I have a design question about (i guess) object interdependence using gtkd.

There is an application class which sets its property mAppWin. The app is passed as an argument to the window constructor. During the window constructor a scale (trackbar) is created which also receives and stores an app reference to later update other elements during an onChange event. The scale can access mApp.mSomeData to set its initial value because app has been passed down. The call to setValue() now triggers onValueChanged() which wants to access the mAppWin property of the app to update a canvas. Since all this happens during the initial 'new AppWin()' call in App, the app's mAppWin property is not set yet, so onValueChanged() will crash.



class App : Application
{
	AppWin mAppWin;

	void onActivate(GioApplication gioApp)
	{
		mSomeData = 123;
		
		mAppWin = new AppWin(app, [...]);



class AppWin : ApplicationWindow
{
	Scale1 mScale1;

	this(Application application, [...])
	{
		mScale1 = new Scale1(0, 100, 1, app);   // (app is application casted)



class Scale1 : VScale
{
	App mApp;

	this([...], App app)
	{
		[...]
		mApp = app;
		[...]
		setValue(max * mApp.mSomeData);
	}

	void onValueChanged(Range range)
	{
		//if (mApp.mAppWin)
			mApp.mAppWin.mCanvas.update();   // mAppWin not set yet, 0



I have several question in mind:
- Is it a bad idea to pass an app around that contains everything for everywhere?
- Should the app pass the data for the initial scale value through the window constructor? Or should it set the scale value after initialization is done?
- How would the scale update the canvas without keeping/walking through a DOM like this. Maybe some asynchronous messaging?

While I could make it work, I wonder what the actual problem is and what it's called like.