vb.net VB.NET中的截屏程序

Screen Capture program in VB.NET

提问by Vighanesh Gursale

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 NullReferenceExceptionoccur can any one tell me whats going wrong here.

我创建了一个应用程序来捕获桌面屏幕的屏幕截图。它与我在表单中使用的按钮配合得很好。但是现在我想使用计时器使那件事自动运行，但是每当我尝试运行程序NullReferenceException时，任何人都可以告诉我这里出了什么问题。

TimerCapture interval=5

TimerSave interval=6

Here is the code can tell you the scenario:

这是代码可以告诉你的场景：

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....

提前致谢....

采纳答案by Jamby

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.

我认为问题出在 timerSave_Tick 中，如果由于某种原因您还没有在 timerCapture_Tick 中重视 Me.PictureBox1.Image，那么它会在尝试访问 PictureBox1.Image 时抛出 NullReferenceException。

Try to modify it in such way:

尝试以这种方式修改它：

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..

无论如何，您应该能够在 Visual Studio 下进行调试，以查看抛出异常的位置..