Cannot access roaming settings when UI dialog open - outlook-addin

Question

I can access the roaming settings from the side panel in the outlook Add-in.But when I am trying to access roaming settings if the UI dialog ( DialogAsync) is open. It getting as undefined.
var _settings = Office.context.roamingSettings;
var numberDetails = _settings.get('PHONENUMBERSLIST');

Answer 1

There are only two Office.js APIs that can be called in the dialog:
messageParent
isSetSupported
See the note about 1/3 of the way down in the is article: Use the Dialog API in your Office Add-ins

Answer 2

RoamingSettings will be only available in the frame that created it. If you need to share some values between your dialog and side panel, you can pass these values as parameters in url:
var url = new URI('Dialog/myDialog.html').absoluteTo(window.location).toString();
url += '?myvalue=' + Office.context.roamingSettings.get('myvalue')
+ '&othervalue=' + Office.context.roamingSettings.get('othervalue');
var dialogOptions = { width: 20, height: 35, displayInIframe: true };
Office.context.ui.displayDialogAsync(url, dialogOptions, function (result) {
settingsDialog = result.value;
settingsDialog.addEventHandler(Microsoft.Office.WebExtension.EventType.DialogMessageReceived, receiveSettingsMessage);
settingsDialog.addEventHandler(Microsoft.Office.WebExtension.EventType.DialogEventReceived, settingsDialogClosed);
});
Then, in your dialog, you can use them or set them again inside $(document).ready() using getUrlParameter('myvalue').
You can also send needed values back to the side panel using:
function sendMessage(param) {
Office.context.ui.messageParent(JSON.stringify(param));
}