CODEWITHSUNDEEP
c#winformsimessagefilter
Yasmin Endusa
Yasmin Endusa

Reputation: 63

Wrong WParam value in IMessageFilter.PreFilterMessage

I am currently in the process to implement a application-wide keyboard hook for one of my applications.
This is done by using a IMessageFilter implementation overriding the PreFilterMessage method and adding that IMessageFilter to my main form.
As far as i was able to test, most of the number and letter keys work without any problem, but when it comes to, let's say, Keys.Left (code 37), the WParam of the Message contains a, as it seems, wrong value (code 39).
And yes, i already did a bit-AND with Keys.KeyCode (which is 65535 btw. which means it wouldn't even matter).

If anyone has an idea or a hint why it works for letter/number keys but not for Keys.Left I would highly appreciate that.

Code:

public bool PreFilterMessage(ref Message m)
{
    if(m.Msg == WM_KEYDOWN)
    {
        _keyTable[(Keys)m.WParam & Keys.KeyCode] = true;
    }

    if(m.Msg == WM_KEYUP)
    {
        _keyTable[(Keys)m.WParam & Keys.KeyCode] = false;
    }

    return false;
}

Upvotes: 0

Views: 557

Answers (1)

Haitham I. Timani
Haitham I. Timani

Reputation: 11

I Faced the same problem in Numpad Keys.

I Did the following:

VB.NET:

    Dim KeyPressed As String
            Select Case CType(m.WParam.ToInt32(), Keys)
                Case Keys.NumPad1 : KeyPressed = "1"
                Case Keys.NumPad2 : KeyPressed = "2"
                Case Keys.NumPad3 : KeyPressed = "3"
                Case Keys.NumPad4 : KeyPressed = "4"
                Case Keys.NumPad5 : KeyPressed = "5"
                Case Keys.NumPad6 : KeyPressed = "6"
                Case Keys.NumPad7 : KeyPressed = "7"
                Case Keys.NumPad8 : KeyPressed = "8"
                Case Keys.NumPad9 : KeyPressed = "9"
                Case Keys.NumPad0 : KeyPressed = "0"
                Case Else : KeyPressed = Microsoft.VisualBasic.ChrW(m.WParam)
            End Select

Upvotes: 1

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