We Keep Coding

WPF DataTemplateSelector is not used

I am trying to modify a existing WPF application in a way so that a newer version of some data object can be used alongside the old one. And so i avoid redundant code by extending the existing ViewModel with new fields where the old ones cannot be reused.
public IList<G1VU.PDR> VuG1 { get; set; }
public IList<G2VU.PDR> VuG2 { get; set; }
public PlacesCompound VuP
{
get
{
if (VuG1 != null && VuG2 == null)
{
return new PlacesCompound {
G1 = VuG1,
G2 = null
};
}
if (VuG2 != null && VuG1 == null)
{
return new PlacesCompound {
G1 = null,
G2 = VuG2
};
}
throw new Exception("G1 and G2 data present or no data present");
}
}
VuG1 has existed before and i have added a new property VuG2 for the new data. As you can see these are not the same class so i cannot interchange them. For that reason i've added a property that will return either of the two in a PlacesCompound class, which is just a class with two properties and nothing else.
In the corresponding usercontrol (lets call it ActivitiesView) we have a DataGrid which binds to the ViewModel and somewhere a TabItem that will display a custom UserControl places which binds to VuG1 on the ViewModel. I have copied it and changed it so it will work with VuG2 Data.
And i created a custom DataTemplateSelector which will decide what Template to use based on which variable of PlacesCompound isnt null.
In VUActivitiesResources.xaml i have then declared 2 DataTemplates one for each places UserControl and the DataTemplateSelector.
<activities:VUActivitiesViewDataTemplateSelector x:Key="PlacesTemplateSelector"/>
<DataTemplate x:Key="VuG2Template">
<places:VUPViewG2 DataContext="{Binding VuG2}" HorizontalAlignment="Left"/>
</DataTemplate>
<DataTemplate x:Key="VuG1Template">
<places:VUPViewG1 DataContext="{Binding VuG1}" HorizontalAlignment="Left"/>
</DataTemplate>
VUActivitiesResources.xaml is being referenced in ActivitiesView as UserControl.Resources.
In the ActivitiesView i placed a ItemsControl into the TabItem replacing the custom places UserControl (ive also tried a ListBox instead of a ItemsControl, but neither works)
<TabItem IsEnabled="{Binding PlacesIsVisible}">
...
<ItemsControl
ItemsSource="{Binding VuP}"
ItemTemplateSelector="{StaticResource PlacesTemplateSelector}"></ItemsControl>
</TabItem>
My question: why PlacesTemplateSelector is never used and how do i make it being used? Because right now while debugging i can see that in ViewModel VuP returns a PlacesCompound object correctly but the Selector is never entered. I want one of the two DataTemplates to show up in the TabItem and right now none is showing.

ItemsSource must be a collection (which your PlacesCompound is not), in your case this would be either VuG1 or VuG2. If the two item classes have no common base class, you can still use IEnumerable:
public IEnumerable VuP => (IEnumerable)VuG1 ?? VuG2;
Then, instead of writing a TemplateSelector, just let the WPF DataTemplating mechanism do its work:
<DataTemplate DataType="{x:Type namespace1:PDR}">
<places:VUPViewG2 HorizontalAlignment="Left"/>
</DataTemplate>
<DataTemplate DataType="{x:Type namespace2:PDR}">
<places:VUPViewG1 HorizontalAlignment="Left"/>
</DataTemplate>
<ItemsControl ItemsSource="{Binding VuP}" />

