How do I correctly use the selected items property of a datagrid following mvvm?

Question

I have a couple of datagrid's in my WPF app like

                        <DataGrid ItemsSource="{Binding FilteredBills}" AutoGenerateColumns="False"   
                                              IsReadOnly="True"  
                                              SelectionUnit="FullRow"  
                                              HeadersVisibility="Column"  
                                              Name="IMPGrid">  
                            <DataGrid.Columns>  
                                <DataGridTextColumn  
                                                Header="Bill No."  
                                                Binding="{Binding Path=BillNo, Mode=OneWay}"  
                                                Width="275"  
                                                IsReadOnly="True" />  
                                <DataGridTextColumn  
                                                Header="Bill Date"  
                                                Binding="{Binding Path=BillDt, Mode=OneWay}"  
                                                Width="75"  
                                                IsReadOnly="True" />  
                                <DataGridTextColumn  
                                                Header="Amount"  
                                                Binding="{Binding Path=Amt, StringFormat=N2, Mode=OneWay}"  
                                                Width="75"  
                                                IsReadOnly="True" />  
                            </DataGrid.Columns>  
                        </DataGrid>  
                        <DataGrid ItemsSource="{Binding AdjBills}" AutoGenerateColumns="False"  
                                              SelectionUnit="FullRow"  
                                              HeadersVisibility="Column"  
                                              Name="EXPGrid">  
                            <DataGrid.Columns>  
                                <DataGridTextColumn  
                                                Header="CNDN No."  
                                                Binding="{Binding Path=CndnNo, Mode=OneWay}"  
                                                Width="275"  
                                                IsReadOnly="True" />  
                                <DataGridTextColumn  
                                                Header="Date"  
                                                Binding="{Binding Path=Date, Mode=OneWay}"  
                                                Width="275"  
                                                IsReadOnly="True" />  
                                <DataGridTextColumn  
                                                Header="Amount"  
                                                Binding="{Binding Path=Value, Mode=OneWay}"  
                                                Width="275"  
                                                IsReadOnly="True" />  
                            </DataGrid.Columns>  
                        </DataGrid>  

The properties representing both the datagrid's columns reside in the same class

public class Bills : ViewModelBase  
    {  
        ...  
        private string _billNo;  
        public string BillNo  
        {  
            get  
            {  
                return _billNo;  
            }  
            set  
            {  
                SetValue(ref _billNo, value);  
            }  
        }  


        private string _billDt;  
        public string BillDt  
        {  
            get  
            {  
                return _billDt;  
            }  
            set  
            {  
                SetValue(ref _billDt, value);  
            }  
        }  

        ...  

        private double _value;  
        public double Value  
        {  
            get  
            {  
                return _value;  
            }  
            set  
            {  
                SetValue(ref _value, value);  
            }  
        }  

    }  

Now, what I'm trying to do is when I selected rows from both the datagrid's and hit the Preview button like this it should generate a PDF like this and if I choose only the first datagrid rows like this it should generate a PDF like this

Previously when I did not use the MVVM pattern I would use these helper classes (using itext5), call it in the button click event like invoice.GenerateDocument(filePath, infoText, lblCity, billsGrid, adjGrid); and it would work fine but now when I try to use it in my current app it is showing error

System.Exception: 'Unable to cast object of type 'DG2PDF.Bills' to type 'System.Data.DataRowView'.'

in the line foreach (DataRowView row in gridView.SelectedItems) of the below section

            foreach (DataRowView row in gridView.SelectedItems)  
            {  

                for (int x = 0; x < 3; x++)  
                {  
                    table.AddCell(new iTextSharp.text.Phrase(row.Row.ItemArray[x].ToString()));  
                }  
                _rowNumber++;  

            }  

If I change the foreach loop to foreach (Bills bill in gridView.SelectedItems) then I would have to hardcode the properties like table.AddCell(new iTextSharp.text.Phrase(bill.BillNo.ToString())); which is a problem as the gridView represents both datagrid's and their properties/columns are different.

How do I fix this ?

Answer 1

Hi @don bradman ,

I added the data table without reproducing your problem, I added AddTable1 and GenerateTable1 and used GenerateTable1 to generate the second table in the preview.

Write a separate method for the second table:

GenerateTable1(document, creditNotesDataGrid, totalCreditNotes, "Less Credit Note/Debit Note", BaseColor.WHITE, BaseColor.WHITE);  
  
private iTextSharp.text.Document GenerateTable1(iTextSharp.text.Document document, DataGrid gridView, decimal total, string headerText, BaseColor primaryHeaderBackgroundColor, BaseColor secondaryHeaderBackgroundColor)  
        {  
            if (gridView.SelectedItems.Count > 0)  
            {  
                var columnsCount = gridView.Columns.Count;  
  
  
               // Generate bills table  
                return document  
                    .AddTable(columnsCount, table =>  
                    {  
                        table.AddPhrase(headerText, _tableHeaderFont, (cell, phrase) =>  
                        {  
                            cell.BackgroundColor = primaryHeaderBackgroundColor;  
                            cell.Colspan = columnsCount;  
                            cell.HorizontalAlignment = (int)Alignment.Center;  
                        });  
                    })  
                    .AddTable1(gridView, _tableHeaderFont, secondaryHeaderBackgroundColor, _helveticaFontSamllStandard)  
                    .AddTable(columnsCount, table =>  
                    {  
                        table  
                            .AddEmptyCell(columnsCount - 1)  
                            .AddStrongUnderlinedPhrase(total.ToDefaultStringFormat(), _tableHeaderFont);  
                    });  
  
  
  
           }  
           return document;  
        }  


public static iTextSharp.text.Document AddTable1(this iTextSharp.text.Document document, DataGrid gridView, iTextSharp.text.Font headerFont, BaseColor headerBackgroundColor, iTextSharp.text.Font bodyFont)  
        {  
            var table = new iTextSharp.text.pdf.PdfPTable(gridView.Columns.Count)  
            {  
                WidthPercentage = 75  
            };  
           table.DefaultCell.Padding = 3;  
           table.HorizontalAlignment = Element.ALIGN_CENTER;  
           foreach (DataGridColumn column in gridView.Columns)  
            {  
                var cell = new iTextSharp.text.pdf.PdfPCell(new iTextSharp.text.Phrase(column.Header.ToString(), headerFont))  
                {  
                    BackgroundColor = headerBackgroundColor  
                };  
  
               table.AddCell(cell);  
            }  
  
  
            foreach (Bills bill in gridView.SelectedItems)  
            {  
                if (bill != null)  
                {  
                    table.AddCell(new iTextSharp.text.Phrase(bill.CndnNo.ToString()));  
                    table.AddCell(new iTextSharp.text.Phrase(bill.Date.ToString()));  
                    table.AddCell(new iTextSharp.text.Phrase(bill.Value.ToString()));  
                }  
  
  
  
           }  
            document.Add(table);  
            return document;  
        }  

Then add it to The GenerateTable:

// Generate body's paragraph  
document.AddParagraph(bodyStartParagraph, _timesRomanNormal, Alignment.Left);  
  
// Generate bills table  
GenerateTable(document, billsDataGrid, totalBills, customerName, new BaseColor(255, 255, 30), new BaseColor(137, 220, 165));  
  
// Generate credits table  
GenerateTable1(document, creditNotesDataGrid, totalCreditNotes, "Less Credit Note/Debit Note", BaseColor.WHITE, BaseColor.WHITE);  

Best Regards,
Jiale

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