让TObject使用他的ClassType？

Question

我怎么才能让我的代码工作呢？:)我已经尝试过这个问题，但在几次失败的尝试之后，我想你们看代码会比看我的“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

使用RTTI而不是显式转换会更容易，例如：

uses
  TypInfo;

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

procedure setCtrlState(objs: array of TObject; bState: boolean = True);
var
  obj: TObject;
  PropInfo: PPropInfo;
begin
  for obj in objs do
  begin
    PropInfo := GetPropInfo(obj, 'ReadOnly');
    if PropInfo <> nil then SetOrdProp(obj, PropInfo, not bState);

    PropInfo := GetPropInfo(obj, 'Enabled');
    if PropInfo <> nil then SetOrdProp(obj, PropInfo, bState);
  end;
end;

Answer 2

您必须将对象显式强制转换为某个类。这应该是可行的：

 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;

Answer 3

您需要将ct对象强制转换为TMemo/TEdit/TButton，然后才能设置该对象的属性。

出现错误的代码行是错误的，因为ct仍然是一个TClass，而不是TButton/等。如果您强制转换为TButton，那么您将能够将enabled设置为true。

我推荐阅读casting in Delphi上的内容。就我个人而言，我建议使用as/is运算符，而不是使用ClassType。在这种情况下，代码会更简单，也更容易理解。

就我个人而言，我更倾向于这样写：

procedure setCtrlState(objs: array of TObject; bState: boolean = True);
var
  obj: TObject;
begin
  for obj in objs do
  begin
    // I believe these could be merged by using an ancestor of TMemo+TEdit (TControl?)
    // but I don't have a good delphi reference handy
    if (obj is TMemo) then
        TMemo(obj).ReadOnly := not bState;

    if (obj is TEdit) then
        TEdit(obj).ReadOnly := not bState;

    if (obj is TButton) then
        TButton(obj).Enabled := bState;
  end;
end;