关于class produre

很好理解
type
TMessageHandler = class     //使得回车消息转换成Tab消息
class procedure AppMessage(var Msg:TMsg;var Handled:Boolean);
end;
var
Form1: TForm1;
implementation
{$R *.dfm}
class procedure TMessageHandler.AppMessage(var Msg: TMsg; var Handled: Boolean);
begin
if Msg.message=WM_KEYDOWN then
if (Msg.wParam=VK_RETURN ) and
(
(Screen.ActiveForm.ActiveControl is TEdit) or
(Screen.ActiveForm.ActiveControl is TComboBox) or
(Screen.ActiveForm.ActiveControl is TCheckBox) or
(Screen.ActiveForm.ActiveControl is TRadioButton)
//可以添加需要的控件
)
then
begin
Msg.wParam:=VK_TAB;
end
else if (Msg.wParam=VK_RETURN) and
(
(Screen.ActiveForm.ActiveControl is TDBGrid)
)
then
begin
{      with Screen.ActiveForm.ActiveControl do
begin
if Selectedindex<(FieldCount-1) then
Selectedindex:=Selectedindex+1// 移动到下一字段
else
Selectedindex:=0;
end;}
end;
end;
procedure TForm1.FormCreate(Sender: TObject);
begin
Application.OnMessage:=TMessageHandler.AppMessage;
end;