB.ToList().ForEach(b => this.m_lstItemBContext.Add(b));
}
private void comboBox2_?(object sender,?EventArgs e)
{
// disable ComboBox if empty
}
#endregion Control event handlers
}
class ItemA
{
public string Key { get; set; }
public ItemA(string sKey)
{
this.Key = sKey;
}
}
class ItemB
{
public string KeyA { get; set; }
public string Name { get; set; }
public ItemB(string sKeyA,string sName)
{
this.KeyA = sKeyA;
this.Name = sName;
}
}
解决方法
这是实现这一目标的一种更简洁的方法（也许不是最优化的方法），保持您的业务模型不变，并且仅在可能的情况下使用ViewModel和XAML：
查看模型：
public class WindowViewModel : INotifyPropertyChanged
{
private ItemA selectedItem;
private readonly ObservableCollection<ItemA> itemsA = new ObservableCollection<ItemA>();
private readonly ObservableCollection<ItemB> itemsB = new ObservableCollection<ItemB>();
private readonly List<ItemB> internalItemsBList = new List<ItemB>();
public WindowViewModel()
{
itemsA = new ObservableCollection<ItemA> { new ItemA(\"aaa\"),new ItemA(\"bbb\"),new ItemA(\"ccc\") };
InvokePropertyChanged(new PropertyChangedEventArgs(\"ItemsA\"));
internalItemsBList = new List<ItemB> { new ItemB(\"aaa\",\"a11\"),new ItemB(\"aaa\",\"a22\"),new ItemB(\"bbb\",\"b11\"),\"b22\") };
}
public ObservableCollection<ItemA> ItemsA
{
get { return itemsA; }
}
public ItemA SelectedItem
{
get { return selectedItem; }
set
{
selectedItem = value;
ItemsB.Clear();
var tmp = internalItemsBList.Where(b => b.KeyA == selectedItem.Key);
foreach (var itemB in tmp)
{
ItemsB.Add(itemB);
}
InvokePropertyChanged(new PropertyChangedEventArgs(\"SelectedItem\"));
}
}
public ObservableCollection<ItemB> ItemsB
{
get { return itemsB; }
}
public event PropertyChangedEventHandler PropertyChanged;
public void InvokePropertyChanged(PropertyChangedEventArgs e)
{
PropertyChangedEventHandler handler = PropertyChanged;
if (handler != null) handler(this,e);
}
}
public partial class Window1
{
public Window1()
{
InitializeComponent();
DataContext = new WindowViewModel();
}
}
<StackPanel>
<ComboBox Name=\"comboBox1\" ItemsSource=\"{Binding ItemsA}\" DisplayMemberPath=\"Key\" SelectedItem=\"{Binding SelectedItem,Mode=TwoWay}\" />
<ComboBox Name=\"comboBox2\" ItemsSource=\"{Binding ItemsB}\" DisplayMemberPath=\"Name\">
<ComboBox.Style>
<Style TargetType=\"{x:Type ComboBox}\">
<Setter Property=\"IsEnabled\" Value=\"true\"/>
<Style.Triggers>
<DataTrigger Binding=\"{Binding ItemsB.Count}\" Value=\"0\">
<Setter Property=\"IsEnabled\" Value=\"false\"/>
</DataTrigger>
</Style.Triggers>
</Style>
</ComboBox.Style>
</ComboBox>
</StackPanel>
SelectedItem
class ItemA
{
public string Key { get; set; }
public ItemA(string sKey)
{
this.Key = sKey;
}
public IEnumerable<ItemB> ListItemsB { get; set;}
}
class ItemB
{
public string Name { get; set; }
public ItemB(string sName)
{
this.Name = sName;
}
}
<ComboBox x:Name=\"cbo_itemA\" ItemsSource=\"{Binding ListItemA}\" DisplayMemberPath=\"Key\"/>
<ComboBox ItemsSource=\"{Binding ElementName=cbo_itemA,Path=SelectedItem.ListItemsB}\"
DisplayMemberPath=\"Name\" />
private ObservableCollection<object> _Items = new ObservableCollection<object>()
{
new { Key = \"a\",Name = \"Item 1\" },new { Key = \"a\",Name = \"Item 2\" },new { Key = \"b\",Name = \"Item 3\" },new { Key = \"c\",Name = \"Item 4\" },};
public ObservableCollection<object> Items { get { return _Items; } }
<StackPanel>
<StackPanel.Resources>
<CollectionViewSource x:Key=\"ItemsSource\" Source=\"{Binding Items}\">
<CollectionViewSource.GroupDescriptions>
<PropertyGroupDescription PropertyName=\"Key\"/>
</CollectionViewSource.GroupDescriptions>
</CollectionViewSource>
</StackPanel.Resources>
<StackPanel.Children>
<ComboBox Name=\"keyCb\" ItemsSource=\"{Binding Source={StaticResource ItemsSource},Path=Groups}\" DisplayMemberPath=\"Name\"/>
<ComboBox ItemsSource=\"{Binding ElementName=keyCb,Path=SelectedItem.Items}\" DisplayMemberPath=\"Name\"/>
</StackPanel.Children>
</StackPanel>
CollectionViewGroup
Name
Items
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