Develop Reference

WPF C# - Binding Enum to ComboBox

I have a combobox with the following options: "HardDelete", "SoftDelete", "MoveToDeletedItems"
I want the default selection to match with the following property of an EmailAction object:
public DeleteMode DeleteMode { get; set; }
Here is the line of code I'm using to try to set this:
cmboDelMode.SelectedItem = emailActionInstance.DeleteMode.ToString();
Related XAML:
<ComboBox x:Name="cmboDelMode" HorizontalAlignment="Left" Margin="149,218,0,0" VerticalAlignment="Top" Width="120">
<ComboBoxItem Content="HardDelete" HorizontalAlignment="Left" Width="118"/>
<ComboBoxItem Content="SoftDelete" HorizontalAlignment="Left" Width="118"/>
<ComboBoxItem Content="MoveToDeletedItems" HorizontalAlignment="Left" Width="118"/>
</ComboBox>
Currently the combobox is defaulting to being empty so is not working as expected. I am able to use "emailActionInstance.DeleteMode.ToString();" to view the data in a text box, so it seems I might just be setting the selected item incorrectly?

The issue is that setting ComboBox.SelectedItem doesn't work unless the ComboBox contains the item you are setting it to. In your case your ComboBox is filled with three ComboBoxItem objects which have their Content property set to a string. So ComboBox.SelectedItem is a ComboBoxItem. You are trying to set the ComboBox.SelectedItem to a string, which will not equal any of the objects contained in the ComboBox. Therefore, nothing happens.
I would suggest setting up Binding for your ComboBox like here:
<ComboBox ItemsSource="{Binding DeleteModes}" SelectedItem="{Binding SelectedDeleteMode}" />
And then create a ViewModel to bind to. If you bind an Enum to a ComboBox it will display correctly so you won't need to call DeleteMode.ToString():
public class ViewModel : INotifyPropertyChanged
{
public ViewModel()
{
DeleteModes = new ObservableCollection<DeleteMode>
{ DeleteMode.HardDelete, DeleteMode.SoftDelete,
DeleteMode.MoveToDeletedItems };
}
public event PropertyChangedEventHandler PropertyChanged;
DeleteMode _selected_delete_mode;
public DeleteMode SelectedDeleteMode {
get { return _selected_delete_mode; }
set {
_selected_delete_mode = value;
PropertyChanged?.Invoke(this, new PropertyChangedEventArgs("SelectedDeleteMode"));
}
}
ObservableCollection<DeleteMode> _delete_modes;
public ObservableCollection<DeleteMode> DeleteModes {
get { return _delete_modes; }
set {
_delete_modes = value;
PropertyChanged?.Invoke(this, new PropertyChangedEventArgs("DeleteModes"));
}
}
public void update_mode(DeleteMode mode) => SelectedDeleteMode = mode;
}

How to get particular property from item selected in ListBox

I have the following:
<ListBox SelectedItem="{Binding SelectedItem}"
ItemsSource="{Binding items}" DisplayMemberPath="s"/>
<TextBlock Text="{Binding SelectedItem.s}"/>
This is definition of SelectedItem
public MemEntity SelectedItem {get; set;}
MemEntity is a class containing
public String s {get; get;}.
Basically, I want s of the selected item to be shown in the TextBlock (same property as shown in ListBox). This doesn't work, so what am I doing wrong?

Try this,
<TextBlock ... Text="{Binding ElementName=items, Path=SelectedItem.s}" />
then add a name to your ListBox as,
<ListBox x:Name="items" SelectedItem="{Binding SelectedItem}"
ItemsSource="{Binding items}" DisplayMemberPath="s"/>

