I have a collectionview that is bound to an ObservableRangeCollectionin my ViewModel.
In my ViewModel there is a Method that runs onAppearing and I want my ColletionViewto be filled from there, but when I do so the collectionveiw dose not display the content only when i reload the content is shown.
View:
<RefreshView Grid.Row="1"
Grid.RowSpan="2"
Command="{Binding RefreshCommand}"
IsRefreshing="{Binding IsBusy, Mode=OneWay}">
<RefreshView.RefreshColor>
<OnPlatform x:TypeArguments="Color">
<On Platform="iOS" Value="White"/>
</OnPlatform>
</RefreshView.RefreshColor>
<CollectionView x:Name="Collection"
ItemsSource="{Binding Locations, Mode=OneWay}"
ItemTemplate="{StaticResource ListDataTemplate}"
RemainingItemsThresholdReachedCommand="{Binding LoadMoreCommand}"
RemainingItemsThreshold="10"
SelectionMode="Single"
BackgroundColor="Transparent"
ItemsLayout="VerticalList"
SelectedItem="{Binding SelectedItem}"
SelectionChangedCommand="{Binding SelectedCommand}">
<CollectionView.EmptyView>
<StackLayout Padding="12">
<Label HorizontalOptions="Center" Text="Keine Daten vorhanden!" TextColor="White"/>
</StackLayout>
</CollectionView.EmptyView>
</CollectionView>
</RefreshView>
ViewModel:
namespace YourPartys.ViewModels
{
public class ListViewModel : ViewModelBase
{
#region Variables
#endregion
#region Propertys
LocationModel selectedItem;
public LocationModel SelectedItem
{
get => selectedItem;
set => SetProperty(ref selectedItem, value);
}
public ObservableRangeCollection<LocationModel> Locations { get;set; } = new ObservableRangeCollection<LocationModel>();
double distance;
public double Distance
{
get => distance;
set => SetProperty(ref distance, value);
}
#endregion
#region Commands
public ICommand FilterButtonCommand { get; }
public ICommand RefreshCommand { get; }
public ICommand SelectedCommand { get; }
public ICommand LoadMoreCommand { get; }
#endregion
//Constructor
public ListViewModel()
{
FilterButtonCommand = new Command(OpenFilter);
RefreshCommand = new AsyncCommand(Refresh);
SelectedCommand = new AsyncCommand(Select);
}
public override async void VModelActive(Page sender, EventArgs eventArgs)
{
base.VModelActive(sender, eventArgs);
var locs = await FirestoreService.GetLocations("Locations");
Locations.AddRange(locs);
}
private void OpenFilter(object obj)
{
PopupNavigation.Instance.PushAsync(new ListFilterPage());
}
private async Task Refresh()
{
IsBusy = true;
var locs = await FirestoreService.GetLocations("Locations");
Locations.AddRange(locs);
IsBusy = false;
}
private async Task Select()
{
if (SelectedItem == null)
return;
var route = $"{nameof(DetailPage)}?Locationid={SelectedItem.Locationid}";
SelectedItem = null;
await AppShell.Current.GoToAsync(route);
}
}
}
There are several problems in your demo.
1.Since you set the BindingContext for your page in xaml as follows:
<ContentPage.BindingContext>
<viewmodels:MainViewModel/>
</ContentPage.BindingContext>
you didn't need to recreate another object MainViewModel in a CS file and reference it. These are two different objects.
MainViewModel viewModel;
viewModel = new MainViewModel();
protected override void OnAppearing()
{
base.OnAppearing();
viewModel.VModelActive(this, EventArgs.Empty);
}
So, you can get the BindingContext in MainPage.xaml.cs in function OnAppearing as follows:
protected override void OnAppearing()
{
base.OnAppearing();
viewModel = (MainViewModel)this.BindingContext;
viewModel.VModelActive(this, EventArgs.Empty);
}
The whole code is
public partial class MainPage : ContentPage
{
MainViewModel viewModel;
public MainPage()
{
InitializeComponent();
// viewModel = new MainViewModel();
}
protected override void OnAppearing()
{
base.OnAppearing();
viewModel = (MainViewModel)this.BindingContext;
viewModel.VModelActive(this, EventArgs.Empty);
}
}
2.when we set the text color of the Label to White,this makes it hard to see the text,so you can reset it to another color,for example Black:
<Label Text="{Binding Name}"
FontSize="30"
TextColor="White"/>
Please check the GIF for the problem.
