How do I preserve a user setting's value when I change the setting's roaming property?

Question

I've come to understand that I can preserve user settings from previous versions using code like this:

        if (Settings.Default.UpgradeRequired)
        {
            Settings.Default.Upgrade();
            Settings.Default.UpgradeRequired = false;
            Settings.Default.Save();
        }

However, that doesn't seem to work if I change a setting's roaming property. Is there any way to get the setting values to carry over and not reset when I change a setting from roaming to local or vice versa?

EDIT: I looked into a possible way to upgrade roaming settings to local settings using the GetPreviousVersion() method, but it doesn't work because if the previous version of a setting was roaming when the current setting isn't, the previous version isn't returned at all.

To reproduce:

1. Make a setting named MySetting.
2. Change MySetting's Roaming property to true.
3. Make sure MySetting's scope is User.

4. Run the following code:

       Console.WriteLine(Settings.Default.GetPreviousVersion("MySetting"));
       Settings.Default.MySetting = "Not the default value.";
       Settings.Default.Save();
   

5. Increment the assembly version.
6. Run the code again, noticing that the new value is outputted.
7. Change MySetting's Roaming property to false.
8. Increment the assembly version again.
9. Run the code again, noticing that the default value is outputted.

Answer 1

If you know which properties have changed from roaming=true to roaming=false, then you can manually add the SettingsManageabilityAttribute to the SettingsProperty.Attributes dictionary, use GetPreviousVersion to retrieve the previous value, then remove the attribute from the dictionary to clean-up:

Console.WriteLine("Current: {0}", Settings.Default.MySetting);
// we don't see the previous value here...
Console.WriteLine("Previous: {0}", Settings.Default.GetPreviousVersion("MySetting"));
// ...so we manually add the SettingsManageabilityAttribute to it...
var setting = Settings.Default.Properties["MySetting"];
setting.Attributes.Add(typeof(SettingsManageabilityAttribute), new SettingsManageabilityAttribute(SettingsManageability.Roaming));
// ...retrieve the previous value...
Console.WriteLine("Previous: {0}", Settings.Default.GetPreviousVersion("MySetting"));
// ...and then clean up after ourselves by removing the attribute.
setting.Attributes.Remove(typeof(SettingsManageabilityAttribute));
// ...now we don't see the previous value anymore.
Console.WriteLine("Previous: {0}", Settings.Default.GetPreviousVersion("MySetting"));