We continue our exploration of Accordion. This time we’ll take a look at some of the template parts, namely ExpandableContentControl. See part 1 and part 2 if you didn’t yet.

ExpandableContentControl

This control is part of AccordionItem and is used to display the content of an accordionItem. It sits in the Primitives namespace, which means it will be used primarily as a part of a template. It solves an important problem: being able to resize (expand/contract) a piece of content, without triggering resize actions on the content itself. With that I mean: if your AccordionItem would use a Grid or a DockPanel as it’s content and I would just be animating the width or the height, you would see the panel changing as it tries to keep up with the new sizes. Ofcourse, that would not be the case if you had set an explicit width or height to the panel, but AccordionItem does not force you to do so.So, during the resize of our AccordionItem, I don’t want the content to have to resize.

Furthermore, it would be nice to make it really easy for you to determine how the animation should look like. Do you want a gradual easein/out, a bump or something different altogether? I want to be able to design my animation in Blend, using the nifty keyspline features!

I accomplish the above goals by throwing in a ScrollViewer and defining a DependencyProperty: Percentage.

ScrollViewer allows Accordion to just determine the size the item will eventually be (after expand action) and set it only once. At that moment the content of the scrollviewer is going to resize itself accordingly. Then, as we animate the width or height of the scrollviewer, its content is none-the-wiser. Hence, no ugly resize actions going on.

Making the actual animation be easily defined inside of Blend, is done by the above-mentioned Percentage DP.
Accordion only determines the size the AccordionItem will eventually be, I call it the TargetSize. ExpandableContentControl will calculate and set its actual size using to the following simple function: actualsize = percentage * TargetSize.

Accordion also triggers a visualstate called either Expanded or Contracted on AccordionItem. Those animate the percentage property on ExpandableContentControl. See this Xaml in the template of AccordionItem:

This makes it possible to design your animation at the correct level (AccordionItem) and makes it a very design friendly experience, because Blend allows you to edit keysplines as follows:

(SL3 is adding a nice collection of other spline types that makes elastic AccordionItems even easier!)

I’ll discuss the remaining points of interest.

RevealMode

Since I expose one property (Percentage) for you to animate, the control needs to know whether that responds to the vertical or horizontal direction. Thus, AccordionItem will set the correct RevealMode, corresponding to its own ExpandDirection.

TargetSize

Already mentioned, setting the TargetSize will set the size of the ScrollViewer. It will also recalculate the percentage. Let’s say I have an item that has a height of 100. Now another item is collapsed, so the Accordion decides the remaining items should have a height of 160. The percentage that was once at 1 is recalculated to be 0.625.
This way we don’t have to restart the full animation, but we can just resize nicely.

I hope that helps understanding this vital piece of the template. In the future, I will either remove it (if the outlined problems can be solved more gracefully in another way) or expose the style of ExpandableContentControl in AccordionItem, so it can be more easily styled.

Completely unrelated to anything on this site, I wanted to talk about IE8 for a minute. It looks like a great browser, but on my home machine, just spinning up a tab took about 3 seconds. When I noticed that other people did not have this problem, I started to investigate. These are the two tips that I’ve found:

The first is by Ed Bot and basically tells you to execute ‘regsvr32 actxprxy.dll’ from an elevated command prompt. That registers a dll that in certain configurations is not registered. It can make a huge difference.

The second on is the the one that saved me. I don’t know the source, but there are several blogs telling you to look at your restricted sites (Tools/InternetOptions/Security/Restricted Sites, press the button labeled ‘sites’ ).
I had used spybot long ago, which had added a huge list of sites there. Apparently this can really slow down outlook and ie!
Remove them by resetting your settings to default (Advanced tab, button labeled ‘reset’).

Now I have a blindingly fast internet explorer, and I must admit, I do love this browser now. Switching back!

I’m glad to see accordion getting the excitement that it’s getting. I’ve gotten great feedback, keep it coming!

Part 1 was concerned with Accordion itself, we will now focus on the individual parts of Accordion.

