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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

UWP Combobox items scrolls to mid for no reason

I noticed that in a combobox which has some itemsource attached to it, when there is no selected item it tends to scroll to middle of the item instead of starting at the top (first item) and when an item is selected it does sometime scroll to the selected item.
So I want to scroll to first item when no item is selected. For that I tried following fixes.
Code
private void ComboBoxKeyboardSelectionBehavior_DropDownOpened(object sender, object e)
{
var comboBox = (ComboBox) sender;
if(comboBox.SelectedIndex == -1)
{
//var scrollviewer = comboBox.GetScrollViewer();
//scrollviewer.ChangeView(0, 0, null);
//var allItems = comboBox.Items.ToList();
//var cccc = comboBox.Items.Count;
//var firstItem = allItems.First();
var ci = comboBox.ContainerFromIndex(0) as ComboBoxItem;
if (ci != null)
{
ci.StartBringIntoView();
}
}
else
{
var ci = comboBox.ContainerFromIndex(comboBox.SelectedIndex) as ComboBoxItem;
if (ci != null)
{
ci.StartBringIntoView();
}
}
}
WinRTXamlToolkit.Controls.Extensions gave me the option to get scrollviewer and then try the ChangeView method but that isn't working. I got the First item from the list successfully and used the ContainerFromItem method but it returned me null. So I also tried ContainerFromIndex method and provided index as 0 because that is supposed to be the first item, but that aint working either.
In case of selected item (else statement) it is working fine with ContainerFromIndex(comboBox.SelectedIndex) but just to test when I tried it with ContainerFromItem it returned null.
Just FYI, this event is in an attached behavior to the combobox style but that shouldn't matter because behavor works flawlessly for selected item scenario.

If you want to scroll to the first item when there is no selected item, you need to change the behavior of the DropDown of a ComboBox instead of ScrollViewer of a ComboBox.
The DropDown of a ComboBox is acutally a Popup, and the position where to show the Popup is defined in the code behind, and we can’t access to it. One workaround is finding the Popup and relocate it when it is opened, but using this method we need to calculate the VerticalOffset property each time when it is opened, and there are quite many scenarios for different value of VerticalOffset.
Therefore, we suggest you custom a control whose behavior like a ComboBox and position to the first item when no item is selected. For example:
Create a UserControl:
<Button x:Name="rootButton" BorderBrush="Gray" BorderThickness="2" Click="Button_Click" MinWidth="80" Background="Transparent" Padding="0">
<Grid VerticalAlignment="Stretch" HorizontalAlignment="Stretch"
Width="{Binding ElementName=rootButton, Path=ActualWidth}">
<Grid.ColumnDefinitions>
<ColumnDefinition Width="*" />
<ColumnDefinition Width="32" />
</Grid.ColumnDefinitions>
<TextBlock Text="{x:Bind selectedItem, Mode=OneWay}" Grid.Column="0" VerticalAlignment="Center" FontSize="15" HorizontalAlignment="Center" />
<FontIcon Grid.Column="1" FontSize="12" FontFamily="Segoe MDL2 Assets" Glyph="" HorizontalAlignment="Right"
Margin="0,10,10,10" VerticalAlignment="Center" />
</Grid>
<FlyoutBase.AttachedFlyout>
<MenuFlyout Placement="Bottom" x:Name="menuFlyout">
<MenuFlyoutItem Text="Item 1" Click="MenuFlyoutItem_Click" />
<MenuFlyoutItem Text="Item 2" Click="MenuFlyoutItem_Click" />
<MenuFlyoutItem Text="Item 3" Click="MenuFlyoutItem_Click" />
<MenuFlyoutItem Text="Item 4" Click="MenuFlyoutItem_Click" />
<MenuFlyoutItem Text="Item 5" Click="MenuFlyoutItem_Click" />
</MenuFlyout>
</FlyoutBase.AttachedFlyout>
And the code behind in this UserControl:
public sealed partial class CustomComboBox : UserControl, INotifyPropertyChanged
{
public CustomComboBox()
{
this.InitializeComponent();
selectedItem = "";
}
private string _selectedItem;
public string selectedItem
{
get { return _selectedItem; }
set
{
_selectedItem = value;
if (PropertyChanged != null)
{
PropertyChanged(this, new PropertyChangedEventArgs("selectedItem"));
}
}
}
public event PropertyChangedEventHandler PropertyChanged;
private void MenuFlyoutItem_Click(object sender, RoutedEventArgs e)
{
var item = sender as MenuFlyoutItem;
selectedItem = item.Text;
}
private void Button_Click(object sender, RoutedEventArgs e)
{
FlyoutBase.ShowAttachedFlyout(sender as Button);
}
}
You can use the CustomComboBox in other page like this:
<local:CustomComboBox VerticalAlignment="Center" HorizontalAlignment="Center" />
By defalult this CustomComboBox will show its DropDown list under it.
In addition, you can also consider using other control such as a ListBox to directly replace the ComboBox to avoid the situation.
Update:
Currently, the ComboBox control does not provide related APIs for setting the starting position of DropDown in a Style, but we have a workaround to get the ScrollViewer inside the DropDown,and then call the ChangeView method to change the position. For example:
Define a custom combo box inherited from ComboBox class to get the ScrollViewer:
public class TestComboBox : ComboBox
{
public ScrollViewer InternalScrollViewer;
protected override void OnApplyTemplate()
{
InternalScrollViewer = GetTemplateChild("ScrollViewer") as ScrollViewer;
base.OnApplyTemplate();
}
}
Call the ChangeView method to change the position after items are initialized by using Task.Delay() in the ComboBoxKeyboardSelectionBehavior_DropDownOpened event handler:
await Task.Delay(50);
comboBox.InternalScrollViewer.ChangeView(0, 0, 1);
Note, use TestComboBox instead of ComboBox in XAML.

