在我的应用程序中，我有一个DataGrid，用户可以通过按Button来添加行。通过按下按钮，将在绑定{{1}的PlaceholderItem上添加ObservableCollection<PlaceholderItem>的新实例。
视图中DataGrid的定义如下：
DataGrid因此<DataGrid ItemsSource="{Binding PlaceholderItems}" AutoGenerateColumns="False" CanUserAddRows="False" CanUserDeleteRows="False"
Background="White" Grid.Row="1" MinHeight="70" MaxHeight="200" Margin="7,0" >
<DataGrid.Columns>
<DataGridTemplateColumn Header="Placeholder-Name" Width="*">
<DataGridTemplateColumn.CellTemplate>
<DataTemplate>
<ComboBox IsEditable="True" VerticalAlignment="Center" Margin="2"
ItemsSource="{Binding DataContext.AvailablePlaceholders, RelativeSource={RelativeSource FindAncestor, AncestorType=Window}}"
DisplayMemberPath="PlaceholderName"
Validation.ErrorTemplate="{StaticResource ComboBoxErrorTemplate}">
<ComboBox.Text>
<Binding Path="PlaceholderName" Mode="TwoWay" UpdateSourceTrigger="PropertyChanged" >
<Binding.ValidationRules>
<local:PlaceholderValidationRule ValidationStep="UpdatedValue">
<local:PlaceholderValidationRule.PlaceholderValidationRuleParamData>
<local:PlaceholderValidationRuleParamData
UsedPlaceholders="{Binding Source={StaticResource proxy}, Path=Data.PlaceholderItems}"
AvailablePlaceholders="{Binding Source={StaticResource proxy}, Path=Data.AvailablePlaceholders}"/>
</local:PlaceholderValidationRule.PlaceholderValidationRuleParamData>
</local:PlaceholderValidationRule>
</Binding.ValidationRules>
</Binding>
</ComboBox.Text>
</ComboBox>
</DataTemplate>
</DataGridTemplateColumn.CellTemplate>
</DataGridTemplateColumn>
<DataGridTemplateColumn Header="Placeholder-Value" Width="*">
<DataGridTemplateColumn.CellTemplate>
<DataTemplate>
<TextBox VerticalAlignment="Center" Validation.ErrorTemplate="{StaticResource PlaceholderItemValueErrorTemplate}">
<TextBox.Text>
<Binding Path="PlaceholderValue" Mode="TwoWay" UpdateSourceTrigger="PropertyChanged" ValidatesOnDataErrors="True">
<!--<Binding.ValidationRules>
<local:PlaceholderValueValidationRule/>
</Binding.ValidationRules>-->
</Binding>
</TextBox.Text>
</TextBox>
</DataTemplate>
</DataGridTemplateColumn.CellTemplate>
</DataGridTemplateColumn>
</DataGrid.Columns>
</DataGrid>
的ItemsSource称为PlaceholderItems。 DataGrid的每一行都由两列组成。第一列是DataGrid，其中ComboBox的名称是可选的。第二列是PlaceholderItem
PlaceholderItem类只有两个实现INotifyPropertyChanged的字符串属性。
每行第一列中的PlaceholderItem绑定到ComboBox。因此，用户可以从ObservableCollection<PlaceholderItem>中选择一项，并将ComboBox的值写入第二列中的PlaceholderItem。
Therfor我在ViewModel中使用以下代码：
TextBox一切正常。
现在的问题：
如果用户添加了新行并从public ObservableCollection<PlaceholderItem> PlaceholderItems
{
get
{
if (placeholderItems == null)
{
placeholderItems = new ObservableCollection<PlaceholderItem>();
placeholderItems.CollectionChanged += PlaceholderItemsOnCollectionChanged;
}
return placeholderItems;
}
}
private void PlaceholderItemsOnCollectionChanged(object sender, NotifyCollectionChangedEventArgs e)
{
if (e.NewItems != null)
{
foreach (PlaceholderItem placeholderItem in e.NewItems.OfType<PlaceholderItem>())
{
placeholderItem.PropertyChanged += PlaceholderItemOnPropertyChanged;
}
}
if (e.OldItems != null)
{
foreach (PlaceholderItem placeholderItem in e.OldItems.OfType<PlaceholderItem>())
{
placeholderItem.PropertyChanged -= PlaceholderItemOnPropertyChanged;
}
}
}
private void PlaceholderItemOnPropertyChanged(object sender, PropertyChangedEventArgs e)
{
if (e.PropertyName == "PlaceholderName")
{
PlaceholderItem targetAvailablePlaceholderItem =
AvailablePlaceholders.FirstOrDefault(p =>
p.PlaceholderName == ((PlaceholderItem)sender).PlaceholderName);
if (targetAvailablePlaceholderItem != null)
{
((PlaceholderItem)sender).PlaceholderValue = targetAvailablePlaceholderItem.PlaceholderValue;
}
}
}
中选择了一个项目，我想从AvailablePlaceholders-Collection中删除选定的项目。这样用户就不能再在其他行中选择它了。
我已经在PlaceholderItemOnProertyChanged-Method中尝试了以下方法：
ComboBox该项目已从集合中删除，但 if (e.PropertyName == "PlaceholderName")
{
PlaceholderItem targetAvailablePlaceholderItem =
AvailablePlaceholders.FirstOrDefault(p =>
p.PlaceholderName == ((PlaceholderItem)sender).PlaceholderName);
if (targetAvailablePlaceholderItem != null)
{
((PlaceholderItem)sender).PlaceholderValue = targetAvailablePlaceholderItem.PlaceholderValue;
AvailablePlaceholders.Remove(targetAvailablePlaceholderItem);
}
((PlaceholderItem)sender).ForcePropertyChanged();
}
中的值现在为空。
是否可以从ComboBox的ItemsSource中删除一项，但是ComboBox的文本属性保留该值？