I am actually using two imagebutton here and change IsVisible, since I couldn't accomplish swapping the image by Binding on the source.
ViewModel:
public bool IsAudioPlaying
{
get => player.IsPlaying;
}
...
public void PlayOrPause()
{
if (player.IsPlaying)
player.Pause();
else
player.Play();
PropertyChanged?.Invoke(this, new PropertyChangedEventArgs("IsAudioPlaying"));
}
XAML:
<ImageButton AbsoluteLayout.LayoutBounds=".5, 0, 100, 100" AbsoluteLayout.LayoutFlags="PositionProportional" Source="play.png" Padding="20" WidthRequest="80" HeightRequest="80"
CornerRadius="40" VerticalOptions="Center" HorizontalOptions ="Center" BackgroundColor="#cea448" Clicked="PlayOrPause" Margin="10" IsVisible="{Binding IsAudioPlaying, Converter={StaticResource InverseBoolConverter}}" />
<ImageButton AbsoluteLayout.LayoutBounds=".5, 0, 100, 100" AbsoluteLayout.LayoutFlags="PositionProportional" Source="pause.png" Padding="20" WidthRequest="80" HeightRequest="80"
CornerRadius="40" VerticalOptions="Center" HorizontalOptions ="Center" BackgroundColor="#cea448" Clicked="PlayOrPause" Margin="10" IsVisible="{Binding IsAudioPlaying}" />
I am actually using two imagebutton here and change IsVisible, since I couldn't accomplish swapping the image by Binding on the source.
Create a View Model.
public class ViewModel : INotifyPropertyChanged
{
private bool _isAudioPlaying;
public bool IsAudioPlaying
{
get
{
return _isAudioPlaying;
}
set
{
_isAudioPlaying = value;
OnPropertyChanged("IsAudioPlaying");
}
}
public event PropertyChangedEventHandler PropertyChanged;
protected virtual void OnPropertyChanged(string propertyName)
{
if (PropertyChanged != null)
{
PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
}
}
}
Use ObservableCollection to update.
ObservableCollection<ViewModel> observableCollection { get; set; }
public MainPage()
{
InitializeComponent();
observableCollection = new ObservableCollection<ViewModel>()
{
new ViewModel(){ IsAudioPlaying=true}
};
this.BindingContext = observableCollection;
}
private void PlayOrPause(object sender, EventArgs e)
{
if (observableCollection[0].IsAudioPlaying == true)
{
observableCollection[0].IsAudioPlaying = false;
imageButton.Source = "pause.png";
}
else
{
observableCollection[0].IsAudioPlaying = true;
imageButton.Source = "play.png";
}
}
I want to bind a CustomLabel to a VM by creating a new bindable property.
In OneWay mode, the first VM data has properly changed the property of the CustomLabel. but It didn't work from second time.
Although The VM event has occur, the Bindable Property of CustomView has not fired its PropertyChanged event.
It works properly in TwoWay mode though.
I've been testing for two days and searching for the cause, but I coudn't find it well.
Anybody tell me how to do?
