修改屏幕的分辨率时，遇到问题
我在程序中修改屏幕的分辨率等信息，在网上查询到例程，如下：
但是，一执行到EnumDisplaySettings 时，就报错：未将对象引用设置到对象的实例，请高手指教，这是怎么回事？
系统：XP，笔记本，.net 2003 vb.net

Private Const CCDEVICENAME As Short = 32
Private Const CCFORMNAME As Short = 32
Private Const DM_PELSWIDTH As Integer = &H80000
Private Const DM_PELSHEIGHT As Integer = &H100000
'刷新频率常量
Private Const DM_DISPLAYFREQUENCY As Integer = &H400000
'调用API函数
Private Declare Function EnumDisplaySettings Lib "user32 " Alias "EnumDisplaySettingsA " (ByVal lpszDeviceName As Integer, ByVal iModeNum As Integer, ByRef lpDevMode As DEVMODE) As Boolean
'调用api函数
Private Declare Function ChangeDisplaySettings Lib "user32 " Alias "ChangeDisplaySettingsA " (ByRef lpDevMode As DEVMODE, ByVal dwflags As Integer) As Integer
'定义结构
Private Structure DEVMODE
Public dmDeviceName As String
Dim dmSpecVersion As Short
Dim dmDriverVersion As Short
Dim dmSize As Short
Dim dmDriverExtra As Short
Dim dmFields As Integer
Dim dmOrientation As Short
Dim dmPaperSize As Short
Dim dmPaperLength As Short
Dim dmPaperWidth As Short
Dim dmScale As Short
Dim dmCopies As Short
Dim dmDefaultSource As Short
Dim dmPrintQuality As Short
Dim dmColor As Short
Dim dmDuplex As Short
Dim dmYResolution As Short
Dim dmTTOption As Short
Dim dmCollate As Short
Public dmFormName As String

Dim dmUnusedPadding As Short
Dim dmBitsPerPel As Short
Dim dmPelsWidth As Integer
Dim dmPelsHeight As Integer
Dim dmDisplayFlags As Integer
Dim dmDisplayFrequency As Integer
End Structure
'改变分辩率过程，参数一宽度，参数二高度
Private Sub ChangeDisp(ByRef iWidth As Single, ByRef iHeight As Single)
Try
Dim blnWorked As Boolean
Dim i As Integer
Dim DevM As New Form3.DEVMODE
DevM.dmDeviceName = " "
DevM.dmFormName = " "
i = 0
Do
blnWorked = EnumDisplaySettings(0, i, DevM)
i = i + 1
Loop Until (blnWorked = False)
With DevM
.dmFields = DM_PELSWIDTH Or DM_PELSHEIGHT Or DM_DISPLAYFREQUENCY
.dmPelsWidth = iWidth
.dmPelsHeight = iHeight
'刷新频率为85
.dmDisplayFrequency = 85
End With
Call ChangeDisplaySettings(DevM, 0)
Catch ex As Exception
MsgBox(ex.Message)

End Try
End Sub
Private Sub btnGetDisp_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnGetDISP.Click
Dim X As Short = System.Windows.Forms.Screen.PrimaryScreen.Bounds.Width
Dim Y As Short = System.Windows.Forms.Screen.PrimaryScreen.Bounds.Height
MsgBox( "您的显示器分辨率是 " & X & " X " & Y)
End Sub
Private Sub btnSetDisp_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnSetDISP.Click
If MsgBox( "您确认要将显示器分辨率改为1024x768吗？ ", MsgBoxStyle.OKCancel, "系统消息 ") = MsgBoxResult.OK Then
'调用改变分辩率过程
ChangeDisp(1024, 768)
End If
End Sub


[解决办法]
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