There are multiple way to do this. One option has already been provided in another answer that focusing on achieving the desired functionality by binding to a view element. Here is another option.
The view is unaware that selected item has changed. look into using INotifyPropertyChanged
You can create a base ViewModel to encapsulate the repeated functionality
public abstract class ViewModelBase : INotifyPropertyChanged {
public event PropertyChangedEventHandler PropertyChanged = delegate { };
protected virtual void OnPropertyChanged([CallerMemberName] string propertyName = null) {
PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
}
}
Have the view models inherit from this base class in order for the view to be aware of changes when binding.
public class ItemsViewModel : ViewModelBase {
public ItemsViewModel() {
items = new ObservableCollection<MemEntity>();
}
private MemEntity selectedItem;
public MemEntity SelectedItem {
get { return selectedItem; }
set {
if (selectedItem != value) {
selectedItem = value;
OnPropertyChanged(); //this will raise the property changed event.
}
}
}
public ObservableCollection<MemEntity> items { get; set; }
}
The view will now be aware when ever the SelectedItem property changes and will update the view accordingly.

Populate TextBox-es depending on selected value in ListBox XAML

So, I have this class
public class Multimedia : INotifyPropertyChanged
{
private string title;
private string artist;
private string genre;
private MediaType type;
public Multimedia (string _title, string _artist, string _genre, MediaType _type)
{
this.title = _title;
this.artist = _artist;
this.genre = _genre;
this.type = _type;
}
public String Title { get { return this.title; } }
public String Artist { get { return this.artist; } }
public String Genre { get { return this.genre; } }
public MediaType Type { get { return this.type; } }
public event PropertyChangedEventHandler PropertyChanged;
}
A collection in which I store the objects:
public class MultiMediaList : ObservableCollection<Multimedia>
{
public MultiMediaList()
{
Add(new Multimedia("YMCA", "Village People", "disco", MediaType.CASSETTE));
Add(new Multimedia("Free", "Rudimental", "D&B/Liquid", MediaType.DVD));
Add(new Multimedia("November Rain", "Guns'n'Roses", "rock", MediaType.CD));
}
}
And the XAML of the ListBox:
<ListBox Name="LB_media" SelectionChanged="ListBox_SelectionChanged" DisplayMemberPath="Title" />
Code-behind of the Window:
MultiMediaList mediaList;
public MainWindow()
{
InitializeComponent();
mediaList = new MultiMediaList();
LB_media.ItemsSource = mediaList;
}
The ListBox I populate with the Title property value of the objects in the collection. Now, I have code-behind function that populates 3 other TextBox elements (for the properties Title, Artist and Genre and I want to populate them with the corresponding property values, depending on which item in the ListBox is selected. But, can I do that in XAML?

You have to set the DataContext for the surrounding container:
<StackPanel DataContext="{Binding ElementName=LB_media, Path=SelectedItem}">
<TextBox x:Name="tbArtist" Text="{Binding Artist}" />
[..]
</StackPanel>
Of couse you could access the SelectedItem directly but this solution is more elegant and robust to changes. If you decide to alter the DataContext you'd only have to replace one line.

You can bind to property of SelectedItem in your ListBox
<StackPanel>
<TextBox Text="{Binding ElementName=LB_media, Path=SelectedItem.Artist, Mode=OneWay}" IsReadOnly="True"/>
<TextBox Text="{Binding ElementName=LB_media, Path=SelectedItem.Genre, Mode=OneWay}" IsReadOnly="True"/>
<TextBox Text="{Binding ElementName=LB_media, Path=SelectedItem.Type, Mode=OneWay}" IsReadOnly="True"/>
</StackPanel>
because you use TextBox and property is read-only you must use Mode=OneWay otherwise you'll have some exceptions

