[litwindow-users] Re: NotifyChanged not causing update?

[Hajo K. <mai...@ha...>]

Hi,

> I used RapidUI with wxWizard as suggested.  It worked great, even
> interfacing to the class data through member functions.

I am glad to hear that.

> Since the UI and data are updated without regard to whether the user cancels
> the action, I passed a new instance of the data structure to RapidUI. If the
> user "Finish"es the wizard, the data is copied into the real data structure.
> I presume that this is the expected usage pattern?

For the moment being, yes.

Later I'll introduce the notion of "commit levels". Commit levels are a 
classification of when the relevant rules will be evaluated. For GUI 
elements there could be
+ immediate - useful for buttons of all kind including checkboxes etc...
+ focus lost - useful for textcontrols etc...
+ explicit - commit must be triggered explicitly, such as with an 
apply/ok button.


> After copying the wizard changes, I called NotifyChanged(g_data).  Nothing
> happened.  Not until I did an insert operation (which also triggers a
> NotifyChanged) did the UI update and show the changes introduced by the
> wizard.

Please post some code.

NotifyChanged accepts three parameters.
1. An accessor pointing to the element that has changed.
2. bool recursive - true meaning that a subelement (member, inherited 
etc...) has changed, false meaning only the topmost view of the element 
will be evaluated. useful for aggregates and containers only.
3. bool immediate - if true, triggers reevaluation immediately, if 
false, wait for another call to NotifyChanged with immediate=true

If you've set up everything correctly and have Start()ed the rapidUI 
mechanism, then NotifyChanged should update all widgets immediately.

> At first I thought that the NotifyChanged might be interacting with my local
> instance of RapidUI, wiz_mediator, instead of m_rapidUI, but none of the

NotifyChanged sends its events to all RapidUI objects currently 
instantiated.

> variations I've tried has yielded any updates.  I even tried creating an
> accessor and using m_rapidUI->ValueChanged(..).  (I used recursion=false,
> but I even tried naming the particular attribute that changed.) How do I
> convince RapidUI to reevaluate the rules?

If it does not reevaluate the rules it probably means that you are 
passing in an object that does not appear in the rules anywhere. No rule 
depends on it. For example, if you pass a local copy of the data to 
RapidUI, then call NotifyChanged(g_data) for the gobal instance, nothing 
will change.

> I also found myself asking these questions: Can NotifyChanged be called on
> any sub-element of the data structure?  If I call NotifyChanged on some leaf
Yes. Either call

NotifyChanged(g_data.this_has_changed);

or use the other version:

NotifyChanged(g_data, "this_has_changed");

> of data will RapidUI know that a Rule referencing a branch containing the
> changed data needs to be reevaluated?

Aahh, now we are coming to the juicy details :)

Suppose you have a data structure:

Top.Middle.Leaf

and these rules:

Rule_1: widget.property = Leaf
Rule_2: widget2.property = Middle

Your question is, if I understand it correctly, if you call 
NotifyChanged for leaf, will Rule_2 be reevaluated as well, since if 
Leaf has changed, Middle has changed implicitly as well.

This situation can get very complex, especially if you consider side 
effects where the value of one leaf is calculated from the value of a 
different leaf such as

bool IsEnabled() const { return m_admin_rights && m_logged_in; }

If you have

Data.Enabled
Data.AdminRights
Data.LoggedIn

properties and change LoggedIn, Enabled will change as well.

For now the library ignores these side effects if you call NotifyChanged 
for the Leaf only. In such situations you must call NotifyChanged for 
the node above the changes and set the 'recursive' parameter to true.

NotifyChanged(Data, true, true);

RapidUI expands this to
NotifyChanged(Data.Enabled, false, false);
NotifyChanged(Data.AdminRights, false, false);
NotifyChanged(Data.LoggedIn, false, false);
NotifyChanged(Data, false, true);

> By the way, the rule that I am expecting to update is of the form:
> RULE("ID_FRAME.Title", make_const<wxString>("MyProg: ") +
> make_expr<wxString>("Name"))
> 
> where Name resolves to GetName().

Looks fine to me. But please post some more code.

Best regards

Hajo