Add textblock text to favorite list on button click

I have two pages: the first is mainpage.xaml and the second is favoriteslist.xaml.
In mainpage.xaml I have a text block, which shows some dynamic text automatically.
And I have a button also on mainpage.xaml.
From which I want when I click on that button, text appears on text block should go to favorite list in favoriteslist.xaml page.
If text already favorite, which text appears on text block should be removed from favorite list on button click.
So finally I need help to implement this functionality textblock which shows dynamically already created but I only need to know how to develop add to favorite functionality.
Textblock:
<TextBlock x:Name="StringTextBlock" Text="" Margin="9,-7,0,0" Style="{StaticResource PhoneTextTitle1Style}" />
Button:
<Button Grid.Row="2" x:Name="AddToFavoritesButton"
Content="Add" Style="{StaticResource ButtonStyle2}" Margin="2"
Click="AddToFavoritesButton_Click"/>
C#
private void AddToFavoritesButton_Click(object sender, RoutedEventArgs e)
{
}
Listbox:
<ListBox x:Name="FavoriteListBox" />

I would use IsolatedStorageSettings to store the list and compare the dynamic text to the list in the isolatedstoragesettings upon button click. Then on FavouritesList page, set itemsource of the listbox to the list in IsolatedStorageSettings.So here are the steps to be followed:
1. Create a model/class to set the dynamic text being shown on the text block
public class favourites
{
public string myText { get; set; }
}
2. In the button click event on MainPage.xaml.cs, first set the dynamic text (where ever you are getting it from) to the text block if you need to and then create the list and/or compare
private void AddToFavoritesButton_Click(object sender, RoutedEventArgs e)
{
//your dynamic text set to textblock
StringTextBlock.Text = myDynamicText;
//Set value of your text to member variable of the model/class
favourites f = new favourites();
f.myText = myDynamicText;
IsolatedStorageSettings settings = IsolatedStorageSettings.ApplicationSettings;
/*Check if "FavouritesList" key is present in IsolatedStorageSettings
which means already a list had been added. If yes, retrieve the
list, compare each item with your dynamic text, add or remove
accordingly and replace the new list in IsolatedStorageSettings
with same key. */
if (settings.Contains("FavouritesList"))
{
List<favourites> l = (List<favourites>)settings["FavouritesList"];
for(int i = 0; i <= l.Count()-1; i++)
{
if (l[i].Equals(myDynamicText))
{
l.RemoveAt(i);
settings["FavouritesList"] = l;
}
else
{
l.Add(f);
settings["FavouritesList"] = l;
}
}
}
//If no key in IsolatedStorageSettings means no data has been added
//in list and IsolatedStorageSettings. So add new data
else
{
List<favourites> l = new List<favourites>();
l.Add(f);
settings["FavouritesList"] = l;
}
settings.Save();
}
