Starting with .NET 4.7, the RichTextBox uses the RichEdit50 control; prior versions used the RichEdit20 control. I do not know the reason for differences in the handling of hyperlinks between the control versions, but there evidently are some differences.
A work-around is to configure your .NET 4.7 application to use the older control. This is done by adding the following to your App.config file.
<runtime>
<AppContextSwitchOverrides value="Switch.System.Windows.Forms.DoNotLoadLatestRichEditControl=true" />
</runtime>
The source of the problem appears to be a hack in the original RichTextBox.CharRangeToString method.
//Windows bug: 64-bit windows returns a bad range for us. VSWhidbey 504502.
//Putting in a hack to avoid an unhandled exception.
if (c.cpMax > Text.Length || c.cpMax-c.cpMin <= 0) {
return string.Empty;
}
When using the Friendly Name Hyperlinks available in the RichEdit50 control, the RichTextBox.Text.Length property can be less than the c.cpMax value as the link is not included in the returned property value. This causes the method to return String.Empty to the calling RichTextBox.EnLinkMsgHandler method that in turn will not raise the LickClicked event if a Empty.String is returned.
case NativeMethods.WM_LBUTTONDOWN:
string linktext = CharRangeToString(enlink.charrange);
if (!string.IsNullOrEmpty(linktext))
{
OnLinkClicked(new LinkClickedEventArgs(linktext));
}
m.Result = (IntPtr)1;
return;
To deal with this bug, a custom RichTextBox class is defined below to modify the logic of the CharRangeToString method. This modified logic is invoked in the WndProc procedure to bypass the default logic.
Imports System.Runtime.InteropServices
Imports WindowsApp2.NativeMthods ' *** change WindowsApp2 to match your project
Public Class RichTextBoxFixedForFriendlyLinks : Inherits RichTextBox
Friend Function ConvertFromENLINK64(es64 As ENLINK64) As ENLINK
' Note: the RichTextBox.ConvertFromENLINK64 method is written using C# unsafe code
' this is version uses a GCHandle to pin the byte array so that
' the same Marshal.Read_Xyz methods can be used
Dim es As New ENLINK()
Dim hndl As GCHandle
Try
hndl = GCHandle.Alloc(es64.contents, GCHandleType.Pinned)
Dim es64p As IntPtr = hndl.AddrOfPinnedObject
es.nmhdr = New NMHDR()
es.charrange = New CHARRANGE()
es.nmhdr.hwndFrom = Marshal.ReadIntPtr(es64p)
es.nmhdr.idFrom = Marshal.ReadIntPtr(es64p + 8)
es.nmhdr.code = Marshal.ReadInt32(es64p + 16)
es.msg = Marshal.ReadInt32(es64p + 24)
es.wParam = Marshal.ReadIntPtr(es64p + 28)
es.lParam = Marshal.ReadIntPtr(es64p + 36)
es.charrange.cpMin = Marshal.ReadInt32(es64p + 44)
es.charrange.cpMax = Marshal.ReadInt32(es64p + 48)
Finally
hndl.Free()
End Try
Return es
End Function
Protected Overrides Sub WndProc(ByRef m As Message)
If m.Msg = WM_ReflectNotify Then
Dim hdr As NMHDR = CType(m.GetLParam(GetType(NMHDR)), NMHDR)
If hdr.code = EN_Link Then
Dim lnk As ENLINK
If IntPtr.Size = 4 Then
lnk = CType(m.GetLParam(GetType(ENLINK)), ENLINK)
Else
lnk = ConvertFromENLINK64(CType(m.GetLParam(GetType(ENLINK64)), ENLINK64))
End If
If lnk.msg = WM_LBUTTONDOWN Then
Dim linkUrl As String = CharRangeToString(lnk.charrange)
' Still check if linkUrl is not empty
If Not String.IsNullOrEmpty(linkUrl) Then
OnLinkClicked(New LinkClickedEventArgs(linkUrl))
End If
m.Result = New IntPtr(1)
Exit Sub
End If
End If
End If
MyBase.WndProc(m)
End Sub
Private Function CharRangeToString(ByVal c As CHARRANGE) As String
Dim ret As String = String.Empty
Dim txrg As New TEXTRANGE With {.chrg = c}
''Windows bug: 64-bit windows returns a bad range for us. VSWhidbey 504502.
''Putting in a hack to avoid an unhandled exception.
'If c.cpMax > Text.Length OrElse c.cpMax - c.cpMin <= 0 Then
' Return String.Empty
'End If
' *********
' c.cpMax can be greater than Text.Length if using friendly links
' with RichEdit50. so that check is not valid.
' instead of the hack above, first check that the number of characters is positive
' and then use the result of sending EM_GETTEXTRANGE to handle the
' possibilty of Text.Length < c.cpMax
' *********
Dim numCharacters As Int32 = (c.cpMax - c.cpMin) + 1 ' +1 for null termination
If numCharacters > 0 Then
Dim charBuffer As CharBuffer
charBuffer = CharBuffer.CreateBuffer(numCharacters)
Dim unmanagedBuffer As IntPtr
Try
unmanagedBuffer = charBuffer.AllocCoTaskMem()
If unmanagedBuffer = IntPtr.Zero Then
Throw New OutOfMemoryException()
End If
txrg.lpstrText = unmanagedBuffer
Dim len As Int32 = CInt(SendMessage(New HandleRef(Me, Handle), EM_GETTEXTRANGE, 0, txrg))
If len > 0 Then
charBuffer.PutCoTaskMem(unmanagedBuffer)
ret = charBuffer.GetString()
End If
Finally
If txrg.lpstrText <> IntPtr.Zero Then
Marshal.FreeCoTaskMem(unmanagedBuffer)
End If
End Try
End If
Return ret
End Function
End Class
While the above code is not that substantial, it requires several methods/structures from the base implementation that are not publicly accessible. A VB version of the methods is presented below. Most are direct conversions from the original C# source.
