TMemo "No parent window" problem

[damichab]

Hi,

I have a normal TForm derived class (normal Builder stuff... a dfm, cpp and h files) that contains a TPanel suitably named 'Panel' and within its constructor I have the following lines of code:

   mem =new TMemo(Panel);
   mem->Parent=Panel;
   mem->Lines->Strings[0]="testing";

mem being a private class variable of type TMemo*. This works without any problems. Next I have a purpose made class derived from TPanel, called from previous said class passing the form (this) as the owner to the TPanel and within its contructor the lines:

MyClass::MyClass(TComponent* owner): TPanel(owner) 
{
   TMemo* mem =new TMemo((TPanel*) this);
   mem->Parent=(TPanel*) this;
   mem->Lines->Strings[0]="testing";
   delete mem;
...

}

Here, however, on the line mem->Lines->Strings[]... I get the error: ...EInvalidOperation with message 'Control '' has no Parent window'... and I just cannot work out why. If anyone can summerise an answer or indicate a link to a previous post with a similar problem, I would be most appreciative.

Thanks in advance,

David.

 

[ctoma2005]

Hy. The problem is that the parent of the memo should be a TWinControl, but the Tpanel class is derived from TControl, so the parent is usually the Form where you want to show the memo. Change mem->parent = Form1(or the name of your form) and comment the line "delete mem" to see it work. Sorry it took so long.

 

[damichab]

Hi ctoma2005,

Thankyou for your response.

The answer, however, turned out to be that I was not setting the Parent's Parent (top level parent). I had tried assigning the parent to the form before posting this question but to no avail. In any case, TWinControl is an ancestor to both TForm and TPanel.

Regards,

David.

 

[ctoma2005]

Ok. My bad. Maybe I didn't copy the exact code that you said, but i got the same error until I changed the parent to TForm.