// HomeViewModel.cs
public class HomeViewModel : INotifyPropertyChanged
{
public event PropertyChangedEventHandler PropertyChanged;
private string _customName = "-";
public string CustomName
{
get
{
Debug.WriteLine("Get_CustomName");
return _customName;
}
set
{
if (value != _customName)
{
Debug.WriteLine("Set_CustomName");
_customName = value;
PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(nameof(CustomName)));
}
}
}
}
// MainPage.cs
public partial class MainPage : ContentPage
{
HomeViewModel Vm = new HomeViewModel();
public MainPage()
{
InitializeComponent();
BindingContext = Vm;
}
void ButtonTrue_Clicked(object sender, EventArgs e)
{
Vm.CustomName = "True";
}
void ButtonFalse_Clicked(object sender, EventArgs e)
{
Vm.CustomName = "False";
}
}
<!-- MainPage.xaml -->
<ContentPage xmlns="http://xamarin.com/schemas/2014/forms"
xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
xmlns:local="clr-namespace:Ex_Binding"
xmlns:d="http://xamarin.com/schemas/2014/forms/design"
xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
mc:Ignorable="d"
x:Class="Ex_Binding.MainPage">
<StackLayout Padding="50,0" VerticalOptions="Center">
<StackLayout Orientation="Horizontal" HorizontalOptions="Center">
<Label Text="Custom Result : " />
<local:CustomLabel x:Name="lbCustom" MyText="{Binding CustomName}" HorizontalOptions="Center" />
</StackLayout>
<StackLayout Orientation="Horizontal">
<Button Text="TRUE" BackgroundColor="LightBlue" HorizontalOptions="FillAndExpand" Clicked="ButtonTrue_Clicked" />
<Button Text="FALSE" BackgroundColor="LightPink" HorizontalOptions="FillAndExpand" Clicked="ButtonFalse_Clicked" />
</StackLayout>
</StackLayout>
</ContentPage>
// CustomLabel.cs
public class CustomLabel : Label
{
public static readonly BindableProperty MyTextProperty = BindableProperty.Create(nameof(MyText), typeof(string), typeof(CustomLabel), null, BindingMode.OneWay, propertyChanged: OnMyTextChanged);
private static void OnMyTextChanged(BindableObject bindable, object oldValue, object newValue)
{
var thisBindable = (CustomLabel)bindable;
if (thisBindable != null)
{
thisBindable.MyText = (string)newValue;
}
}
public string MyText
{
get => (string)GetValue(MyTextProperty);
set
{
SetValue(MyTextProperty, value);
Text = value;
}
}
}
Cause :
thisBindable.MyText = (string)newValue;
Because you set the value of MyText when its value changed . So it will never been invoked next time (in TwoWay the method will been invoked multi times).
Solution:
You should set the Text in OnMyTextChanged directly .
private static void OnMyTextChanged(BindableObject bindable, object oldValue, object newValue)
{
var thisBindable = (CustomLabel)bindable;
if (thisBindable != null)
{
thisBindable.Text = (string)newValue;
}
}
public string MyText
{
get => (string)GetValue(MyTextProperty);
set
{
SetValue(MyTextProperty, value);
//Text = value;
}
}
I am trying to show a list of images in my UWP Xamarin project.
I don't want to use ImageCell.
That's a sample code from Xamarin Forum.
But I can't complete this code to run successfully.
Here is my code.
<ListView x:Name="listView">
<ListView.ItemTemplate>
<DataTemplate>
<ViewCell>
<StackLayout BackgroundColor="#eee"
Orientation="Vertical">
<StackLayout Orientation="Horizontal">
<Image Source="{Binding image}" />
<Label Text="{Binding title}"
TextColor="#f35e20" />
<Label Text="{Binding subtitle}"
HorizontalOptions="EndAndExpand"
TextColor="#503026" />
</StackLayout>
</StackLayout>
</ViewCell>
</DataTemplate>
</ListView.ItemTemplate>
</ListView>
public class ImageItem {
string title;
ImageSource image;
string subtitle;
}
ImageItem a= new ImageItem();
a.title = "XXX";
a.image = ImageSource.FromFile(String.Format("{0}{1}.png", Device.OnPlatform("Icons/", "", "Assets/"), "noimage"));
a.subtitle = "XXX";
list.Add(a);
listview.itemsSource = list;
I have noimage.png in Assets folder of UWP Xamarin Project.
How can I do?
I believe you will need ImageItem to implement the INotifyPropertyChanged interface if you want to use bindings. Can you try setting up the class ImageItem like so:
public class ImageItem : INotifyPropertyChanged
{
public event PropertyChangedEventHandler PropertyChanged;
string _title;
public string title
{
get
{
return _title;
}
set
{
if (_title != value)
_title = value;
if (PropertyChanged != null)
{
PropertyChanged(this, new PropertyChangedEventArgs("title"));
}
}
}
ImageSource _image;
public string image
{
get
{
return _image;
}
set
{
if (_image != value)
_image = value;
if (PropertyChanged != null)
{
PropertyChanged(this, new PropertyChangedEventArgs("image"));
}
}
}
string _subtitle;
public string subtitle
{
get
{
return _subtitle;
}
set
{
if (_subtitle != value)
_subtitle = value;
if (PropertyChanged != null)
{
PropertyChanged(this, new PropertyChangedEventArgs("subtitle"));
}
}
}
}
I want multi select drop down list for my mvvm cross UWP app. So is there any predefined control? Or I need to implement custom control to achieve this.
