Question

我在Watermark TextBox in WinForms中找到了代码，但它是C＃版本，所以我使用http://converter.telerik.com/将代码转换为VB版本，但我仍然遇到错误......

此行发生错误： -

SendMessage（Me.Handle，＆amp; H1501，DirectCast（1，IntPtr），mCue）

我该如何解决？

错误消息：BC30311类型值＆＃39;整数＆＃39;无法转换为＆＃39; IntPtr＆＃39;。

Imports System.ComponentModel
Imports System.Windows.Forms
Imports System.Runtime.InteropServices

Class CueTextBox
    Inherits TextBox
    <Localizable(True)> _
    Public Property Cue() As String
        Get
            Return mCue
        End Get
        Set
            mCue = value
            updateCue()
        End Set
    End Property

    Private Sub updateCue()
        If Me.IsHandleCreated AndAlso mCue IsNot Nothing Then
            SendMessage(Me.Handle, &H1501, DirectCast(1, IntPtr), mCue)   'this line get the error msg
        End If
    End Sub
    Protected Overrides Sub OnHandleCreated(e As EventArgs)
        MyBase.OnHandleCreated(e)
        updateCue()
    End Sub
    Private mCue As String

    ' PInvoke
    <DllImport("user32.dll", CharSet := CharSet.Unicode)> _
    Private Shared Function SendMessage(hWnd As IntPtr, msg As Integer, wp As IntPtr, lp As String) As IntPtr
    End Function
End Class

Answer 1

根据PInvoke.net，VB.Net中SendMessage的正确签名是：

<DllImport("user32.dll", SetLastError:=True, CharSet:=CharSet.Auto)> _
Private Shared Function SendMessage(ByVal hWnd As IntPtr, ByVal Msg As UInteger, ByVal wParam As IntPtr, ByVal lParam As IntPtr) As IntPtr
End Function

无论如何，问题在于这一行：

SendMessage(Me.Handle, &H1501, DirectCast(1, IntPtr), mCue)

尝试通过以下方式替换它：

SendMessage(Me.Handle, &H1501, New IntPtr(1)), mCue)

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