Question

I am working on a Windows Form to create a Employee Card Layout. In addition to that I have added a Button named “Print” which will Print the Panel Content. When I run the code It shows Error when Form loads:

Here is my code:

namespace SimpleReport
{
public partial class EmployeeCardForm : Form
{
    //Declare following Object Variables
    PrintDocument printdoc1 = new PrintDocument();
    PrintPreviewDialog previewdlg = new PrintPreviewDialog();
    Panel pannel = null;

    public EmployeeCardForm()
    {
        InitializeComponent();
        //declare event handler for printing in constructor
        printdoc1.PrintPage += new PrintPageEventHandler(printdoc1_PrintPage);
    }

    Bitmap MemoryImage;
    public void GetPrintArea(Panel pnl)
    {
        MemoryImage = new Bitmap(pnl.Width, pnl.Height);
        Rectangle rect = new Rectangle(0, 0, pnl.Width, pnl.Height);
        pnl.DrawToBitmap(MemoryImage, new Rectangle(0, 0, pnl.Width, pnl.Height));
    }
    protected override void OnPaint(PaintEventArgs e)
    {
        e.Graphics.DrawImage(MemoryImage, 0, 0);
        base.OnPaint(e);
    }
    void printdoc1_PrintPage(object sender, PrintPageEventArgs e)
    {
        Rectangle pagearea = e.PageBounds;
        e.Graphics.DrawImage(MemoryImage, (pagearea.Width / 2) - (this.panel1.Width / 2), this.panel1.Location.Y);
    }

    public void Print(Panel pnl)
    {
        pannel = pnl;
        GetPrintArea(pnl);
        previewdlg.Document = printdoc1;
        previewdlg.ShowDialog();
    }

    private void button1_Click(object sender, EventArgs e)
    {
        Print(this.panel1);
    }
  }
}

When I debugged the code I came to know that It crashes on first line of OnPaint Event.
Please help me out.

Answer 1

MemoryImage is null before GetPrintArea() has been called.

Try this:

protected override void OnPaint(PaintEventArgs e)
{
    if (MemoryImage != null)
    {
        e.Graphics.DrawImage(MemoryImage, 0, 0);
    }
    base.OnPaint(e);
}

That’s only if you don’t want to draw it when it is null. Because it’s null initially and then you set it in GetPrintArea(). Depending on your circumstance, you could call GetPrintArea() instead of the null check or you could initialise MemoryImage immediately, it all depends on how you want it to work.