Delphi: Call a function whose name is stored in a string - string

Question

Is it possible to call a function whose name is stored in a string in Delphi?

Answer 1

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.

Answer 2

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.

Answer 3

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

Answer 4

With Delphi 2010 you can uses JSON and SuperObject to invoke method with parametters.
http://code.google.com/p/superobject/source/browse/#svn/trunk
If you need, there is also an xml parser to transform xml to json.
TForm1 = class(TForm)
Button1: TButton;
procedure Button1Click(Sender: TObject);
private
{ Private declarations }
public
{ Public declarations }
procedure TestMethod(const value: string);
end;
var
Form1: TForm1;
implementation
uses superobject;
{$R *.dfm}
procedure TForm1.Button1Click(Sender: TObject);
begin
SOInvoke(Self, 'TestMethod', SO('{value: "hello"}'));
end;
procedure TForm1.TestMethod(const value: string);
begin
Caption := value;
end;

Answer 5

If you are asking if there is something like the JavaScript eval() is possible in Delphi, no this is not (easily) achievable since Delphi compiles to native code.
If you need only to support some strings you can always do many if or a case... Something like:
if myString = 'myFunction' then
myFunction();

Answer 6

OK, I'm very late to the party, but you can definitely call routines by name with this code (There are some limitations thought)
type
TExec = procedure of Object;
// rest of section...
procedure TMainForm.ExecuteMethod(MethodName : String);
var
Exec : TExec;
Routine : TMethod;
begin
Routine.Data := Pointer(Form1);
Routine.Code := Form1.MethodAddress(MethodName);
if Not Assigned(Routine.Code) then
Exit;
Exec := TExec(Routine);
Exec;
end;
Just in case someone needs this for Delphi 7 / 2010

Answer 7

Put each function in an Action. Then you can find the Action by name and Execute it
function ExecuteActionByName(const S: String);
var
I: Integer;
begin
for I := 0 to MainForm.ComponentCount-1 do
if (MainForm.Components[I] is TAction)
and SameText(TAction(MainForm.Components[I]).Name,S) then
begin
TAction(MainForm.Components[I]).Execute;
Break;
end;
end;

Answer 8

You can do something like this by crafting one or more classes with published properties that use functions to implement their read and write functionality. The properties can then be discovered using RTTI reflection and referenced, causing the underlying functions to get called.
Alternatively, you can store function pointers in a table, or even the Object property of TStringList and effectively index them by string name.
Straight calling of a function by name is not possible in Delphi.

Answer 9

The following simple solution using exports and GetProcAddress also works for old Delphi versions:
type
TMyProc = procedure(const value: Integer);
procedure Test(const value: Integer);
exports Test;
implementation
procedure Test(const value: string);
begin
ShowMessage('It works! ' + value);
end;
procedure TForm1.Button1Click(Sender: TObject);
var
p: TMyProc;
begin
p := GetProcAddress(HInstance, 'Test');
if Assigned(p) then P('Yes');
end;

Answer 10

function ExecuteMethod(AClass : TClass; AMethodName : String; const AArgs: Array of TValue) : TValue;
var
RttiContext : TRttiContext;
RttiMethod : TRttiMethod;
RttiType : TRttiType;
RttiObject : TObject;
begin
RttiObject := AClass.Create;
try
RttiContext := TRttiContext.Create;
RttiType := RttiContext.GetType(AClass);
RttiMethod := RttiType.GetMethod(AMethodName);
Result := RttiMethod.Invoke(RttiObject,AArgs);
finally
RttiObject.Free;
end;
end;