[英]Multiple ListBox/Collection Items Selected for MVVM
我有一個綁定到Names的ObservableCollection的列表框。 列表中的某些項目將具有一個打開/關閉的復選框,表示該項目已被選中。
如何根據Master-Details概念從第一個列表框的選定項創建ObservableCollection?
(我打算使用我的MasterViewModel作為我的DetailsView的DataContext,它顯示所選的項目集合。)
提前致謝!
是的,我之前也遇到過這種情況。 ListBoxes等具有名為'SelectedItem'的依賴屬性,但'SelectedItems'(帶有's')屬性未實現為一個屬性。
我發現最干凈的解決方案就是將列表框子類化,並創建自己的依賴屬性,稱為'SelectedItems'。 沒有樂趣,但我覺得這是最好的解決方案。
UPDATE
首先我們的ViewModel:
class ViewModel : INotifyPropertyChanged
{
// Set up our collection to be read from the View
public ObservableCollection<String> Collection { get; private set; }
// This collection will maintain the selected items
public ObservableCollection<String> SelectedItems { get; private set; }
public ViewModel()
{
// Instantiate
this.Collection = new ObservableCollection<String>();
this.SelectedItems = new ObservableCollection<String>();
// Now let's monitor when this.SelectdItems changes
this.SelectedItems.CollectionChanged += SelectedItems_CollectionChanged;
// Fill our collection with some strings (1 to 10).
// (1) Generate the numbers 1 - 10
// (2) Convert each number to a string
// (3) Cast into a list so we can use foreach
// (4) Add each item to the collection.
Enumerable.Range(1, 10)
.Select(number => number.ToString())
.ToList()
.ForEach(this.Collection.Add);
// Remember! Never reset the ObservableCollection.
// That is, never say this.Collection = new... (or you'll break the binding).
// instead use this.Collection.Clear(), and then add the items you want to add
}
void SelectedItems_CollectionChanged(object sender, System.Collections.Specialized.NotifyCollectionChangedEventArgs e)
{
if (e.Action == System.Collections.Specialized.NotifyCollectionChangedAction.Add)
{
foreach (String str in this.SelectedItems)
System.Diagnostics.Debug.WriteLine("New item added {0}", str);
}
}
public event PropertyChangedEventHandler PropertyChanged;
}
然后我們的擴展ListBoxEx:
class ListBoxEx : ListBox
{
// Use the 'new' keyword so that we 'hide' the base property.
// This means that binding will go to this version of SelectedItems
// rather than whatever the base class uses. To reach the base 'SelectedItems' property
// We just need to use base.SelectedItems instead of this.SelectedItems
// Note that we register as an observable collection.
new DependencyProperty SelectedItemsProperty =
DependencyProperty.Register("SelectedItems", typeof(ObservableCollection<String>), typeof(ListBoxEx));
// Accessor. Again, note the 'new'.
new public ObservableCollection<String> SelectedItems
{
get { return (ObservableCollection<String>) GetValue(SelectedItemsProperty); }
set { SetValue(SelectedItemsProperty, value); }
}
protected override void OnSelectionChanged(SelectionChangedEventArgs e)
{
// Guard against ViewModel being null
if (this.SelectedItems != null)
{
// Clear the list
this.SelectedItems.Clear();
// (1) On selection changed. Get the new base.SelectedItems
// (2) Cast each item to a String ("Make a string collection")
// (3) Cast to list, and use foreach to add each item to
// this.SelectedItems (note this is different from the original base.SelectedItems)
base.SelectedItems.Cast<String>()
.ToList()
.ForEach(this.SelectedItems.Add);
}
}
}
最后我們的觀點:
<Window.DataContext>
<lol:ViewModel />
</Window.DataContext>
<Grid>
<lol:ListBoxEx ItemsSource="{Binding Collection}" SelectedItems="{Binding SelectedItems}"
SelectionMode="Multiple"/>
</Grid>
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