We Keep Coding

How do I handle SelectionChange when the ComboBox is

I have a ListBox, where the list element has a ComboBox, a TextBox and a slider. Depending on the selction of the ComboBox either the TextBox or the slider should be visible.
<ListBox Name="lstPWM" >
<ListBox.ItemTemplate>
<DataTemplate>
<Grid>
<Grid.ColumnDefinitions>
<ColumnDefinition Width="80"/>
<!-- more definitions -->
</Grid.ColumnDefinitions>
<ComboBox ItemsSource="{Binding Path=Gebertyp, Converter={local1:EnumToCollectionConverter}, Mode=OneTime}"
SelectedValuePath="Value"
DisplayMemberPath="Description"
SelectionChanged="PWMTyp_SelectionChanged"
SelectedValue="{Binding Path=Gebertyp}" />
<TextBox Visibility="{Binding GeberVisible}" Text="{Binding GeberNmr, Mode=TwoWay}"/>
<Slider Visibility="{Binding WertVisible}" Value="{Binding Wert, Mode=TwoWay}"/>
</Grid>
</DataTemplate>
</ListBox.ItemTemplate>
</ListBox>
The code behind is:
public partial class MainWindow : Window
{
public ObservableCollection<PWMKanal> PWM_col { get; set; } = new();
private void Window_Loaded(object sender, RoutedEventArgs e)
{
lstPWM.ItemsSource = PWM_col;
foreach (var item in Board.PWM) PWM_col.Add(item); //Board.PWM is the data source.
}
private void PWMTyp_SelectionChanged(object sender, SelectionChangedEventArgs e)
{
ComboBox box = sender as ComboBox; // Finding the line in the ListBox.
PWMKanal PWM = box.DataContext as PWMKanal;
int z = PWM_col.IndexOf(PWM);
Board.PWM[z].Gebertyp = (QuellePWM)box.SelectedValue;
if (Board.PWM[z].Gebertyp == QuellePWM.Sender)
{
PWM_col[z].GeberVisible = Visibility.Visible; // I thought that i may change the
PWM_col[z].WertVisible = Visibility.Hidden; // ObservableColelction directly
} // but the display is not updated.
else // In Debug mode i see, that PWM_coll
{ // is changed as expected, but no effect
PWM_col[z].GeberVisible = Visibility.Hidden; // on the GUI.
PWM_col[z].WertVisible = Visibility.Visible;
}
if (PWM_col.Count != 0) // this code is intended to update the GUI, but every time
{ // a new item is added the Selection Change fires again
PWM_col.Clear(); // and i get a stack overflow in an endless loop.
foreach (var item in Board.PWM) PWM_col.Add(item);
}
}
}
The comments describe my approaches and problems:
I change the selected element of the ObservableCollection directly, but this has no effect on GUI. At least tho code doesn't crash.
I clear the list ObservableCollection PWM_col, but then i get an infinite loop: every time an element is added to the list the SelectionChange event fires, calling the routin again. Result is stack overflow.
Now my questions to my approaches:
Is it possible to change an element of an ObservableCollection directly by code, and the display is automatically refreshed?
Is it possible to somehow catch the SelectionChanged event before the handler is executed? Or is it possible to temporary dissable the event?
Any other idear?
Thank you for your help!

CollectionChanged does notify, that collection itself, not the
single items, is changed. Therefore to see the changes item's
property need to implement INotifyPropertyChanged. Also remove Mode=OneTime
You can of course set the flag, that PWMTyp_SelectionChanged is
running:
private bool selChangedIsRunning = false;
private void PWMTyp_SelectionChanged(object sender, SelectionChangedEventArgs e)
{
if(selChangedIsRunning) return;
selChangedIsRunning = true;
// do stuff ....
selChangedIsRunning = false;
}
Other idea is - don't use the SelectionChange event, but do bind
Slider.Visibility and TextBox.Visibility to the
ComboBox.SelectedValue and use value converter to define the
Visibilty, also you can use the ConverterParameter.
<ComboBox x:Name="CmbPWMTyp" ItemsSource="{Binding Path=Gebertyp, Converter={local1:EnumToCollectionConverter}, Mode=OneTime}"
SelectedValuePath="Value"
DisplayMemberPath="Description"
SelectionChanged="PWMTyp_SelectionChanged"
SelectedValue="{Binding Path=Gebertyp}" />
<TextBox Visibility="{Binding ElementName=CmbPWMTyp, Path=SelectedValue, Converter={StaticResource YourConverter}, ConverterParameter=TBX}" Text="{Binding GeberNmr, Mode=TwoWay}"/>
<Slider Visibility="{Binding ElementName=CmbPWMTyp, Path=SelectedValue, Converter={StaticResource YourConverter}, ConverterParameter=SLDR}" Value="{Binding Wert, Mode=TwoWay}"/>
This link can be also very helpful for you: Difference between SelectedItem SelectedValue and SelectedValuePath

