VB.NET中的屏幕截图程序 [英] Screen Capture program in VB.NET

问题描述

我创建了一个应用程序来捕获桌面屏幕截图。它与我在表单中使用的按钮非常好。但是现在我想让这个东西自动使用计时器，但是每当我尝试运行程序 NullReferenceException 发生时，任何人都可以告诉我这里发生了什么。

  TimerCapture interval = 5 
 
 TimerSave interval = 6 
  

这是代码可以告诉你的情况：

 公共类Form1 
 
 
 Private Sub timerCapture_Tick（ByVal sender As System.Object，ByVal e As System.EventArgs）处理timerCapture.Tick 
 Dim bounds As Rectangle 
 Dim screenshot As System .Drawing.Bitmap 
 Dim图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 =截图
 End Sub 
 
 
 
 
私有子计时器Save_Tick（ByVal sender As System.Object，ByVal e As System.EventArgs）句柄timerSave.Tick 
 Me.PictureBox1.Image.Save（d：\\\capture.bmp）
 
 End Sub 
 
 Private Sub Form1_Load（ByVal发件人As System.Object，ByVal e As System.EventArgs）处理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）处理timerClose.Tick 
 Me.Close（）
 
 End Sub 
 
 Private Sub capture_btn_Click（ByVal sender As System.Object，ByVal e As System.EventArgs）处理capture_btn.Click 
 Dim bounds As Rectangle 
 Dim screenshot As System.Drawing.Bitmap 
 Dim graph As Graphics 
 bounds = Scre en.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 
 
私人Sub save_btn_Click（ByVal sender As System.Object，ByVal e As System.EventArgs）处理save_btn.Click 
 Me.PictureBox1.Image.Save（d：\\\capture.bmp）
结束Sub 
结束类
  

提前感谢...

$ b $我认为问题在timerSave_Tick中，如果由于某种原因你还没有在TimerCapture_Tick中重视Me.PictureBox1.Image，那么它会抛出NullReferenceException而尝试访问PictureBox1.Image。

尝试以这种方式修改：

  P如果（Me.PictureBox1.Image IsNot Nothing）然后
 Me.PictureBox1.Image.Save（ d：\\\capcap.bmp）
如果
结束Sub 
  

无论如何，您应该可以在Visual Studio下进行调试，以查看Exception被抛出的位置。

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....

解决方案

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..

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