[英]Why is my Dependency Property Binding is not working as expected?
I am trying to make a customized UserControl which includes a ListView.我正在尝试制作一个包含 ListView 的自定义 UserControl。 I would like to bind the SelectedItem Property to my View Model.
我想将 SelectedItem 属性绑定到我的视图 Model。 I therefore created a DP in my User Control and bound the SelectedItem Property of the ListView to the new Dependency Property.
因此,我在我的用户控件中创建了一个 DP,并将 ListView 的 SelectedItem 属性绑定到新的 Dependency 属性。
public static readonly DependencyProperty SelectedItemProperty = DependencyProperty.Register(
"SelectedItem",
typeof(object),
typeof(DragAndDropListView),
new PropertyMetadata(SelectedItemPropertyChangedCallback));
private static void SelectedItemPropertyChangedCallback(DependencyObject d,
DependencyPropertyChangedEventArgs e)
{
if (d is DragAndDropListView dragAndDropListView)
{
}
}
public object SelectedItem
{
get => GetValue(SelectedItemProperty);
set => SetValue(SelectedItemProperty, value);
}
In the xaml code I then made a binding然后在 xaml 代码中,我进行了绑定
<ListView Name="ListView"
PreviewMouseLeftButtonDown="ListViewPreviewMouseLeftButtonDown"
AllowDrop="True"
MouseMove="ListViewMouseMove"
DragEnter="ListViewDragEnter"
Drop="ListViewDrop"
SelectedItem="{Binding Path= SelectedItem}"/>
And to make sure it works I assigned the UserControl as DataContext to the ListView为了确保它有效,我将 UserControl 作为 DataContext 分配给 ListView
public DragAndDropListView()
{
InitializeComponent();
ListView.ItemsSource = Items;
ListView.DataContext = this;
}
And then I added a binding where I use the UserControl.然后我在使用 UserControl 的地方添加了一个绑定。
<userControls:DragAndDropListView
Items="{Binding SelectedCustomers}"
SelectedItem="{Binding SelectedCustomer}"
DisplayMemberPath="Name"
Grid.Column="0"
Grid.Row="0"/>
As you may see I thought, that I don't need a SelectedItemPropertyChangedCallback.如您所见,我认为我不需要 SelectedItemPropertyChangedCallback。 First I didn't even implement it.
首先,我什至没有实施它。 I added it later to add a break point to see if it even works.
我后来添加了它以添加一个断点以查看它是否有效。 When I select an item in the listView it calls the callback.
当我 select 列表视图中的一个项目时,它会调用回调。 But the setter of the SelectedCustomer in my ViewModel is never called.
但是我的 ViewModel 中的 SelectedCustomer 的设置器永远不会被调用。
I would expect this to work.我希望这能奏效。 Please help me to understand my mistake.
请帮助我理解我的错误。
The Binding must be TwoWay:绑定必须是双向的:
SelectedItem="{Binding SelectedCustomer, Mode=TwoWay}"
You could declare the property such that it binds TwoWay by default:您可以声明该属性,使其默认绑定 TwoWay:
public static readonly DependencyProperty SelectedItemProperty =
DependencyProperty.Register(
nameof(SelectedItem),
typeof(object),
typeof(DragAndDropListView),
new FrameworkPropertyMetadata(
null,
FrameworkPropertyMetadataOptions.BindsTwoWayByDefault,
SelectedItemPropertyChangedCallback));
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