Any help or suggestions would be appreciated.
Thank You
Surprised that such common scenario is still not supported by built-in UWP ComboBox and that I couldn't found any working solutions anywhere.
Here is my minimal solution in case anyone else is looking.
XAML:
<UserControl
x:Class="MonoTorrent.GUI.Controls.MultiSelectComboBox"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
mc:Ignorable="d"
d:DesignHeight="300"
d:DesignWidth="400">
<StackPanel x:Name="rootElement" Orientation="Vertical" Margin="0">
<Button x:Name="comboBoxButton" BorderBrush="Gray" BorderThickness="2" Background="Transparent"
VerticalAlignment="Top" Click="ComboBoxButton_Click"
HorizontalAlignment="Stretch" FontSize="14" MinHeight="26" Height="26" Padding="0"
Width="{Binding ElementName=rootElement, Path=ActualWidth}">
<Grid VerticalAlignment="Stretch" Width="{Binding ElementName=rootElement, Path=ActualWidth}">
<Grid.ColumnDefinitions>
<ColumnDefinition Width="*" />
<ColumnDefinition Width="32" />
</Grid.ColumnDefinitions>
<TextBlock x:Name="SelectedValueTextBlock"
Grid.Column="0" VerticalAlignment="Center" FontSize="15" HorizontalAlignment="Left" Padding="7,0,0,0" />
<FontIcon Grid.Column="1" FontSize="12" FontFamily="Segoe MDL2 Assets" Glyph="" HorizontalAlignment="Right"
Margin="0,5,10,5" VerticalAlignment="Center" />
</Grid>
</Button>
<Popup x:Name="comboBoxPopup" IsLightDismissEnabled="True">
<Border BorderBrush="{ThemeResource ComboBoxDropDownBorderBrush}"
BorderThickness="{ThemeResource ComboBoxDropdownBorderThickness}"
Background="{ThemeResource ComboBoxDropDownBackground}"
HorizontalAlignment="Stretch">
<ListView x:Name="listView"
SelectionMode="Multiple"
SingleSelectionFollowsFocus="False"
SelectionChanged="ListView_SelectionChanged">
</ListView>
</Border>
</Popup>
</StackPanel>
</UserControl>
C#:
using System.Linq;
using System.Runtime.InteropServices.WindowsRuntime;
using Windows.Foundation;
using Windows.Foundation.Collections;
using Windows.UI.Xaml;
using Windows.UI.Xaml.Controls;
using Windows.UI.Xaml.Controls.Primitives;
using Windows.UI.Xaml.Data;
using Windows.UI.Xaml.Input;
using Windows.UI.Xaml.Media;
using Windows.UI.Xaml.Navigation;
namespace MonoTorrent.GUI.Controls
{
public sealed partial class MultiSelectComboBox : UserControl
{
#region ItemsSource dependency property
public object ItemsSource
{
get { return GetValue(ItemsSourceProperty); }
set
{
SetValue(ItemsSourceProperty, value);
listView.ItemsSource = value;
}
}
public static readonly DependencyProperty ItemsSourceProperty =
DependencyProperty.Register("ItemsSource", typeof(object), typeof(MultiSelectComboBox), new PropertyMetadata(new List<object>(), OnItemsSourcePropertyChanged));
private static void OnItemsSourcePropertyChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
{
MultiSelectComboBox instance = d as MultiSelectComboBox;
if (instance != null && e.NewValue != null)
{
instance.listView.ItemsSource = e.NewValue;
}
}
#endregion
#region ItemTemplate dependency property
public DataTemplate ItemTemplate
{
get { return (DataTemplate)GetValue(ItemTemplateProperty); }
set
{
SetValue(ItemTemplateProperty, value);
listView.ItemTemplate = value;
}
}
public static readonly DependencyProperty ItemTemplateProperty =
DependencyProperty.Register("ItemTemplate", typeof(DataTemplate), typeof(MultiSelectComboBox), new PropertyMetadata(null, OnItemTemplatePropertyChanged));
private static void OnItemTemplatePropertyChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
{
MultiSelectComboBox instance = d as MultiSelectComboBox;
if (instance != null && e.NewValue as DataTemplate != null)
{
instance.listView.ItemTemplate = (DataTemplate)e.NewValue;
}
}
#endregion
#region SelectedItems dependency property
public IList<object> SelectedItems
{
get { return (IList<object>)GetValue(SelectedItemsProperty); }
set { SetValue(SelectedItemsProperty, value); }
}
public static readonly DependencyProperty SelectedItemsProperty =
