Is there a silverlight repeater control (like in ASP.NET)? - silverlight

I need to show a list of many text strings, each on a line.
I need items to be selectable, so i cant use an ItemsControl.
I only need one "column" and no sorting, so a DataGrid might be too heavyweight (???)
I need up to 1000 items, so a Listbox might be too lightweight (???)
What Silverlight control (or Toolkit control) would be best for this use?

The functional equivalent of is indeed .
If you need an ItemsControl that has Selection, use one of the classes the inherit from Selector (which coincidently itself inherits from ItemsControl):
1. ComboBox
2. ListBox
3. TreeView (Selector API)
4. AutoCompleteBox (Selector API)
All of these support the same ItemsControl API of ItemsControl.ItemTemplate=DataTemplate.

DataGrid has good performance because of virtualization:
The DataGrid boasts excellent performance with large sets of data
because it uses virtualization, unlike any other Silverlight control. That means the
DataGrid only retains in-memory objects for the data that’s currently visible, not the
entire set of data that’s loaded. This reduces the memory overhead dramatically and
allows it to practically hold thousands (or even millions) of rows. The only tradeoff is
that the DataGrid is slightly slower when scrolling, because it needs to clear the current
set of DataGridRow objects and load the information that corresponds to the new rows.

I would add the HeaderedItemsControl from the Silverlight Toolkit. Here's an article: HEADEREDCONTENTCONTROL & HEADEREDITEMSCONTROL

Related

Is a custom `RadioButtonList` based on `ListBox` necessary in WPF?

