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MethodAddress - How do I call the Method found

Posted on 1997-04-02
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Last Modified: 2010-04-06
I have a class containing three procedures, each of which
expect a string as a parameter.  I can find the address
of the procedure to call by using MethodAddress.  However,
when I call the procedure using the address returned, and
pass a string, the value of the string is being passed as
empty to the procedure.

How do I overcome this?  I have been through the
documentation and source without luck.

The code below is a test of MethodAddress I have created
as an example.  The user enters a string in a text box and presses a button.  The first char entered is the procedure
to be executed, and the remaining characters are passed to
the procedure.

<SNIP - uses & form def>

  TGenericMethod = procedure(StringIn : string);

  TProcedures = class(TObject)
    procedure A(StringIn : string);
    procedure B(StringIn : string); virtual;
    procedure C(StringIn : string);
  end;

var
  Form1: TForm1;
  Procedures : TProcedures;

implementation

{$R *.DFM}

procedure TProcedures.A(StringIn : string);
begin
  MessageDlg('Procedure A - ' + StringIn, mtInformation, [mbOK], 0);
end;

procedure TProcedures.B(StringIn : string);
begin
  MessageDlg('Procedure B - ' + StringIn, mtInformation, [mbOK], 0);
end;

procedure TProcedures.C(StringIn : string);
begin
  MessageDlg('Procedure C - ' + StringIn, mtInformation, [mbOK], 0);
end;

procedure TForm1.btnRunProcClick(Sender: TObject);
var
  CallMethod : TGenericMethod;
  StringPar : string;
begin
  Procedures := TProcedures.Create;
  CallMethod := Procedures.MethodAddress(Copy(edtProcName.Text,1,1));
  StringPar  := Copy(edtProcName.Text,2,Length(edtProcName.Text) - 1);
  if Assigned(CallMethod) then
    CallMethod(StringPar)
  else
    MessageDlg('Procedure doesn''t exist', mtError, [mbOK], 0);
  Procedures.Free;
end;

0
Comment
Question by:sheldon040297
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8 Comments
 
LVL 3

Expert Comment

by:mheacock
ID: 1335106
A code snippet would be helpful.

Also, why are you using MethodAddress to call the method?
0
 

Author Comment

by:sheldon040297
ID: 1335107
Edited text of question
0
 
LVL 3

Expert Comment

by:sperling
ID: 1335108
TGenericMethod = procedure(StringIn : string);

should be

TGenericMethod = procedure(StringIn : string) of object;

Regards,

Erik.
0
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Author Comment

by:sheldon040297
ID: 1335109
This does not compile - Incompatible types: 'TGenericMethod'
and 'Pointer'.  What else needs to be added?
0
 

Author Comment

by:sheldon040297
ID: 1335110

0
 
LVL 3

Accepted Solution

by:
sperling earned 300 total points
ID: 1335111
Oops. Sorry, I forgot...

use a var
  Met   : TMethod

Met.Code := TProcedures.MethodAddress('A');
Met.Data := Procedures;

CallMethod := TGenericMethod(Met);

And then make the call...


Regards,

Erik.
0
 

Author Comment

by:sheldon040297
ID: 1335112
sperling's answer was exceptional!  But I could find no reference
to the steps used for the solution in the Delphi manuals.  If
anyone, in particular sperling, has a good reference for such
things I would really appreciate it (and wouldn't need to ask
questions here all the time).
0
 
LVL 3

Expert Comment

by:sperling
ID: 1335113
I usually look at the RTL/VCL source...

Docs? None that I know about... Might be in some 3rd-party Delphi book though...

I'd say you just need to spend some time to get acknowledged with the internal workings of the RTL/VCL. Read the source ;)


Regards,

Erik.
0

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