Making controls transparent to mouse interaction in WPF

I am trying to make a WPF listbox replicate the behaviour of an old Winforms CheckedListBox, or the checked list box used in e.g. AnkhSVN. I have seen examples that show how to use a DataTemplate to create a check box for every time (e.g. Wpf CheckedListbox - how to get selected item), but this feels very clunky compared to the winforms control:
The logic of "If the user changes a check state, ensure that check state changes for all selected items" is not present by default.
The hit area to change an item from checked to unchecked is the box /and/ the title, rather than just the box as in Winforms
I can handle the first issue by adding a listener to the PropertyChanged event on each item in the bound collection, and if IsChecked changes, then set IsChecked to the same value for all currently selected items.
However, I cannot find a good solution to the second issue. By splitting the DataTemplate into a Checkbox with no title, and a TextBlock with the title, I can reduce the hit area to change the check state to only the desired square. However, all mouse interaction which hits the TextBlock does nothing - I would like it to behave the same as in a normal listbox, or in the dead space outside of the Textblock: If the user is holding shift, then select everything up to and including this item, if not, then clear the selection and select only this item. I could try to implement something where I handled Mouse* events on the TextBlock, but that seems brittle and inelegant - I'd be trying to recreate the exact behaviour of the ListBox, rather than passing events to the listbox.
Here's what I've got currently:
XAML:
<ListBox x:Name="_lstReceivers" SelectionMode="Extended" Margin="10,41,6,15"
ItemsSource="{Binding Receivers}">
<ListBox.ItemTemplate>
<DataTemplate>
<ListBoxItem>
<StackPanel Orientation="Horizontal">
<CheckBox IsChecked="{Binding IsChecked}" IsHitTestVisible="True"/>
<TextBlock Text="{Binding Item}" Background="{x:Null}" IsHitTestVisible="False"/><!--Attempt to make it pass mouse events through. Doesn't work. Yuk.-->
</StackPanel>
</ListBoxItem>
</DataTemplate>
</ListBox.ItemTemplate>
</ListBox>
Code behind to get the "Change all checks at the same time" logic (removed some error handling for clarity):
private void ListBoxItem_PropertyChanged(object sender, PropertyChangedEventArgs e)
{
var item = sender as CheckableItem<Receiver>;
if (item == null)
return;
if (e.PropertyName == nameof(CheckableItem<Receiver>.IsChecked))
{
bool newVal = item.IsChecked;
foreach (CheckableItem<Receiver> changeItem in _lstReceivers.SelectedItems)
{
changeItem.IsChecked = newVal;
}
}
}
By trying various combinations of Background = "{x:Null}" and IsHitTestVisible="False", I did manage to get the entire item to not respond to mouse click events - but I could not make it have only the Checkbox respond to mouse events, while everything else is passed to the ListBox for proper selection processing.
Any help would be greatly appreciated.

Answering my own question again.
Well, I couldn't find a clean way to do it, so I ended up setting the ListBoxItem to have IsHitTestVisible="False", and manually tracing mouse events using PreviewMouseDown.
Final code:
XAML:
<ListBox x:Name="_lstReceivers" SelectionMode="Extended" Margin="10,41,6,15"
ItemsSource="{Binding Receivers}" PreviewMouseDown="_lstReceivers_MouseDown">
<ListBox.ItemTemplate>
<DataTemplate>
<ListBoxItem IsSelected="{Binding IsSelected}" IsHitTestVisible="False">
<StackPanel Orientation="Horizontal" Background="{x:Null}">
<CheckBox IsChecked="{Binding IsChecked}" IsHitTestVisible="True" Checked="CheckBox_Checked" Unchecked="CheckBox_Checked"/>
<TextBlock Text="{Binding Item}" Background="{x:Null}" IsHitTestVisible="False"/>
</StackPanel>
</ListBoxItem>
</DataTemplate>
</ListBox.ItemTemplate>
</ListBox>
Code behind:
//Logic to handle allowing the user to click the checkbox, but have everywhere else respond to normal listbox logic.
private void _lstReceivers_MouseDown(object sender, System.Windows.Input.MouseButtonEventArgs e)
{
Visual curControl = _lstReceivers as Visual;
ListBoxItem testItem = null;
//Allow normal selection logic to take place if the user is holding shift or ctrl
if (Keyboard.IsKeyDown(Key.LeftCtrl) || Keyboard.IsKeyDown(Key.RightCtrl) || Keyboard.IsKeyDown(Key.LeftShift) || Keyboard.IsKeyDown(Key.RightShift))
return;
//Find the control which the user clicked on. We require the relevant ListBoxItem too, so we can't use VisualTreeHelper.HitTest (Or it wouldn't be much use)
for (int i = 0; i < VisualTreeHelper.GetChildrenCount(curControl); i++)
{
var testControl = (Visual)VisualTreeHelper.GetChild(curControl, i);
var rect = VisualTreeHelper.GetDescendantBounds(testControl);
var pos = e.GetPosition((IInputElement)curControl) - VisualTreeHelper.GetOffset(testControl);
if (!rect.Contains(pos))
continue;
else
{
//There are multiple ListBoxItems in the tree we walk. Only take the first - and use it to remember the IsSelected property.
if (testItem == null && testControl is ListBoxItem)
testItem = testControl as ListBoxItem;
//If we hit a checkbox, handle it here
if (testControl is CheckBox)
{
//If the user has hit the checkbox of an unselected item, then only change the item they have hit.
if (!testItem.IsSelected)
dontChangeChecks++;
((CheckBox)testControl).IsChecked = !((CheckBox)testControl).IsChecked;
//If the user has hit the checkbox of a selected item, ensure that the entire selection is maintained (prevent normal selection logic).
if (testItem.IsSelected)
e.Handled = true;
else
dontChangeChecks--;
return;
}
//Like recursion, but cheaper:
curControl = testControl;
i = -1;
}
}
}
//Guard variable
int dontChangeChecks = 0;
//Logic to have all selected listbox items change at the same time
private void CheckBox_Checked(object sender, RoutedEventArgs e)
{
if (dontChangeChecks > 0)
return;
var newVal = ((CheckBox)sender).IsChecked;
dontChangeChecks++;
try
{
//This could be improved by making it more generic.
foreach (CheckableItem<Receiver> item in _lstReceivers.SelectedItems)
{
item.IsChecked = newVal.Value;
}
}
finally
{
dontChangeChecks--;
}
}
This solution works, but I don't like the coupling it introduces between my code and the exact behaviour of the ListBox implementation:
Checking the Keyboard state
It won't handle dragging if the user starts dragging inside a checkbox
It should happen on mouseup, not mousedown. But it's close enough for my needs.
PS: The bound class, even though it's irrelevant and obvious what it would have:
public class CheckableItem<T> : INotifyPropertyChanged
{
public T Item { get; set; }
private bool _isSelected;
public bool IsSelected
{
get => _isSelected;
set
{
if (_isSelected == value)
return;
_isSelected = value;
PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(nameof(IsSelected)));
}
}
private bool _checked;
public bool IsChecked
{
get => _checked;
set
{
if (_checked == value)
return;
_checked = value;
PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(nameof(IsChecked)));
}
}
public event PropertyChangedEventHandler PropertyChanged;
}

