We are seeing some strange behavior surrounding the SelectedItem property in our DataGrid. Some background information:
The DataGrid displays the result of a query to our database.
There is a button that allows the user to manually refresh the results in the DataGrid. There is an auto-refresh mechanism whereby the results will automatically refresh every 30 seconds.
What we are seeing is the SelectedItem property will always become index 0 of the ItemsSource for the Datagrid when the auto-refresh occurs. But we want the currently selected row to remain the selected row after the refresh. However, if the user manually clicks refresh, the selected row remains the same after the refresh which is strange because the same code is running for the refresh logic. And yes, we have code that remembers the currently selected item which then gets set again after the refresh has been completed.
Here is some of the relevant code:
<UserControl.Resources>
<CollectionViewSource Source="{Binding DataGridResults}" x:Key="ReferralItemsSource"/>
</UserControl.Resources>
<customControls:CustomDataGrid x:Name="GridControl"
ItemsSource="{Binding Source={StaticResource ReferralItemsSource}}"
SelectedItem="{Binding DataContext.SelectedReferral, RelativeSource={RelativeSource AncestorType={x:Type UserControl}}}"
IsReadOnly="False"
IsSynchronizedWithCurrentItem="True"
SelectionMode="Single">
private async void RefreshWorklist(bool invokedByAutoRefresh = false)
{
try
{
if (Initialising || ShowSpinner || IsProcessing || ShowRefreshSpinner || IsCurrentWorklistDeleted || !_sessionData.IsActive()) return;
IsProcessing = true;
RefreshWorklistCommand.RaiseCanExecuteChanged();
if (CurrentWorklistId != null)
{
var selectedReferralId = SelectedReferral.pk_Referral_ID;
if (invokedByAutoRefresh)
{
// Refresh has been invoked by _timer, so show spinner on the results page only
ShowRefreshSpinner = true;
}
else
{
// User has manually clicked refresh button so show app wide spinner
ShowSpinner = true;
if (_timer != null)
{
SetupWorklistRefreshTimer(); // Setup _timer again so that it will refresh again at an appropriate time
}
}
Referrals = await _referralRepository.GetReferralsFromWorklistAsync(CurrentWorklistId.Value, invokedByAutoRefresh);
if (Filters.Count > 0)
{
var listOfReferralPks = ReferralFiltering.GetFilteredResults(Referrals, Filters.Where(f => f.HasBeenApplied).ToList());
var filteredResults = Referrals.Where(r => listOfReferralPks.Contains(r.pk_Referral_ID)).ToList();
DataGridResults = MapReferralLookupItemsToReferralLookupItemViewModels(filteredResults);
}
else
{
DataGridResults = MapReferralLookupItemsToReferralLookupItemViewModels(Referrals);
}
SelectedReferral = DataGridResults.FirstOrDefault(r => r.pk_Referral_ID == selectedReferralId);
}
}
catch (Exception e)
{
_errorHandler.DisplayError(e);
}
}
As explained earlier, RefreshWorklist() is called by the manual refresh invoked through a Command:
private void Execute_RefreshWorklist()
{
RefreshWorklist();
}
Or automatically through the use of a Timer:
private void SetupWorklistRefreshTimer()
{
_timer?.Dispose();
var refreshInterval = _userSettingsRepository.GetIntegerSystemSetting("ReferralsWorklistRefreshInterval");
if (refreshInterval <= 0) return; // If this is 0 or below then the refresh should be disabled
if (refreshInterval < 10) // If it is less than 10 then set it to 10 to avoid too many MT calls
{
refreshInterval = 10;
}
var timeUntilFirstTick = refreshInterval * 1000;
_timer = new Timer((s) => RefreshWorklist(true), null, timeUntilFirstTick, refreshInterval * 1000);
}
And finally the SelectedItem property view model binding property:
public ReferralLookupItemViewModel SelectedReferral
{
get { return _selectedReferral; }
set
{
if (_selectedReferral != value)
{
_selectedReferral = value;
OnPropertyChanged();
}
}
}
Does anybody have any idea as to why this behavior is occurring? Is it something to do with the Timer? I appreciate this is not a simple question so please ask away for more information.