how to access label name in nested listview datatemplate on a check box event

I have defined a label with name and I'm trying to access it but no luck. Let me explain my problem with my code.
<ListView Name="gridListView" ItemsSource="{Binding... }">
<ListView.ItemContainerStyle>
<Style TargetType="ListViewItem">
<Setter Property="Focusable" Value="false"/>
</Style>
</ListView.ItemContainerStyle>
<ListView.ItemTemplate>
<DataTemplate>
<Border>
<StackPanel Orientation="Vertical">
<Label x:Name="vLabel" Content="{Binding VCValue}"/>
<ListView Name="checkBoxListView" ItemsSource="{Binding CList}">
<ListView.ItemTemplate>
<DataTemplate>
<CheckBox Margin="5" Click="CheckBox_Click" IsChecked="{Binding SelectedValue, Mode=TwoWay}" Content="{Binding Current, Mode=OneWay }"/>
</DataTemplate>
</ListView.ItemTemplate>
</ListView>
</StackPanel>
</Border>
</DataTemplate>
</ListView.ItemTemplate>
</ListView>
In the above code, I have two listview, gridListView and checkBoxListView. Here, I want to access the label vLabel which is inside the datatemplate of gridListView when the one of the value in checkbox(which is inside checkBoxListView) is clicked.
I understand it can't be accessed directly as its within datatemplate so i tried below code as suggested in other forums but gridListView.SelectedIndex is always -1 so i know i'm not doing the right thing. When I just hardcoded gridListView.SelectedIndex to index 0, 1 or 2 its giving me the right value of vLabel so the below code will work if gridListView.SelectedIndex is correct.
private void CheckBox_Click(object sender, RoutedEventArgs e)
{
CheckBox chk =(CheckBox)sender;
int index = gridListView.Items.IndexOf(chk.DataContext);
ListViewItem item = gridListView.ItemContainerGenerator.ContainerFromIndex(gridListView.SelectedIndex) as ListViewItem;
if (item!=null)
{
//get the item's template parent
ContentPresenter templateParent = GetFrameworkElementByName<ContentPresenter>(item);
DataTemplate dataTemplate = gridListView.ItemTemplate;
if (dataTemplate != null && templateParent != null)
{
var lab = dataTemplate.FindName("vLabel", templateParent) as Label;
var v = lab.Content;
}
}
private static T GetFrameworkElementByName<T>(FrameworkElement referenceElement) where T : FrameworkElement
{
//I can post this function if need be
....
}
Appreciate any help that will help me access vLabel.
Thanks in advance

you are setting focusable to false, so you cant select the item by clicking. also the checkbox-checked happens before the selection, even if you were to set focusable to true, so selected index would still be -1.
you can find your label simply like this:
public Label FindLabel(CheckBox checkBox)
{
var listView = VisualTreeHelper.GetParent(checkBox);
while (listView.GetType() != typeof(ListView))
{
listView = VisualTreeHelper.GetParent(listView);
}
return (listView as FrameworkElement).FindName("vLabel") as Label;
}
but i suggest you tell us what you want to achieve, because this doesnt seem like a clean solution.
can you perhaps do this on your StackPanel:
<StackPanel CheckBox.Checked="CheckBox_Click" Orientation="Vertical">
and then access your two desired properties as following:
private void CheckBox_Click(object sender, RoutedEventArgs e)
{
var outerItem = (sender as FrameworkElement).DataContext;
var innerItem = (e.OriginalSource as FrameworkElement).DataContext;
}
and then do whatever you want to do?

