I use a ListView to show a list of errors as they occur in my application. It behaves and looks exactly like the Error List in Visual Studio. I want to add auto-scrolling when the last error item is selected (like how Visual Studio's Log Window auto-scrolls when you place the caret at the end).
The list of errors is in an ObservableCollection, which is passed to the ListView.ItemsSource like this:
public ObservableCollection<ErrorListItem> Items;
...
MyListView.ItemsSource = _Items;
I tried performing the auto-scroll in the _Items_CollectionChanged event handler, but because this is the event on the ItemsSource and not on the actual ListViewItems, it's a pain to figure out if the last item is selected, select the new row, etc. It's especially hard since it seems the ListViewItems are not created instantly. I managed to make it auto-scroll by delaying the call to set the last item selected like this:
void _Items_CollectionChanged(object sender, NotifyCollectionChangedEventArgs e)
{
// determine the last item to select from 'e'
...
_ItemPendingToBeScrolled = newItemToSelect;
ListView.SelectedItem = newItemToSelect;
Dispatcher.BeginInvoke(DispatcherPriority.Background,
(ThreadStart)delegate
{
if (_ItemPendingToBeScrolled != null)
{
ListView.ScrollIntoView(_ItemPendingToBeScrolled);
ItemPendingToBeScrolled = null;
}
})
}
But that's obviously not the right way to do it. Also, I want things to keep working if the list is filtered (not checking the last item in my source, but the last ListViewItem in the ListView).
Is there a way to listen to events when a ListViewItem gets added to the ListView following an addition to the bound collection? That would be the ideal event to capture in order to properly do my auto-scrolling. Or is there another technique I could use?
I have a lot of issues with listboxes/listviews and their scrolling, however, you mentioned hooking to the listview's changed event, is it because you can't listen to the observable collection's CollectionChanged event? ObservableCollection is way more stable than List controls, and you'll get the same notifications.
You can also bubble these events up if it's not working in the UI and you don't have access, this way you treat your scrolling in the UI without having access to the actual collection, just keep a reference to the Selected Item in your custom EventArgs class
Related
I have a ListView (on the 'master' side) whose selection drives a ContentControl's Content property (on the 'detail' side). The ContentControl's visual tree comes from either of two DataTemplate resources that use DataType to choose which detail view to render based on what is selected in the ListView.
That part works fine.
The part I'm struggling with is that there is a particular control inside (one of) the templates that I need to obtain a reference to whenever it changes (e.g. the template selected changes or the ListView selection changes such that the instance of the control is recreated.)
In my ListView.SelectionChanged event handler, I find the ContentControl has not yet been updated with its new visual tree, so initially it's empty on the first selection, and for subsequent selections its visual tree matches the old selection instead of the new one.
I've tried delaying my code by scheduling on the Dispatcher with a priority as low as DispatcherPriority.Loaded, which works for the first selection but on subsequent selections my code still runs before the visual tree is updated.
Is there a better event I should be hooking to run whenever the ContentControl's visual tree is changed to reflect a changed data-bound value to its Content property?
Extra info: the reason I need to reach into the expanded DataTemplate is that I need to effectively set my view model's IList SelectedItems property to a DataGrid control's SelectedItems property. Since DataGrid.SelectedItems is not a dependency property, I have to do this manually in code.
The fix required a combination of techniques. For the first selection that populates the visual tree, I needed to handle ContentControl.OnApplyTemplate() which is only a virtual method rather than an event. I derived from it and exposed it as an event:
public class ContentControlWithEvents : ContentControl
{
public event EventHandler? TemplateApplied;
public override void OnApplyTemplate()
{
base.OnApplyTemplate();
this.TemplateApplied?.Invoke(this, EventArgs.Empty);
}
}
In the XAML I used the above class rather than ContentControl:
<local:ContentControlWithEvents
Content="{Binding SelectedAccount}"
x:Name="BankingSelectedAccountPresenter"
TemplateApplied="BankingSelectedAccountPresenter_TemplateApplied" />
Then I handle the event like this:
void BankingSelectedAccountPresenter_TemplateApplied(object sender, EventArgs e) => this.UpdateSelectedTransactions();
private void UpdateSelectedTransactions()
{
if (this.MyListView.SelectedItem?.GetType() is Type type)
{
DataTemplateKey key = new(type);
var accountTemplate = (DataTemplate?)this.FindResource(key);
Assumes.NotNull(accountTemplate);
if (VisualTreeHelper.GetChildrenCount(this.BankingSelectedAccountPresenter) > 0)
{
ContentPresenter? presenter = VisualTreeHelper.GetChild(this.BankingSelectedAccountPresenter, 0) as ContentPresenter;
Assumes.NotNull(presenter);
presenter.ApplyTemplate();
var transactionDataGrid = (DataGrid?)accountTemplate.FindName("TransactionDataGrid", presenter);
this.ViewModel.Document.SelectedTransactions = transactionDataGrid?.SelectedItems;
}
}
}
Note the GetChildrenCount check that avoids an exception thrown from GetChild later if there are no children yet. We'll need that for later.
