数据网格数据模板中的项目源不起作用

Question

I am trying to show MultiSelectComboBox in Datagrid cell but even though combo box works alone, it shows empty if I put it inside the data grid.

I think it is related to <UserControl.Resources> vs <DataGrid.Resources> but I couldn't find a fix.

You can find the solution from here .

My Model:

public class Blocks : BaseViewModel
    {
        private bool _isSelected;
        private int _id;
        private string _name;

        public Blocks(string name)
        {
            _name = name;
        }

        public bool IsSelected
        {
            get => _isSelected;
            set
            {
                if (_isSelected == value) return;
                _isSelected = value;
                OnPropertyChanged();
            }
        }

        public int ID
        {
            get => _id;
            set
            {
                if (_id == value) return;
                _id = value;

                OnPropertyChanged();
                // multicombox default filtreleme için name kullanıyor
                _name = value.ToString();
            }
        }

        public string Name
        {
            get => _name;
            set
            {
                if (_name != null && string.Compare(_name, value, StringComparison.InvariantCulture) == 0)
                {
                    return;
                }

                _name = value;
                OnPropertyChanged();
            }
        }
        
        public override string ToString()
        {
            return ID.ToString();
        }
    }

My ViewModel:

public class ListItemsViewModel : BaseViewModel { private ObservableCollection _routes;

public ObservableCollection<int> Routes
{
    get => _routes ?? (_routes = new ObservableCollection<int>());
    set
    {
        _routes = value;
        OnPropertyChanged();
    }
}

// multi combo box
private ICommand _selectedStatusItemsChangedCommand;
private ObservableCollection<Blocks> _includedBlocks;
private ObservableCollection<Blocks> _selectedBlocks;

public ObservableCollection<Blocks> IncludedBlocks
{
    get => _includedBlocks ?? (_includedBlocks = new ObservableCollection<Blocks>());
    set
    {
        _includedBlocks = value;
        OnPropertyChanged();
    }
}

public ObservableCollection<Blocks> SelectedBlocks
{
    get => _selectedBlocks ?? (_selectedBlocks = new ObservableCollection<Blocks>());
    set
    {
        _selectedBlocks = value;
        OnPropertyChanged();
    }
}

public ICommand SelectedItemsChangedCommand
    => _selectedStatusItemsChangedCommand ?? (_selectedStatusItemsChangedCommand = new CommandHandler(SelectedItemsChanged));

public ListItemsViewModel(ObservableCollection<Blocks> list, ObservableCollection<int> ints)
{
    _includedBlocks = list;
    _routes = ints;
}


// Multi select combo box
public int SelectedStatusItemsCount { get; set; }

private void UpdateSelectedStatusItemsCount(int count)
{
    SelectedStatusItemsCount = count;
    OnPropertyChanged();
}

private void SelectedItemsChanged(object parameter)
{
    if (parameter is SelectedItemsChangedEventArgs args)
    {
        foreach (var virtualRailBlock in _includedBlocks)
        {
            var selectedItemIndex = args.Selected.Cast<Blocks>().ToList().IndexOf(virtualRailBlock);
            virtualRailBlock.IsSelected = selectedItemIndex > -1;
        }

        UpdateSelectedStatusItemsCount(args.Selected.Count);
    }
}

}

My View:

<UserControl x:Class="MultiSelectControlCodes.View.ListItemsView"
        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"
        xmlns:sdl="http://schemas.sdl.com/xaml"
        xmlns:viewModel="clr-namespace:MultiSelectControlCodes.ViewModel"
        xmlns:model="clr-namespace:MultiSelectControlCodes.Model"
        mc:Ignorable="d" d:DesignHeight="200" d:DesignWidth="400" 
             d:DataContext="{d:DesignInstance viewModel:ListItemsViewModel}">
    <Grid>

        <DataGrid
                 ItemsSource="{Binding Routes}"
                 SelectionUnit="FullRow"
                 SelectionMode="Extended"
                 AutoGenerateColumns="False"
                 IsReadOnly="False"
                 CanUserAddRows="True"
                 CanUserDeleteRows="True">
            <DataGrid.Resources>
                <DataTemplate x:Key="MultiSelectComboBox.Dropdown.ListBox.ItemTemplate" DataType="Block">
                    <Grid>
                        <Grid.ColumnDefinitions>
                            <ColumnDefinition Width="*"/>
                        </Grid.ColumnDefinitions>
                        <TextBlock Grid.Column="0" VerticalAlignment="Center" Text="{Binding Path=Name}"/>
                    </Grid>
                </DataTemplate>