Thank you for all your guidance. I did get hint from Milan's code to achieve solution for my issue. Here, I'm trying to get reference parent of listviewItem(i.e stackpanel) and then access its child. In my case, stack panels child at index 0 is Label and at index 1 is ListView. So then I go through visualtreehelper to get reference to its child at index 0 which is what i need access to. So here is the code snippet.
private void CheckBox_Click(object sender, RoutedEventArgs e)
{
CheckBox checkBox = (CheckBox)sender;
//to access parent of the checkbox
ListViewItem listViewItem =
GetVisualAncestor<ListViewItem>((DependencyObject)sender);
//to access parent of the listViewItem(which is parent of checkbox)
StackPanel stackPanel =
GetVisualAncestor<StackPanel>((DependencyObject)listViewItem);
int childCount = VisualTreeHelper.GetChildrenCount(stackPanel);
//to access child of stackpanel to access the current vLabel
var vValue = VisualTreeHelper.GetChild(stackPanel, 0) as Label;
}
private static T GetVisualAncestor<T>(DependencyObject o)where T : DependecyObject
{
...
}

In a HierarchicalDataTemplate Label transforms to TextBlock

While trying to implement Drag&Drop in my application I've encountered some strange behavior. I am using a HierarchicalDataTemplate to represent my data structure in a TreeView like so:
XAML:
<TreeView Name="treeViewNotes" AllowDrop="True" PreviewMouseLeftButtonDown="treeViewNotes_PreviewMouseLeftButtonDown" PreviewMouseMove="treeViewNotes_PreviewMouseMove" Drop="treeViewNotes_Drop" DragEnter="treeViewNotes_DragEnter" SelectedItemChanged="treeViewNotes_SelectedItemChanged">
<TreeView.Resources>
<HierarchicalDataTemplate DataType="{x:Type local:NoteCategory}" ItemsSource="{Binding Notes}">
<StackPanel Orientation="Horizontal">
<Image Height="16" Source="{Binding TreeViewIcon}" Tag="{Binding Self}"/>
<Label Content="{Binding Title}" Tag="{Binding Self}" Margin="3"/>
</StackPanel>
</HierarchicalDataTemplate>
<HierarchicalDataTemplate DataType="{x:Type local:TextNote}">
<StackPanel Orientation="Horizontal">
<Image Height="16" Source="{Binding TreeViewIcon}" Tag="{Binding Self}"/>
<Label Content="{Binding Title}" Tag="{Binding Self}" Margin="3"/>
</StackPanel>
</HierarchicalDataTemplate>
</TreeView.Resources>
</TreeView>
CODE:
private void buttonCreateNote_Click(object sender, RoutedEventArgs e)
{
ObservableCollection<NoteCategory> NoteCategoriesList = new ObservableCollection<NoteCategory>();
NoteCategory category1 = new NoteCategory("Category 1", Properties.Resources.FolderIcon);
TextNote textNote1 = new TextNote("Text note 1", Properties.Resources.TextNoteIcon, category1, "Blah blah. Content for note 1");
TextNote textNote2 = new TextNote("Text note 2", Properties.Resources.TextNoteIcon, category1, "Blah blah. Content for note 2");
NoteCategory category2 = new NoteCategory("Category 2", Properties.Resources.FolderIcon);
TextNote textNote4 = new TextNote("Text note 4", Properties.Resources.TextNoteIcon, category2, "Blah blah. Content for note 4");
TextNote textNote5 = new TextNote("Text note 5", Properties.Resources.TextNoteIcon, category2, "Blah blah. Content for note 5");
NoteCategoriesList.Add(category1);
NoteCategoriesList.Add(category2);
treeViewNotes.ItemsSource = NoteCategoriesList;
}
RESULT:
This works great, so now I want to be able to drag&drop notes between categories, so I implemented partially the code from here
CODE:
private void treeViewNotes_PreviewMouseMove(object sender, MouseEventArgs e)
{
Point mousePos = e.GetPosition(null);
Vector diff = Utils.DragDropStartPoint - mousePos;
if (Utils.IsDragDropping == false &&
(e.LeftButton == MouseButtonState.Pressed || e.RightButton == MouseButtonState.Pressed) &&
(Math.Abs(diff.X) > SystemParameters.MinimumHorizontalDragDistance || Math.Abs(diff.Y) > SystemParameters.MinimumVerticalDragDistance))
{
// Get the dragged ListViewItem
TreeView treeView = sender as TreeView;
if (e.OriginalSource is Image || e.OriginalSource is Label)
{
FrameworkElement elem = e.OriginalSource as FrameworkElement;
if (elem.Tag == null)
MessageBox.Show(elem.GetType() + "\n\nNULL");
else
MessageBox.Show(elem.GetType() + "\n\n" + elem.Tag.ToString());
}
else
MessageBox.Show(e.OriginalSource.GetType().ToString());
}
}
The key to the whole operation is binding the Tag to the TextNote object itself, so I can extract it when the user drags either the Label or Image of the TreeViewItem. And it works for the Image. But when I try to drag by clicking the Label the e.OriginalSource actually comes to the handler as a TextBlock with an empty Tag. I couldn't make the Label fire the event no matter where I click and drag the mouse. The question is why?
I did a workaround by using a TextBlock instead of a Label in the HierarchicalDataTemplate and it works, but I am still curious to why the other approach does not work.

