计时器进程会影响德尔福中的用户界面

Question

我开发了从读卡器读取信息的应用程序。在这里，我使用计时器每五秒获取一次信息，因此每五秒用户界面变慢因为它从读者那里获取信息。如何在不影响用户界面的情况下在后台运行计时器

unit frmVistorreg;
interface
uses
 Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms;
type
 thread1=class(TThread)
 private
 FEvent: THandle;
 protected
 procedure Execute; override;
 public
 procedure MyTerminate;
end;

TForm3 = class(TForm)     
txt_name: TEdit;   
txt_cardno.Text  TEdit;        
private
public
end;
var
Form3: TForm3;
implementation
{$R *.dfm}

procedure thread1.Execute;
var
idcard_info :array[0..1024*5] of byte;
flag :Integer;
portflag :Integer;
st :TStrings;
str :string;  
begin
FEvent:= CreateEvent(nil, False, false, nil);
try
while not Terminated do begin
if  MainForm.PortFlag=0 then
begin
 Form3.Label11.Caption:='port has been successfully opened';
 Form3.Label11.Font.Color :=32768;
 flag := GetIdCardInfo(@idcard_info[0],1024*5,5);
 str := byteArray2Str(@idcard_info[0],1024*5);
        if(flag=0) then
        begin
           st := TStringList.Create;
           try
              SplitStr('^_^',str,st);
              Form3.txt_name.Text := st.Strings[0]; 
              Form3.txt_cardno.Text := st.Strings[5]; 
          finally
        st.Free;
          end;
        end;
end
else
begin 
Form3.Label11.Caption:='Please open the port';
Form3.Label11.Font.Color:=clRed;
end;
if WaitForSingleObject(FEvent, 500) <> WAIT_TIMEOUT // 5 seconds timeout
then Terminate;
end;
finally
CloseHandle(FEvent);
end;
end;

procedure thread1.MyTerminate;
begin
 SetEvent(FEvent);
end;

procedure TForm3.FormClose(Sender: TObject; var Action: TCloseAction);
var
Objthread1:thread1;
begin   
Objthread1.MyTerminate;
Action := caFree;
end;

procedure TForm3.FormCreate(Sender: TObject);
var
Objthread1:thread1;
begin
Objthread1:=thread1.Create(false);  
end;
end.

当我关闭表单时出现错误，例如

Project MDIAPP.exe raised exception class EAccessViolation with message 'Access violation at address 0051B9F1 in module 'MDIAPP.exe'. Read of address 00000198'.

我该如何解决这个问题。

Answer 1

你不需要一个计时器组件，你需要一个后台线程。最简单的解决方案是在线程中使用Sleep函数：

unit Unit2;
interface
uses
  Classes;
type
  TMyThread = class(TThread)
  protected
    procedure Execute; override;
  end;
implementation
procedure TMyThread.Execute;
begin
  while not Terminated do begin
// do your processing here
    Sleep(5000);   // wait 5 seconds
  end;
end;
end.

更好的方法是使用 WaitForSingleObject 和事件而不是 Sleep，以便能够立即终止后台线程而不会延迟 5 秒：

unit Unit2;
interface
uses
  Windows, Classes;
type
  TMyThread = class(TThread)
  private
    FEvent: THandle;
  protected
    procedure Execute; override;
  public
    procedure MyTerminate;
  end;
implementation
procedure TMyThread.Execute;
begin
  FEvent:= CreateEvent(nil, False, False, nil);
  try
    while not Terminated do begin
// do your processing here
// ..
      if WaitForSingleObject(FEvent, 5000) <> WAIT_TIMEOUT // 5 seconds timeout
        then Terminate;
    end;
  finally
    CloseHandle(FEvent);
  end;
end;
procedure TMyThread.MyTerminate;
begin
  SetEvent(FEvent);
end;
end.

在关闭窗体时终止实例TMyThread从窗体的事件处理程序调用MyTerminate方法OnClose。

是的，知道您收到的错误消息很有趣，而不仅仅是"显示错误"。