WPF Binding in ComboBox with UserControl list

In two combobox A and B.
A's ItemsSource is Custom list. and B's ItemsSource is UserControl list.
When manually setting the SelectedItem, A combobox works well, but B combobox UI do not show the selected Item. (In debugging, SelectedItem's value mapping is right, but the combobox B's UI do not be changed.)
All the other structure is same between A and B. What is the reason?
MainWindow.xaml
...
<ComboBox ItemsSource="{Binding FruitList}" SelectedItem="{Binding SelectedFruit}"
DisplayMemberPath="FruitName" />
<Button Content="Button" HorizontalAlignment="Left"
VerticalAlignment="Top" Width="75" Click="Button_Click"/>
<ComboBox ItemsSource="{Binding UserControlList}" SelectedItem="{Binding SelectedUserControl}" DisplayMemberPath="ItemName" />
<Button Content="Button" HorizontalAlignment="Left" VerticalAlignment="Top" Width="75" Click="Button_Click2"/>
</Grid>
MainWindow.xaml.cs
public partial class MainWindow : Window, INotifyPropertyChanged
{
public MainWindow()
{
InitializeComponent();
this.DataContext = this;
FruitList.Add(f1);
FruitList.Add(f2);
FruitList.Add(f3);
UserControlList.Add(u1);
UserControlList.Add(u2);
UserControlList.Add(u3);
}
Fruit f1 = new Fruit { FruitName = "Apple" };
Fruit f2 = new Fruit { FruitName = "Banana" };
Fruit f3 = new Fruit { FruitName = "Lemon" };
MyUserControl u1 = new MyUserControl { ItemName = "Apple" };
MyUserControl u2 = new MyUserControl { ItemName = "Banana" };
MyUserControl u3 = new MyUserControl { ItemName = "Lemon" };
ObservableCollection<Fruit> _FruitList = new ObservableCollection<Fruit>();
public ObservableCollection<Fruit> FruitList
{
get { return _FruitList; }
set
{
_FruitList = value;
OnPropertyChanged();
}
}
Fruit _SelectedFruit;
public Fruit SelectedFruit
{
get { return _SelectedFruit; }
set
{
_SelectedFruit = value;
OnPropertyChanged();
}
}
ObservableCollection<MyUserControl> _UserControlList = new ObservableCollection<MyUserControl>();
public ObservableCollection<MyUserControl> UserControlList
{
get
{
return _UserControlList;
}
set
{
_UserControlList = value;
OnPropertyChanged();
}
}
MyUserControl _SelectedUserControl;
public MyUserControl SelectedUserControl
{
get { return _SelectedUserControl; }
set
{
_SelectedUserControl = value;
OnPropertyChanged();
}
}
public event PropertyChangedEventHandler PropertyChanged;
void OnPropertyChanged([CallerMemberName] string caller = "")
{
if (PropertyChanged != null)
{
PropertyChanged(this, new PropertyChangedEventArgs(caller));
}
}
private void Button_Click(object sender, RoutedEventArgs e)
{
this.SelectedFruit = f3;
}
private void Button_Click2(object sender, RoutedEventArgs e)
{
this.SelectedUserControl = u3;
}
}
public class Fruit
{
public string FruitName { get; set; }
}
}
UserControl
public partial class MyUserControl : UserControl
{
public MyUserControl()
{
InitializeComponent();
}
public string ItemName { get; set; }
}

This is not the good way of achieving this. Better define the ItemTemplate for the combobox to have the UserControl in it like:
<ComboBox ItemsSource="{Binding ItemList}" SelectedItem="{Binding SelectedItem}" >
<ComboBox.ItemTemplate>
<DataTemplate>
<myControls:MyUserControl/>
</DataTemplate>
</ComboBox.ItemTemplate>
</ComboBox>
and define the class Item
public class Item
{
public string ItemName { get; set; }
}
ObservableCollection<Item> _ItemsList = new ObservableCollection<Item>();
public ObservableCollection<Item> ItemsList
{
get
{
return _ItemsList ;
}
set
{
_ItemsList = value;
OnPropertyChanged();
}
}
Here DataContext of your UserControl will be Item object. you can bind the ItemName within you user control to show it in anyway you want.
in your user control you can have:
<TextBlock Text="{Binding ItemName}"></TextBlock>

