c# - 将 ListView 的 SelectedItems 绑定(bind)到 ViewModel

Question

我有一个 ListView ，它将项目与 View 模型中的属性绑定(bind)。

<ListView Height="238" 
          HorizontalAlignment="Left" 
          Name="listView" 
          VerticalAlignment="Top" 
          Width="503"
          ItemsSource="{Binding BusinessCollection}"
          SelectionMode="Multiple">
    <ListView.View>
        <GridView>
            <GridView.Columns>
                <GridViewColumn>
                    <GridViewColumn.CellTemplate>
                        <DataTemplate>
                           <CheckBox  IsChecked="{Binding RelativeSource={RelativeSource AncestorType={x:Type ListViewItem}}, Path=IsSelected}" />  
                       </DataTemplate>
                    </GridViewColumn.CellTemplate>
                </GridViewColumn>
                <GridViewColumn DisplayMemberBinding="{Binding ID}" Header="ID" />
                <GridViewColumn DisplayMemberBinding="{Binding Name}" Header="Name" />
            </GridView.Columns>
        </GridView>
    </ListView.View>
</ListView>

在 View 模型中。

ICollectionView _businessCollection

public ICollectionView BusinessCollection
{
    get { return _businessCollection; }
    set {
          _businessCollection = value;
          RaisePropertyOnChange("BusinessCollection");
        }
}

如何在 View 模型中获取选中的businesscollection项？

Answer 1

<强>1。源绑定(bind)的一种方法:

您必须使用 SelectionChanged 事件。最简单的方法是在代码隐藏中编写事件处理程序以“绑定(bind)选定项”到 View 模型。

//ViewModel
public ICollectionView BusinessCollection {get; set;}
public List<YourBusinessItem> SelectedObject {get; set;}

//Codebehind
private void ListView_SelectionChanged(object sender, SelectionChangedEventArgs e)
{
    var viewmodel = (ViewModel) DataContext;
    viewmodel.SelectedItems = listview.SelectedItems
        .Cast<YourBusinessItem>()
        .ToList();
}

这仍然符合 MVVM 设计，因为 View 和 View 模型的职责是分开的。您在代码隐藏中没有任何逻辑，并且 View 模型是干净且可测试的。

<强>2。双向绑定(bind):

如果您还需要更新 View ，当 View 模型更改时，您必须附加到 ViewModel 的 PropertyChanged 事件和所选项目的 CollectionChanged 事件。当然你可以在代码隐藏中做到这一点，但在这种情况下，我会创建一些更可重用的东西:

//ViewModel
public ObservableCollection<YourBusinessItem> SelectedObject {get; set;}

//in codebehind:
var binder = new SelectedItemsBinder(listview, viewmodel.SelectedItems);
binder.Bind();

或者可以创建自定义附加属性，因此您可以在 xaml 中使用绑定(bind)语法:

<ListView local:ListViewExtensions.SelectedValues="{Binding SelectedItem}" .../>

public class SelectedItemsBinder
{
    private ListView _listView;
    private IList _collection;


    public SelectedItemsBinder(ListView listView, IList collection)
    {
        _listView = listView;
        _collection = collection;

        _listView.SelectedItems.Clear();

        foreach (var item in _collection)
        {
            _listView.SelectedItems.Add(item);
        }
    }

    public void Bind()
    {
        _listView.SelectionChanged += ListView_SelectionChanged;

        if (_collection is INotifyCollectionChanged)
        {
            var observable = (INotifyCollectionChanged) _collection;
            observable.CollectionChanged += Collection_CollectionChanged;
        }
    }

    public void UnBind()
    {
        if (_listView != null)
            _listView.SelectionChanged -= ListView_SelectionChanged;

        if (_collection != null && _collection is INotifyCollectionChanged)
        {
            var observable = (INotifyCollectionChanged) _collection;
            observable.CollectionChanged -= Collection_CollectionChanged;
        }
    }

    private void Collection_CollectionChanged(object sender, NotifyCollectionChangedEventArgs e)
    {
        foreach (var item in e.NewItems ?? new object[0])
        {
            if (!_listView.SelectedItems.Contains(item))
                _listView.SelectedItems.Add(item);
        }
        foreach (var item in e.OldItems ?? new object[0])
        {
            _listView.SelectedItems.Remove(item);
        }
    }

    private void ListView_SelectionChanged(object sender, SelectionChangedEventArgs e)
    {
        foreach (var item in e.AddedItems ?? new object[0])
        {
            if (!_collection.Contains(item))
                _collection.Add(item);
        }

        foreach (var item in e.RemovedItems ?? new object[0])
        {
            _collection.Remove(item);
        }
    }
}

附加属性实现

public class ListViewExtensions
{

    private static SelectedItemsBinder GetSelectedValueBinder(DependencyObject obj)
    {
        return (SelectedItemsBinder)obj.GetValue(SelectedValueBinderProperty);
    }

    private static void SetSelectedValueBinder(DependencyObject obj, SelectedItemsBinder items)
    {
        obj.SetValue(SelectedValueBinderProperty, items);
    }

    private static readonly DependencyProperty SelectedValueBinderProperty = DependencyProperty.RegisterAttached("SelectedValueBinder", typeof(SelectedItemsBinder), typeof(ListViewExtensions));


    public static readonly DependencyProperty SelectedValuesProperty = DependencyProperty.RegisterAttached("SelectedValues", typeof(IList), typeof(ListViewExtensions),
        new FrameworkPropertyMetadata(null, OnSelectedValuesChanged));


    private static void OnSelectedValuesChanged(DependencyObject o, DependencyPropertyChangedEventArgs value)
    {
        var oldBinder = GetSelectedValueBinder(o);
        if (oldBinder != null)
            oldBinder.UnBind();

        SetSelectedValueBinder(o, new SelectedItemsBinder((ListView)o, (IList)value.NewValue));
        GetSelectedValueBinder(o).Bind();
    }

    public static void SetSelectedValues(Selector elementName, IEnumerable value)
    {
        elementName.SetValue(SelectedValuesProperty, value);
    }

    public static IEnumerable GetSelectedValues(Selector elementName)
    {
        return (IEnumerable)elementName.GetValue(SelectedValuesProperty);
    }
}