AccordionItem

AccordionItem is to Accordion as is ListboxItem to Listbox. Accordion will only work with AccordionItems, and that is why, if you feed Accordion an item that is not of type AccordionItem, it will wrap it inside of one.

AccordionItem has several important jobs:

• It needs to display a header and content.
• It needs to be able to ‘open’ and ‘close’
• It needs to be able to work in several ExpandDirections (Left, Right, Top, Bottom)

AccordionItem mimicks Expander in many ways (although I changed the template considerably) but inherits from HeaderedContentControl. Therefore, it has two important properties it gains from HeaderedContentControl: HeaderTemplate and ContentTemplate.
These templates are used to allow you to customize the header and content.

I will use KeyValue pairs to easily create a few AccordionItems:

            acc.ItemsSource = new[]

                                  {

                                          new KeyValuePair<string, string>("A header", "And the content of the accordion item"),

                                          new KeyValuePair<string, string>("Hello", "World")

Let’s take a look at an Accordion and it’s Xaml:

ExpandDirection

An AccordionItem has the same ExpandDirection property as Accordion. When contained within an Accordion, AccordionItem will get the correct ExpandDirection from Accordion and will not allow you to change it individually.

ExpandDirection may only be set by Accordion, to prevent from weird mixes of ExpandDirections. Unfortunately, that does limit a few scenario’s (as in horizontal Accordion layout with vertical AccordionItems). If this turns out to be a common featurerequest, I’ll look into opening this up.

Accordion.ItemContainerGenerator

Accordion exposes an ItemContainerGenerator which has very helpful methods, such as ‘ContainerFromItem’ and even ContainerFromIndex’. So it is really easy to go from AccordionItem, to Item and vice versa.
This code might make you happy:

            for (int i = 0; i < acc.Items.Count; i++)

            {

                AccordionItem item = acc.ItemContainerGenerator.ContainerFromIndex(i) as AccordionItem;

Locking mechanism

In certain SelectionModes, Accordion must make sure that at least one item is selected. It does so by locking an item if it is the last one open. If you somehow force it to close (through code), Accordion will just open the first AccordionItem in the list. However, that is not that simple, since an AccordionItem may not be unselected, while it is locked.

Since AccordionItem will actually throw an exception when it is unselected while locked, I expose a boolean ‘IsLocked’ that you can use to make sure you don’t accidently do this.
I expose a VisualState that allows you to visualize the lock if you’d like.

The best way to unselect the AccordionItem while in such a mode, is to select a different item.

ExpandableContentControl and AccordionButton

These are two template parts on the AccordionItem. The first takes care of opening and closing in a nice fashion and the latter makes it easier to template the header. It is not necessary, but adds a nice touch. I will talk more about templating them in a follow up post.
In the meantime, it is noteworthy that there is a property AccordionButtonStyle that you can use to style the button more easily.

Selected and Unselected events

Subscribe to these events to know when the user has selected an AccordionItem. Alternatively, you can use the SelectionChanged event on Accordion.

Layout

Under the covers, there is a lot of layout action going on! The item needs to know how to open itself, and also needs to be told _when_ to do so. The actual opening and closing does not correspond to the IsSelected state. In other words: IsSelected will be set whenever an item is selected, which could mean the AccordionItem is still closed. Accordion will instruct AccordionItem to actually open to visualize the new IsSelected state.

Templating

The most important part of the template is:

  1           <Border x:Name="Background" 

  2 			      Padding="{TemplateBinding Padding}" 

  3 			      BorderBrush="{TemplateBinding BorderBrush}" 

  4 			      BorderThickness="{TemplateBinding BorderThickness}" 

  5 			      CornerRadius="1,1,1,1">

  6               <Grid>

  7                   <Grid.RowDefinitions>

  8                       <RowDefinition Height="Auto" x:Name="rd0"/>

  9                       <RowDefinition Height="Auto" x:Name="rd1"/>

 10                   </Grid.RowDefinitions>

 11                   <Grid.ColumnDefinitions>

 12                       <ColumnDefinition Width="Auto" x:Name="cd0"/>

 13                       <ColumnDefinition Width="Auto" x:Name="cd1"/>

 14                   </Grid.ColumnDefinitions>

 15 

 16                   <layoutPrimitivesToolkit:AccordionButton

 17 					          x:Name="ExpanderButton"

