Question

A simple code that should show an image using PictureBox doesn’t work (frm is my form):

PictureBox pb = new PictureBox();
pb.Image = new Bitmap("1.jpg");
pb.SizeMode = PictureBoxSizeMode.Zoom;
frm.Controls.Add(pb);

When event with this code happens I have NullReferenceExcpetion

The error occurs at frm.Controls.Add(pb)

The exception is:

System.NullReferenceException: Object reference not set to an instance
of an object. at Form1.HotKeyManager_HotKeyPressed(Object sender,
HotKeyEventArgs e) in C:\Users\Алексей\Documents\Visual Studio
2010\Projects\NotepadCSharpSetup\WinFormsAgain\RealTrayForm\Test.cs:line
52

Full code :

static void HotKeyManager_HotKeyPressed(object sender, HotKeyEventArgs e)
{
    Size ScreenSize = Screen.PrimaryScreen.Bounds.Size;

    Bitmap image = new Bitmap(ScreenSize.Width, ScreenSize.Height);
    using (Graphics g = Graphics.FromImage(image))
    {
        g.CopyFromScreen(Point.Empty, Point.Empty, ScreenSize);
    }
    Bitmap preview = new Bitmap(image.Width / 10, image.Height / 10);
    using (Graphics gr = Graphics.FromImage(preview))
    {
        gr.SmoothingMode = SmoothingMode.AntiAlias;
        gr.InterpolationMode = InterpolationMode.HighQualityBicubic;
        gr.PixelOffsetMode = PixelOffsetMode.HighQuality;
        gr.DrawImage(image, new Rectangle(0, 0, image.Width / 10, image.Height / 10));
    }
    preview.Save("1.jpg");

    Form frm = (Form)sender;
    PictureBox pb = new PictureBox();
    pb.Image = new Bitmap("1.jpg");
    pb.SizeMode = PictureBoxSizeMode.Zoom;
    frm.Controls.Add(pb);

}

Answer 1

I don’t believe the new keyword returns Null, unless you have no memory. The bet is that the sender is not the Form

Form frm = (Form)sender;

I think this line is null, that’s why frm.Controls.Add(pb) fails.