Saving a Form state (related to separating ui from logic)

[Curt Carpenter]

I have a form representing an instrument control panel.  The virtual panel contains a significant number of different lazarus visual controls (sliders, switches, edit boxes, combo boxes etc.).  Is there a good way to take a "snapshot" of the state of all of those visual controls and store them to disk so that they can be read back from disk at a later time and restored to the form?  This is a routine operation not difficult to build into a procedure,  but writing the procedure is routine and tedious. Is there something like a "TSaveDialog" that saves the state of the controls on a form ("TSaveFormState" perhaps) rather than a file?

[jamie]

Look at the "SessionsProperty" in the form.

[Curt Carpenter]

A starting point.   Thank you.

[cdbc]

Hi
Maybe use RTTI to save all the published properties, of all the controls on the form to an ...xml-file?!? Lends itself, on the account of structuring, layout etc...
Just an idea 
Regards Benny

[Curt Carpenter]

Amazing -- and works like a charm.  Decided to use the JSONProperties storage rather than XML.   Many thanks!

[cdbc]

Hi
Cool  Good on you mate 
Regards Benny

[egsuh]

You alrealy have the answer. I'm just adding.

I have defined "class", which contains the necessary fields and published properties, and forms have RTTI controls. In that way, data are controled within the "class" --- both retrieving from and saving to your storage (a file, database, whatever).

[jcmontherock]

Curt, could you give us a little example of JSONProperties storage for saving form ?

[Curt Carpenter]

With some stuff deleted for clarity and TJSONPropStorage components from the MISC palette placed on two different forms, my use looks like this:

Code: Pascal  [Select][+][-]

1. procedure TForm1.BSaveControlsClick(Sender: TObject);
2. begin
3.   if (SaveDialog1.Execute) then
4.    begin
5.     FMain.JSONPropMain.JSONFileName :=  SaveDialog1.FileName+'.1'{Main form};
6.     FMain.JSONPropMain.Save;
7.     FSampling.JSONPropSampling.JSONFileName := SaveDialog1.FileName+'.2'{Sampling controls};
8.     FSampling.JSONPropSampling.Save;
9.    end;
10. end;
11.  
12. procedure TForm1.BLoadControlsClick(Sender: TObject);
13. begin
14.   if (OpenDialog1.Execute) then
15.     FMain.JSONPropMain.JSONFileName :=  OpenDialog1.FileName+'.1'; {Main form}
16.     FMain.JSONPropMain.Restore;
17.     FSampling.JSONPropSampling.JSONFileName := OpenDialog1.FileName+'.2'; {Sampling Controls}
18.     FSampling.JSONPropSampling.Restore;
19.    end;
20. end;  

Each pair of ".1" and ".2" files contains a different setup for an instrument I'm working on.

I'm using Linux, so I also get the file that is automatically created (in my home directory) each time I close my project that combines the JSON image of both of my forms. This feature is causing me some problems that I'm still working on.  Hope that makes sense and is helpful.

[jcmontherock]

Nice, thanks a lot.

Could you give us more details about the definition of:
FMain
FSampling
and which unit should we add in uses definitions ?

[Curt Carpenter]

Yes, sorry.

My project includes two forms:  One I've named "FMain" and one named "FSampling." 

Each of those forms contains a TJSONPropertyStorage component (dropped on it from the "Misc" section of the Lazarus component palette). 

On the FMain form, I've named the TJSONPropertyStorage component "JSONPropMain."  On the FSampling form, it is named "JSONPropSampling."

JSONFileName is a property of the TJSONPropertyStorage component.  .Save and .Restore are component methods. 

Placing a TJSONPropertyStorage component on the form causes a JSONPropStorage clause to be added to the form's USES statement.

More details are here: https://lazarus-ccr.sourceforge.io/docs/lcl/jsonpropstorage/tjsonpropstorage.html 

PS:  This is my first experience with this component, so I'm by no means an expert with it.

[jcmontherock]

I will try it. Thanks a lot.

[Thaddy]

All a bit strange, because saving a form state comes as standard.
Simply study the form streaming mechanism, which is what you want.
Also note your own properties can have the stored modifier.
Storing form state dates even from Delphi 1.
There are multiple examples, also for Lazarus and on this forum, on how to do that.
It is basic..... and some of the answers are simply annoying. 

Any component state can be saved for its published properties by just using the provided streaming mechanisims.

Of course reading back simply uses the same mechanism.
Again, all of this is plain standard Lazarus-Delphi standard.

[Curt Carpenter]

It's a little more complicated that just saving a form -- but thanks for your standard obnoxious input anyway.
Have a nice day!