VB.NET使用AccessibleObjectFromWindow遇到的问题

zhanglei1371

参考了vba的代码和网上的一些相关代码，想测试使用AccessibleObjectFromWindow来获取当前的Office对象，但是获取到的对象总是为空，代码如下：

[Visual Basic .NET] 纯文本查看 复制代码

Private Declare Function AccessibleObjectFromWindow Lib "oleacc" (ByVal Hwnd As Int32,
    ByVal dwId As Int32,
    ByRef riid As Guid,
    <MarshalAs(UnmanagedType.IUnknown)> ByRef ppvObject As Object) As Int32

        Private Sub Form1_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles MyBase.Load
        Dim varChild As IAccessible
        Dim a, b, c As IntPtr
        a = FindWindowEx(IntPtr.Zero, IntPtr.Zero, "XLMAIN", Nothing)
        b = FindWindowEx(a, IntPtr.Zero, "XLDESK", Nothing)
        c = FindWindowEx(b, IntPtr.Zero, "EXCEL7", Nothing)
        Dim hWnd As Int32 = c.ToInt32()
        Dim ID As Int32 = &HFFFFFFF0
        Dim IID_IAcce As Guid = New Guid("{00020400-0000-0000-C000-000000000046}")
        Dim aaVal As Int32 = AccessibleObjectFromWindow(hWnd, ID, IID_IAcce, varChild)
        '这里获得的varChild总是为空，不知哪里有问题
    End Sub

测试到Excel句柄获取部分都正常，
其中的Guid、ID常量均无问题。
不知该怎么修改？