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Implementing CEchoPropPage::Apply

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[The feature associated with this page, Windows Media Player SDK, is a legacy feature. It has been superseded by MediaPlayer. MediaPlayer has been optimized for Windows 10 and Windows 11. Microsoft strongly recommends that new code use MediaPlayer instead of Windows Media Player SDK, when possible. Microsoft suggests that existing code that uses the legacy APIs be rewritten to use the new APIs if possible.]

The CEchoPropPage::Apply method is implemented in EchoPropPage.cpp. It executes when the user clicks Apply in the property page dialog box in Windows Media Player. The plug-in wizard sample code provides an implementation to handle a single property. You can modify this code for one of the Echo sample properties, and then add code to store the other property value.

Declaring the Apply Method Variables

First, you must remove the declaration of fScaleFactor. Then, add variable declarations that you will need. The following example shows the completed variable declarations:

TCHAR   szStr[MAXSTRING] = { 0 };
DWORD   dwDelayTime = 1000;  // Initialize the delay time.
DWORD   dwWetmix = 50;       // Initialize a DWORD for effect level.
double  fWetmix = 0.50;      // Initialize a double for effect level.

Retrieving the Values from the Property Page

You must implement code to retrieve and validate the user input. The following code example retrieves the delay time value from the IDC_DELAYTIME edit box, and then verifies that the value is within a specified range:

// Get the delay time value from the dialog box.
GetDlgItemText(IDC_DELAYTIME, szStr, sizeof(szStr) / sizeof(szStr[0]));

dwDelayTime = atoi(szStr);

// Make sure delay time is valid.
if ((dwDelayTime < 10) || (dwDelayTime > 2000))
{
    if (::LoadString(_Module.GetResourceInstance(), IDS_DELAYRANGEERROR, szStr, sizeof(szStr) / sizeof(szStr[0])))
    {
        MessageBox(szStr);
    }

    return E_FAIL;
}

If the user input is not in the specified range, the code displays a message box. Notice the use of the string resource you created earlier for the error message.

The following example retrieves the effect level from the IDC_WETMIX edit box and then verifies that the value is within a specified range:

// Get the effects level value from the dialog box.
GetDlgItemText(IDC_WETMIX, szStr, sizeof(szStr) / sizeof(szStr[0]));

dwWetmix = atoi(szStr);

// Make sure wet mix value is valid.
if ((dwWetmix < 0) || (dwWetmix > 100))
{
    if (::LoadString(_Module.GetResourceInstance(), IDS_MIXRANGEERROR, szStr, sizeof(szStr) / sizeof(szStr[0])))
    {
        MessageBox(szStr);
    }

    return E_FAIL;
}

Storing the Property Values in the Registry

Next, your code must persist the new property values to the registry. The following code stores both property values:

// update the registry
CRegKey key;
LONG    lResult;

// Write the delay time value to the registry.
lResult = key.Create(HKEY_CURRENT_USER, kszPrefsRegKey);
if (ERROR_SUCCESS == lResult)
{
    lResult = key.SetValue( dwDelayTime , kszPrefsDelayTime );
}

// Write the wet mix value to the registry.
lResult = key.Create(HKEY_CURRENT_USER, kszPrefsRegKey);
if (ERROR_SUCCESS == lResult)
{
    lResult = key.SetValue( dwWetmix , kszPrefsWetmix );
}

Updating the Echo Plug-in Property Values

The Apply method must inform the Echo plug-in that the property values have changed. The following code calls the property put method for each property using the interface pointer retrieved in CEchoPropPage::SetObjects:

// update the plug-in
if (m_spEcho)
{
    m_spEcho->put_delay(dwDelayTime);

    // Convert the wet mix value from DWORD to double.
    fWetmix = (double)dwWetmix / 100;
    m_spEcho->put_wetmix(fWetmix);
}

Notice that the wet mix value is converted to floating point before being passed to the plug-in.

Disabling the Apply Button

As a final step, your code should disable Apply in the property page dialog box as a signal to the user that the values have been successfully updated. This requires the following single line of code:

m_bDirty = FALSE; // Tell the property page to disable Apply.

Modifying the Echo Sample Property Page