Enumerate over each item of listbox to compare internal element values

I have a listbox with a data template bound to a list<class> in the program.
<DataTemplate x:Key="pTemplate">
<StackPanel Orientation="Horizontal">
<TextBlock Text="{Binding Ref}" Padding="5,0,0,0"/>
<StackPanel Name="taggedA" Tag="{Binding A}" Orientation="Horizontal">
<TextBlock Name="selectedA" Text="{B}" />
</StackPanel>
<Image Name="ind" Width="40" Height="40" />
</StackPanel>
</DataTemplate>
On button click, I want to go over all the elments of the listbox and check if the stackPanel taggedA's tag == textblock selectedA's text.
This is to be done for each of the items in the list box and the data template is as above. How can this be done?

Easier to compare the binding source directly:
ListBox l = myListBox;
for (int i = 0; i < l.Items.Count; i++)
{
var boundObject = (MyClass)l.Items[i];
MessageBox.Show("They are equal? " + (boundObject.A == boundObject.B));
}

I would agree with #dbaseman. But if you are set on doing it you could do the following:
private void button_click(object sender, RoutedEvent e)
{
foreach(var item in MyListBox.Items)
{
ListBoxItem lbi = MyListBox.ItemContainerGenerator.ContainerFromItem(item);
StackPanel taggedApanel = (lbi.Content as StackPanel).Children[1];
//Do whatever you need to do here
}
}

Adding content to a TreeViewItem programmatically

I'm trying to create a new TreeViewItem with a control in it like:
<TreeViewItem>
<TreeViewItem.Header>
<StackPanel>
<Button/>
</StackPanel>
<TreeViewItem.Header>
<TreeViewItem>
Except, I'd like to do it at runtime (I'm using C#), but I can't work out how to do this. Can you help?
This is my code that I'm using to generate the node. Somewhere in here I would like to insert a numeric up/down control. I don't have that control yet, but for arguement's sake, let's say that I want to insert a button.
private void TreeView_AfterSelect(object sender, System.Windows.Forms.TreeViewEventArgs e)
{
if (TreeView.SelectedNode != null)
{
if (((vcvscompiler.DataTypes.dataObjectv)(TreeView.SelectedNode.Tag))._vcardName.re == "adr_work")
{
foreach (string k in ((vcvscompiler.DataTypes.dataObjectv)(TreeView.SelectedNode.Tag))._prefs)
{
TreeViewItem newChild = new TreeViewItem();
newChild.Header = k;
treeView1.Items.Add(newChild);
}
}
}
}
WPF:
<Window.Resources>
<DataTemplate x:Key="myTaskTemplate">
<StackPanel>
<Button content="This is a button!" />
</StackPanel>
</DataTemplate>
</Window.Resources>

new TreeViewItem {
Header = new StackPanel {
Children = {
new Button { ... }
}
}
}