Access Violation when assigning component property on Data Module
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13-09-2019 - |
Question
I'm on Delphi 2009, and my application contains a data module, which has a custom component named 'Globals' on it.
In another form in the application, I'm trying to change a published property (a string) on the Globals component:
dm.Globals.qhProject := _ProjectName.Text; //always gives access violation
The _ProjectName control is a TLabeledEdit descendant. I always get an access violation here if there's any text in the box.
However, if I manually assing a string to the property, I don't get the AV:
dm.Globals.qhProject := 'some text'; //works
Here's the declaration of the qhProject property:
FqhProject: string;
property qhProject: string read FqhProject write FqhProject;
I can't figure out why there's an AV here at all. I've tried moving the auto create order of the forms/data module around, but I always get the AV.
What am I doing wrong here?
Update:
I'm using Billenium Effects TFormContainer to switch between different forms in the application. Both forms that are involved here are in the form container. One form, TdlgSummary, contains the following:
procedure TdlgSummary.SyncVars;
begin
dm.Globals.qhProject := _ProjectName.Text
end;
The other form, TdlgFinalize, contains the following:
dlgSummary.SyncVars;
If I run SyncVars inside of dlgSummary, it works fine. If I call it from dlgFinalize, I get the AV. This seems to be the crux of the problem, but I can't figure out what's going wrong. Even if I switch control to dlgFinalize, dlgSummary hasn't been destroyed, because I can go back to it. Any ideas?
Solution
Looks to me like _ProjectName is nil. Try putting a breakpoint at this line and examine _ProjectName, see if it gives a valid reference or not.