You need to assign properties in Binding with the UI on the UI thread.
Replace your Timer with a DispatcherTimer or use Dispatcher.Invoke or Dispatcher.BeginInvoke inside the existing Timer callback when calling RefreshWorklist.
By pressing the Button you are already on the UI thread, but Timer has its own thread that is different from the UI thread.
DispatcherTimer callback are called on the UI thread instead https://learn.microsoft.com/en-us/dotnet/api/system.windows.threading.dispatchertimer?view=netframework-4.0
Related
I am not quite sure if I am asking the right question. I assume other people have had this issue.
I built my own Blazor Grid component. I am using an bound to a property.
I have a function to load my grid. I changed my bound property to a full getter,setter. In the setter, I call my function to load the grid. This works fast and easy in pretty much all instances. But, I have one grid that when binding it will take a few extra seconds to complete.
The problem: I can't seem to figure out how to get my waiting spinner component to show when loading my grid.
Example Blazor Markup:
#if (dataGrid == null)
{
<hr />
<BitcoSpinner></BitcoSpinner>
}
else
{
<BitcoGrid TheGrid="dataGrid"></BitcoGrid>
}
Here is my property and GridLoading:
private string selectedGroup1 = "";
public string selectedGroup
{
get => selectedGroup1;
set
{
selectedGroup1 = value;
LoadGrid();
}
}
private void LoadGrid()
{
dataGrid = null;
PT_Grid_Admin ptGrid = new PT_Grid_Admin(permitTraxLibrary, gridParams);
dataGrid = ptGrid.ADMIN_FeeList(feeList.Fee_Key, selectedGroup);
}
You should define LoadGrid method asynchronously. Therefore, at the beginning of the program, when the data grid value is set, your spinner will be displayed until the data grid value is not received. Then, after receiving the data grid value, the else part of the condition will be executed and its value will be displayed to the user.
It may not take much time to receive information from the DB in local mode, so the following code can be used to simulate the delay:
System.Threading.Thread.Sleep(5000);
In general, I think that if your code changes like this, you can see the spinner.
private string selectedGroup1 = "";
public string selectedGroup
{
get => selectedGroup1;
set
{
selectedGroup1 = value;
LoadGrid();
}
}
private async Task LoadGrid()
{
dataGrid = null;
System.Threading.Thread.Sleep(5000);
.
.
}
Of course, it is better to load the datagrid in OnInitializedAsync method. For more info you can refer to this link.
I have a combobox with a custom enum (just true/false). I have a function that checks conditions if the SelectedValue changes from false to true and if the conditions are wrong it changes the combobox SelectedValue back to false. This changes the SelectedValue to false if you check it in code, but when you look at the UI it's still on true.
Here's the xaml for the combobox:
<ComboBox x:Name="comboEnabled1" Width="80" Height="26"
ItemsSource="{Binding Path=TrueFalseChoices}"
SelectedValue="{Binding Path=Enable1, Mode=TwoWay}"/>
Here's the viewmodel
private TrueFalse _enable1 = TrueFalse.False;
public TrueFalse Enable1
{
get { return _enable1; }
set
{
if (_enable1 != value)
{
_enable1 = value;
base.OnPropertyChanged("Enable1");
OnEnableChanged(EventArgs.Empty);
}
}
}
And here's the function that I'm using to check the conditions
public void HandleEnable(object sender, EventArgs e)
{
if(Enable1 == TrueFalse.True)
{
if(!connected)
{
HandleMessage("Can't enable, not connected");
Enable1 = TrueFalse.False;
}
else if (!_main.CBCheck(_main.cbReason))
{
Enable1 = TrueFalse.False;
}
}
Console.WriteLine("Enabled {0}", Enable1);
}
Was thinking I'm changing the value too rapidly, but the last Console.Writeline produces the right outcome each time.
Any help appreciated!