Now all that is left is show the always updated list in the FavouritesList Page. I added a 'NoData' textblock that should be visible when there is nothing in the list. Else the list will be displayed.
In FavouritesList.xaml
<ListBox x:Name="FavoriteListBox" Visibility="Collapsed">
<ListBox.ItemTemplate>
<DataTemplate>
<TextBlock Text="{Binding myText}"/>
</DataTemplate>
</ListBox.ItemTemplate>
</ListBox>
<TextBlock Name="NoData"
Text="No Data"
Visibility="Collapsed"
Width="50"
Height="50"/>
In FavouritesList.xaml.cs
IsolatedStorageSettings settings = IsolatedStorageSettings.ApplicationSettings;
if (settings.Contains("FavouritesList"))
{
List<favourites> l = (List<favourites>)settings["FavouritesList"];
if(l.Count!= 0)
{
NoData.Visibility = System.Windows.Visibility.Collapsed;
FavoriteListBox.Visibility = System.Windows.Visibility.Visible;
FavoriteListBox.ItemsSource = l;
}
}
else
{
FavoriteListBox.Visibility = System.Windows.Visibility.Collapsed;
NoData.Visibility = System.Windows.Visibility.Visible;
}
I have not tested this but should definitely work. Hope it helps!

Make specific ListView item not clickable in Universal Windows Platform

I am using a ListView element in my XAML:
<ListView
x:Name="myList"
IsItemClickEnabled="true"
ItemClick="onDrawerItemClick"
SelectionMode="Single"
ScrollViewer.VerticalScrollBarVisibility="Hidden">
<ListView.ItemTemplate>
<DataTemplate>
<Grid
Width="260">
<Grid.ColumnDefinitions>
<ColumnDefinition
Width="44" />
<ColumnDefinition
Width="*" />
</Grid.ColumnDefinitions>
<Image
x:Name="image"
Source="{Binding myIcon}"
Grid.Column="0" />
<TextBlock
Text="{Binding myTxt}"
Grid.Column="1" />
</Grid>
</DataTemplate>
</ListView.ItemTemplate>
</ListView>
and I populate it using Bind property like so:
List<MyObj> listData = a list with title + image uri;
myList.ItemsSource = listData;
I need to disable click only for some items depending on some value from MyObj in my list but the others to have it. In Android we use adapter for that, how should I handle it here?

First, you should create a new bool property called Disabled inside your MyObj object.
Then, subscribe to myList's ContainerContentChanging event where you have access to the ListViewItem and its corresponding Item, which in this case is your MyObj. So, if MyObj.Disabled is true, make that ListViewItem non-clickable.
private void myList_ContainerContentChanging(ListViewBase sender, ContainerContentChangingEventArgs args)
{
var listViewItem = args.ItemContainer;
if (listViewItem != null)
{
var model = (MyObj)args.Item;
if (model.Disabled)
{
listViewItem.IsHitTestVisible = false;
// OR
//listViewItem.IsEnabled = false;
}
}
}
Keep in mind that you might want to use listViewItem.IsEnabled = false if you want that item to appear dimmed. This is because the default ListViewItemstyle has a Disabled state that reduces its Opacity; while setting listViewItem.IsHitTestVisible = false won't change its appearance in any way.

