Question

Really having an issue debugging this…the reason why is probably very simple but I’m still an amateur at WPF.

It’s easier if you see the code but I’ll give you the specific problem. My listbox is set to contain a grid format and each listboxitem has a ListBoxItem.PreviewMouseLeftButtonDown event. The problem is, the selected item is always set to the previous item.

Here is what happens in steps:

1. My image loads up

2. I click a button to generate a grid overlay of 32×32 cells over the image, each a listboxitem in a cell of that overlay

3. I click on a cell

4. OnSelected method fires (each listboxitem is tied to this handler through the Selected event)

5. The SelectedItem is null when I click on cell (0,0)

6. If I click on cell (0,1), the Selected event fires but now the SelectedItem is set to the object in the previous cell (0,0) instead of (0,1). Then, clicking on (0,0) will show the SelectedItem as being (0,1) and so on.

7. Repeat for any other cell.

XAML

 <DockPanel Name="dockTest">
        <Menu DockPanel.Dock="Top" Width="Auto" Height="Auto">
            <MenuItem Header="File">
                <MenuItem Header="Load Image" Command="Open"></MenuItem>
                <Separator />
                <MenuItem Header="Exit" Command="Close"></MenuItem>
            </MenuItem>
        </Menu>
        <ListBox Name="lstTiles" DockPanel.Dock="Right" PreviewMouseRightButtonDown="grdMain_MouseRightButtonDown" 
             PreviewMouseRightButtonUp="grdMain_MouseRightButtonUp"  SelectionMode="Extended">
            <ListBox.ItemContainerStyle>
                <Style>
                <EventSetter Event="ListBoxItem.Selected" Handler="OnSelected" />
                <Setter Property="ListBox.RenderTransformOrigin" Value="0.5,0.5" />
                <Setter Property="Grid.Row" Value="{Binding RelativeSource={x:Static RelativeSource.Self},
                    Path=Content.Row}"/>
                    <Setter Property="Grid.Column" Value="{Binding RelativeSource={x:Static RelativeSource.Self},
                    Path=Content.Column}"/>
                    <Setter Property="ListBoxItem.Height" Value="{Binding RelativeSource={x:Static RelativeSource.Self},
                    Path=Content.Height}" />
                    <Setter Property="ListBoxItem.Width" Value="{Binding RelativeSource={x:Static RelativeSource.Self},
                    Path=Content.Width}" />
                <Setter Property="ListBoxItem.IsHitTestVisible" Value="True" />
                <Style.Resources>
                        <SolidColorBrush x:Key="{x:Static SystemColors.HighlightBrushKey}" Color="Blue" Opacity=".3" />
                        <SolidColorBrush x:Key="{x:Static SystemColors.ControlBrushKey}" Color="Transparent" />
                    </Style.Resources>
                </Style>
            </ListBox.ItemContainerStyle>
            <ListBox.ItemsPanel>
                <ItemsPanelTemplate>
                    <Grid ShowGridLines="True" IsItemsHost="True" Background="{DynamicResource LoadedImage}" 
                      Name="grdMain" MaxHeight="600" MaxWidth="800" MinHeight="600" MinWidth="800" >
                    </Grid>
                </ItemsPanelTemplate>
            </ListBox.ItemsPanel>
        </ListBox>
    <StackPanel DockPanel.Dock="Left">
        <Label Margin="5">Tile Size</Label>
        <ComboBox Name="cmbGridSize">
            <TextBlock Name="txt3232">32x32</TextBlock>
            <TextBlock Name="txt1616">16x16</TextBlock>
            <TextBlock Name="txt88">8x8</TextBlock>
        </ComboBox>
        <Button Name="btnChangeGrid" Click="GridBtn_Click" Margin="4">Make Grid</Button>
        <Label>Tile Type</Label>
        <ComboBox Name="cmbTileType" SelectionChanged="cmbTileType_SelectionChanged">

        </ComboBox>
        <TextBlock Name="txtTest"></TextBlock>
        <Label>Tile Characteristic</Label>
        <ComboBox Name="cmbTileCharacteristic" SelectionChanged="cmbTileCharacteristic_SelectionChanged">
        </ComboBox>
        <Button Name="btnExport" Click="btnExport_Click">Export</Button>
        <Label>Edit Cell</Label>
        <Button Name="btnEdit" Click="btnEdit_Click">Edit Cell</Button>
    </StackPanel>
</DockPanel>

Code Behind

    private void MainWindow_Loaded(object sender, RoutedEventArgs e)
    {
        //Stores enum array of tile type enums
        tileTypes = Enum.GetNames(typeof(Tile.TileType));

        //Stores enum array of tile characteristics
        tileCharacteristics = Enum.GetNames(typeof(Tile.TileCharacteristic));

        //Gets main grid in template of main page
        mainGrid = Helpers.FindItemsPanel(lstTiles) as Grid;

        //Sets combobox to array of types of tiles
        cmbTileType.ItemsSource = tileTypes;

        //Sets combobox to array of characteristics
        cmbTileCharacteristic.ItemsSource = tileCharacteristics;

    }  //Generates the grid overlay
    private void Grid_Build()
    {
        //Sets grid overlay to user preferences of tile size
        if (tileList.Count > 0)
        {
            tileList.Clear();
        }

        if (mainGrid.RowDefinitions.Count > 0)
        {
            mainGrid.RowDefinitions.Clear();
        }

        if (mainGrid.ColumnDefinitions.Count > 0)
        {
            mainGrid.ColumnDefinitions.Clear();
        }

        int numberOfColumns = Convert.ToInt32(Math.Ceiling((float)imageWidth / (float)dimension));
        int numberOfRows = Convert.ToInt32(Math.Ceiling((float)imageHeight / (float)dimension));

        for (int i = 0; i < numberOfRows; i++)
        {
            mainGrid.RowDefinitions.Add(new RowDefinition());
        }

        for (int i = 0; i < numberOfColumns; i++)
        {
            mainGrid.ColumnDefinitions.Add(new ColumnDefinition());
        }

        int addCounter = 0;

        //Stores and generates tile objects in generated rows and columns
        for (int row = 0; row < numberOfRows; row++)
        {
            for (int col = 0; col < numberOfColumns; col++)
            {
                Tile tempTile = (new Tile(row, col, dimension, dimension, addCounter, Tile.TileType.None, Tile.TileCharacteristic.Empty));
                tempTile.IsHitTestVisible = true;
                tileList.Add(tempTile);
                addCounter++;
            }
        }

        //Sets listbox of tiles in xaml to the list of tile objects
        lstTiles.ItemsSource = tileList;
    }

    //Occurs when a listbox item is selected
    private void OnSelected(object sender, RoutedEventArgs e)
    {
        //If a single tile object is selected
        if (lstTiles.SelectedItems.Count == 1)
        {
            //Stores array of selected tile listboxitems in listbox
            var items = lstTiles.SelectedItems;

            foreach (Tile it in items)
            {
                txtTest.Text = it.Row.ToString() + " " + it.Column.ToString();

                //Sets tile type combobox to the property set in each tile object
                cmbTileType.SelectedItem = (string)Enum.GetName(typeof(Tile.TileType), it.Type);

                //Sets tile characteristic combobox to the property set in each tile object
                cmbTileCharacteristic.SelectedItem = (string)Enum.GetName(typeof(Tile.TileCharacteristic), it.Characteristic);
            }
        }
    }

Answer 1

Problem was Selected was a premature event for getting the listbox’s selecteditems container. What I should have been using was SelectionChanged