错误PInvoking函数

Question

我有以下代码作为控件的一部分。SetReaderMode函数创建结构并调用此处解释的函数，http://msdn.microsoft.com/en-us/library/bb775599（VS.85）.aspx

当我运行此代码时，我得到错误

尝试读取或写入受保护的内存。这通常表示其他内存已损坏。

我不确定问题出在哪里。我做错了什么？

        <DllImport("Comctl32.dll", EntryPoint:="#383", _
         CallingConvention:=CallingConvention.StdCall)> _
    Private Shared Sub DoReaderMode(prmi As READERMODEINFO)
    End Sub
    <StructLayout(LayoutKind.Sequential)>
    Private Structure READERMODEINFO
        Dim cbSize As UInt32
        Dim hwnd As IntPtr
        Dim fFlags As UInt32
        Dim prc As IntPtr
        Dim pfnScroll As ReaderScrollCallbackDelegate
        Dim fFlags2 As TranslateDispatchCallbackDelegate
        Dim lParam As IntPtr
    End Structure
    Private Sub SetReaderMode()
        Dim Info As New READERMODEINFO
        Info.hwnd = Me.Handle
        Info.fFlags = 0
        Info.prc = IntPtr.Zero
        Info.pfnScroll = New ReaderScrollCallbackDelegate(AddressOf ReaderScrollCallback)
        Info.fFlags2 = New TranslateDispatchCallbackDelegate(AddressOf TranslateDispatchCallback)
        Info.lParam = IntPtr.Zero
        Info.cbSize = Marshal.SizeOf(Info)
        DoReaderMode(Info)
    End Sub

    Private Delegate Function ReaderScrollCallbackDelegate(ByVal prmi As READERMODEINFO, dx As Integer, dy As Integer) As Boolean
    Private Delegate Function TranslateDispatchCallbackDelegate(lpmsg As IntPtr) As Boolean
    <AllowReversePInvokeCalls()>
    Private Function TranslateDispatchCallback(lpmsg As IntPtr) As Boolean
        Return True
    End Function
    <AllowReversePInvokeCalls()>
    Private Function ReaderScrollCallback(ByVal prmi As READERMODEINFO, dx As Int32, dy As Int32) As Boolean
        Return True
    End Function

Answer 1

不是一个容易破解的螺母。假设回调在签名/调用约定方面是正确的，那么问题可能是由于carbage收集器在函数SetReaderMode的末尾收集Info，因此回调地址无效。因此，请尝试将Info声明为成员变量。如果错误保持回调签名有问题，但正如我所说，不太容易一眼看到错误。

Answer 2

我已经想通了。在更仔细地查看了文档之后，我在DoReaderMode定义和ReaderScrollCallback定义中添加了ByRef，因为参数被定义为指向结构的指针，而不仅仅是结构。我还添加了一些其他代码来传递ReaderModeInfo结构中的矩形。

以下是工作代码。有趣的是，文档中指出，您可以单击退出ReaderMode，但在测试时，似乎必须按住按钮并释放才能退出。

    <DllImport("Comctl32.dll", EntryPoint:="#383", _
         CallingConvention:=CallingConvention.StdCall)> _
    Private Shared Sub DoReaderMode(ByRef prmi As READERMODEINFO)
    End Sub
    <StructLayout(LayoutKind.Sequential)>
    Private Structure READERMODEINFO
        Dim cbSize As UInt32
        Dim hwnd As IntPtr
        Dim fFlags As UInt32
        Dim prc As IntPtr
        Dim pfnScroll As ReaderScrollCallbackDelegate
        Dim fFlags2 As TranslateDispatchCallbackDelegate
        Dim lParam As IntPtr
    End Structure

    Private Sub SetReaderMode()
        Dim SetReaderModeInfo As READERMODEINFO
        Dim rect As New Interop.RECT(Me.Width / 2 - 20, Me.Height / 2 - 20, Me.Width / 2 + 20, Me.Height / 2 + 20)
        Dim pnt As IntPtr = Marshal.AllocHGlobal(Marshal.SizeOf(rect))
        Marshal.StructureToPtr(rect, pnt, True)
        SetReaderModeInfo = New READERMODEINFO
        SetReaderModeInfo.hwnd = Me.Handle
        SetReaderModeInfo.fFlags = 1
        SetReaderModeInfo.prc = pnt
        SetReaderModeInfo.pfnScroll = New ReaderScrollCallbackDelegate(AddressOf ReaderScrollCallback)
        SetReaderModeInfo.fFlags2 = New TranslateDispatchCallbackDelegate(AddressOf TranslateDispatchCallback)
        SetReaderModeInfo.lParam = IntPtr.Zero
        SetReaderModeInfo.cbSize = Marshal.SizeOf(SetReaderModeInfo)
        DoReaderMode(SetReaderModeInfo)
        Marshal.FreeHGlobal(pnt)
    End Sub
    Private Delegate Function ReaderScrollCallbackDelegate(ByRef prmi As READERMODEINFO, dx As Integer, dy As Integer) As Boolean
    Private Delegate Function TranslateDispatchCallbackDelegate(ByRef lpmsg As Interop.MSG) As Boolean
    Private Function TranslateDispatchCallback(ByRef lpmsg As Interop.MSG) As Boolean
        Return False
    End Function
    Private Function ReaderScrollCallback(ByRef prmi As READERMODEINFO, dx As Int32, dy As Int32) As Boolean
        Return True
    End Function