 18                     Style="{TemplateBinding AccordionButtonStyle}"

 19 					          Content="{TemplateBinding Header}"

 20 					          ContentTemplate="{TemplateBinding HeaderTemplate}"

 21 					          IsChecked="{TemplateBinding IsSelected}"

 22 					          IsTabStop="True"

 23 					          Grid.Row="0"

 24 					          Padding="0,0,0,0"

 25 					          Margin="0,0,0,0"

 26 					          FontFamily="{TemplateBinding FontFamily}"

 27 					          FontSize="{TemplateBinding FontSize}"

 28 					          FontStretch="{TemplateBinding FontStretch}"

 29 					          FontStyle="{TemplateBinding FontStyle}"

 30 					          FontWeight="{TemplateBinding FontWeight}"

 31 					          Foreground="{TemplateBinding Foreground}"

 32 					          VerticalContentAlignment="{TemplateBinding VerticalContentAlignment}" 

 33 					          HorizontalAlignment="Stretch"

 34 					          VerticalAlignment="Stretch" 

 35                     HorizontalContentAlignment="{TemplateBinding HorizontalContentAlignment}"

 36                     Background="{TemplateBinding Background}" />

 37 

 38                   <layoutPrimitivesToolkit:ExpandableContentControl

 39 					          x:Name="ExpandSite"

 40 					          Grid.Row="1"

 41 					          IsTabStop="False"

 42 					          Percentage="0"

 43 					          RevealMode="{TemplateBinding ExpandDirection}"

 44 					          Content="{TemplateBinding Content}"

 45 					          ContentTemplate="{TemplateBinding ContentTemplate}"

 46 					          Margin="0,0,0,0"

 47 					          FontFamily="{TemplateBinding FontFamily}"

 48 					          FontSize="{TemplateBinding FontSize}"

 49 					          FontStretch="{TemplateBinding FontStretch}"

 50 					          FontStyle="{TemplateBinding FontStyle}"

 51 					          FontWeight="{TemplateBinding FontWeight}"

 52 					          Foreground="{TemplateBinding Foreground}"

 53 					          HorizontalContentAlignment="Left"

 54 					          VerticalContentAlignment="Top" 

 55 					          HorizontalAlignment="Stretch"

 56 					          VerticalAlignment="Stretch"/>

 57               </Grid>

 58           </Border>

Lines 7 through 14 create a grid with 2 columns and 2 rows.
Line 16 shows the AccordionButton, which is the little arrow + header.The arrow always points to the content and is in different locations, depending on the ExpandDirection.
Line 38 is the ExpandableContentControl, which takes care of the content.

An AccordionItem has, amongst others, 4 visual states for ExpandDirection. I will show the ExpandLeft state:

  1                   <vsm:VisualState x:Name="ExpandLeft">

  2                       <Storyboard>

  3                           <ObjectAnimationUsingKeyFrames Duration="0" Storyboard.TargetName="ExpanderButton" Storyboard.TargetProperty="(Grid.ColumnSpan)">

  4                               <DiscreteObjectKeyFrame KeyTime="0" Value="1"/>

  5                           </ObjectAnimationUsingKeyFrames>

  6                           <ObjectAnimationUsingKeyFrames Duration="0" Storyboard.TargetName="ExpandSite" Storyboard.TargetProperty="(Grid.ColumnSpan)">

  7                               <DiscreteObjectKeyFrame KeyTime="0" Value="1"/>

  8                           </ObjectAnimationUsingKeyFrames>

  9                           <ObjectAnimationUsingKeyFrames Duration="0" Storyboard.TargetName="ExpanderButton" Storyboard.TargetProperty="(Grid.RowSpan)">