I inherited a project that uses a RadioButtonList which inherits from a ListBox. It was taken off the web (currently cannot find a link to), and contains RadioButtonList.cs (which contains six dependency properties) and RadioButtonList.xaml (which is just styles and control templates).
This control is used in over a hundred places. It causes problems because it is not a complete and professional control. Problems such as, focus issues, keyboard navigation, and so on. (See comments.)
After much research at different times over the last couple years, it seems that this control is really not necessary. All that is needed is to set the GroupName property on a group of radio-buttons. And, the only reason why a RadioButtonList control is used is to help with data-binding a list of options through the inherited ListBox.
1) Is this control really necessary? Is there a better way?
2) Is there a professional control, open-source or otherwise, that will allow me to get the benefits of data-binding without the headaches? (We use Infragistics and DevExpress, but I am not familiar with all the controls these suites offer.)
My Answers
1a) Is this control really necessary?
If you only need one list of radio buttons, then no this control is not necessary.
If your applicaton uses many lists of radio buttons, then yes this control is necessary.
If you use a list of radio buttons in different applications, then yes this control is probably necessary.
1b) Is there a better way?
I say that deriving from a ListBox, ItemsControl, or whatever then creating styles and templates is the only way to create this control; therefore, no there is no better way.
2) Is there a professional control...
Definitely, the ListBoxEdit with the RadioListBoxEditStyleSettings.
Comments Regarding Answers
All the answers indicate that creating a RadioButtonList control is not necessary. Yet, if you need more than a couple lists of radio buttons, by the time you create the styles and control templates and maybe data template, you will end up with a collection of code artifacts that can be called a radio-button-list-control. Therefore, in my opinion, a RadioButtonList is necessary.
Moreover, my understanding is a RadioButtonList was dropped in an early WPF CTP. Which I can understand, because of the limited need for such a control that can easily be created.
Comment Regarding Accepted Answer
2) Is there a professional control...
Definitely, the ListBoxEdit with the RadioListBoxEditStyleSettings.
Lastly Comment on Mike Strobel's Answer
The RadioButtonList that I have is the end-result of his answer. While I am good at creating custom-controls, I rather let third-party component makers, such as Infragistics and DevExpress, create and support a basic control like this one.
Is this control really necessary? Is there a better way?
As #lawc points out, no, it is not necessary. It may, however, be preferable, depending on what level of flexibility you desire. A reusable style is easy enough to create, but doing it "correctly" is a bit more involved than simply setting a custom ItemTemplate.
Using Styles
An ItemsControl in WPF will wrap its items in appropriate containers. Each of the selector controls in core WPF overrides the logic which determines whether an item is capable of serving as its own container, as well as the factory code which produces new item containers. A ListBox, for example, will wrap each of its items in a ListBoxItem (unless the item itself is already a ListBoxItem). The style applied to these containers can be set for the parent ItemsControl via the ItemContainerStyle property. This differs from the ItemTemplate property, which allows you to control the appearance of the item within the container. More specifically, it overrides the content template applied to the ContentPresenter within the container.
Since a RadioButton does not derive from ListBoxItem, simply setting the ItemTemplate will produce a list of RadioButton controls embedded within ListBoxItem controls, which means they will still have the same selection chrome normally associated with ListBox controls, and possibly some layout and focus oddities. This is probably not what you want.
Instead, override the ItemContainerStyle and use it to assign a custom ListBoxItem template which embeds a RadioButton. You can probably get away with not setting the GroupName property at all, which eliminates possible name collisions. Instead, just establish a two-way binding between the RadioButton.IsChecked property and the templated parent's ListBoxItem.IsSelected property.
In order to use this technique conveniently, one generally creates a Style resource (available application-wide) which can be applied to the appropriate ListBox instances, and which sets the ItemContainerStyle. Alternatively, you can make the container style available as a global resource and set that on your ListBox instances. Either way, you need to set a property.
Using a Custom Control
While WPF evangelists often recite the philosophy of preferring custom styles over custom controls, in practice this is not always convenient. You may find it more convenient to create a RadioButtonList which extends the ListBox control, and then give it a default style which automatically applies the custom style described above. This gets you out of manually assigning the list style or container style on every ListBox instance, but it's not a huge win.
But maybe you want a bit more control over the appearance of the RadioButton items. For instance, you may want to:
Adjust the margin around the "bullet" of each RadioButton item;
Adjust the vertical alignment of the bullets relative to the content;
Support both horizontal and vertical orientations;
Automatically disable the RadioButton content for items which are not selected.
Creating your own implementation, most likely derived from ListBox, allows you to add these features easily, even after you are already using your radio list across your application. This could be done with the technique above too, though it may require an attached behavior or some attached properties, in which case you end up with a somewhat fragmented design.
Third-Party Solutions
Is there a professional control, open-source or otherwise, that will allow me to get the benefits of data-binding without the headaches?
This is not an uncommon use case, and I have no doubt there are some implementations floating around. Some may be in open source frameworks, and some may be extracted from open source applications. As for third-party implementations, I do know that Actipro ships a RadioButtonList in their Shared WPF library, which is included with all of their WPF components. When last I checked, it was not available on its own. It does, however, support all of the additional features I listed above.
I can only tell you that DevExpress uses a ListBoxEdit with a RadioListBoxEditStyleSettings to represent a group of RadioButtons. Practically it is the same as your control you are using, but i think it provides better functionality and is well tested. A RadioButton is not provided by DevExpress and in my application i use the Default RadionButton-Control provided by WPF/Silverlight.
You use the RadioListBoxEdit of DevExpress as follows:
<dxe:ListBoxEdit SelectedItem={Binding CheckItem, Mode=TwoWay}>
<dxe:ListBoxEdit.StyleSettings>
<dxe:RadioListBoxEditStyleSettings />
</dxe:ListBoxEdit.StyleSettings>
</dxe:ListBoxEdit>
More information about the ListBoxEdit of DevExpress can be found here
In my opinion you don't need this control.
You can simply use .Net ListBox to achieve all your existing functionality.
Using ListBox.ItemsSource you can data bind your options collection
Specify ListBox.ItemTemplate containing the RadioButton, in this template you can data bind your view model property to RadioButton.GroupName
IMHO, a control deriving from ItemsControl would be the cleanest approach.
Then you probably would override
IsItemItsOwnContainerOverride() with return item is RadioButton;
GetContainerForItemOverride() to return a new RadioButton() for each item and
PrepareContainerForItemOverride() to set up binding of ToggleButton.IsCheckedProperty and ContentControl.ContentProperty.
While these parts are just boilerplate code, some more efforts may lie in the implementation of the keyboard behavior.

slow page trasitions due to databinding

I am making a search app in wp7. Every record's data is bound to a user control. I have introduced an infinite loading instead giving page numbers. So when the number of instances of the UserControl is increased in the screen the transition from one page to another page (like the preview or settings pages) or coming back from that page to the current page is getting slower. I cannot change the design (infinite loading concept).
What are the ways to handle this scenario? How about changing the visibility of the controls? And reference or suggestion will be highly appreciated.
Note I tagged WPF and Silverlight because the binding happens the same way in them, expected those to have dealt with scenarios like these.
EDIT Check this question, which is asked by me. Because of having UserControl's in the listbox the vertical offset is not being maintained. So I had no option other than using ItemsControl with scrollViewer around it. ItemsControl contains a list of 5 - 6 usercontrols which intern have itemsControls inside them, I thought virtualization may not happen in such cases. Am I right?
In WPF, this is done by Virtualization
Using Virtualization, only one copy (or a few copies) of the UserControl actually gets created, and switching to another user control actually just swaps out the DataContext that the control is bound to. It doesn't actually create a new UserControl.
For example, if you have an VirtualizingStackPanel with 100,000 items, and only 10 are visible at a time, it will only render about 14 items (extra items for a scroll buffer). When you scroll, the DataContext behind those 14 controls gets changed, but the actual controls themselves will never get replaced. In contrast, a regular StackPanel would actually render 100,000 items when it gets loaded, which would dramatically decrease the performance of your application.
This question about Virtualizing an ItemsControl can probably get you going in the right direction.
Take a look at this post, I believe the solution provided by Rico is what you are looking for. :)

