delphi - 使用他的 ClassType 来转换 TObject？

Question

我怎样才能让我的代码工作？ :) 我试图提出这个问题，但经过几次失败的尝试后，我认为你们通过查看代码会比阅读我的“解释”更快地发现问题。谢谢。

setCtrlState([ memo1, edit1, button1], False);

_

procedure setCtrlState(objs: array of TObject; bState: boolean = True);
var
  obj: TObject;
  ct: TClass;
begin
  for obj in objs do
  begin
    ct := obj.ClassType;


    if (ct = TMemo) or (ct = TEdit) then
      ct( obj ).ReadOnly := not bState;        // error here :(

    if ct = TButton then
      ct( obj ).Enabled:= bState;        // and here :(

  end;
end;

Answer 1

您必须将对象显式转换为某个类。这应该有效:

 procedure setCtrlState(objs: array of TObject; bState: boolean = True);
 var
   obj: TObject;
   ct: TClass;
 begin
  for obj in objs do
  begin
    ct := obj.ClassType;

    if ct = TMemo then
      TMemo(obj).ReadOnly := not bState
    else if ct = TEdit then
      TEdit(obj).ReadOnly := not bState
    else if ct = TButton then
      TButton(obj).Enabled := bState;
  end;
end;

这可以使用“is”运算符来缩短 - 不需要 ct 变量:

 procedure setCtrlState(objs: array of TObject; bState: boolean = True);
 var
   obj: TObject;
 begin
   for obj in objs do
   begin
     if obj is TMemo then
       TMemo(obj).ReadOnly := not bState
     else if obj is TEdit then
       TEdit(obj).ReadOnly := not bState
     else if obj is TButton then
       TButton(obj).Enabled := bState;
   end;
 end;