                <DataTemplate x:Key="MultiSelectComboBox.SelectedItems.ItemTemplate" DataType="Block">
                    <StackPanel Orientation="Horizontal" Margin="0,-4">
                        <TextBlock VerticalAlignment="Center" Text="{Binding Path=Name}" Margin="2,0" />
                    </StackPanel>
                </DataTemplate>
            </DataGrid.Resources>

            <DataGrid.Columns >
                <DataGridTemplateColumn Header="Routes" Width="100">
                    <DataGridTemplateColumn.CellTemplate>
                        <DataTemplate>
                            <sdl:MultiSelectComboBox
                                    Margin="2" 
                                    VerticalAlignment="Top"
                                    Height="50"
                                    IsEditable="true"
                                    SelectionMode="Multiple"
                                    SelectedItems="{Binding SelectedBlocks}"
                                    ItemsSource="{Binding IncludedBlocks}"
                                    SelectedItemTemplate="{StaticResource MultiSelectComboBox.SelectedItems.ItemTemplate}"
                                    DropdownItemTemplate="{StaticResource MultiSelectComboBox.Dropdown.ListBox.ItemTemplate}"
                                    sdl:SelectedItemsChangedBehaviour.SelectedItemsChanged="{Binding SelectedItemsChangedCommand}"/>
                        </DataTemplate>
                    </DataGridTemplateColumn.CellTemplate>
                </DataGridTemplateColumn>
            </DataGrid.Columns>
        </DataGrid>

    </Grid>
</UserControl>

Resulting window:

Working View:

<UserControl x:Class="MultiSelectControlCodes.View.ListItemsView"
        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"
        xmlns:sdl="http://schemas.sdl.com/xaml"
        xmlns:viewModel="clr-namespace:MultiSelectControlCodes.ViewModel"
        xmlns:model="clr-namespace:MultiSelectControlCodes.Model"
        mc:Ignorable="d" d:DesignHeight="200" d:DesignWidth="400" 
             d:DataContext="{d:DesignInstance viewModel:ListItemsViewModel}">
    <UserControl.Resources>
        <DataTemplate x:Key="MultiSelectComboBox.Dropdown.ListBox.ItemTemplate" DataType="Block">
            <Grid>
                <Grid.ColumnDefinitions>
                    <ColumnDefinition Width="*"/>
                </Grid.ColumnDefinitions>
                <TextBlock Grid.Column="0" VerticalAlignment="Center" Text="{Binding Path=Name}"/>
            </Grid>
        </DataTemplate>

        <DataTemplate x:Key="MultiSelectComboBox.SelectedItems.ItemTemplate" DataType="Block">
            <StackPanel Orientation="Horizontal" Margin="0,-4">
                <TextBlock VerticalAlignment="Center" Text="{Binding Path=Name}" Margin="2,0" />
            </StackPanel>
        </DataTemplate>
    </UserControl.Resources>
    <Grid>
        <sdl:MultiSelectComboBox
            Margin="2" 
            VerticalAlignment="Top"
            Height="50"
            IsEditable="true"
            SelectionMode="Multiple"
            SelectedItems="{Binding SelectedBlocks}"
            ItemsSource="{Binding IncludedBlocks}"
            SelectedItemTemplate="{StaticResource MultiSelectComboBox.SelectedItems.ItemTemplate}"
            DropdownItemTemplate="{StaticResource MultiSelectComboBox.Dropdown.ListBox.ItemTemplate}"
            sdl:SelectedItemsChangedBehaviour.SelectedItemsChanged="{Binding SelectedItemsChangedCommand}"/>
    </Grid>
</UserControl>

Working Result:

Answer 1

Bind to the properties of the view model using a RelativeSource :

<sdl:MultiSelectComboBox
    Margin="2" 
    VerticalAlignment="Top"
    Height="50"
    IsEditable="true"
    SelectionMode="Multiple"
    SelectedItems="{Binding DataContext.SelectedBlocks, RelativeSource={RelativeSource AncestorType=DataGrid}}"
    ItemsSource="{Binding DataContext.IncludedBlocks, RelativeSource={RelativeSource AncestorType=DataGrid}}"
    SelectedItemTemplate="{StaticResource MultiSelectComboBox.SelectedItems.ItemTemplate}"
    DropdownItemTemplate="{StaticResource MultiSelectComboBox.Dropdown.ListBox.ItemTemplate}"
    sdl:SelectedItemsChangedBehaviour.SelectedItemsChanged="{Binding SelectedItemsChangedCommand}"/>

The default DataContext the root element in a CellTemplate is the current item in the ItemsSource , ie an int in Routes in this case, and this one doesn't have any IncludedBlocks or SelectedBlocks property to bind to.