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.
Related
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. :)
I'm building a WPF application to visualize a load of items (a few thousand). For this i'm using an ItemsControl of which the ItemsSource is set to a BindingList.
I've noticed that it takes some time to initialize the screen... The main bottleneck is the creation of TextBlock elements (the data template of the items contains 4 TextBlock elements). Once the screen is initialized (when all WPF elements are created), rendering is quite OK.
I've implemented zooming and panning, so i was thinking about making the appearance of the items dependent on the zoom level and the center point (a bit like Google Maps: data is only visualized for regions that are into the view).
How can this be done? Is there any way in WPF to ask the item or item container if it is currently clipped?
You can make your list virtualized. This way only the items that are visible will have UI controls created for them.
Check the ListView documentation, or this link may help:
http://www.codeproject.com/KB/WPF/WpfDataVirtualization.aspx
Jogy
I have the following components in a WPF application:
(1) Window
(2) ContentPresenter in the Window that is bound to a property in the underlying ViewModel. This Property references another ViewModel.
(3) A DataTemplate for the ViewModel that will be bound to the ContentPresenter referenced above. This data template instantiates a third-party grid that displays some data.
Whenever the ContentPresenter renders the data from the DataTemplate, it takes approximately three to four seconds for the UI to render. This causes the UI to hang for the duration of the time that it takes to render the content. Since I have little to no control over how the third-party control renders itself - my question involves whether or not it is possible to render content in a way that the UI will not hang.
Please advise.
Thanks.
Chris
How many rows is the grid displaying? And how many of those rows are visible on screen?
I'm asking because it's possible that you've got a UI layout that defeats virtualization. Usually, controls that show a scrollable list of data will perform virtualization. (The built-in ListBox does this, and any 3rd party grid of tolerable quality should do the same.) This is critical for performance, because it means your UI only needs to instantiate those items that are actually visible, rather than everything in your list.
But it's relatively easy to defeat this virtualization by accident. One way is to wrap the list or grid control in a ScrollViewer. You need virtualizing controls to be able to manage their own scrolling for virtualization to work, so the scrolling needs to happen on the inside. Wrapping a control in a ScrollViewer prevents it from doing its own scrolling. Another way it can go wrong is if you plug in a different ItemsPanel. A third possibility is that your list/grid control actually needs to be told to use virtualization.
But if you're using a control that simply takes a long time to render just the stuff you need to show on screen, then there's not much you can do - you'd need to contact the control vendor, or consider using a different vendor...
Seen various examples of WPF applications I've seen the use of the Grid control for almost anything, even simplest things with only 1 column or row.
Also, the WPF templates start with an empty grid.
For me, using StackPanel or DockPanel is less verbose and are better for maintenance (think adding a row later and having to add +1 to all the other rows)
Why is Grid better or what I am missing?
Two words: Star sizing. The Grid makes it possible to size content to the space that contains it without explicitly providing a size for the container. The panel controls don't.
I think part of the reason for Grid being the default element is that it's (slightly) more designer-friendly.
With a Grid, there is no restriction on having multiple elements within a single Grid "cell", which allows a designer with free placement to have the same flexibility as a Canvas, but still have the automatic layout capabilities that Grid (and the other nicer layout controls like StackPanel and DockPanel) contains.
not missing anything. I have quite a lot of grids in my application(s), but not necessarily as top level element and definitely not to the extend you describe.
Could be many people just dont realize that they can remove the initial grid, and instead they put their own control into the grid.
I have found that for more elaborate windows, it is easier to break it down into functional areas that are fairly independent (movement and size wise) of the others. Grids allow those areas to coexist in a single panel, and allow them to be positioned without regard for where other controls are (to some extent).
For instance in a project I am working on right now, I have a window that is going to be a shipping manager. I want three list views (Shipments, Packages, Items) I have a grid control with two columns; one with the Packages list and a grid splitter, the other with a nested grid with the other two lists and a grid splitter.
i have seen many designers break their window down into areas like this, and doing it with anything other than a grid just doesn't work since there are no discreet "cells" that items indirectly live in. Quite a few program windows take this design and so I guess when they had a meeting and asked what should be the default container panel, grid was the choice based on that fact.
Cory
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