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How to create a toggle image on Windows Phone
This article explains how to use visual states to animate collapsing and expanding an image on the page.
A picture is worth a thousand words but, even so, sometimes it can take too much screen real estate. There are a number of approaches to this problem: one is to display only part of the image and provide a mechanism so it can be expanded to full size.
This article shows how to create a page containing both text and an image such that the page opens with the image only partially visible - in order to draw attention to the text. The image can be expanded and collapsed when tapped by the user. This is accomplished using visual states and a nice animation.
Create the initial page
First set up the initial state of the page, create a new basic Windows Phone project and add following XAML to the ContentPanel of the MainPage.xaml:
<Grid x:Name="ContentPanel" Grid.Row="1" Margin="0">
<RowDefinition Height="Auto" />
<RowDefinition Height="*" />
<Image x:Name="Image" HorizontalAlignment="Left" VerticalAlignment="Top"
Source="/Assets/war_of_the_worlds_doomsday_final.jpg" Opacity="0.4" Height="100" Width="480" Stretch="UniformToFill" Tap="image_Tap"/>
<Image x:Name="IconExpand" Grid.Row="0" Width="40"
Source="/Assets/arrow.expand.png" HorizontalAlignment="Right" VerticalAlignment="Top" IsHitTestVisible="False" />
<RichTextBox Name="Article" Margin="12,0,12,0">
<Run FontWeight="Bold" FontSize="22" Text="The Coming of the Martians" />
<Run Text="After introductory remarks, the narrative opens in an astronomical observatory at Ottershaw where explosions are seen on the surface of the planet Mars, creating much interest in the scientific community. Later a meteor lands on Horsell Common, near the narrator's home in Woking, Surrey. He is among the first to discover that the object is an artificial cylinder that opens, disgorging Martians who are big and greyish with oily brown skin, the size, perhaps, of a bear, with two large dark-coloured eyes, and a lipless V-shaped mouth surrounded by Gorgon groups of tentacles. The narrator finds them at once vital, intense, inhuman, crippled and monstrous. They briefly emerge, have difficulty in coping with the Earth's atmosphere, and rapidly retreat into the cylinder. A human deputation (which includes the astronomer Ogilvy) approaches the cylinder with a white flag, but the Martians incinerate them and others nearby with a heat-ray before beginning to assemble their machinery. Military forces arrive that night to surround the common, including Maxim guns. The population of Woking and the surrounding villages are reassured by the presence of the military. A tense day begins, with much anticipation of military action by the narrator." />
With that in place you get a page that resembles the first screenshot above. The image is not fully visible and we've tweaked the opacity to draw less attention to it. There is also a small icon in the top right hand corner to provide a hint to the user that the image can be enlarged.
Create the open and closed states
For things like this I tend to use Blend, because it offers a visual interface to define and work with Visual States!
- Open the project in Blend and go to the States tab, click on the Add state group icon and name your new group ImageViewGroup
- Select the newly added state group and click twice on the Add state icon, name those states ClosedState and OpenState.
Also be sure to select the Default transition and click on the EasingFunction icon - this will set the actual visual animation that will be used when switching from one visual state to the other. I've selected the Cubic InOut, but be sure to try out a few that fits your taste! Next, we need to define how long this animation will take. So to the right of the EasingFunction icon, set the amount of seconds you prefer. I've chosen 0.3 seconds, but this also is something you need to test out.
Check the Visual states screenshot to verify your settings
Now select the OpenState line an be sure to notice that Blend tells you that OpenState state recording is on in the middle on the MainPage.xaml tab. In the Objects and Timeline tab, open up the ContentPanel and select the Image. When the Image is selected, change it's Height to 250 in the Properties tab on the right, also change the Opacity to 100%. Click on the IconExpand and set it's Opacity to 0%
Check the OpenState settings screenshot to verify your settings
For the ClosedState we do something similar, so select it in Blend and again open the ContentPanel. Select the Image and set it's Opacity back to the original value 40%. That's all for this state, so you can now save everything and close Blend.
Detect tap and open animation
There is only one more thing left to do and that is trigger the change from one state to the other, when the user taps the image! So open the project again in Visual Studio and open the code behind of the MainPage.xaml. In here add the following code underneath the constructor:
private bool _isOpen = false;
private void image_Tap(object sender, System.Windows.Input.GestureEventArgs e)
VisualStateManager.GoToState(this, "ClosedState", true);
_isOpen = false;
VisualStateManager.GoToState(this, "OpenState", true);
_isOpen = true;
We are using the VisualStateManager that is build in the Windows Phone SDK to go to the correct state when the user taps the image. We also need to keep track what state we are in to go to the other one.
With this all in place you get a nice visual animation when the user taps the image, to open or close it.
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A complete working demo can be downloaded here: File:ImageSelection.zip