We Keep Coding

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;
}

How to remove an item from a Xamarin Forms ListView?

I'm trying to remove items/rows from a ListView but the difficulty is that I need to also pass in some delegate or fire some event or something, so when a person clicks a button to remove that row, my code handles some other logic, elsewhere (eg. remove the item from the DB or whatever).
I have a custom control I made:
public class SportsTeam : StackLayout { .. }
Inside this control, one of the elements is a ListView which lists all the people in a sporting team.
var viewModel = teamMembers.Select(x => new SportsTeamViewModel(x));
return new ListView
{
HasUnevenRows = true,
ItemSource = viewModel,
ItemTemplate = new DataTemplate(typeof(SportsTeamViewCell));
};
Inside the SportsTeamViewCell I have the following:
private Grid CreateContent()
{
var grid = new Grid();
// Setup row and column definitions.
// Add items to the Grid
grid.Children.Add(...);
var removeButton = RemoveButton;
grid.Children.Add(removeButton);
Grid.SetRowSpan(removeButton, 2);
return grid;
}
private Button RemoveButton
{
get
{
var button = new Button
{
Image = "Icons/remove.png"
};
return button;
}
}
From here, I don't know how to make it so that the button fires an event or some delete could be passed in via the constructor, so some custom logic is performed against the individual cell/row/item that is to be removed.

Here is what you could do :
This be my model class :
public class Item
{
public string ItemName { get; set; }
public string ItemDetails { get; set; }
}
And in my XAML or you can write this in code as well, bind to the Command Parameter of your Item template :
<Button Text="Delete" CommandParameter="{Binding ItemName}" Clicked="DeleteClicked"></Button>
Full Item Template will be like below :
<ListView.ItemTemplate>
<DataTemplate>
<ViewCell>
<ViewCell.View>
<StackLayout Orientation="Horizontal">
<Label Text="{Binding ItemName}" HorizontalOptions="StartAndExpand" FontSize="30"></Label>
<Button Text="Delete" CommandParameter="{Binding ItemName}" Clicked="DeleteClicked">
</Button>
</StackLayout>
</ViewCell.View>
</ViewCell>
</DataTemplate>
</ListView.ItemTemplate>
And in you code file you can do this :
public void DeleteClicked(object sender, EventArgs e)
{
var item = (Xamarin.Forms.Button)sender;
Item listitem = (from itm in allItems
where itm.ItemName == item.CommandParameter.ToString()
select itm)
.FirstOrDefault<Item>();
allItems.Remove(listitem);
}
IMPORTANT : This would only delete the item from the bound collection. To delete it from the original list you need to use ObservableCollection
Here is the full source code of the explained scenario - Handling Child Control Event in Listview using XAMARIN.FORMS.
Also the Tutorial - How to handle Row selection and delete Button in Row For Custom ListView using Xamarin.Forms explain deletion from a listview as well.

I've found a similar approach and I want to share it. I filled the list with an ObservableCollection<MyObject>. Then I filled the CommandParameter with just CommandParameter="{Binding .}". So I got the whole Object back. Then you can just cast the CommandParameterto your Object and remove it from the ObservableCollection<MyObject> List
XAML:
CommandParameter="{Binding .}"
Filling my List:
savingExpensesCollection = new ObservableCollection<SavingsExpensesEntry> ();
savingExpensesCollection .Add (new SavingsExpensesEntry ("1000 mAh Akku", "Dampfgarten", new DateTime (635808692400000000), 8.95));
savingExpensesCollection .Add (new SavingsExpensesEntry ("Cool-Mint Aroma", "Dampfgarten", new DateTime (635808692400000000), 3.95));
savingExpensesCollection .Add (new SavingsExpensesEntry ("Basis", "Dampfgarten", new DateTime (635808692400000000), 13.65));
savingExpensesList.ItemsSource = savingExpenses;
EventHandler:
void OnDelete(object sender, EventArgs e)
{
var menuItem = ((MenuItem)sender);
SavingsExpensesEntry see ((SavingsExpensesEntry)menuItem.CommandParameter);
savingExpensesCollection .Remove (see);
}
I've using a MenuItem but it's the same approach with a Button

I just did using delete button
public void OnDelete(object sender, EventArgs e)
{
var mi = ((MenuItem)sender);
PhotoViewModel photo= ((photoViewModel)mi.CommandParameter);
photoModel.Remove(photo);
}

c# - how to handle with null selectedItem?