Edit: Calling Handleenable here:
protected void OnEnableChanged(EventArgs e)
{
EventHandler handler = EnableChanged;
if (handler != null)
handler(this, e);
}
And in the ViewModel funct:
EnableChanged += HandleEnable;
Changing the Enable1 in any other place worked as it should have, only having issues in HandleEnable function.Also tried changing other comboboxes in the HandleEnable function and that worked as it should have.
I would recommend actually disabling the ComboBox if the requirements are not met.
But if you insist on reverting Enable1 back to False if conditions are not met, you should push the notification properly through the dispatcher.
set
{
var effectiveValue = condition ? value : TrueFalse.False;
if (effectiveValue == TrueFalse.False && value == TrueFalse.True)
System.Windows.Threading.Dispatcher.CurrentDispatcher.BeginInvoke(
new Action(() => base.OnPropertyChanged("Enable1"), null));
//your regular set-code follows here
}
It happens because WPF is already responding to that event, and therefore ignoring the subsequent calls until it's done. So you immediately queue another pass as soon as the current one is finished.
But I would still recommend disabling the ComboBox when it is effectively disabled. Accessing the dispatcher from a viewmodel does not smell good no matter how you look at it.
UPD: You can also solve that with {Binding Enable1, Delay=10} if your framework is 4.5.1+.
I have a ListView with a ItemSource data binding and a SelectedItem data binding.
The ListView is populated with a new ItemSource every time I press the Next or Previous button.
The SelectedItem is updated accordingly, the items in the ItemSource have the Selected state, so it can be remembered when the user navigates back and forth.
While debugging, everything seems to work perfectly. The VM updates the controls as expected, and I can also see that the ListView has the correct selected value when I navigate with the next and previous buttons.
The problem is, that regardless of the fact that the ListView has a correct SelectedItem, the ListView does not visualize the SelectedItem as highlighted.
XAML:
<ListView
x:Name="_matchingTvShowsFromOnlineDatabaseListView"
Grid.Row="0"
Grid.Column="0"
Grid.RowSpan="3"
ItemsSource="{Binding AvailableMatchingTvShows}"
SelectedItem="{Binding AcceptedMatchingTvShow, Mode=TwoWay}">
<ListView.ItemTemplate>
<DataTemplate>
<TextBlock Text="{Binding Name}"/>
</DataTemplate>
</ListView.ItemTemplate>
</ListView>
Behaviour in ViewModel responsible for repopulating the ItemSource and the SelectedItem:
private void UpdateForCurrentVisibleTvShow()
{
var selectedTvShow = FoundTvShows[CurrentTvShow];
// Update the available matches
var availableMatchingTvShows = new ObservableCollection<IWebApiTvShow>();
if (AvailableTvShowMatches[selectedTvShow] != null)
{
foreach (var webApiTvShow in AvailableTvShowMatches[selectedTvShow])
{
availableMatchingTvShows.Add(webApiTvShow);
}
}
AvailableMatchingTvShows = availableMatchingTvShows;
// Update the selected item
AcceptedMatchingTvShow = availableMatchingTvShows.FirstOrDefault(webApiTvShow => webApiTvShow.Accepted);
// Update the progress text
CurrentTvShowInfoText = string.Format(
"TV Show: {0} ({1} of {2} TV Shows)",
FoundTvShows[CurrentTvShow],
CurrentTvShow + 1,
FoundTvShows.Count);
// Update the AcceptedMatchingTvShow selection in the listview
OnPropertyChanged("AcceptedMatchingTvShow");
}
The implementation of AcceptedMatchingTvShow:
public IWebApiTvShow AcceptedMatchingTvShow
{
get
{
IWebApiTvShow acceptedTvShow = null;
if (FoundTvShows.Count > 0)
{
var tvShowName = FoundTvShows[CurrentTvShow];
acceptedTvShow = AvailableTvShowMatches[tvShowName].FirstOrDefault(webApiTvShow => webApiTvShow.Accepted);
}
return acceptedTvShow;
}
set
{
if (value != null)
{
var tvShowName = FoundTvShows[CurrentTvShow];
var currentlyAcceptedTvShow =
AvailableTvShowMatches[tvShowName].FirstOrDefault(webApiTvShow => webApiTvShow.Accepted);
if (currentlyAcceptedTvShow != null)
{
currentlyAcceptedTvShow.Accepted = false;
}
value.Accepted = true;
}
OnPropertyChanged();
}
}
I hope somebody can point me in the right direction. Just to be clear, the ListView has the correct items, and the SelectedItem is set with the correct item.
