Implementing a "fisheye" view with a ListBox

Question

I am new to Windows Phone Programming. In my application, I Have a listbox which lists the phone contacts. Currently it is listed as a regular list with equal size for list items in the UI.I am looking to modify the front end like this :

I dont want to have different sizes /back ground color for each list items rather a fixed UI and let the lists scroll through it and the list item in the view, at any time, should be displayed as in the picture.

I dont expect any codes as answers but any examples are welcome too, just want to know using what feature this kind of functionality is possible so that i can do my reading!

Thanks, Deepak

Answer 1

So Finally I did manage to find a way to do it. First approach was as @Murkaeus suggested, Using UserControl and ManipulationDelta event handler. However for some reason the manipulationDelta event was triggered only for 2 finger gestures (Zoom, Pinch..etc), I have no clue why. And after some trying I had to give up on this.

The next approach was using Listbox itself. The source of the Listbox was set as the List( of Models objects) that I create after reading the contact information from phone. The height and color of the listbox item was bound to a property in my model named "scaleLevel" and was accordingly converted by implementing IValueConvertors to give predefined color and height values for different scale levels.

I created an attached property for the scrollviewer vertical offset like mentioned [here] (http://www.scottlogic.co.uk/blog/colin/2010/07/exposing-and-binding-to-a-silverlight-scrollviewer%E2%80%99s-scrollbars/)! This event is triggered on change of the vertical offset and every time there is a scroll, I find out which listbox item to be enlarged and which reduced based current vertical offset.

Once I have this information, I change the property ("scaleLevel") of the affected items in the List (of Model) (which is bound to listbox height and color). This change is updated in UI using the INotifyPropertyChanged Event.

I have no idea if this the best way of doing it , but it works well and there is no considerable in updating the UI despite the processing involved.

I would like to hear your opinion about the implementation and any other solution which you feel will work better.

Answer 2

It would be difficult to modify an existing control (ListBox for example) to act like this, so your best bet would probably be an ItemsControl with its RenderTransform set as a TranslateTransform.

If you place a Rectangle (with Fill="Transparent") over the ItemsControl, you can attach handlers to the ManipulationStarted, ManipulationDelta, and ManipulationCompleted events to control the "scrolling" by setting the TranslateTransform's Y offset.

To resize the items in the list there are two options: a custom panel or manual setting.

Custom Panel

You could create a custom Panel implementation that will appropriately resize its Children based on a property you would create to represent the scroll position. Set the ItemsControl to use your panel, and either through binding or attaching a handler to the panel's Loaded event and keeping a pointer to the panel, update the aforementioned property from inside the ManipulationDelta handler.

Manual Setting

From inside of the ManipulationDelta handler, you can also calculate the various heights of the boxes and use MyItemsControl.ItemContainerGenerator.ContainerFromIndex to get the visual for each item and set its height.

I would suggest putting this all inside of a custom UserControl.

You may have issues with clipping using the TranslateTransform but hopefully this will get you started. Unfortunately, this looks like a rather difficult control to try making as your first windows phone project!