The TemplateApplied event is raised only once -- when the ContentControl is first given its ContentPresenter child. We still the UpdateSelectedTransactions method to run when the ListView in the 'master' part of the view changes selection:
void BankingPanelAccountList_SelectionChanged(object sender, SelectionChangedEventArgs e) => this.UpdateSelectedTransactions();
On initial startup, SelectionChanged is raised first, and we skip this one with the GetChildrenCount check. Then TemplateApplied is raised and we use the current selection to find the right template and search for the control we need. Later when the selection changes, the first event is raised again and re-triggers our logic.
The last trick is we must call ContentPresenter.ApplyTemplate() to force the template selection to be updated before we search for the child control. Without that, this code may still run before the template is updated based on the type of item selected in the ListView.
One of those 'Why is this so hard?" questions.
I have a ListBox (containing details of share portfolios). The listbox item uses a grid to display attributes of the portfolio. Source is a list of portfolios in the View Model.
ListBox is multiselect - when selection changes, a list of the constituents of the selected portfolios is re-populated.
What I want to do is put a button (or menu or whatever) on the listboxitem to display a list of possible actions (Trade, Unitise, Delete etc).
When an action is selected I need to execute the action against the appropriate portfolio. Ideally I want the actions to be available for both selected and unselected items.
I can handle the event, but how do I detect which item (portfolio) the user selected? I've looked at GotFocus() but it doesn't seem to fire.
In other words if a control in a Listboxitem, fires an event, how does the event 'know' which ListBoxItem raised it?
For me, the solution here, seen as you mentioned MVVM, would be to have the ListBox populated by a collection of ViewModels, e.g., something like ObservableCollection<PortfolioViewModel>.
It would then just be a case of binding the Command property of the Button to an ICommand on the ViewModel that executes whatever work you need doing.
I can handle the event, but how do I detect which item (portfolio) the user selected? I've looked at GotFocus() but it doesn't seem to fire.
You could cast the DataContext of the clicked Button to the corresponding object in te ListBox, e.g.:
private void DeleteButton_Clicked(object sender, RoutedEventArgs e)
{
Button deleteButton = sender as Button;
var portfolio = deleteButton.DataContext as Portfolio; //or whatever your type is called
//access any members of the portfolio...
}
I have two listviews. One of left handside and another on right hand side. I have two buttons to add and remove items from the two listviews.
LHSListview is bound to List and RHSListview is bound to List. Column class has two variables 'order' and 'Id'.
when I click on the add button all the selected items from LHSListview must move to RHSListview. And vice versa when clicked on remove button.
This is what I am trying to do on the click of add button
var list1 = new ArrayList(lstAllFields.SelectedItems);
foreach (var item in list1)
{
lstAllFields.Items.Remove(item);
SelectedFields.Items.Add(item);
}
But this throws an error on lstAllFields.Items.Remove(item); this line saying "Operation is not valid while ItemsSource is in use. Access and modify elements with ItemsControl.ItemsSource instead."
You mentioned you're using MVVM, so you probably know that you shouldn't be changing the items from the ListViews inside the view. What you should do is modify the collection you are bound to in the ViewModel.
Problem is it's kind of tricky to get the multiple selections in MVVM, because the SelectedItems property isn't a Dependency Property.
There are 2 ways to achieve what you're after, both support MVVM:
The shorter and easier way is to listen to the Button_Click in the View's CodeBehind, create a new list of the selected items and pass it to the VM to do the logic of adding and removing items.
So a short version would look like this:
Code Behind:
private void MyButton_OnClick(object sender, RoutedEventArgs e)
{
List<MyObject> mySelectedItems = new List<MyObject>();
foreach (MyObject item in listview1.SelectedItems)
{
mySelectedItems.Add(item);
}
(this.DataContext as MainVM).MoveMethod(mySelectedItems);
}
View Model (in my class I called it MainVM)
public void MoveMethod(List<MyObject> selected)
{
foreach (var item in selected)
{
List1.Remove(item);
List2.Add(item);
}
}
That's it. Just remember, the List1 and List2 (which are the ItemSource's that ListView1 and ListView2 bind to, must be ObservableCollection to see the update in the UI.