Forcing bound UI components to refresh

I know this has been asked a few times but none of the answers work for me.
I've got this list of elements in a TreeView which when clicked show their parameters in a panel (with texboxes, labels, combos and other components). I also have a button that allows copying data from one element chosen in a combo to the one currently shown on the data panel ("copy data from...").
All the data in the panel is bound to a class and its properties, and the treeview is bound to a collection of those objects.
The problem is, when I press the copy button (i.e. copying data from object A to current object) the changes are not reflected. Yet, if I change the element to be displayed (clicking another object in the TreeView) then go back to the changed object, the changes are there. So it is in fact changing the actual data, but not refreshing de data bindings.
Strangely enough, If I press the Copy button twice, changes are indeed reflected.
Which may be the cause of this, and how would I solve it?
This is the XAML example of a control that should be updated (I only post one because there are lots, and none of them is working), the copy button and the treeview:
Copiar datos del protocolo:
Copiar
<TreeView SelectedItemChanged="TvProtocolosSelectedItemChanged" Margin="10,5" Name="tvProtocolos" HorizontalAlignment="Stretch" VerticalAlignment="Top" Width="200" Height="292" MinWidth="0">
<TreeView.ItemContainerStyle>
<Style TargetType="TreeViewItem">
<Setter Property="IsEnabled" Value="{Binding Path=Activo}"/>
<Setter Property="IsExpanded" Value="False"/>
</Style>
</TreeView.ItemContainerStyle>
<TreeView.ItemTemplate>
<HierarchicalDataTemplate ItemsSource="{Binding Path=Children}">
<StackPanel Orientation="Horizontal">
<Image Source="imagenes\file_icon.gif" Margin="0,0,5,0" />
<TextBlock Text="{Binding Path=Name}" ></TextBlock>
</StackPanel>
</HierarchicalDataTemplate>
</TreeView.ItemTemplate>
</TreeView>
And this is the code-behind file:
public partial class NewXP2 : Window
{
private const int nProtocolos = 100;
private Experiencia2 _exp2Class = new Experiencia2(nProtocolos);
private readonly TreeView _tvProtocolos;
public NewXP2()
{
InitializeComponent();
_tvProtocolos.ItemsSource = _expClass.Protocolos;
xpControlsPanel.DataContext = _exp2Class.GetProtocolo(0);
for(int i=0;i<nProtocolos;i++)
copyFromCombo.Items.Add("Protocolo " + (i+1));
copyFromCombo.SelectedIndex = 0;
}
private void CopyfromButtonClick(object sender, RoutedEventArgs e)
{
int protIndex = copyFromCombo.SelectedIndex;
int indiceProtocolo = 0;
if (_tvProtocolos == null)
return;
var g = _tvProtocolos.SelectedItem as Composite;
_listaData = GetData();
_tvProtocolos.ItemsSource = _listaData;
TreeViewItem tvi;
if (g != null)
{
tvi = _tvProtocolos.ItemContainerGenerator.ContainerFromIndex(g.Indice) as TreeViewItem;
if (tvi != null)
{
tvi.IsSelected = true;
}
indiceProtocolo = g.Indice;
}
_exp2Class.SetProtocolo(indiceProtocolo, _exp2Class.Protocolos[protIndex]);
}
And this is the class bound to the panel (with the textbox)
public class ProtocoloExp2: ISerializable, IDataErrorInfo
{
public ProtocoloExp2(int idx)
{
IndiceProtocolo = idx;
IndiceVisual = idx + 1;
}
public float TimeToShowTarget { get; set; }
(...)
}

Check "How to: Implement the INotifyPropertyChanged Interface" out. And consider using ObservableCollection for your lists. Implementation of INotifyPropertyChanged interface is a requirement for wpf controls view models it basically allows views to refresh themselves when data changes.

