我有以下内容ComboBox在 WPF 中。我知道我可以添加选项ALL与 CompositeCollection，但我不知道如何。如果有人帮助我提供一个简短的教程，那就太好了。
<ComboBox SelectionChanged="ComboBoxOperatingPoints_SelectionChanged"
x:Name="ComboBoxOperatingPoints"
DropDownOpened="ComboBoxOperatingPoints_DropDownOpened_1"
FontSize="30"
HorizontalAlignment="Right"
Margin="40,40,0,0"
VerticalAlignment="Top"
Width="200"
Height="50"
IsSynchronizedWithCurrentItem="True"
ItemsSource="{Binding OperatingPoints}"
DisplayMemberPath="name"
SelectedValue="{Binding OperatingPointID,UpdateSourceTrigger=PropertyChanged,TargetNullValue=''}"
SelectedValuePath="operating_point_id">
</ComboBox>
尝试这个 （msdn):
<ComboBox x:Name="ComboBoxOperatingPoints"
SelectionChanged="ComboBoxOperatingPoints_SelectionChanged"
Width="200" Height="50"
IsSynchronizedWithCurrentItem="True"
DisplayMemberPath="name"
SelectedValuePath="operating_point_id">
<ComboBox.Resources>
<CollectionViewSource x:Key="comboBoxSource" Source="{Binding Path=OperatingPoints}" />
</ComboBox.Resources>
<ComboBox.ItemsSource>
<CompositeCollection>
<local:OpPoint name="all" operating_point_id="-1" />
<CollectionContainer Collection="{Binding Source={StaticResource comboBoxSource}}" />
</CompositeCollection>
</ComboBox.ItemsSource>
</ComboBox>
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