Value 'onSettingsChanged' not available in all function scopes.

Question

I have a datafield. I am trying to add a background process to download some json file from the web. (I know new devices can do it in the foreground, but I also want it to work for older devices).

So I added (:background) annotation to the class of MyApp:

import Toybox.Application;
import Toybox.Lang;
import Toybox.WatchUi;

(:background)
class MyApp extends Application.AppBase {
    hidden var view as MyView?;

    function initialize() {
        AppBase.initialize();
    }

    (:typecheck(false))
    function getInitialView() as Array<Views or InputDelegates>? {
        self.view = new MyView();
        return [ self.view ] as Array<Views or InputDelegates>;
    }

    (:foreground)
    function onSettingsChanged() as Void {
        if (view != null && !isRunningInBackground()) {
            view.onSettingsChanged(SETTINGS_CHANGED_FROM_CONNECT_IQ);
        }
    }
}

(:no_ciq_2_4_0, :background)
function isRunningInBackground() as Boolean {
    try {
        var app = getApp();
        app.setProperty(PROPERTY_NON_EXSISTANT, 1);
        app.deleteProperty(PROPERTY_NON_EXSISTANT);
        return false;
    } catch (ex) {
        return true;
    }
}
(:ciq_2_4_0, :background)
function isRunningInBackground() as Boolean {
    try {
        Properties.setValue(PROPERTY_EXSISTANT, false);
        return false;
    } catch (ex) {
        return true;
    }
}

Until now in onSettingsChanged it called view.onSettingsChanged which was always set (IMHO), but now when the background app will run there won't be a view obviously.

The (:foreground) annotation doesn't help, I guess the whole class is in the background code, so if the onSettingsChanged method is overridden then it calls it. I get the following compilation errors. How can I make this compile?

ERROR: fr955: MyApp.mc:68,12: Value 'onSettingsChanged' not available in all function scopes.
ERROR: fr955: MyApp.mc:68,12: Cannot find symbol ':onSettingsChanged' on type 'Null'.
ERROR: fr955: MyApp.mc:68,12: Value 'SETTINGS_CHANGED_FROM_CONNECT_IQ' not available in all function scopes.

The 2nd error is just a bug in the compiler, as it should know that view isn't null, but what can I do if I don't want this code to run at all if the background?

flowstate · Answer

Not to state the obvious, but the "foreground annotation" doesn't help bc foreground isn't a built-in CIQ annotation which does what you want it to do (exclude code from the background process). Someone (I think jim_m_58) explained that the PRG is laid out in such a way that it's possible for the background process to only include the background code, but the foreground process has to include all of the code. I think maybe all the FG-only code and data is at the end of the PRG. 
 e.g. PRGs might look like this: 
 ------------------- |Header | ----------------- - |... | ------------------ |BG/FG code/data | ----------------- - |FG-only code/data| ----------------- -- 
 Anyway, I think the solution is to create a global function (lacking the background annotation) to handle the duties of onSettingsChanged(), then conditionally call that from MyApp.OnSettingsChanged() if the symbol exists. 
 If you have lots of stuff that needs to be foreground only you can make it a class or a module if that would be cleaner. 
 (:background)
class MyApp extends Application.AppBase {
 // ...
 function onSettingsChanged() as Void {
 if ($ has :onSettingsChanged && view != null) {
 $.onSettingsChanged(view);
 }
 }
}

function onSettingsChanged(view as MyView) as Void {
 view.onSettingsChanged(SETTINGS_CHANGED_FROM_CONNECT_IQ);
}

Value 'onSettingsChanged' not available in all function scopes.

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