Imports System.Runtime.InteropServices
Imports System.Text
Public Class NativeMthods
Friend Const EN_Link As Int32 = &H70B
Friend Const WM_NOTIFY As Int32 = &H4E
Friend Const WM_User As Int32 = &H400
Friend Const WM_REFLECT As Int32 = WM_User + &H1C00
Friend Const WM_ReflectNotify As Int32 = WM_REFLECT Or WM_NOTIFY
Friend Const WM_LBUTTONDOWN As Int32 = &H201
Friend Const EM_GETTEXTRANGE As Int32 = WM_User + 75
Public Structure NMHDR
Public hwndFrom As IntPtr
Public idFrom As IntPtr 'This is declared as UINT_PTR in winuser.h
Public code As Int32
End Structure
<StructLayout(LayoutKind.Sequential)>
Public Class ENLINK
Public nmhdr As NMHDR
Public msg As Int32 = 0
Public wParam As IntPtr = IntPtr.Zero
Public lParam As IntPtr = IntPtr.Zero
Public charrange As CHARRANGE = Nothing
End Class
<StructLayout(LayoutKind.Sequential)>
Public Class ENLINK64
<MarshalAs(UnmanagedType.ByValArray, SizeConst:=56)>
Public contents(0 To 55) As Byte
End Class
<StructLayout(LayoutKind.Sequential)>
Public Class CHARRANGE
Public cpMin As Int32
Public cpMax As Int32
End Class
<StructLayout(LayoutKind.Sequential)>
Public Class TEXTRANGE
Public chrg As CHARRANGE
Public lpstrText As IntPtr ' allocated by caller, zero terminated by RichEdit
End Class
Public MustInherit Class CharBuffer
Public Shared Function CreateBuffer(ByVal size As Int32) As CharBuffer
If Marshal.SystemDefaultCharSize = 1 Then
Return New AnsiCharBuffer(size)
End If
Return New UnicodeCharBuffer(size)
End Function
Public MustOverride Function AllocCoTaskMem() As IntPtr
Public MustOverride Function GetString() As String
Public MustOverride Sub PutCoTaskMem(ByVal ptr As IntPtr)
Public MustOverride Sub PutString(ByVal s As String)
End Class
Public Class AnsiCharBuffer : Inherits CharBuffer
Friend buffer() As Byte
Friend offset As Int32
Public Sub New(ByVal size As Int32)
buffer = New Byte(0 To size - 1) {}
End Sub
Public Overrides Function AllocCoTaskMem() As IntPtr
Dim result As IntPtr = Marshal.AllocCoTaskMem(buffer.Length)
Marshal.Copy(buffer, 0, result, buffer.Length)
Return result
End Function
Public Overrides Function GetString() As String
Dim i As Int32 = offset
Do While i < buffer.Length AndAlso buffer(i) <> 0
i += 1
Loop
Dim result As String = Encoding.Default.GetString(buffer, offset, i - offset)
If i < buffer.Length Then
i += 1
End If
offset = i
Return result
End Function
Public Overrides Sub PutCoTaskMem(ByVal ptr As IntPtr)
Marshal.Copy(ptr, buffer, 0, buffer.Length)
offset = 0
End Sub
Public Overrides Sub PutString(ByVal s As String)
Dim bytes() As Byte = Encoding.Default.GetBytes(s)
Dim count As Int32 = Math.Min(bytes.Length, buffer.Length - offset)
Array.Copy(bytes, 0, buffer, offset, count)
offset += count
If offset < buffer.Length Then
buffer(offset) = 0
offset += 1
End If
End Sub
End Class
Public Class UnicodeCharBuffer : Inherits CharBuffer
Friend buffer() As Char
Friend offset As Int32
Public Sub New(ByVal size As Int32)
buffer = New Char(size - 1) {}
End Sub
Public Overrides Function AllocCoTaskMem() As IntPtr
Dim result As IntPtr = Marshal.AllocCoTaskMem(buffer.Length * 2)
Marshal.Copy(buffer, 0, result, buffer.Length)
Return result
End Function
Public Overrides Function GetString() As String
Dim i As Int32 = offset
Do While i < buffer.Length AndAlso AscW(buffer(i)) <> 0
i += 1
Loop
Dim result As New String(buffer, offset, i - offset)
If i < buffer.Length Then
i += 1
End If
offset = i
Return result
End Function
Public Overrides Sub PutCoTaskMem(ByVal ptr As IntPtr)
Marshal.Copy(ptr, buffer, 0, buffer.Length)
offset = 0
End Sub
Public Overrides Sub PutString(ByVal s As String)
Dim count As Int32 = Math.Min(s.Length, buffer.Length - offset)
s.CopyTo(0, buffer, offset, count)
offset += count
If offset < buffer.Length Then
buffer(offset) = ChrW(0)
offset += 1
End If
End Sub
End Class
<DllImport("user32.dll", CharSet:=CharSet.Auto)>
Public Shared Function SendMessage(ByVal hWnd As HandleRef, ByVal msg As Int32, ByVal wParam As Int32, ByVal lParam As TEXTRANGE) As IntPtr
End Function
End Class
Add these classes to our project and perform a build. RichTextBoxFixedForFriendlyLinks should be available in the Toolbox. You can use it where you would normally use the RichTextBox control.
This issue has been posted on MS Developer Community as: WinForm RichTextBox LinkClicked event fails to fire when control loaded with RTF containing a friendly name hyperlink