Well, I found 'a solution' to the problem after a lot of debugging and digging. I would REALLY like to understand if this is how WPF meant the control to behave, or if this is a bug in the ListViews data binding part. If anyone could tell me that, I am very very curious to the correct answer (and maybe I solved this problem in the wrong way, and somebody could explain me how I should've done this).
Anyway, the problem seems to be resolved when I create a copy of the object:
public IWebApiTvShow AcceptedMatchingTvShow
{
get
{
IWebApiTvShow acceptedTvShow = null;
if (FoundTvShows.Count > CurrentTvShow)
{
var tvShowName = FoundTvShows[CurrentTvShow];
acceptedTvShow = AvailableTvShowMatches[tvShowName].FirstOrDefault(webApiTvShow => webApiTvShow.Accepted);
}
if (acceptedTvShow != null)
{
// I MUST create a new instance of the original object for the ListView to update the selected item (why??)
return new WebApiTvShow(acceptedTvShow);
}
return null;
}
set
{
if (value != null)
{
var tvShowName = FoundTvShows[CurrentTvShow];
var availableTvShowMatch = AvailableTvShowMatches[tvShowName];
var currentlyAcceptedTvShow = availableTvShowMatch.FirstOrDefault(webApiTvShow => webApiTvShow.Accepted);
if (currentlyAcceptedTvShow != null)
{
currentlyAcceptedTvShow.Accepted = false;
}
value.Accepted = true;
}
OnPropertyChanged();
}
}
Note the call to the copy constructor :
return new WebApiTvShow(acceptedTvShow);
It works, but seems really ridiculous and smells like a bug in ListView to me. Is it?
I tried to explain the same problem in a simpler example here, if anybody can confirm the bug or can explain me how this should've been implemented I would greatly appreciate the insights.
A bit late to the game, but I had been jumping through hoops to solve this Problem in a similar setup. Setting the SelectedItem in a ListView using a bound Property in the Viewmodel or similar using a bound SelectedIndex just would not work. Until I tried to do it async:
Task.Factory.StartNew(() =>
{
BoundSelectedIndex = index;
});
Seems to work - more advanced contributors may answer why...
i know this is an old post but what worked is overriding the Equals and GetHashCode on your SelectedItem object so the listview can compare the SelectedItem with the bound collection
I am building a custom VirtualizingPanel to be used in and ListBox control.
I am doing some testing where i faced a problem in the method
IItemContainerGenerator.IndexFromGeneratorPosition(position)
It returns -1 if I set the ListBox's ItemsSource in the constructor(which is before the Loaded event) of my UserControl where it hosts the ListBox. However, it does not returns -1 if I were to set the ListBox's ItemsSource in the Loaded event.
The problem arises when a NullReferenceException occurs when i execute the IItemContainerGenerator.Remove(position, offset) method.
The code below shows the method where i virtualize the items
private void CleanupItems()
{
IItemContainerGenerator iGenerator = this.ItemsOwner.ItemContainerGenerator;
for (int i = this.InternalChildren.Count - 1; i >= 0; i--)
{
GeneratorPosition position = new GeneratorPosition(i, 0);
int itemIndex = iGenerator.IndexFromGeneratorPosition(position);
if (itemIndex < this.StartIndex || itemIndex > this.EndIndex)
{
iGenerator.Remove(position, 1);
this.RemoveInternalChildRange(i, 1);
}
}
}
currently i put this(fix?hack?) in my VirtualizingPanel's constructor
Loaded += (s, e) =>
{
if (ItemsOwner.ItemsSource != null)
{
this.InvalidateMeasure();
}
};
how should i fix this issue the correct way? any suggestions?
