Rob Kennedy wrote: > heromed wrote: > > procedure TForm1.Button1Click(Sender: TObject); > > var Str : string; > > begin > > Str := ComponentToString(Panel1); > > Panel2 := StringToComponent(Str); // the line with the error > > end; > > > > When compiling, I get the following error: > > > > "Incompatible types: 'TPanel' and 'TComponent'" > > It gives you that error for the same reason this would: > > var > panel: TPanel; > begin > panel := TComponent.Create(nil); > end; > > Here's a better example: > > function NewComponent: TComponent; > begin > Result := TPanel.Create(nil); > end; > > var > panel: TPanel; > begin > panel := NewComponent; > end; > > Do you recognize the problem now? > > The function's declared return type is TComponent. When Delphi sees you > call that function, it cannot assume anything more about the return > value except that it will be a TComponent. It might be a TPanel, since > TPanel descends from TComponent, but it might also be a TEdit, or a > TPopupMenu, or even a TFoo that nobody's even written yet. > > Now, we know that NewComponent will always return a TPanel, so if the > compiler were sufficiently smart, it might realize that and accept the > assignment to the Panel variable anyway. But the StringToComponent > function makes *no* mention of what kind of object it might produce. > That information isn't determined until run time when the function reads > the contents of the string, so the compiler has no way of knowing > whether it is safe to assign the return value to a TPanel variable. > > To tell the compiler to treat a value of one type as a value of a > subtype, you can type-cast: > > panel := NewComponent as TPanel; > > If the returned component isn't really a TPanel, then you'll get an > exception at run time. > > -- > Rob > > > ----------------------------------------------------- > Home page: http://groups.yahoo.com/group/delphi-en/ > To unsubscribe: [EMAIL PROTECTED] > > > > SPONSORED LINKS > C programming language > <http://groups.yahoo.com/gads?t=ms&k=C+programming+language&w1=C+programming+language&w2=Java+programming+language&w3=C+++programming+language&w4=Concept+of+programming+language&c=4&s=126&.sig=wfHwnNNuJ9PRdPKzWXnmJA> > > Java programming language > <http://groups.yahoo.com/gads?t=ms&k=Java+programming+language&w1=C+programming+language&w2=Java+programming+language&w3=C+++programming+language&w4=Concept+of+programming+language&c=4&s=126&.sig=eIq6WSkMZB-e3QTGyXydYA> > > C programming language > <http://groups.yahoo.com/gads?t=ms&k=C+++programming+language&w1=C+programming+language&w2=Java+programming+language&w3=C+++programming+language&w4=Concept+of+programming+language&c=4&s=126&.sig=aXkBBJrbB2_-_2wwbyfLoQ> > > > Concept of programming language > <http://groups.yahoo.com/gads?t=ms&k=Concept+of+programming+language&w1=C+programming+language&w2=Java+programming+language&w3=C+++programming+language&w4=Concept+of+programming+language&c=4&s=126&.sig=9Ug4n_hw8V4Ui50VPPq_xQ> > > > > > ------------------------------------------------------------------------ > YAHOO! GROUPS LINKS > > * Visit your group "delphi-en > <http://groups.yahoo.com/group/delphi-en>" on the web. > > * To unsubscribe from this group, send an email to: > [EMAIL PROTECTED] > <mailto:[EMAIL PROTECTED]> > > * Your use of Yahoo! Groups is subject to the Yahoo! Terms of > Service <http://docs.yahoo.com/info/terms/>. > > > ------------------------------------------------------------------------ > >------------------------------------------------------------------------ > >No virus found in this incoming message. >Checked by AVG Free Edition. >Version: 7.1.362 / Virus Database: 267.12.8/161 - Release Date: 3/11/2005 > > When I tried: Panel2 := (StringToComponent(Str)) as TPanel; I get a Runtime error: "Class TPanel not found"
What am I doing wrong ? Regards Bob Stanton ------------------------ Yahoo! Groups Sponsor --------------------~--> Fair play? Video games influencing politics. Click and talk back! http://us.click.yahoo.com/T8sf5C/tzNLAA/TtwFAA/i7folB/TM --------------------------------------------------------------------~-> ----------------------------------------------------- Home page: http://groups.yahoo.com/group/delphi-en/ To unsubscribe: [EMAIL PROTECTED] Yahoo! Groups Links <*> To visit your group on the web, go to: http://groups.yahoo.com/group/delphi-en/ <*> To unsubscribe from this group, send an email to: [EMAIL PROTECTED] <*> Your use of Yahoo! Groups is subject to: http://docs.yahoo.com/info/terms/