i have an issue with selectedItem of a listbox. When I select an item of the listbox, a popup would be displayed where you click the add button to select an image (it contains a value of selectedItem) which is working fine. But after clicking the add button to select the image, then you realise the image is wrong, so you click the add button again to select another image, it started problem because selectedItem is null. How to handle it? How to stay the value of selectedItem? Your given code much appreciated.
if (lstDinner.SelectedItem != null)
{
output = _imageInserter.InsertImage(imageName, lstDinner.SelectedItem.ToString());
PopupToysImage.IsOpen = true;
strDinner.DinnersDetails = lstDinner.SelectedItem.ToString()
}
else
{
// strDinner.DinnersDetails = null that cause a problem.
output = _imageInserter.InsertImage(imageName, strDinner.DinnersDetails);
PopupDinnerImage.IsOpen = true;
}
UPDATE HERE:
WPF:
<ListBox Style="{DynamicResource ListBoxStyle1}" DisplayMemberPath="Dinner" BorderBrush="#FFF0F0F0" x:Name="lstDinner" FontSize="20" HorizontalAlignment="Left" Margin="0,110,0,72.667" Width="436" SelectionMode="Extended" PreviewMouseLeftButtonDown="MouseDownHandler" ScrollViewer.CanContentScroll="True" UseLayoutRounding="False" KeyDown="lstDinner_KeyDown" MouseDoubleClick="lstDinner_MouseDoubleClick" >
events in C#:
private void MouseDownHandler(object sender, MouseButtonEventArgs e)
{
var parent = (ListBox)sender;
_dragSource = parent;
var data = GetObjectDataFromPoint(parent, e.GetPosition(parent));
if (e.ChangedButton == MouseButton.Left && e.ClickCount == 1)
{
if (data != null)
DragDrop.DoDragDrop(parent, data, DragDropEffects.Move);
}
}
private void lstDinner_KeyDown(object sender, KeyEventArgs e)
{
if (e.Key == Key.Delete)
{
RemoveItemsFromDatabase();
}
}
private void lstDinner_MouseDoubleClick(object sender, MouseButtonEventArgs e)
{
_dinnerImage = new DinnerImageExtractor();
BitmapImage getImage = new BitmapImage();
if (lstDinner.SelectedItem != null)
{
getImage = _dinnerImage.GetDinnerImages(lstDinner.SelectedItem.ToString());
if (getImage != null)
{
DinnerImagePopup.Source = getImage;
}
else
{
DinnerImagePopup.Source = new BitmapImage(new Uri("/DinnerApplicationWPF;component/Menu/Images/noImage-icon-pink.png", UriKind.Relative));
}
PopupDinnerImage.IsOpen = true;
// PopupInstrcution.IsOpen = false;
}
}

I would suggest something like this
if ( lstDinner.SelectedItem == null)
{
output = _imageInserter.InsertImage(imageName, lstToys.SelectedItem.ToString());
PopupToysImage.IsOpen = true;
lstDinner.Databind();
}
Note: This may not work as I dont have your actual code. I have added DataBind() in the if statement, if the selected item was null. It should refresh the list.

Best thing is to use two different Listbox item templates for selected and unselected items. So without displaying popup, you can add button into the selected item template.

Are you disabling the ListBox while you select the image?
If so I believe by simply disabling the ListBox the SelectedItem will be set to null.
EDIT:
I imagine you want your event handlers (like the mouse double click) to happen when an item in your list is double clicked, not when the ListBox is double clicked. You need to change your XAML to this:
<ListBox Style="{DynamicResource ListBoxStyle1}" DisplayMemberPath="Dinner" BorderBrush="#FFF0F0F0" x:Name="lstDinner" FontSize="20" HorizontalAlignment="Left" Margin="0,110,0,72.667" Width="436" SelectionMode="Extended" PreviewMouseLeftButtonDown="MouseDownHandler" ScrollViewer.CanContentScroll="True" UseLayoutRounding="False" KeyDown="lstDinner_KeyDown">
<ListBox.Resources>
<Style TargetType="ListBoxItem">
<EventSetter Event="MouseDoubleClick" Handler="lstDinner_MouseDoubleClick" />
</Style>
</ListBox.Resources>
</ListBox>
My selected item does not come up null when I run this code.

ListView - select index only programmatically

i am trying to implement listbox (or listview):
<ListView ItemsSource="{Binding Players}" SelectedIndex="{Binding SelectedIndex}">
My problem is, that i want to bind selected index to property in code-behind.
It work only on form start, but i need to disable user to change selection. Selectin will be changed ONLY programmaticaly.
Thanks for all advices or solutions :)

So, working solution:
private void playersList_SelectionChanged(object sender, SelectionChangedEventArgs e)
{
if (sender.GetType() == typeof(ListView))
{
(sender as ListView).SelectedIndex = GameObserver.Instance.core.SelectedIndex;
e.Handled = true;
}
}
In XAML:
<ListView ItemsSource="{Binding Players}" SelectedIndex="{Binding SelectedIndex}" SelectionChanged="playersList_SelectionChanged">
And bounded property:
private int selectedIndex = 1;
public int SelectedIndex
{
get
{
return selectedIndex;
}
}

You have two tasks here:
Selecting programmatically: WPF ListView Programmatically Select Item
And disabling user selection: WPF ListView turn off selection

Just have no set
Public Int SelectedIndex
{
get { return selectedindex; }
}
public void mysub()
{
selectedindex = 2;
NotifyPropertyChanged("SelectedIndex");
}

