How can I change Expander button when the radtreeview is opened or closed?

Question

I had two icons,which is a and b; I need my radtreeviewitem showed Expander button with icon a when it opened, and showed icon b when it closed. The fllowing are two icons

<Style x:Key="ExpanderStyleOpen" TargetType="ToggleButton">
            <Setter Property="IsEnabled" Value="True" />
            <Setter Property="IsTabStop" Value="False" />
            <Setter Property="ToggleButton.IsChecked" Value="True" />
            <Setter Property="Cursor" Value="Hand" />
            <Setter Property="Template">
                <Setter.Value>
                    <ControlTemplate TargetType="ToggleButton">
                        ...
                    </ControlTemplate>
                </Setter.Value>
            </Setter>
        </Style>
        <Style x:Key="ExpanderStyleClose" TargetType="ToggleButton">
            <Setter Property="IsEnabled" Value="True" />
            <Setter Property="IsTabStop" Value="False" />
            <Setter Property="ToggleButton.IsChecked" Value="False" />
            <Setter Property="Cursor" Value="Hand" />
            <Setter Property="Template">
                <Setter.Value>
                    <ControlTemplate TargetType="ToggleButton">
                       ...
                    </ControlTemplate>
                </Setter.Value>
            </Setter>
        </Style>

then my radtreeview...

<telerik:RadTreeView Name="radTreeView"
<!--static can't change...:(-->
                             ExpanderStyle="{StaticResource ExpanderStyleClose}"
                             FontSize="12"
                             IsLineEnabled="True"
                             IsRootLinesEnabled="False"
                             Visibility="{Binding IsVisible}">

Answer 1

By using a Trigger, you can combine your two styles into one.

The idea is:

1. Set the closed image as the style's actual image.
2. Create a Trigger to change the ToggleButton's IsChecked property. It's false when "closed", true when opened.

Something like this should work:

<Style x:Key="ExpanderStyle" TargetType="{x:Type ToggleButton}">
    <Setter Property="IsEnabled" Value="True" />
    <Setter Property="IsTabStop" Value="False" />
    <Setter Property="Cursor" Value="Hand" />
    <Setter Property="Template">
        <Setter.Value>
            <ControlTemplate TargetType="{x:Type ToggleButton}">
                <StackPanel Orientation="Horizontal">
                    <Grid SnapsToDevicePixels="False" Background="Transparent">
                        <Image x:Name="expanderImage" Source="..." />
                    </Grid>
                    <ContentPresenter />
                </StackPanel>
                <ControlTemplate.Triggers>
                    <Trigger Property="IsChecked" Value="false">
                        <Setter Property="Source" TargetName="expanderImage" Value="..." />
                    </Trigger>
                </ControlTemplate.Triggers>
            </ControlTemplate>
        </Setter.Value>
    </Setter>
</Style>