Quite simple Windows Phone question, but couldn't find anything about it searching the web.
I want to fire an event when a user has scrolled to the end of a ListBox (originally containing 100 items), so that I can asyncronously load some more items from my API.
IntelliSense didn't show any event I thought could be useful - perhaps somebody here can show me in the right direction on how I can have this type of functionality?
Kris
Using whats given here you can detect the end of scrolling and trigger an event on the code behind which will call for more items. Once you add them to your Observable Collection which will be bounded to your listbox's itemsource. The items will appear automatically. I hope it helps :)
Related
I'm looking for some animations for my listbox. When i swipe right on a listbox item, it goes to the bottom of the listbox and ideally, all the other listitems should gracefully go up. Similarly when I swipe left, that item gets deleted, and as before, the items needs to reposition.
I have implemented the functionality on swipe right and swipe left. But it is not graceful due to the lack of animations. How do I create those? Could someone share some blogs or msdn articles on how to create them. Or just give me some intro on this. I have never done animations before.
Thank you,
The Windows Phone Toolkit has some transition effects that could help you. I assume you already know it since you implemented the swipe functionality unless you didn't use the provided gestures from it??
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
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!
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.
I created a simple application with nested ListBox and strings in it. If i scroll it really fast - there is empty spaces.Can i increase the rendering speed or
Can i slow down scrolling speed in ListBox somehow ?
Inorder to overcome the black occurrence on scrolling you need to virtualize your scroll control. For that you should inherit IList and create a Collection of your own similar to ObservableCollection in which you will have to override the default indexer depending on your caching requirement and simultaneously maintain a cache for your items. I feel this might be what you are looking for: http://blogs.msdn.com/b/ptorr/archive/2010/08/16/virtualizing-data-in-windows-phone-7-silverlight-applications.aspx
There is a sample project on that page. Try that out.
I also feel that you are facing this problem http://blog.rsuter.com/?p=258. I guess this will be solved using virtualization itself. Hope it helps
The blog Milan posted is a good source to start with. Virtualizing data works by changing the item template of the list item while scrolling. This will not work up to the expectations when there is a complex layout.
But I suggest you work more on the layout you are working on. Having too many stack panels in order to make the layout a bit generic will destroy the performance.
I saw here and in some articles that I should use GestureListener to get Tap from user then use SelectionChanged. I tried it and I like it. But I have problem with it. When my listbox moves (scrolls) and I try tap I get bad item (I get item from last tap). When I scroll and wait for stopping scroll and then tap everything is fine (I get exactly item which I tap on). Anyone else with this problem? Any solution? Thanks
As (according to your tags) you're targetting 7.1, there is no need to have to use a GestureListener to detect Tap events.
All UIElements in Silverlight 4 (which 7.1 is based on) support a built in Tap event. See http://msdn.microsoft.com/en-us/library/system.windows.uielement.tap(v=vs.95).aspx
Using a GestureListener has an unnecessary performance overhead and can cause other issues as you're discovering.
You should use a Tap event in the individual ListBoxItems or the SelectionChanged event on the ListBox not both.
If you create a new Databound Application, the code in the default project files will show an example of how to use SelectionChanged and in that instance trigger a page navigation.
In future, you may also get a better, faster answer by showing the code you are having problems with, not just describing it.
I am trying to give a ListBox drag and drop ordering functionality and I have hit a wall. I got it to work when I specify the list box items in xaml but it does not work when I bind to a list it no longer works because the items are no longer of a listboxitem type.
I found this code http://blog.dobaginski.com/josh/?p=52 that allows me to get the underlying ListBoxItem but I can't get the mouse move event to fire.
I have went through other tutorials but have not been able to find one that deals with a ListBox. Has anyone done this with a ListBox.
The events I am using are SelectedChange, MouseMove, and LeftMouseButtonUp (I think that name is right). I am not using LeftMouseButtonDown because I couldn't get it to fire.
As far as i know you cannot get at the listbox item container when using data binding. YOu could in Beta 1.
You also cannot set a mouse event handler in the style, you must use a data template, just so you know.
You will likely have to use the mouse move event from a parent element, probably the UserControl or main layout control that hosts the listbox.
State changes and animations need to be in the style though so... you still cant get at the listbox item, just the element inside it in the data template.
Oh and if doing drag and drop HitTest is now protected so that will make the Drop harder.
since today you can download the final 2.0 version of Silverlight with some add ons, check the Scott's web log
I've been trying to do the same thing in WPF,
but have only found many buggy implementations.
One person has guided me towards the blog of Beatriz Costa,
and from what I remember she's one of those rare geniouses,
so I suggest you read that as well... I know I will
Blog of Beatriz Costa