我正在使用viewmodel模式,所以我的自定义用户控件的DataContext实际上是真实数据的视图模型包装。如何在不清除依赖属性的情况下设置DataContext?
我的自定义控件可以包含自定义控件的分层实例。
我在自定义控件中为真实数据创建了一个DependencyProperty,并希望在通过绑定设置数据时为其创建新的视图模型,然后将用户控件的datacontext设置为新的viewmodel。但是,似乎设置DataContext属性会导致我的真实数据DependencyProperty无效并设置为空。任何人都知道解决这个问题的方法,或者更确切地说,我应该使用viewmodels?
用户控件:
public partial class ArchetypeControl : UserControl
{
public static readonly DependencyProperty ArchetypeProperty = DependencyProperty.Register(
"Archetype",
typeof(Archetype),
typeof(ArchetypeControl),
new PropertyMetadata(null, OnArchetypeChanged)
);
ArchetypeViewModel _viewModel;
public Archetype Archetype
{
get { return (Archetype)GetValue(ArchetypeProperty); }
set { SetValue(ArchetypeProperty, value); }
}
private void InitFromArchetype(Archetype newArchetype)
{
if (_viewModel != null)
{
_viewModel.Destroy();
_viewModel = null;
}
if (newArchetype != null)
{
_viewModel = new ArchetypeViewModel(newArchetype);
// calling this results in OnArchetypeChanged getting called again
// with new value of null!
DataContext = _viewModel;
}
}
// the first time this is called, its with a good NewValue.
// the second time (after setting DataContext), NewValue is null.
static void OnArchetypeChanged(DependencyObject obj, DependencyPropertyChangedEventArgs args)
{
var control = (ArchetypeControl)obj;
control.InitFromArchetype(args.NewValue as Archetype);
}
}
视图模型:
class ArchetypeComplexPropertyViewModel : ArchetypePropertyViewModel
{
public Archetype Value { get { return Property.ArchetypeValue; } }
}
的XAML:
<Style TargetType="{x:Type TreeViewItem}">
<Style.Triggers>
<DataTrigger Binding="{Binding ViewModelType}" Value="{x:Type c:ArchetypeComplexPropertyViewModel}">
<Setter Property="Template" Value="{StaticResource ComplexPropertyTemplate}" />
</DataTrigger>
</Style.Triggers>
</Style>
<ControlTemplate x:Key="ComplexPropertyTemplate" TargetType="{x:Type TreeViewItem}">
<Grid>
<c:ArchetypeControl Archetype="{Binding Value}" />
</Grid>
</ControlTemplate>
修剪的什么,我试图做样本在这个问题中提到了这个问题的Cannot databind DependencyProperty评论,但从未得到解决
从外部混合绑定集(从而隐式使用DataContext),并设置新的DataContext不起作用,正如您发现的那样。另见http://stackoverflow.com/questions/25672037/how-to-correctly-bind-to-a-dependency-property-of-a-usercontrol-in-a-mvvm-framew – 2016-07-19 09:30:50