My Delphi 2010 is sick

[Stevie]

The GradientChange event is assigned to edtSteps which is created before the CheckBox (by reading the form from the dfm file). Reading the value and setting it to the spin edit then triggers the event.

There are several ways to fix this:

If you have access to the code of the spinedit:
- define the events after all other properties so they are assigned after the value is set (because of the order they are written to the dfm then)

If you don't have access to the code:
- add a condition to your GradientChange event that prevents it from being triggered during form creation

[Furtbichler]

Another possibility would be to reverse the creation order of the components.
However, this is not a robust way to generally solve the problem once and for all.

Stevie's ideas are -of course- correct, but I don't like having to add code in each and every event handler for the rest of my (programmers) life just to make sure, I don't get caught in these side effects caused by the loading order of components.

Personally, I would remove the design time links from the component events to the event handlers and add them in the FormActivate, after everything has been loaded. As FormActivate is called each time the form is displayed (i.e. 'activated'), I would also make sure, my initialization code is only called once.

This is a decent and robust design pattern which avoids all those caveats during form initialization:

Delphi-Quellcode:

Procedure TMyForm.MyFormInitialize;
Begin
  MyControl.OnDoSomething := MyFormDoSomethingEventHandler;
// ... more init stuff here
End;

Procedure TMyForm.FormActivate(Sender : TObject);
Begin
  if not FInitialized Then MyFormInitialize;
  FInitialized := True;
End;

[himitsu]

Es muß nichtmal am OnGradientChange liegen, denn dieses wird auch nochmal im OnColorChange aufgerufen.

Zitat von Furtbichler:

Delphi-Quellcode:

Procedure TMyForm.MyFormInitialize;
Begin
  MyControl.OnDoSomething := MyFormDoSomethingEventHandler;
// ... more init stuff here
End;

Procedure TMyForm.FormActivate(Sender : TObject);
Begin
  if not FInitialized Then MyFormInitialize;
  FInitialized := True;
End;

Also entweder das Event später dranhängen

oder es ignorieren (innerhalb der Komponente oder im Event)

Delphi-Quellcode:

procedure TGradientDialog.GradientChange(Sender: TObject);
var
  I: Integer;
  A: TColorArray;
begin
  if FUpdate or not Assigned(cbReverse) then Exit;

Delphi-Quellcode:

procedure TGradientDialog.GradientChange(Sender: TObject);
var
  I: Integer;
  A: TColorArray;
begin
  if FUpdate or not Assigned(cbReverse) then Exit;

Es wird ja am Ende sowieso aufgerufen, also kann man es auch einfach überspringen, ohne etwas zu beachten.
TGradientDialog.Create => ColorChange => GradientChange

[WojTec]

Thanks guys for ideas. Temporary I changed creation order, but it isn't real solution.

[Stevie]

Zitat von Furtbichler:

Stevie's ideas are -of course- correct, but I don't like having to add code in each and every event handler for the rest of my (programmers) life just to make sure, I don't get caught in these side effects caused by the loading order of components.

That is true for the second solution which would only be a workaround for a bug in the TBMDSpinEdit class. Fixing this was my first solution because reading a component from the dfm should not trigger events on itself. (for example TEdit never triggers the OnChange when reading its Text property from the dfm)