ListBox ScrollIntoView when using CollectionViewSource with GroupDescriptions (i.e. IsGrouping == True)

Short version
I would like to scroll the ListBox item into view when the selection is changed.
Long version
I have a ListBox with the ItemsSource bound to a CollectionViewSource with a GroupDescription, as per the example below.
<Window.Resources>
<CollectionViewSource x:Key="AnimalsView" Source="{Binding Source={StaticResource Animals}, Path=AnimalList}">
<CollectionViewSource.GroupDescriptions>
<PropertyGroupDescription PropertyName="Category"/>
</CollectionViewSource.GroupDescriptions>
</CollectionViewSource>
</Window.Resources>
<ListBox x:Name="AnimalsListBox"ItemsSource="{Binding Source={StaticResource AnimalsView}}" ItemTemplate="{StaticResource AnimalTemplate}" SelectionChanged="ListBox_SelectionChanged">
<ListBox.GroupStyle>
<GroupStyle HeaderTemplate="{StaticResource CategoryTemplate}" />
</ListBox.GroupStyle>
</ListBox>
There is a SelectionChanged event in the a code-behind file.
public List<Animal> Animals { get; set; }
private void ListBox_SelectionChanged(object sender, SelectionChangedEventArgs e)
{
ListBox control = (ListBox)sender;
control.ScrollIntoView(control.SelectedItem);
}
Now. If I set the AnimalsListBox.SelectedItem to an item that is currently not visible I would like to have it scroll in view. This is where it gets tricky, as the ListBox is being groups (the IsGrouped property is true) the call to ScrollIntoView fails.
System.Windows.Controls.ListBox via Reflector. Note the base.IsGrouping in the OnBringItemIntoView.
public void ScrollIntoView(object item)
{
if (base.ItemContainerGenerator.Status == GeneratorStatus.ContainersGenerated)
{
this.OnBringItemIntoView(item);
}
else
{
base.Dispatcher.BeginInvoke(DispatcherPriority.Loaded, new DispatcherOperationCallback(this.OnBringItemIntoView), item);
}
}
private object OnBringItemIntoView(object arg)
{
FrameworkElement element = base.ItemContainerGenerator.ContainerFromItem(arg) as FrameworkElement;
if (element != null)
{
element.BringIntoView();
}
else if (!base.IsGrouping && base.Items.Contains(arg))
{
VirtualizingPanel itemsHost = base.ItemsHost as VirtualizingPanel;
if (itemsHost != null)
{
itemsHost.BringIndexIntoView(base.Items.IndexOf(arg));
}
}
return null;
}
Questions
Can anyone explain why it does not work when using grouping?
The ItemContainerGenerator.ContainerFromItem always returns null, even though it's status states that all the containers have been generated.
How I can achieve the scrolling into view when using grouping?

I have found a solution to my problem. I was certain that I wasn't the first person to hit this issue so I continued to search StackOverflow for solutions and I stumbled upon this answer by David about how ItemContainerGenerator works with a grouped list.
David's solution was to delay accessing the ItemContainerGenerator until after the rendering process.
I have implemented this solution, with a few changes that I will detail after.
private void ListBox_SelectionChanged(object sender, SelectionChangedEventArgs e)
{
ListBox control = (ListBox)sender;
if (control.IsGrouping)
{
if (control.ItemContainerGenerator.Status == GeneratorStatus.ContainersGenerated)
Dispatcher.BeginInvoke(DispatcherPriority.Render, new Action(DelayedBringIntoView));
else
control.ItemContainerGenerator.StatusChanged += ItemContainerGenerator_StatusChanged;
}
else
control.ScrollIntoView(control.SelectedItem);
}
private void ItemContainerGenerator_StatusChanged(object sender, EventArgs e)
{
if (ItemContainerGenerator.Status != GeneratorStatus.ContainersGenerated)
return;
ItemContainerGenerator.StatusChanged -= ItemContainerGenerator_StatusChanged;
Dispatcher.BeginInvoke(DispatcherPriority.Render, new Action(DelayedBringIntoView));
}
private void DelayedBringIntoView()
{
var item = ItemContainerGenerator.ContainerFromItem(SelectedItem) as ListBoxItem;
if (item != null)
item.BringIntoView();
}
Changes:
Only uses the ItemContainerGenerator approach when it IsGrouping is true, otherwise continue to use the default ScrollIntoView.
Check if the ItemContainerGenerator is ready, if so dispatch the action, otherwise listen for the ItemContainerGenerator status to change.. This is important as if it is ready then the StatusChanged event will never fire.

The out of the box VirtualizingStackPanel does not support virtualizing grouped collection views. When a grouped collection is rendered in an ItemsControl, each group as a whole is an item as opposed to each item in the collection which results in "jerky" scrolling to each group header and not each item.
You'll probably need to roll your own VirtualizingStackPanel or ItemContainerGenerator in order to keep track of the containers displayed in a group. It sounds ridiculous, but the default virtualization with grouping in WPF is lacking to say the least.