WPF How to access control from DataTemplate

I have a datatemplate which contains a grid and inside the grid I have a combobox.
<DataTemplate x:Key="ShowAsExpanded">
<Grid>
<ComboBox Name ="myCombo" Grid.Column="1" HorizontalAlignment="Stretch" VerticalAlignment="Top" Margin="5"
IsSynchronizedWithCurrentItem="True"
ItemsSource="{Binding}"
ItemTemplate="{StaticResource MyItems}">
<ComboBox.ItemsPanel>
<ItemsPanelTemplate>
<VirtualizingStackPanel />
</ItemsPanelTemplate>
</ComboBox.ItemsPanel>
</ComboBox>
</Grid>
</DataTemplate>
I then I have a grid that refers to that template through styling.
<Grid>
<ContentPresenter Name="_contentPresenter" Style="{DynamicResource StyleWithCollapse}" Content="{Binding}" />
</Grid>
How can I access through code behing the myCombo to basically set its DataContext?

Three ways which I know of.
1.Use FindName
ComboBox myCombo =
_contentPresenter.ContentTemplate.FindName("myCombo",
_contentPresenter) as ComboBox;
2.Add the Loaded event to the ComboBox and access it from there
<ComboBox Name ="myCombo" Loaded="myCombo_Loaded" ...
private void myCombo_Loaded(object sender, RoutedEventArgs e)
{
ComboBox myCombo = sender as ComboBox;
// Do things..
}
3.Find it in the Visual Tree
private void SomeMethod()
{
ComboBox myCombo = GetVisualChild<ComboBox>(_contentPresenter);
}
private T GetVisualChild<T>(DependencyObject parent) where T : Visual
{
T child = default(T);
int numVisuals = VisualTreeHelper.GetChildrenCount(parent);
for (int i = 0; i < numVisuals; i++)
{
Visual v = (Visual)VisualTreeHelper.GetChild(parent, i);
child = v as T;
if (child == null)
{
child = GetVisualChild<T>(v);
}
if (child != null)
{
break;
}
}
return child;
}

First of all, I can't even find the relation between the Resource (ShowAsExpanded) and the usage inside the ContentPresenter. But for the moment, let's assume that the DynamicResource should point to ShowAsExpanded.
You can't and shouldn't access the combobox via code. You should bind the datacontext to the grid that uses the style. If you don't want to do that, you will have to find the content at runtime and search for the child combobox.

you need to use FindName. check out http://msdn.microsoft.com/en-us/library/system.windows.frameworktemplate.findname.aspx

Cannot drag activities from WPF ListBox into WorkflowView

I'm trying to host the Workflow Designer in a WPF application. The WorkflowView control is hosted under a WindowsFormsHost control. I've managed to load workflows onto the designer which is successfully linked to a PropertyGrid, also hosted in another WindowsFormsHost.
WorkflowView workflowView = rootDesigner.GetView(ViewTechnology.Default) as WorkflowView;
window.WorkflowViewHost.Child = workflowView;
The majority of the rehosting code is the same as in http://msdn.microsoft.com/en-us/library/aa480213.aspx.
I've created a custom Toolbox using a ListBox WPF control bound to a list of ToolboxItems.
<ListBox Grid.Row="1" Margin="0 0 0 4" BorderThickness="1" BorderBrush="DarkGray" ItemsSource="{Binding Path=ToolboxItems}" PreviewMouseLeftButtonDown="ListBox_PreviewMouseLeftButtonDown" AllowDrop="True">
<ListBox.Resources>
<vw:BitmapSourceTypeConverter x:Key="BitmapSourceConverter" />
</ListBox.Resources>
<ListBox.ItemTemplate>
<DataTemplate DataType="{x:Type dd:ToolboxItem}">
<StackPanel Orientation="Horizontal" Margin="3">
<Image Source="{Binding Path=Bitmap, Converter={StaticResource BitmapSourceConverter}}" Height="16" Width="16" Margin="0 0 3 0" />
<TextBlock Text="{Binding Path=DisplayName}" FontSize="14" Height="16" VerticalAlignment="Center" />
<StackPanel.ToolTip>
<TextBlock Text="{Binding Path=Description}" />
</StackPanel.ToolTip>
</StackPanel>
</DataTemplate>
</ListBox.ItemTemplate>
</ListBox>
In the ListBox_PreviewMouseLeftButtonDown handler:
private void ListBox_PreviewMouseLeftButtonDown(object sender, MouseButtonEventArgs e)
{
ListBox parent = (ListBox)sender;
UIElement dataContainer;
//get the ToolboxItem for the selected item
object data = GetObjectDataFromPoint(parent, e.GetPosition(parent), out dataContainer);
//if the data is not null then start the drag drop operation
if (data != null)
{
DataObject dataObject = new DataObject();
dataObject.SetData(typeof(ToolboxItem), data);
DragDrop.DoDragDrop(parent, dataObject, DragDropEffects.Move | DragDropEffects.Copy);
}
}
With that setup, I'm unable to drag any item from my custom Toolbox onto the designer. The cursor is always displayed as "No" anywhere on the designer.
I've been trying to find anything about this on the net for half a day now and I really hope some can help me here.
Any feedback is much appreciated. Thank you!
Carlos