DependencyProperty.Register("SelectedItems", typeof(IList<object>), typeof(MultiSelectComboBox), new PropertyMetadata(new List<object>()));
#endregion
#region PopupHeight dependency property
public double PopupHeight
{
get { return (double)GetValue(PopupHeightProperty); }
set
{
SetValue(PopupHeightProperty, value);
if (value != 0)
{
listView.Height = value;
}
}
}
public static readonly DependencyProperty PopupHeightProperty =
DependencyProperty.Register("PopupHeight", typeof(double), typeof(MultiSelectComboBox), new PropertyMetadata(0.0, OnPopupHeightPropertyChanged));
private static void OnPopupHeightPropertyChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
{
MultiSelectComboBox instance = d as MultiSelectComboBox;
if (instance != null && (double)e.NewValue != 0)
{
instance.listView.Height = (double)e.NewValue;
}
}
#endregion
#region PopupWidth dependency property
public double PopupWidth
{
get { return (double)GetValue(PopupWidthProperty); }
set
{
SetValue(PopupWidthProperty, value);
if (value != 0)
{
listView.Width = value;
}
}
}
public static readonly DependencyProperty PopupWidthProperty =
DependencyProperty.Register("PopupWidth", typeof(double), typeof(MultiSelectComboBox), new PropertyMetadata(0.0, OnPopupWidthPropertyChanged));
private static void OnPopupWidthPropertyChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
{
MultiSelectComboBox instance = d as MultiSelectComboBox;
if (instance != null && (double)e.NewValue != 0)
{
instance.listView.Width = (double)e.NewValue;
}
}
#endregion
#region NoSelectionText dependency property
public string NoSelectionText
{
get { return (string)GetValue(NoSelectionTextProperty); }
set { SetValue(NoSelectionTextProperty, value); }
}
public static readonly DependencyProperty NoSelectionTextProperty =
DependencyProperty.Register("NoSelectionText", typeof(string), typeof(MultiSelectComboBox), new PropertyMetadata("No selection"));
#endregion
#region MultipleSelectionTextFormat dependency property
public string MultipleSelectionTextFormat
{
get { return (string)GetValue(MultipleSelectionTextFormatProperty); }
set { SetValue(MultipleSelectionTextFormatProperty, value); }
}
public static readonly DependencyProperty MultipleSelectionTextFormatProperty =
DependencyProperty.Register("MultipleSelectionTextFormat", typeof(string), typeof(MultiSelectComboBox), new PropertyMetadata("{0} selected"));
#endregion
public MultiSelectComboBox()
{
this.InitializeComponent();
this.Loaded += MultiSelectComboBox_Loaded;
}
private void MultiSelectComboBox_Loaded(object sender, RoutedEventArgs e)
{
this.UpdateSelectionText();
}
private void ComboBoxButton_Click(object sender, RoutedEventArgs e)
{
listView.SelectedItems.Clear();
foreach (var item in SelectedItems)
{
listView.SelectedItems.Add(item);
}
this.comboBoxPopup.IsOpen = true;
}
private void ListView_SelectionChanged(object sender, SelectionChangedEventArgs e)
{
if (!comboBoxPopup.IsOpen)
{
return;
}
this.SelectedItems = listView.SelectedItems.ToList();
UpdateSelectionText();
}
private void UpdateSelectionText()
{
if (this.SelectedItems == null || this.SelectedItems.Count == 0)
{
this.SelectedValueTextBlock.Text = NoSelectionText;
}
else if (this.SelectedItems.Count == 1)
{
this.SelectedValueTextBlock.Text = this.SelectedItems.First().ToString();
}
else
{
this.SelectedValueTextBlock.Text = String.Format(MultipleSelectionTextFormat, this.SelectedItems.Count);
}
}
}
}
Usage:
<controls:MultiSelectComboBox x:Name="MultiSelectComboBox"
ItemsSource="{Binding Values}"
SelectedItems="{Binding SelectedValues, Mode=TwoWay}"
NoSelectionText="{Binding EmptySelectionString}"
MultipleSelectionTextFormat="{Binding MultipleSelectedFormatString}"
PopupHeight="500" PopupWidth="200"
HorizontalAlignment="Stretch" FontSize="14" MinHeight="26" Height="26">
<controls:MultiSelectComboBox.ItemTemplate>
<DataTemplate>
<TextBlock Text="{Binding}" />
</DataTemplate>
</controls:MultiSelectComboBox.ItemTemplate>
</controls:MultiSelectComboBox>
Notes:
In current state can only be bound to a primitive type collection
like List< String >.
