Events for Visual Basic 6 COM interoperability

As mentioned inside the tutorial How to synchronize the container application with the API, Visual Basic 6 results unreliable when dealing with delegates and callbacks in general so, when using the API in conjunctions with this development environment, a set of COM compatible events is provided.

In order to enable the usage of the provided events you need to invoke the COMEventEnable method, for each type of event you are going to manage, immediately after initializing the API through the InitEditor method, then you need to manually enter the event management routine.

Inside the snippet below you can see an example of management of events generated by the editor through the OnPercentage event handler when a sound file is loaded and through the OnVuMeterValueChange event when VU Meter values are changed; the text of a label is modified when monitored events are reported and a progress bar is managed as well to inform about operations advancement:

Visual Basic 6

' declare the API

Public WithEvents m_SoundEditorApi As AudioSoundEditorApi.AudioSoundEditorApiObj

Private Sub m_SoundEditorApi_OnPercentage(ByVal nOperation As enumOperationsWithPercentage, ByVal nPercentage As Integer)

If ProgressBar1.Value = nPercentage Then

' no change

Exit Sub

End If

ProgressBar1.Visible = True

ProgressBar1.Value = nPercentage

If nOperation = enumOperationsWithPercentage_OPERATION_SOUND_LOADING Then

LabelStatus.Caption = "Status: Loading... " & nPercentage & "%"

ElseIf nOperation = enumOperationsWithPercentage_OPERATION_WAVE_ANALYSIS Then

LabelStatus.Caption = "Status: Analyzing waveform... " & nPercentage & "%"

End If

ProgressBar1.Refresh

LabelStatus.Refresh

End Sub

Private Sub m_SoundEditorApi_OnVUMeterValueChange(ByVal nPeakLeft As Integer, ByVal nPeakRight As Integer)

' draw VU-Meter's bands using the graphic bars

m_SoundEditorApi.GraphicBarsManagerGet().SetValue m_hWndVuMeterLeft, nPeakLeft

m_SoundEditorApi.GraphicBarsManagerGet().SetValue m_hWndVuMeterRight, nPeakRight

End Sub

Private Sub Form_Load()

' instance the API

Set m_SoundEditorApi = New AudioSoundEditorApi.AudioSoundEditorApiObj

' init the control

m_SoundEditorApi.InitEditor

' enable events percentage of advancement events and VU Meter events for COM clients like VB6

m_SoundEditorApi.COMEventEnable enumEventTypesEdt_EVENT_TYPE_EDT_PERC

m_SoundEditorApi.COMEventEnable enumEventTypesEdt_EVENT_TYPE_EDT_VU_METER

LabelStatus.Caption = "Status: Idle"

ProgressBar1.Visible = False

' load the new song

m_SoundEditorApi.SetLoadingMode enumLoadingModes_LOAD_MODE_NEW

Dim nResult As enumErrorCodes

nResult = m_SoundEditorApi.LoadSound(strPathname)

If nResult <> enumErrorCodes_ERR_NOERROR Then

MsgBox "Cannot load the file due to the following error: " & nResult

Exit Sub

End If

ProgressBar1.Value = 0

' request full waveform analysis using default resolution

m_SoundEditorApi.DisplayWaveformAnalyzerGet().AnalyzeFullSound

ProgressBar1.Visible = False

LabelStatus.Caption = "Status: Idle"

End Sub

as seen for regular ActiveX controls, the name of the event management routine is made of a number of parts: the name of the component (in this case "m_SoundEditorApi" which was originally declared with the "WithEvents" attribute) followed by the underscore "_" character and by the name of the event (in this case "OnPercentage") and related parameters.