IItemContainerGenerator.IndexFromGeneratorPosition will return -1 in case containers for your items are not generated.
At the time of constructor your items are not rendered on UI. Hence no containers but they are available once your UI is rendered. That's why you are getting them after loaded event.
You can check Status of your ItemContainerGenerator, it should be ContainersGenerated before processing your request. Hook to StatusChanged event
ItemsOwner.ItemContainerGenerator.StatusChanged += (s, args) =>
{
if (ItemsOwner.ItemContainerGenerator.Status ==
GeneratorStatus.ContainersGenerated)
{
// Your code goes here.
}
};
I have overrided the method OnSourceInitialized and I have one problem. After populating my combobox with source property from c# code I want automatically an item will appear selected in the combobox when a page is loaded (default value) but for some reason after onsourceinitialized method, the combobox selected item change to null.
EDIT
First of all, very good explanation thanks.
I'll try to explain more and I post some code following. I have made some modifications but without success. It continues not working.
My goal is to show a default value selected in the combobox when window is loaded and it is shown.
Initially, when user selects a option in menu application I do the following:
WinMain.xaml.cs:
namespace MyNamespace
{
public partial class WinMain : Window
{
<...>
private void mnuItemPreferences_Click(object sender, RoutedEventArgs e)
{
MyNamespace.Windows.EditPreferences editPrefWnd =
new MyNamesapece.Windows.EditPreferences();
//
// Modal window that I want to open with default values in comboboxes
//
editPrefWnd.ShowDialog();
}
<...>
} // end WinMain class
} // end namespace
EditPreferences.xaml.cs:
namespace MyNamespace.Windows
{
public partial class EditPreferences : Window
{
<...>
// My constructor
public EditPreferences()
{
//
// Handlers
//
Loaded += PreferencesWindow_Loaded;
Closing += PreferencesWindow_Closing;
InitializeComponent();
if (System.Environment.OSVersion.Version.Major < 6)
{
this.AllowsTransparency = true;
_bolAeroGlassEnabled = false;
}
else
{
_bolAeroGlassEnabled = true;
}
this.ShowInTaskbar = false;
} // end constructor
private void PreferencesWindow_Loaded(object sender,
System.Windows.RoutedEventArgs e)
{
if (this.ResizeMode != System.Windows.ResizeMode.NoResize)
{
//this work around is necessary when glass is enabled and the
//window style is None which removes the chrome because the
//resize mode MUST be set to CanResize or else glass won't display
this.MinHeight = this.ActualHeight;
this.MaxHeight = this.ActualHeight;
this.MinWidth = this.ActualWidth;
this.MaxWidth = this.ActualWidth;
}
//
// Populate comboboxes
//
cbLimHorasExtra.ItemsSource = Accessor.GetLimHorasExtraSorted();
cbFracHorasExtra.ItemsSource = Accessor.GetFracHorasExtraSorted();
//
// Fill controls with default values (see below)
//
FillControls();
//
// Install other handlers
//
rdoBtnOTE.Checked += this.rdoBtnOTE_Checked;
rdoBtnOTM.Checked += this.rdoBtnOTM_Checked;
chkboxRestrict.Checked += this.chkboxRestrict_Checked;
expAdditionalDetails.Collapsed +=
this.expAdditionalDetails_Collapsed;
expAdditionalDetails.Expanded += this.expAdditionalDetails_Expanded;
cbLimHorasExtra.SelectionChanged +=
this.cbLimHorasExtra_SelectionChanged;
cbFracHorasExtra.SelectionChanged +=
this.cbFracHorasExtra_SelectionChanged;
}
protected override void OnSourceInitialized(System.EventArgs e)
{
base.OnSourceInitialized(e);
if (_bolAeroGlassEnabled == false)
{
//no aero glass
this.borderCustomDialog.Background =
System.Windows.SystemColors.ActiveCaptionBrush;
this.tbCaption.Foreground =
System.Windows.SystemColors.ActiveCaptionTextBrush;
this.borderCustomDialog.CornerRadius =
