wpf 正确使用 PropertyChangedTrigger 和 ChangePropertyAction
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Proper use of PropertyChangedTrigger and ChangePropertyAction
提问by eran otzap
I'm trying to set a default selected value when ItemsSourceproperty changes on my ComboBox
当ItemsSource我的属性发生变化时，我试图设置一个默认的选定值ComboBox
My xaml :
我的 xaml ：
<ComboBox ItemsSource="{Binding SelectedItemsSource, Mode=OneWay}" x:Name="c1">
<i:Interaction.Triggers>
<ei:PropertyChangedTrigger Binding="{Binding ItemsSource,RelativeSource={RelativeSource Self}}">
<ei:ChangePropertyAction PropertyName="SelectedIndex" Value="{StaticResource zero}" TargetName="c1"/>
</ei:PropertyChangedTrigger>
</i:Interaction.Triggers>
</ComboBox>
The SelectedItemsSource in my VM changes dynamically and I want to have the first item selected each time this happens .
我的 VM 中的 SelectedItemsSource 动态更改，我希望每次发生这种情况时都选择第一个项目。
Any idea why this doesn't work?
知道为什么这不起作用吗？
回答by Rohit Vats
Try setting property IsSynchronizedWithCurrentItemto truefor your combobox and remove the trigger completely -
尝试属性设置IsSynchronizedWithCurrentItem到true您的组合框和完全删除触发器-
<ComboBox ItemsSource="{Binding SelectedItemsSource, Mode=OneWay}"
IsSynchronizedWithCurrentItem="True">
</ComboBox>
回答by eran otzap
has in addition to the current answers which led me on the way to my solution what i actually needed to accomplish is retrieving the last selected item when switching between itemsSources (plural)
除了当前的答案，这些答案让我走上了我的解决方案，我真正需要完成的是在 itemsSources（复数）之间切换时检索最后一个选定的项目
from an article i found : "for each ItemsSource binding, a unique CollectionView is generated.."
从我发现的一篇文章中： “对于每个 ItemsSource 绑定，都会生成一个唯一的 CollectionView..”
i concurred that as long as the view exists each binding would generate its own CollectionView and thus hold a reference to CurrentItem and CurrentPosition if decorated with
我同意，只要视图存在，每个绑定都会生成自己的 CollectionView，因此如果装饰有对 CurrentItem 和 CurrentPosition 的引用
IsSynchronizedWithCurrentItem="True"
IsSynchronizedWithCurrentItem="True"
so i created my own ChangePropertyActionClass :
所以我创建了自己的ChangePropertyAction类：
public class RetriveLastSelectedIndexChangePropertyAction : ChangePropertyAction
{
public int LastSelectedIndex
{
get { return (int)GetValue(LastSelectedIndexProperty); }
set { SetValue(LastSelectedIndexProperty, value); }
}
public static readonly DependencyProperty LastSelectedIndexProperty =
DependencyProperty.Register("LastSelectedIndex", typeof(int), typeof(RetriveLastSelectedIndexChangePropertyAction), new UIPropertyMetadata(-1));
protected override void Invoke(object parameter)
{
var comboBox = this.AssociatedObject as ComboBox;
this.SetValue(LastSelectedIndexProperty, comboBox.Items.CurrentPosition);
}
}
and invoked it using PropertyChangedTriggeras follows :
并使用PropertyChangedTrigger调用它 ，如下所示：
<ComboBox ItemsSource="{Binding SelectedItemsSource, Mode=OneWay}"
x:Name="c1"
IsSynchronizedWithCurrentItem="True">
<i:Interaction.Triggers>
<ei:PropertyChangedTrigger Binding="{Binding ElementName=c1,Path=ItemsSource}">
<local:RetriveLastSelectedIndexChangePropertyAction
PropertyName="SelectedIndex"
Value="{Binding LastSelectedIndex}"
TargetName="c1"/>
</ei:PropertyChangedTrigger>
</i:Interaction.Triggers>
</ComboBox>
hope this helps if any one needing to retrieve their last selected item with out any messy code in their DataContext , enjoy.
如果有人需要在 DataContext 中没有任何凌乱的代码的情况下检索他们最后选择的项目，希望这会有所帮助。
回答by K Mehta
Try changing your binding from:
尝试更改您的绑定：
<ei:PropertyChangedTrigger Binding="{Binding ItemsSource,RelativeSource={RelativeSource Self}}">
to
到
<ei:PropertyChangedTrigger Binding="{Binding ItemsSource,ElementName=c1}">
