如何創建水印文本框？

Question

我發現代碼Watermark TextBox in WinForms但它是C＃的版本，所以我用http://converter.telerik.com/的代碼到VB版本轉換，但我仍然得到錯誤......

錯誤發生在這條線： -

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

我怎樣才能解決這個問題？

錯誤消息：BC30311'Integer'類型的值無法轉換爲'IntPtr'。

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

根據PInvoke.net在VB.Net爲SendMessage正確的簽名是：

<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 

無論如何，問題是在這一行：

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

試圖取代它通過：

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