Delphi: Call a function whose name is stored in a string
Please give more details on what are you trying to achieve.
As far as I know:
- It is not possible to call a random function like that.
- For class and object functions (MyObject.Function) this can be done with RTTI, but it's a lot of work.
- If you just need to call one particular type of functions (say, function(integer, integer): string), it's a lot easier.
For the last one, declare a function type, then get a function pointer and cast it like this:
type
TMyFuncType = function(a: integer; b: integer): string of object;
TMyClass = class
published
function Func1(a: integer; b: integer): string;
function Func2(a: integer; b: integer): string;
function Func3(a: integer; b: integer): string;
public
function Call(MethodName: string; a, b: integer): string;
end;
function TMyClass.Call(MethodName: string; a, b: integer): string;
var m: TMethod;
begin
m.Code := Self.MethodAddress(MethodName); //find method code
m.Data := pointer(Self); //store pointer to object instance
Result := TMyFuncType(m)(a, b);
end;
{...}
//use it like this
var MyClass: TMyClass;
begin
MyClass := TMyClass.Create;
MyClass.Call('Func1', 3, 5);
MyClass.Call('Func2', 6, 4);
MyClass.Destroy;
end.
You didn't specify your Delphi version, However if you have Delphi 2010(+) you can do it using the enhanced RTTI, I'm not expert on them, but I tried this sample for you:
TProcClass = class
public
procedure SayHi;
function GetSum(X,Y:Integer): Integer;
end;
uses
Rtti;
{ TProcClass }
procedure TProcClass.SayHi;
begin
ShowMessage('Hi');
end;
function TProcClass.GetSum(X, Y: Integer): Integer;
begin
ShowMessage(IntToStr(X + Y));
end;
procedure ExecMethod(MethodName:string; const Args: array of TValue);
var
R : TRttiContext;
T : TRttiType;
M : TRttiMethod;
begin
T := R.GetType(TProcClass);
for M in t.GetMethods do
if (m.Parent = t) and (m.Name = MethodName)then
M.Invoke(TProcClass.Create,Args)
end;
procedure TForm1.FormCreate(Sender: TObject);
begin
ExecMethod('SayHi',[]);
ExecMethod('GetSum',[10,20]);
end;
The good things, if you have procedure or function with parameters it will work without more work.
I'm surprised no one has suggested a dispatch table. This is exactly what it's for.
program RPS;
uses
SysUtils,
Generics.Collections;
type
TDispatchTable = class(TDictionary<string, TProc>);
procedure Rock;
begin
end;
procedure Paper;
begin
end;
procedure Scissors;
begin
end;
var
DispatchTable: TDispatchTable;
begin
DispatchTable := TDispatchTable.Create;
try
DispatchTable.Add('Rock', Rock);
DispatchTable.Add('Paper', Paper);
DispatchTable.Add('Scissors', Scissors);
DispatchTable['Rock'].Invoke; // or DispatchTable['Rock']();
finally
DispatchTable.Free;
end;
end.
The implementation I wrote uses generics so it would only work with Delphi 2009+. For older versions it would probably be easiest to implement using TStringList and the command pattern