Screen Capture program in VB.NET - vb.net

Question

I had created an application that captures the screenshot of desktop screen. It works very well with button I have used in form. But now I want to make that thing works automatically using timers but whenever I try to run program NullReferenceException occur can any one tell me whats going wrong here.
TimerCapture interval=5
TimerSave interval=6
Here is the code can tell you the scenario:
Public Class Form1
Private Sub timerCapture_Tick(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles timerCapture.Tick
Dim bounds As Rectangle
Dim screenshot As System.Drawing.Bitmap
Dim graph As Graphics
bounds = Screen.PrimaryScreen.Bounds
screenshot = New System.Drawing.Bitmap(bounds.Width, bounds.Height, System.Drawing.Imaging.PixelFormat.Format32bppArgb)
graph = Graphics.FromImage(screenshot)
graph.CopyFromScreen(bounds.X, bounds.Y, 0, 0, bounds.Size, CopyPixelOperation.SourceCopy)
PictureBox1.Image = screenshot
End Sub
Private Sub timerSave_Tick(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles timerSave.Tick
Me.PictureBox1.Image.Save("d:\\capture.bmp")
End Sub
Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
' Me.WindowState = FormWindowState.Minimized
'Me.ShowInTaskbar = False
End Sub
Private Sub timerClose_Tick(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles timerClose.Tick
Me.Close()
End Sub
Private Sub capture_btn_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles capture_btn.Click
Dim bounds As Rectangle
Dim screenshot As System.Drawing.Bitmap
Dim graph As Graphics
bounds = Screen.PrimaryScreen.Bounds
screenshot = New System.Drawing.Bitmap(bounds.Width, bounds.Height, System.Drawing.Imaging.PixelFormat.Format32bppArgb)
graph = Graphics.FromImage(screenshot)
graph.CopyFromScreen(bounds.X, bounds.Y, 0, 0, bounds.Size, CopyPixelOperation.SourceCopy)
PictureBox1.Image = screenshot
End Sub
Private Sub save_btn_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles save_btn.Click
Me.PictureBox1.Image.Save("d:\\capture.bmp")
End Sub
End Class
Thanks in advance....

Answer 1

I think the problem is in timerSave_Tick, if, for some reason you haven't already valued Me.PictureBox1.Image in timerCapture_Tick, it would throw NullReferenceException while trying to access to PictureBox1.Image.
Try to modify it in such way:
Private Sub timerSave_Tick(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles timerSave.Tick
If(Me.PictureBox1.Image IsNot Nothing) Then
Me.PictureBox1.Image.Save("d:\\capture.bmp")
End If
End Sub
Anyway, you should be able to debug under Visual Studio, to see where the Exception is thrown..