 10                               <DiscreteObjectKeyFrame KeyTime="0" Value="2"/>

 11                           </ObjectAnimationUsingKeyFrames>

 12                           <ObjectAnimationUsingKeyFrames Duration="0" Storyboard.TargetName="ExpandSite" Storyboard.TargetProperty="(Grid.RowSpan)">

 13                               <DiscreteObjectKeyFrame KeyTime="0" Value="2"/>

 14                           </ObjectAnimationUsingKeyFrames>

 15 

 16                           <ObjectAnimationUsingKeyFrames Duration="0" Storyboard.TargetName="ExpanderButton" Storyboard.TargetProperty="(Grid.Column)">

 17                               <DiscreteObjectKeyFrame KeyTime="0" Value="1"/>

 18                           </ObjectAnimationUsingKeyFrames>

 19                           <ObjectAnimationUsingKeyFrames Duration="0" Storyboard.TargetName="ExpandSite" Storyboard.TargetProperty="(Grid.Row)">

 20                               <DiscreteObjectKeyFrame KeyTime="0" Value="0"/>

 21                           </ObjectAnimationUsingKeyFrames>

 22                           <ObjectAnimationUsingKeyFrames Duration="0" Storyboard.TargetName="rd0" Storyboard.TargetProperty="Height">

 23                               <DiscreteObjectKeyFrame KeyTime="0" Value="*"/>

 24                           </ObjectAnimationUsingKeyFrames>

 25                           <ObjectAnimationUsingKeyFrames Duration="0" Storyboard.TargetName="cd0" Storyboard.TargetProperty="Width">

 26                               <DiscreteObjectKeyFrame KeyTime="0" Value="*"/>

 27                           </ObjectAnimationUsingKeyFrames>

 28                       </Storyboard>

 29                   </vsm:VisualState>

Everything in there is actually repositioning the AccordionButton (header) and the ExpandableContentControl (content) inside different grid cells.

In this case, you can imagine the header being in column 1 and the content taking up column 2.

You should not need to have to style an accordionItem itself that much. Most of the template is just about positioning the Header versus the Content. The only reason I see for restyling accordionItem is if you are unhappy with the defaults (easily changed) or with the position of the header and content. All the other styling would be done in either AccordionButton or ExpandableContentControl. Let me know if this is not the case for your scenario.

Accordion is a fun control with a lot of properties and options. I had great fun building it and I hope you will have great fun while using it. This post gives an overview of the control. Next parts will look into other controls that are used with Accordion.

You can see a live demo here, or go to our sample browser (SL2, SL3) to play around with the control. I have a little ‘studio’ there, that will allow you to set some options and see how the control behaves.

The Accordion shown in the picture above is build like this:

  1     <layoutToolkit:Accordion x:Name="acc" Grid.Column="0" >

  2       <layoutToolkit:AccordionItem Content="item 1" Header="A"  />

  3       <layoutToolkit:AccordionItem Content="item 2" Header="B -  long header" />

  4       <system:String>regular string item 3</system:String>

  5     </layoutToolkit:Accordion>

As you can see, three items are added. The first two are AccordionItems, allowing us to set a header and content. The last one is a String, which Accordion will wrap in an AccordionItem behind the scenes.

Accordion

Accordion can be best described as an ItemsControl that displays Expanders. The items shown are actually of type AccordionItem and can expand or collapse.
We use the paradigm of Selection, instead of Expanding/Collapsing, so from now on you will here me talk about a selected AccordionItem, which amounts to an expanded AccordionItem.

The Accordion class manages these AccordionItems and is responsible for the following:

• Easily styling the AccordionItems (ItemContainerStyle)
• Setting a default ContentTemplate and HeaderTemplate
• Setting the ExpandDirection
• Single select and multi select. Actually, Accordion allows a couple of SelectionModes that I will talk about
• Managing a SelectedItem and SelectedIndex
• Managing SelectedItems and SelectedIndices
• Scheduling when a selected item is expanded or contracted (!)