The listView is a strange control as it does not have any mechanism to disable selection.
So what I suggest you do is rather handle the event that notifies the framework that an item has been selected by attaching an event handler to ItemSelectionChanged and in there perform a deselect on the item:
yourListView.ItemSelectionChanged += yourListView_ItemSelectionChanged;
private void yourListView_ItemSelectionChanged(
object sender,
ListViewItemSelectionChangedEventArgs e)
{
if (e.IsSelected)
e.Item.Selected = false;
}
Please let me know if my answer helps :)

showing multiple pushpins on a map in windows phone using mvvm model

I have the following view in my mvvm model based app which should display all the pushpins I bind to it using binding property "PushPinLocation" from my view model.
<MapNS:Map
Center="{Binding MapCenter, Mode=TwoWay}" Margin="0,0,-5,0"
CartographicMode="{Binding MapMode, Mode=TwoWay}"
LandmarksEnabled="True" PedestrianFeaturesEnabled="True"
ZoomLevel="{Binding MapZoomLevel, Mode=TwoWay}"
Foreground="AliceBlue" Grid.Row="1" Height="713" Width="425"
x:Name="mapPanoramaAddress" >
<!--Adding Location to show map initially until the data arrived-->
<maptk:MapExtensions.Children>
<maptk:MapItemsControl Name="StoresMapItemsControl" >
<maptk:MapItemsControl.ItemTemplate>
<DataTemplate>
<maptk:Pushpin x:Name="PushPins" Background="White"
GeoCoordinate="{Binding PushPinLocation}"
Content="{Binding PushPinDisplayText}"
Visibility="Visible" />
</DataTemplate>
</maptk:MapItemsControl.ItemTemplate>
</maptk:MapItemsControl>
<maptk:UserLocationMarker GeoCoordinate="{Binding PushPinLocation}" x:Name="UserLocationMarker" Visibility="Visible" />
</maptk:MapExtensions.Children>
</MapNS:Map>
In the geolocator positionchanged event which triggers for every few meters I am setting the value for binding property "PushPinLocation" (from my view model) which is common for pushpin and location marker.
//PushPinLocation
private GeoCoordinate _PushPinLocation = new GeoCoordinate(40.712923, -74.013292); //cannot assign null
public GeoCoordinate PushPinLocation
{
get { return _PushPinLocation; }
set
{
if (_PushPinLocation != value)
{
_PushPinLocation = value;
RaisePropertyChanged("PushPinLocation");
}
}
}
in the same viewmodel geolocator_Position changed event I am setting the pushpinlocation:
private void geolocator_PositionChanged(Geolocator sender, PositionChangedEventArgs args)
{
this.PushPinLocation = args.Position.Coordinate.ToGeoCoordinate();
}
But I always see the latest one showing up and old ones are never shown on the map.Is there any way I can retain the old ones as well.

This post is a year old, but unanswered, so here is my answer:
Instead of binding to a single PushPinLocation, use a collection. In your ViewModel, add this:
private List<GeoCoordinate> _pushPinLocations;
public List<GeoCoordinate> PushPinLocations
{
get { return _pushPinLocations; }
set
{
_pushPinLocations = value;
OnPropertyChanged("PushPinLocations");
}
}
and change your event to:
private void geolocator_PositionChanged(Geolocator sender, PositionChangedEventArgs args)
{
this.PushPinLocations.Add(args.Position.Coordinate.ToGeoCoordinate());
}
That will add the new location to the list and as long as its bound to this list of locations, all pins will show.
<maptk:MapItemsControl Name="StoresMapItemsControl" >
<maptk:MapItemsControl.ItemTemplate>
<DataTemplate>
<maptk:Pushpin x:Name="PushPins" Background="White"
GeoCoordinate="{Binding PushPinLocations}"
Content="{Binding PushPinDisplayText}"
Visibility="Visible" />
</DataTemplate>
</maptk:MapItemsControl.ItemTemplate>
</maptk:MapItemsControl>