SelectedValues has to be List< object >, you can use
Cast< T > to convert from List< String >.
There is no built-in multi-select combobox in UWP, but you can build your own like this - Issue with multiselect combobox control in Windows 8 .
Basically you can add checkboxes to each item in a combobox and create a logic that will gather the selected items and provide a bindable way to access them.
To make it even simpler, you can create a special class that will have a IsChecked property and just add the checkbox with two-way binding to this property. This will ensure checking of the box in the UI will be reflected in the class and you can then just enumerate all the items to find those that have IsChecked set to true.
I would build it something like this...
First build your class
public class MultiSelectComboBox : ComboBox
{
public List<ComboBoxItem> SelectedItems
{
get { return (List<ComboBoxItem>)GetValue(SelectedItemsProperty); }
set { SetValue(SelectedItemsProperty, value); }
}
public static readonly DependencyProperty SelectedItemsProperty =
DependencyProperty.Register("SelectedItems", typeof(List<ComboBoxItem>), typeof(MultiSelectComboBox), new PropertyMetadata(new List<ComboBoxItem>()));
public static void SetIsSelected(UIElement element, bool value)
{
element.SetValue(IsSelectedProperty, value);
}
public static bool GetIsSelected(UIElement element)
{
return (bool)element.GetValue(IsSelectedProperty);
}
public static readonly DependencyProperty IsSelectedProperty =
DependencyProperty.RegisterAttached("IsSelected", typeof(bool), typeof(ComboBoxItem), new PropertyMetadata(false, OnIsSelectedChanged));
public static void SetParentComboBox(UIElement element, MultiSelectComboBox value)
{
element.SetValue(ParentComboBoxProperty, value);
}
public static MultiSelectComboBox GetParentComboBox(UIElement element)
{
return (MultiSelectComboBox)element.GetValue(ParentComboBoxProperty);
}
public static readonly DependencyProperty ParentComboBoxProperty =
DependencyProperty.RegisterAttached("ParentComboBox", typeof(MultiSelectComboBox), typeof(MultiSelectComboBox), new PropertyMetadata(null));
protected override DependencyObject GetContainerForItemOverride()
{
ComboBoxItem comboBoxitem = new ComboBoxItem();
MultiSelectComboBox.SetParentComboBox(comboBoxitem, this);
return comboBoxitem;
}
private static void OnIsSelectedChanged(object comboBoxItem, DependencyPropertyChangedEventArgs args)
{
ComboBoxItem item = comboBoxItem as ComboBoxItem;
if (item != null)
{
MultiSelectComboBox parent = MultiSelectComboBox.GetParentComboBox(item);
if (MultiSelectComboBox.GetIsSelected(item))
{
parent.SelectedItems.Add(item);
}
else
{
parent.SelectedItems.Remove(item);
}
}
}
}
Then create your items template
<local:MultiSelectComboBox ItemsSource="{Binding Items}" SelectedItems="{Binding SelectedItems, Mode=TwoWay}">
<local:MultiSelectComboBox.ItemTemplate>
<DataTemplate>
<CheckBox Content="{Binding ItemContent}" IsChecked="{Binding RelativeSource={RelativeSource AncestorType=ComboBoxItem}, Path=IsSelected, Mode=TwoWay}"/>
</DataTemplate>
</local:MultiSelectComboBox.ItemTemplate>
</local:MultiSelectComboBox>
However, this might take some massaging to get working. In the end you want to subclass Combobox and make it do some new stuff.