Cfrgtkky

I'm writing app (my first using WPF) that shows data for products in datagrid. I succeded with connecting datagrid with MS SQL database. I stuck on creating calculated column.
I'm interested in multiplying values from two columns. I want to use Pcs_DC_col and Qty_multi_col to calcule values in Qty_DC_col.
From what I understand I have to use converter and because i use more than 1 columns I shoud use IMultiValueConverter. But don't know how to write code that would show me something diffient than blank cells or dependencyproperty.unsetvalue. What should I add or change to make it work?

XAML code:

<Window.Resources>

        <local:ColumnConverter x:Key="ColumnConversion"/>

    </Window.Resources>

    

    <Grid>

                    <DataGrid x:Name="matrix" SelectionUnit="FullRow" SelectionChanged="PLU_row_selected" 

                              AutoGenerateColumns="False" CanUserAddRows="False">

                      

                        <DataGrid.Columns>

                            <DataGridTextColumn Header="PLU" Binding="{Binding PLU}"/>

                            <DataGridTextColumn Header="config" Binding="{Binding config}"/>

                            <DataGridTextColumn Header="Name" Binding="{Binding Name}"/>

                            <DataGridTextColumn Header="Colour" Binding="{Binding Colour}"/>

                            <DataGridTextColumn Header="Promo" Binding="{Binding Promo}"/>

                            <DataGridTextColumn Header="Department" Binding="{Binding Department}"/>

                            <DataGridTextColumn Header="Category" Binding="{Binding Category}"/>

                            <DataGridTextColumn Header="Price" Binding="{Binding Price}"/>

                            <DataGridTextColumn x:Name="Pcs_DC_col" Header="Pc.s DC" Binding="{Binding Pcs Dc}"/>

                            <DataGridTextColumn Header="Allocated Pcs" Binding="{Binding Allocated Pcs}"/>



                            <DataGridTextColumn x:Name="Qty_DC_col" Header="Qty DC">

                                <DataGridTextColumn.Binding>

                                    <MultiBinding Converter="{StaticResource ColumnConversion}">

                                        <Binding ElementName="Pcs_DC_col" Path="Text"/>

                                        <Binding ElementName="Qty_multi_col" Path="Text"/>

                                    </MultiBinding>

                                </DataGridTextColumn.Binding>

                            </DataGridTextColumn>                            

                          

                            <DataGridTextColumn Header="Qty All" Binding="{Binding obliczenia}"/>

                            <DataGridTextColumn Header="Qty Tra" Binding="{Binding  Qty Tra}"/>

                            <DataGridTextColumn Header="Qty Str" Binding="{Binding  Qty Str}"/>

                            <DataGridTextColumn x:Name="Qty_multi_col" Header="Qty multiple" Binding="{Binding Qty Multiple}"/>

                            <DataGridTextColumn Header="% all" Binding="{Binding Percent_Allo}"/>

                            <DataGridTextColumn Header="Value all" Binding="{Binding Value_allocated}"/>

                        </DataGrid.Columns>

                    </DataGrid>

    </Grid>

Converter code:

public class ColumnConverter : IMultiValueConverter

{

    public object Convert(object values, Type targetType, object parameter, CultureInfo culture)

    {

        if (values == null) return 0;



        try

        {

            return String.Format("{0}", values[0]);

        } 



        catch

        {

            return 0;

        }



    } // Convert()

This version shows me blank column, and if I change code for:

 return String.Format("{0}", values[0]);

That fill my column with dependencyproperty.unsetvalue.

Code how I load data from database to Grid:

  private void load_products_to_grid()

    {

        SqlConnection myConnection = new SqlConnection();

        myConnection.ConnectionString = @"Server = batorego426coreSQL; Database = CorpCore; Integrated Security=true;";

        myConnection.Open();

        SqlCommand query = new SqlCommand();

        query.CommandText = "select * from [products]";

        query.Connection = myConnection;

        SqlDataAdapter adapter = new SqlDataAdapter(query);

        DataTable product_table = new DataTable("products");

        adapter.Fill(product_table);



        matrix.ItemsSource = product_table.DefaultView;

    } 

EDIT:

I changed biding as Andy suggested to

<DataGridTextColumn x:Name="Qty_DC_col" Header="Qty DC">

                            <DataGridTextColumn.Binding>

                                <MultiBinding Converter="{StaticResource ColumnConversion}">

                                    <Binding Path="Pcs_DC_col"/>

                                    <Binding Path="Qty_multi_col"/>

                                </MultiBinding>

                            </DataGridTextColumn.Binding>

                        </DataGridTextColumn>

And converter code:

 public object Convert(object values, Type targetType, object parameter, CultureInfo culture)

    {

        if (values == null) return 0;



            return (int)values[0]*(int)values[1];

    } 

But still I get empty column, and I tried changing code in converter to check if can see any value to:

String.Format("{0}", values[0]);

But then get "dependencyproperty.unsetvalue" in that column. So I guess data is still not connected and is not even null but no tset. What else I can do?

Your bindings in the multibinding should be to the data and just the column names. If they are Pcs_DC_col and Qty_multi_col then

<MultiBinding Converter="{StaticResource ColumnConversion}">

      <Binding  Path="Pcs_DC_col"/>

      <Binding  Path="Qty_multi_col"/>

</MultiBinding>

The object values array will have two values in it. These are presumably double but as far as the code knows these are just objects so cast and add them together. Return that as a number. Something like:

return (double)values[0] * (double)values[1];

You may have to null trap etc.
And that column better not be editable.

For most datagrids I would have a viewmodel to represent each row out the database and I could put calculations etc in there. So there'd be a property which summed the two columns.
And of course I'd have somewhere to put other logic such as validation.
Binding directly to a datatable is quite limiting.

As an alternative you could modify your sql-query to:

"select *, (Pcs_DC_col * Qty_multi_col) as Qty_DC_col from [products]"

and then bind normally to that column. (or whatever the column is named)