Render UI Using BackgroundWorker

I am binding my ContentPresenter to a ViewModel that has a type-referential DataTemplate which contains an instance of a third-party control (DevExpress' GridControl). When this control is bound to a modestly sized collection (i.e. 1000 items), the control takes a noticable four or five seconds to load. So, to my question - for controls that take a while to render, can this somehow be done using a BackgroundWorker such that the UI doesn't hang? Keep in mind that I my controls reside in a DataTemplate, so any code-behind is not a desirable option.
Thanks!
Unfortunately creating the actual UI (in your case, creating, positioning, and rendering controls) must be done on the UI thread due to compatibility constraints - all UI components must be created by the UI thread, and they can only be altered by the UI thread as well.
One thing I would recommend looking at is virtualization - if you're not displaying the datatemplate of 1000 items, why create all of the controls? You can find examples around like Virtualized WPF Canvas, or using the built-in VirtualizingStackPanel. Using these techniques will be more work than simply binding a viewmodel to an item with a datatemplate, but will give much, much better performance.
If the actual issue is just that the DevExpress GridControl is super slow with 1000 items, then you'll want to see if you can set it to a virtual mode, or switch to a different 3rd party control.
Your ItemsControl should contain a VirtualizingStackPanel which ListView and ListBox do, but make sure that virtualisation is switched on and you use container recylcling
<ItemsControl
VirtualizingStackPanel.IsVirtualizing="true"
VirtualizingStackPanel.VirtualizationMode="Recycling">

Using the DragDropTarget with a traditional Grid

Silverlight 4 now provides controls to handle Drag and Drop actions. All the Target Controls seem to inherit from DragDropTarget Like so
public class MyControlDragDropTarget : DragDropTarget<TItemsControlType,TItemsContainerType>
.
.
.
A number of controls have pre-defined DragDropTargets including the DataGrid, ListBox, Panels
Which is all very well, but I want to drag and drop from a grid not a datagrid, and there is no pre-defined one for a normal grid.
I actually want to drag a given row from the grid, but without a Container Type for a Grid I cannot work out how to define a DragDropTarget control for the grid.
Only way I can think is instead of using a grid - I use a listbox (for which there is a DragDropTarget) and then place a StackPanel or Grid in each row (which has one row of 'n' columns)
Anyone got any ideas
Ta in advance
A "normal grid" is simply another form of panel, there is no need for specialised DragDropTarget for the Grid, the existing PanelDragDropTarget is sufficient for a "normal grid".
Its important grasp that the Grid does not support the concept of "rows containing cells containing UI elements". The rows and columns of a Grid are entirely equal and are defined purely for layout purposes. UIElement children of a Grid are laid out entirely independently of each other, there is no concept of a set of values belonging to either a column or a row that can be moved or operated on as a group (like picking up a row and dragging it).
Sounds like you have already got an answer for yourself, use the ListBox instead.
BTW, DragDropTarget isn't provided by Silverlight 4 but rather the Silverlight Toolkit. This is an important distinction because the current quality band assigned to DragDropTarget is "Experimental". You need to think carefully about this if you want to use such code in some production release of your own.

What is the difference between a stackpanel and a virtualizingstackpanel in WPF?

What is the difference between a stackpanel and a virtualizingstackpanel in WPF?
A VirtualizingStackPanel can offer performance benefits when working with very large collections. It does so by only rendering and processing a subset of the data which is visible to the user vs. processing the entire list of data. By creating only UI elements for the visible items, this can greatly reduce the amount of work it has to do.
This is really only handy though if
You are data binding non-UI elements or elements for which UI must be created in the particular panel
You are data binding a lot of data
A StackPanel on the other hand, will up front create the controls for all elements contained within the StackPanel.
The VirtualizingStackPanel MSDN page has a decent discussion: http://msdn.microsoft.com/en-us/library/system.windows.controls.virtualizingstackpanel.aspx
This is to do with the visual tree. The virtualizingstackpanel works with things like list boxes etc to reduce the size of the visual tree by only displaying visible items - this is useful where databinding is taking place.

Resources