Accordion manages AccordionItems just as ListBox would be managing ListBoxItems. Let’s first look at the concepts that you know from other ItemControls and see how Accordion handles them.

ItemTemplate versus ContentTemplate and HeaderTemplate

When an item is added to an ItemsControl, Accordion will check if it is already an instance of type AccordionItem. If it is not, the item will be wrapped inside an AccordionItem.
You might expect to be able to define how your item will look with an ItemTemplate, but that does not make that much sense, given that we expect you to want to set a header and a content separately.

Instead, Accordion exposes a ContentTemplate and HeaderTemplate DP. There is some talk to drop the ContentTemplate and just use the ItemTemplate for it, let me know what your thoughts on that are.

I do make sure that both Content and Header datacontext is set appropriately, so you might do something like this:

        <layoutToolkit:Accordion>

          <layoutToolkit:Accordion.ContentTemplate>

            <DataTemplate>

              <StackPanel Orientation="Horizontal">

                <TextBlock Text="Content:" />

                <TextBlock Text="{Binding}" />

              </StackPanel>

            </DataTemplate>

          </layoutToolkit:Accordion.ContentTemplate>

          

          <layoutToolkit:Accordion.HeaderTemplate>

            <DataTemplate>

              <StackPanel Orientation="Horizontal">

                <TextBlock Text="Header:" />

                <TextBlock Text="{Binding}" />

              </StackPanel>

            </DataTemplate>

          </layoutToolkit:Accordion.HeaderTemplate>

          

          <System:String>hello</System:String>

          <System:String>world</System:String>

        </layoutToolkit:Accordion>

You would end up with an accordion that looks like:

In my opinion there are two main scenario’s to use an itemscontrol like Accordion:

1. Bind to businessobjects: use ContentTemplate and HeaderTemplate to determine what is shown
2. Set items inline: use AccordionItem directly.

Selection

An Accordion allows for the following SelectionModes: One, OneOrMore, ZeroOrOne and ZeroOrMore.

Since there can be more than 1 item selected, Accordion supplies a few properties (and events to match) to let you know what’s up:

• SelectedItem: The selected item. If Accordion allows multiple items, this property will have the last selected item
• SelectedIndex: The index of the selected item. This is necessary because you could have multiple AccordionItems based on the same item.
• SelectedItems: A collection of all the items that are selected.
• SelectedIndices: A collection of indexes.

By setting a SelectionMode, the behavior of Accordion is changed quite profoundly. When SelectionMode One or OneOrMore is chosen, Accordion will always make sure there is at least one AccordionItem selected. It does so by making it impossible to unselect an item if it is the last one selected. If no item is selected when the mode is set to One*, the first item in the list will be auto-selected.

ExpandDirection

You can specify in which direction the Accordion should open by setting an ExpandDirection (Left, Right, Up, Down). I’ll go in-depth in how you can template your AccordionItems appropriately. In the default template there is a little funky arrow that points to the content, that arrow is repositioned according to the ExpandDirection.

SelectionSequence

When the user selects an item, Accordion might have unselect another item (in the ZeroOrOne or One modes). The de-selection will happen immediate, however, Accordion gives you the option to influence when the actual animations happen. The SelectionSequence property takes values of 'CollapseBeforeExpand’ and ‘Simultaneous’.

The CollapseBeforeExpand mode will actually schedule collapse animations before expands. The effect is quite nice.

Please let us know if you are interested in different scheduling schema’s. I can for instance think of an Accordion that starts the next animation when it is halfway through the first one. Not sure if it looks good though!

The big one: Layout

Accordion will behave completely different when it has a fixed size versus no size. In the first case, the items will share all the space amongst each other that the parent has. In the latter, each item will take the space it desires.

I will revisit the layout topic more in-depth, because there are a few intricacies in how it works.

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Next parts will look at AccordionItem, ExpandableContentControl and LayoutTransformer.