I promised a longer option too, for that see the great 3-part blog post on the subject:
MVVM and Multiple Selection – Part I
MVVM and Multiple Selection – Part II
MVVM and Multiple Selection – Part III
Whenever I change the ItemsSource (or it fires a collection reset), WPF doesn't reset the scrollbar position of ListView/DataGrid to the top. This is no big deal if there is a nice way of doing this manually, but it seems there isn't.
Currently I do:
ScrollViewer.ScrollToTop();
ScrollViewer.UpdateLayout();
Grid.ItemsSource = Data;
Which is causing some flicker because of UpdateLayout repainting the control first.
The other way is to do:
Grid.ItemsSource = Data;
ScrollViewer.ScrollToTop();
This doesn't seem to cause any flicker, but because the scroll position is changed AFTER ItemsSource is set, it causes WPF to first iterate over the wrong items in the ItemsSource, before it gets the right items (with offset 0). Because the collection is virtualized this causes needless SQL queries for items that will never be displayed.
Is there another way of doing this which doesn't flicker or retrieves the wrong items first?
Just attached this event on the control that will hold the collection:
Assuming that it is a listbox:
lstItems.SourceUpdated += new EventHandler<DataTransferEventArgs>(lstItems_SourceUpdated);
Then you will have a event that looks like this.
void lstItems_SourceUpdated(object sender, DataTransferEventArgs e)
{
ScrollViewerName.ScrollToTop();
}
I'm using a DataGrid in my silverlight application to display some data that's refreshed on a timer. My problem is that when this happens the vertical scrollbar in the grid resets to the top, whereas I want it to stay in the same position. Does anyone know how I can make this happen?
I've tried overriding the ItemsSource property on the grid to store the vertical scroll position and then reset it, but this only affects the scrollbar and doesn't force the correct rows to be displayed. Is there a way to force this behaviour?
Here is a similar question about Setting the scroll bar position on a ListBox
After rebinding Silverlight Listbox control how do you get it listbox to scroll to back to the top?
Since the DataGrid also supports a ScrollIntoView method, you should be able to use a similar technique such as
theDataGrid.ItemsSource = data;
theDataGrid.UpdateLayout();
theDataGrid.ScrollIntoView(theDataGrid.SelectedItem, theDataGrid.Columns[0]);
I couldn't find a decent answer last time I looked. I wanted to keep the current element selected in the grid but that wouldn't work on an ICollectionView refresh (I use MVVM and get automatic updates from the server).
ScrollIntoView() was not an option for me because the currently selected item may NOT be in view. Having the CurrentChanged event firing out of control was also quite a bother.
In the end, I used the Infragistics grid and it does just that out of the box. Problem solved for me.
You may have a look at the DevExpress free grid. I think it had the same nice behaviour (I tested it but I can't remember the outcome).
You could try setting the SelectedItem thro the UI thread, so that the UI can refresh itself,
like so
private void Button_Click(object sender, RoutedEventArgs e)
{
Person p = new Person() { Name="sss",Age=11}; //datagird's itemsSource is Collection<person>
people.Add(p);
dg.SelectedItem = p; //dg is my datagrid name
Dispatcher.BeginInvoke(() => { dg.SelectedItem = p; });
}
Im assuming that new rows are loaded thro the ViewModel, so thats why it makes sense to place the BeginInvoke there. Since the ViewModel operations run on a different thread, and just setting the SelectedItem on its own might not work, this has worked for someone else
I've also had issues with this. I solved it by remembering the item I want to scroll to, then re-binding the DataGrid. I handle the LayoutUpdated event in order to implement the desired functionality:
void MyDataGrid_LayoutUpdated(object sender, EventArgs e)
{
// Reference the data item in the list you want to scroll to.
object dataItem = yourDataItem;
// Make sure the item is not null and didn't already scroll to the item.
if (dataItem != null && this.dataItemScrolledTo != dataItem)
{
// Remember the item scrolled to.
this.dataItemScrolledTo = dataItem;
// Scroll datagrid to the desired item.
MyDataGrid.ScrollIntoView(dataItem, MyDataGrid.Columns[0]);
}
}
I've modified CodeMaster's solution so that you don't need a class level variable. Put this code in the method that updates the ItemsSource. It will dynamically create the eventhandler, attach it, then detach it.
EventHandler MyDataGrid_LayoutUpdated = null;
MyDataGrid_LayoutUpdated = (s, e) =>
{
MyDataGrid.ScrollIntoView(dataItem, MyDataGrid.Columns[0]);
MyDataGrid.LayoutUpdated -= MyDataGrid_LayoutUpdated;
};
MyDataGrid.LayoutUpdated += MyDataGrid_LayoutUpdated;