How to create the MouseDown event on the desktop screen

Question

How can I create a MouseDown event on the desktop screen using Visual Basic? I want to trigger a specific action when the left mouse button is clicked. Any suggestions or examples would be appreciated.

I got such a response, but it is not possible to make changes in the form from the event received.Answer 'Q&A Assist'

Answer 1

Hi @Mansour_Dalir ,

You can use the SetWindowsHookEx function from the Windows API to capture global mouse events. Here's an example that demonstrates how to capture the global mouse down event and trigger an action when the left mouse button is clicked:

Imports System.Runtime.InteropServices

Public Class Form1

    ' Define constants for hook types
    Private Const WH_MOUSE_LL As Integer = 14
    Private Const WM_LBUTTONDOWN As Integer = &H201

    ' Declare the hook handle
    Private hookID As IntPtr = IntPtr.Zero

    ' Declare the hook callback delegate
    Private mouseProc As LowLevelMouseProc = Nothing

    ' Declare the structure to store mouse information
    <StructLayout(LayoutKind.Sequential)>
    Private Structure MSLLHOOKSTRUCT
        Public pt As POINT
        Public mouseData As UInteger
        Public flags As UInteger
        Public time As UInteger
        Public dwExtraInfo As IntPtr
    End Structure

    <StructLayout(LayoutKind.Sequential)>
    Private Structure POINT
        Public x As Integer
        Public y As Integer
    End Structure

    ' Declare the delegate for the low-level mouse procedure
    Private Delegate Function LowLevelMouseProc(nCode As Integer, wParam As IntPtr, lParam As IntPtr) As IntPtr

    ' Import the necessary Windows API functions
    <DllImport("user32.dll", SetLastError:=True)>
    Private Shared Function SetWindowsHookEx(idHook As Integer, lpfn As LowLevelMouseProc, hMod As IntPtr, dwThreadId As UInteger) As IntPtr
    End Function

    <DllImport("user32.dll", SetLastError:=True)>
    Private Shared Function UnhookWindowsHookEx(hhk As IntPtr) As Boolean
    End Function

    <DllImport("user32.dll", SetLastError:=True)>
    Private Shared Function CallNextHookEx(hhk As IntPtr, nCode As Integer, wParam As IntPtr, lParam As IntPtr) As IntPtr
    End Function

    <DllImport("kernel32.dll", SetLastError:=True)>
    Private Shared Function GetModuleHandle(lpModuleName As String) As IntPtr
    End Function

    ' Set up the mouse hook
    Private Sub Form1_Load(sender As Object, e As EventArgs) Handles MyBase.Load
        mouseProc = AddressOf MouseHookCallback
        hookID = SetHook(mouseProc)
    End Sub

    ' Release the hook when the form closes
    Private Sub Form1_FormClosing(sender As Object, e As FormClosingEventArgs) Handles MyBase.FormClosing
        UnhookWindowsHookEx(hookID)
    End Sub

    ' Hook function to set the mouse hook
    Private Function SetHook(proc As LowLevelMouseProc) As IntPtr
        Using curProcess = Process.GetCurrentProcess()
            Using curModule = curProcess.MainModule
                Return SetWindowsHookEx(WH_MOUSE_LL, proc, GetModuleHandle(curModule.ModuleName), 0)
            End Using
        End Using
    End Function

    ' The callback function that handles the mouse events
    Private Function MouseHookCallback(nCode As Integer, wParam As IntPtr, lParam As IntPtr) As IntPtr
        If nCode >= 0 AndAlso wParam = CType(WM_LBUTTONDOWN, IntPtr) Then
            ' The left mouse button was clicked - trigger the action
            TriggerAction()
        End If

        ' Call the next hook in the chain
        Return CallNextHookEx(hookID, nCode, wParam, lParam)
    End Function

    ' Define the action to trigger on mouse click
    Private Sub TriggerAction()
        MessageBox.Show("Left mouse button clicked!")
    End Sub

End Class

Best Regards.

Jiachen Li

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Answer 2

To create a MouseDown event on the desktop screen using Visual Basic, you can use a low-level mouse hook to detect mouse events. Here is an example code snippet that demonstrates how to do this:

Imports System.Runtime.InteropServices

Public Class Form1
    Private Const WH_MOUSE_LL As Integer = 14
    Private Const WM_LBUTTONDOWN As Integer = &H201

    Private Delegate Function LowLevelMouseProc(ByVal nCode As Integer, ByVal wParam As IntPtr, ByVal lParam As IntPtr) As IntPtr

    Private Shared Function HookCallback(ByVal nCode As Integer, ByVal wParam As IntPtr, ByVal lParam As IntPtr) As IntPtr
        If nCode >= 0 AndAlso wParam = New IntPtr(WM_LBUTTONDOWN) Then
            ' Left mouse button was clicked
            ' Add your code here to perform the desired action
        End If
        Return CallNextHookEx(IntPtr.Zero, nCode, wParam, lParam)
    End Function

    Private Shared _hookID As IntPtr = IntPtr.Zero
    Private Shared _proc As LowLevelMouseProc = AddressOf HookCallback

    Private Declare Function SetWindowsHookEx Lib "user32" Alias "SetWindowsHookExA" (ByVal idHook As Integer, ByVal lpfn As LowLevelMouseProc, ByVal hMod As IntPtr, ByVal dwThreadId As UInteger) As IntPtr
    Private Declare Function CallNextHookEx Lib "user32" (ByVal hhk As IntPtr, ByVal nCode As Integer, ByVal wParam As IntPtr, ByVal lParam As IntPtr) As IntPtr
    Private Declare Function UnhookWindowsHookEx Lib "user32" (ByVal hhk As IntPtr) As Boolean

    Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
        _hookID = SetWindowsHookEx(WH_MOUSE_LL, _proc, IntPtr.Zero, 0)
    End Sub

    Private Sub Form1_FormClosing(ByVal sender As System.Object, ByVal e As System.Windows.Forms.FormClosingEventArgs) Handles MyBase.FormClosing
        UnhookWindowsHookEx(_hookID)
    End Sub
End Class

This code sets up a low-level mouse hook that listens for left mouse button clicks. When a left mouse button click is detected, you can add your own code to perform the desired action. Note that this code will detect left mouse button clicks anywhere on the desktop screen, not just within your application.

References:

• Handling User Input - Mouse Events
• Using mouse events (Windows Forms .NET)