如何在使用Delphi的演员表中使用参数

Question

How to do this in Delphi:

procedure ToggleVisibility(ControlClass : TControlClass);
var
  i : integer;
begin
  for i := 0 to ComponentCount - 1 do
    if Components[i] is ControlClass then
      ControlClass(Components[i]).Visible := not Control(Components[i]).Visible;
end;

Compiler doesn't allow the cast in this case. Any ideas?

I'm using Delphi 2007.

Answer 1

Since the component is a TControl or a descendant you have to cast to TControl :

procedure ToggleVisibility(ComponentClass : TControlClass);
var
  i : integer;
begin
  for i := 0 to ComponentCount - 1 do begin
    if Components[i] is ComponentClass then
      TControl(Components[i]).Visible := not TControl(Components[i]).Visible;
  end;
end;

Answer 2

(Components[i] as ComponentClass).Visible

Answer 3

It does not make sense to cast ComponentClass(Components[i]).Visible, because .Visible needs to be of a specific class, in order to be compiled properly. Therefore, you need to specify the exact class that should be cast to. For instance, if TControl has a .Visible property, but a derived class creates a new kind of .Visible property, the compiler would not know, which of these two properties it should compile for.

So the question is, do you want to invert the TControl.Visible, then you should write (Components[i] as TControl).Visible. I guess that's what you want.

If you want to invert the .Visible of any TControl descendent, no matter if it relates to the control being Visible or not, and no matter if it is related to TControl.Visible or not, then you should go for the RTTI solution described elsewhere.

Answer 4

Try this option using the RTTI

Uses
 TypInfo;

procedure TForm1.ToggleVisibility(ComponentClass: TClass);
var
  i       : integer;
  PropInfo: PPropInfo;
  aValue  : Variant;
begin
  for i := 0 to ComponentCount - 1 do
    if Components[i] is ComponentClass then
     begin
      PropInfo := GetPropInfo(Components[i].ClassInfo, 'Visible');
      if Assigned(PropInfo) then
      begin
       aValue:=GetPropValue(Components[i], 'Visible');
       if PropInfo.PropType^.Kind=tkEnumeration then //All enumerated types. This includes Boolean, ByteBool, WordBool, LongBool and Bool
       SetOrdProp(Components[i], PropInfo, Longint(not Boolean(aValue)));
      end;
     end;
end;

To execute

ToggleVisibility(TEdit);