Component property disappears from DFM

[aehimself 399]

Hello all,

 

I have an issue with some of our components in the application we support where an event handler simply disappears (gets unlinked, code stays in .pas) when a frame is opened.

The main container is a frame which is the 3rd or 4th descendant of a simple TFrame (with 2-3 levels of visual inheritance included). The event handler is the OnDataChange event of a custom TDataSource descendant component. This frame has ~50 of these datasources, but only 2 are affected. No other datasources / frames have the same issue (which we have hundreds, if not thousands).

 

When you open the file in Delphi, the tab indicator already shows that it is modified and can be saved. Upon saving the event handler is simply unlinked, leaving the actual code in the .pas file. Restoration is easy, just double-click the handler in object inspector so it gets linked back which you can save perfectly... until next time someone forgets to check the modifications and roll back the removals; which already happened at least 5 times in the past half a year.

inherited frmCustom: TfrmCustom
  [...]
  object dtsMyDTS: TCustomDataSource
    [...]
    OnDataChange = dtsMyDTSDataChange   <-- this line disappears
    [...]
  end
  [...]
end

I bet it will be some rare edge case but it already caused lots of headaches and it would be a blessing if it could be fixed. I am not able to share the sources as they are proprietary plus you'd need the whole custom component package as well to be able to open it 🙂 I'm simply looking for indicators, what I can try, what I can check to find the root cause.

 

Anyone saw something like this?

 

Cheers!

[corneliusdavid 220]

I think I have seen this but it's been a while, like maybe in an older version of Delphi?  In what version is this happening?

 

It may be that while Delphi is loading the DFM, it can't find the source for the component so it thinks it's an invalid or old property and removes it--somewhat like loading a form that has been descended from a custom base form but the base form is not part of the project. You do mention descendants, so maybe include all the ancestor frames in the project if they aren't already?

[aehimself 399]

1 hour ago, corneliusdavid said:

I think I have seen this but it's been a while, like maybe in an older version of Delphi?  In what version is this happening?

 

It may be that while Delphi is loading the DFM, it can't find the source for the component so it thinks it's an invalid or old property and removes it--somewhat like loading a form that has been descended from a custom base form but the base form is not part of the project. You do mention descendants, so maybe include all the ancestor frames in the project if they aren't already?

Unfortunately I do not remember the 10.4 era, but this definitely happened under Delphi 11.2 and now Delphi 12. The project (and probably this frame) originally was created with Delphi 7 but was slowly upgraded to the most recent version.

 

The source of said component is in Browsing path, Library path points to the precompiled DCU. All frame files (including the first one inherited from TFrame) is a part of the project.

 

We have ~1500 frames with at least 20-50 of these custom datasources on each and this problem only occures on one frame, two datasources (always the same 2). This makes me believe that fixing it won't be something generic - e.g. on component or project level.

[corneliusdavid 220]

Just now, aehimself said:

We have ~1500 frames with at least 20-50 of these custom datasources on each and this problem only occures on one frame, two datasources (always the same 2). This makes me believe that fixing it won't be something generic - e.g. on component or project level.

Oh, yeah, you mentioned this in the first post and I just skipped right over that--you're right, it'll be something specific about these two datasource components.

 

So, then what is different about these datasources from all the rest?  Are they hooked to a different type of dataset or have any other properties set uniquely?  Does changing the creation order in the DFM have any effect?

[aehimself 399]

41 minutes ago, corneliusdavid said:

Oh, yeah, you mentioned this in the first post and I just skipped right over that--you're right, it'll be something specific about these two datasource components.

 

So, then what is different about these datasources from all the rest?  Are they hooked to a different type of dataset or have any other properties set uniquely?  Does changing the creation order in the DFM have any effect?

By the first look... nothing seems different, that's my issue. The create order is an excellent idea, I'll doublecheck that tomorrow!

[Pat Foley 51]

Does baseform have the onMyEvent assigned to empty event simply a frameclick(Sender:TObject)begin..end?  

 

doing that allows the inherited form a stub to hook up its event.  

[aehimself 399]

Just now, Pat Foley said:

Does baseform have the onMyEvent assigned to empty event simply a frameclick(Sender:TObject)begin..end?  

 

doing that allows the inherited form a stub to hook up its event.  

The datasource is on the last frame not on an ascendant (object dtsMyDTS instead of inherited dtsMyDTS). Inheritance only plays a role here if Delphi bugs out due to the long frame chain I think.

[PeterBelow 239]

19 hours ago, aehimself said:

We have ~1500 frames with at least 20-50 of these custom datasources on each and this problem only occures on one frame, two datasources (always the same 2). This makes me believe that fixing it won't be something generic - e.g. on component or project level.

In this case just override the Loaded method of the frame and link the event handler in code there, after calling the inherited method first. That will fix the issue even if you cannot figure out why it happens in the first place. Not really satisfactory, of course, but the only reason I can think of would be if somebody cleared the Name property of the dataset in question or moved the handler method from published to public scope by accident.