Since you have asked "What is the reason?":
The reason why the second combo box does not show any selection is that ComboBox handles items of type ContentControl specially. In the read-only selection box, it is not the ContentControl that is used to display the value, but the content of the ContentControl. Since a UserControl is a ContentControl, the content of the UserControl is displayed inside the selection box, and therefore you have lost the data context of the UserControl; in the end, an empty string is displayed even though SelectedItem contains a reference to the UserControl that still has a valid data context. (As far as I know this behavior is undocumented; but you can see that it works like this by examining the ComboBox's code on http://referencesource.microsoft.com/#PresentationFramework/src/Framework/System/Windows/Controls/ComboBox.cs, especially the UpdateSelectionBoxItem() method).
By setting IsEditable="True" on the second ComboBox, you can see that everything works fine if the combo box has no read-only selection box.
Therefore, you generally should avoid adding UI elements to combo boxes, especially if you are using the DisplayMemberPath property, i.e. if you never want to actually display the UI element.
The recommended way to display ComboBox items with non-standard appearance (e.g. with UserControls) is described in the answer of #nit.
If you, however, insist on passing a UserControl item list to the ComboBox, you might remove DisplayMemberPath and use something like this:
<ComboBox ItemsSource="{Binding UserControlList}" SelectedItem="{Binding SelectedUserControl}" >
<ComboBox.ItemTemplate>
<DataTemplate>
<TextBlock Text="{Binding ItemName}"/>
</DataTemplate>
</ComboBox.ItemTemplate>
</ComboBox>
Furthermore, in the constructor of your UserControl, you must place this line:
((FrameworkElement) Content).DataContext = this;
This is necessary to make sure that the correct data context is available in the read-only selection box, which only contains the content of the user control, not the user control itself.
Please note, that with the above example, the drop-down list contains text only (i.e. the item names), but the selection box will contain the fully rendered user control.

Binding Comboboxes which are in listbox to the viewmodels property(s)

Please look at the image below:
Only three items in the listbox are displayed in the above image but it can be any number of items depending on the user's choice.
Now, as you can see in the image above each item has two comboboxes. Now I want to have selectedItem or SelectedValue in my viewModel from which I should be able to get the user's selection. Now I don't know how to bind these comboboxes for getting the user's selection.
Suppose I have only one item instead of the list then I would declare a property of type int so that I can easily get the selectedValue but for the list I am very much confused. Can anybody point me to the right direction?

To start of, lets say the class you are going to be binding the combo box is
public class UnitSource :INotifyPropertyChanged
{
public IEnumerable Units
{
get { return new[] { "Test Unit", "Alternate Unit" }; }
}
string _selectedComboItem1;
public string SelectedComboItem1
{
get
{
return _selectedComboItem1;
}
set
{
if (_selectedComboItem1 == value)
return;
_selectedComboItem1 = value;
OnPropertyChanged();
}
}
string _selectedComboItem2;
public string SelectedComboItem2
{
get
{
return _selectedComboItem2;
}
set
{
if (_selectedComboItem2 == value)
return;
_selectedComboItem2 = value;
OnPropertyChanged();
}
}
public event PropertyChangedEventHandler PropertyChanged;
protected virtual void OnPropertyChanged([CallerMemberName]string propertyName = null)
{
var handler = PropertyChanged;
if (handler != null) handler(this, new PropertyChangedEventArgs(propertyName));
}
}
Then in your view model you will have an ObservableCollection of the UnitSource Like below
public ObservableCollection<UnitSource> MuchoUnitSources
{
get; set;
}
To get the selected ListBoxItem have this in your ViewModel
private UnitSource _selectedUnitSource;
public UnitSource SelectedUnitSource
{
get
{
return _selectedUnitSource;
}
set
{
if (_selectedUnitSource == value)
return;
_selectedUnitSource = value;
OnPropertyChanged();
}
}
Lets assume it is initialized like so
MuchoUnitSources = new ObservableCollection<UnitSource>(new []{ new UnitSource(),new UnitSource() });
The in your view your listbox should look like below
<ListBox Name ="TestList1" ItemsSource="{Binding MuchoUnitSources}" SelectedItem="{Binding SelectedUnitSource}">
<ListBox.ItemTemplate>
<DataTemplate>
<StackPanel Orientation="Vertical">
<ComboBox SelectedItem="{Binding SelectedComboItem1}" ItemsSource="{Binding Units}" />
<ComboBox SelectedItem="{Binding SelectedComboItem2}" ItemsSource="{Binding Units}" />
</StackPanel>
</DataTemplate>
</ListBox.ItemTemplate>
</ListBox>
Now whenever you select an item from any of the combobox they will update the objectbeing bound to.