[英]cast TObject using his ClassType?
how can i make my code to work ? 我怎样才能使我的代码工作? :) i`ve tried to formulate this question but after several failed attempts i think you guys will spot the problem faster looking at the code than reading my 'explanations'.
:)我试图制定这个问题,但经过几次失败的尝试后,我认为你们会更快地发现问题,而不是阅读我的“解释”。 thank you.
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;
You must explicitly cast object to some class. 您必须显式地将对象强制转换为某个类。 This should work:
这应该工作:
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;
This can be shortened using " is
" operator - no need for ct variable: 这可以使用“
is
”运算符缩短 - 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;
It would be easier to use RTTI instead of explicit casting, ie: 使用RTTI而不是显式转换会更容易,即:
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;
You need to cast the ct object to a TMemo/TEdit/TButton before you can set properties on the object. 在设置对象的属性之前,需要将ct对象强制转换为TMemo / TEdit / TButton。
The line where you're getting errors are erroring because ct is still a TClass, not a TButton/etc. 你遇到错误的行是错误的,因为ct仍然是TClass,而不是TButton /等。 If you cast to a TButton, then you'll be able to set enabled to true.
如果你转换为TButton,那么你将能够将enabled设置为true。
I recommend reading up on casting in Delphi . 我建议阅读Delphi中的cast 。 Personally, I would recommend using the as/is operators instead of using ClassType, as well.
就个人而言,我建议使用as / is运算符,而不是使用ClassType。 The code will be simpler in that case, and much more understandable.
在这种情况下,代码将更简单,更容易理解。
Personally, I would write this more like: 就个人而言,我会更喜欢这样写:
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;
There is no need to cast to TMemo and TEdit separately, as they are both descendants from common parent class, which have ReadOnly property: 没有必要单独转换为TMemo和TEdit,因为它们都是来自公共父类的后代,它具有ReadOnly属性:
procedure TForm1.FormCreate(Sender: TObject);
procedure P(const Obj: TComponent);
begin
if Obj is TCustomEdit then
TCustomEdit(Obj).ReadOnly := True;
end;
begin
P(Memo1);
P(Edit1);
end;
You can avoid referencing various units and the explicit casting if you do not mind a small performance hit and limit the changes to published properties. 如果您不介意小的性能损失并限制对已发布属性的更改,则可以避免引用各种单位和显式转换。 Have a look at the TypInfo unit included with Delphi.
看看Delphi附带的TypInfo单元。
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