This might sound stupid as my system is shutting down. :) But can you check your WorkflowView for whether AllowDrop is set? Have you handled the DragEnter event?

Finally got Drag and Drop working. There were three things that needed doing, for whatever reason WorkflowView has:
1.) I had to use System.Windows.Forms.DataObject instead of System.Windows.DataObject when serializing the ToolboxItem when doing DragDrop.
private void ListBox_MouseDownHandler(object sender, MouseButtonEventArgs e)
{
ListBox parent = (ListBox)sender;
//get the object source for the selected item
object data = GetObjectDataFromPoint(parent, e.GetPosition(parent));
//if the data is not null then start the drag drop operation
if (data != null)
{
System.Windows.Forms.DataObject dataObject = new System.Windows.Forms.DataObject();
dataObject.SetData(typeof(ToolboxItem), data as ToolboxItem);
DragDrop.DoDragDrop(this, dataObject, DragDropEffects.Move | DragDropEffects.Copy);
}
}
2.) DragDrop.DoDragDrop source must be set to the IToolboxService set in the IDesignerHost. The control holding the ListBox implements IToolboxService.
// "this" points to ListBox's parent which implements IToolboxService.
DragDrop.DoDragDrop(this, dataObject, DragDropEffects.Move | DragDropEffects.Copy);
3.) The ListBox should be bound to a list of ToolboxItems returned by the following helper method, passing it the Type of the activities to show in the tool box:
...
this.ToolboxItems = new ToolboxItem[]
{
GetToolboxItem(typeof(IfElseActivity))
};
...
internal static ToolboxItem GetToolboxItem(Type toolType)
{
if (toolType == null)
throw new ArgumentNullException("toolType");
ToolboxItem item = null;
if ((toolType.IsPublic || toolType.IsNestedPublic) && typeof(IComponent).IsAssignableFrom(toolType) && !toolType.IsAbstract)
{
ToolboxItemAttribute toolboxItemAttribute = (ToolboxItemAttribute)TypeDescriptor.GetAttributes(toolType)[typeof(ToolboxItemAttribute)];
if (toolboxItemAttribute != null && !toolboxItemAttribute.IsDefaultAttribute())
{
Type itemType = toolboxItemAttribute.ToolboxItemType;
if (itemType != null)
{
// First, try to find a constructor with Type as a parameter. If that
// fails, try the default constructor.
ConstructorInfo ctor = itemType.GetConstructor(new Type[] { typeof(Type) });
if (ctor != null)
{
item = (ToolboxItem)ctor.Invoke(new object[] { toolType });
}
else
{
ctor = itemType.GetConstructor(new Type[0]);
if (ctor != null)
{
item = (ToolboxItem)ctor.Invoke(new object[0]);
item.Initialize(toolType);
}
}
}
}
else if (!toolboxItemAttribute.Equals(ToolboxItemAttribute.None))
{
item = new ToolboxItem(toolType);
}
}
else if (typeof(ToolboxItem).IsAssignableFrom(toolType))
{
// if the type *is* a toolboxitem, just create it..
//
try
{
item = (ToolboxItem)Activator.CreateInstance(toolType, true);
}
catch
{
}
}
return item;
}
GetToolboxItem method is from http://msdn.microsoft.com/en-us/library/aa480213.aspx source, in the ToolboxService class.
Cheers,
Carlos