new CornerRadius(10, 10, 0, 0);
this.borderCustomDialog.Padding =
new Thickness(4, 0, 4, 4);
this.borderCustomDialog.BorderThickness =
new Thickness(0, 0, 1, 1);
this.borderCustomDialog.BorderBrush =
System.Windows.Media.Brushes.Black;
}
else
{
//aero glass
if (VistaAeroAPI.ExtendGlassFrame(this,
new Thickness(0, 25, 0, 0)) == false)
{
//aero didn't work make window without glass
this.borderCustomDialog.Background =
System.Windows.SystemColors.ActiveCaptionBrush;
this.tbCaption.Foreground =
System.Windows.SystemColors.ActiveCaptionTextBrush;
this.borderCustomDialog.Padding =
new Thickness(4, 0, 4, 4);
this.borderCustomDialog.BorderThickness =
new Thickness(0, 0, 1, 1);
this.borderCustomDialog.BorderBrush =
System.Windows.Media.Brushes.Black;
_bolAeroGlassEnabled = false;
}
}
}
private void FillControls()
{
tblPreferencias tbl_pref = null;
//
// Obtain data (a record with fields)
// Accessor is a class where I define the methods to
// obtain data of different tables in my database
//
tbl_pref = Accessor.GetActualPreferencias();
//
// Only returns one register
//
if (tbl_pref != null)
{
rdoBtnOTE.IsChecked = (bool)tbl_pref.OTE;
rdoBtnOTM.IsChecked = (bool)tbl_pref.OTM;
chkboxRestrict.IsChecked =
(bool)tbl_pref.RestriccionHExtraTipoA;
// Here the value assigned is always in the range of the values
// which combo has been populated.
// With one 0 ... 8
// I debbugged it and works.
// selected value (no null) and text gets the correct value I
// want but after OnSourceInitialized method is executed I note
// that for some rease selected value property gets value null
cbLimHorasExtra.Text = tbl_pref.LimiteHorasExtra.ToString();
cbFracHorasExtra.Text =
tbl_pref.FraccionDeMinutosExtra.ToString();
}
}
<...>
} // end EditPreferences class
} // end namespace
EditPreferences.xaml (I put as example one of the comboboxes):
<Window x:Class="MyNamespace.Windows.EditPreferences"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
Title="EditPreferences" Height="Auto" Width="500"
Background="{x:Null}"
SnapsToDevicePixels="True" SizeToContent="Height"
WindowStartupLocation="CenterScreen"
ResizeMode="NoResize"
WindowStyle="None"
Margin="0,0,0,0"
>
<...>
<ComboBox x:Name="cbLimHorasExtra"
DisplayMemberPath="LimHora"
SelectedValuePath="Id"
SelectedItem="{Binding Path=Id}"
VerticalAlignment="Center"
HorizontalContentAlignment="Right"
Width="50"/>
<...>
</Window>
Accessor.cs:
namespace GesHoras.Classes
{
class Accessor
{
<...>
// This method is used to populate the combobox with its values
// tblLimHorasExtra is a table in my SQL Database
// Its fields are:
//
// Id : int no null (numbers 1 ... 9)
// LimHora: int no null (numbers 0 ... 8)
//
public static System.Collections.IEnumerable GetLimHorasExtraSorted()
{
DataClassesBBDDDataContext dc = new
DataClassesBBDDDataContext();
return (from l in dc.GetTable<tblLimHorasExtra>()
orderby l.LimHora
select new { Id=l.Id, LimHora=l.LimHora });
}
// tblPreferencias is a table in my SQL Database
// Its fields are:
//
// Id : int no null
// Descripcion : varchar(50) no null
// OTE : bit no null
// OTM : bit no null
// LimiteHorasExtra : int no null
// FraccionDeMinutosExtra : int no null
// RestriccionHExtraTipoA : bit no null
//
public static tblPreferencias GetActualPreferencias()
{
DataClassesBBDDDataContext dc = new
DataClassesBBDDDataContext();
return (from actP in dc.GetTable<tblPreferencias>()
where (actP.Id == 3)
select actP).SingleOrDefault<tblPreferencias>();
}
<...>
} // end class
} // end namespace
The problem I see is that when method fillControls is executed all is ok, selectedvalue and text property for the combobox is correct (I have debbugged it and is correct) but after executing OnSourceInitialized method, selectedvalue property for the combobox gets null value.
Also I note that, when window opens, the comboboxes appear with the default values selected that I want but quickly I see that for some reason their values selected turns to empty in the comboboxes. It's like some event (I think after executing OnSourceMethod because I have debugged and see how it change to null) makes the selected default values that appears ok in the comboboxes turn to empty.
I have tested that comboboxes are populated correctly because once the window is shown I click in the comboboxes and I can see they are populated ok.
EDIT 2
Also I have forced selected index for combobox in fillControls method by doing:
cbLimHorasExtra.SelectedIndex = 1;
but without success...
The combobox is populated with values: 0 to 8 both included.
Cause
This appears to be the problem:
SelectedItem="{Binding Path=Id}"
If the "Id" property in the DataContext is not an item in the ItemsSource, SelectedItem will be set to null.
Timing
When InitializeComponent is called, it parses the XAML which sets the SelectedItem binding. If the DataContext is not set, then initially this will be null. Later when DataContext is set, the binding is re-evaluated. If Id is in the list at that point, the SelectedItem is set. Otherwise it is set to null.
Any binding that cannot be evaluated initially during InitializeComponent is scheduled using the dispatcher to be re-evaluated once all events have fired. Without details on how your DataContext is being set I can't give specifics, but my guess is that one of your binding is getting deferred so your {Binding Path=Id} binding is evaluated in a dispatcher callback.
A dispatcher callback is not an event - it is a prioritized work queue. If you have this kind of situations your choices are:
Change the bindings so they can be evaluated during initialization
Use a Dispather.BeginInvoke to schedule your own callback to execute after the Binding completes
Let the Binding take care of setting the SelectedItem rather than setting manually in code
Additional notes
Your use of SelectedValueSource looks suspicious. Your binding to SelectedItem seems to indicate that each item in the ItemsSource is an "Id", but your definition of SelectedValueSource seems to indicate that each item in the ItemsSource contains an "Id". It is rare to find a data structure where the structure itself is called "Id" by another structure, yet it itself has an "Id" field. Thus I suspect some confusion here. Without seeing your actual data structures I can't say more.
Your use of OnSourceInitialized also makes it appear you have a misunderstanding. The "Source" in the name of OnSourceInitialized refers to a "presentation source" such as a Win32 hWnd, not a source of data. The purpose of OnSourceInitialized is to interact at a low level with the Windows operating system, or to update your application based on where it is being presented. Your use seems completely unrelated to this. I would recommend you stay away from OnSourceInitialized. Generally the best time to initialize ComboBoxes and such is to just provide it in your view model and let data binding take care of it. As soon as the view model is available the data will be populated with no code required.
Set the SelectedIndex property at the end of your override, by the way, i can't seem to find OnSourceInitialised, only Initialised. But it should still work if you set it at the end of your code.
private void MyListBox_Initialized(object sender, EventArgs e)
{
// Run some code
if (MyListBox.Items.Count > 0)
{
MyListBox.SelectedIndex = 0;
}
}
I don't have a real answer to your question, but OnSourceInitialized seems to be too early in the initialization process.
Again, I have not tried your exact scenario, but many problems like this one are solved by calling FillControls (i.e. setting the selected item) in the Loaded event instead of earlier.
I have solved it!
The problem was in binding the SelectedItem property in EditPreferences.xaml:
<ComboBox x:Name="cbLimHorasExtra"
DisplayMemberPath="LimHora"
SelectedValuePath="Id"
SelectedItem="{Binding Path=Id}"
VerticalAlignment="Center"
HorizontalContentAlignment="Right"
Width="50"/>
The solution is to change to:
<ComboBox x:Name="cbLimHorasExtra"
DisplayMemberPath="LimHora"
SelectedValuePath="Id"
SelectedItem="Id"
VerticalAlignment="Center"
HorizontalContentAlignment="Right"
Width="50"/>