现在我有一个使用ADO运行查询的函数，并返回recordset：
Recordset Execute(Connection connection, String commandText)
{
//[pseudo-code]
Recordset rs = new Recordset();
rs.CursorLocation = adUseClient;
rs.CursorType = adOpenForwardOnly;
rs.Open(commandText, connection,
adOpenForwardOnly, //CursorType; the default
adLockReadOnly, //LockType
adCmdText);
return rs;
}
这很好。它同步运行，并返回查询的记录集。
现在我想要一个类似的版本，它显示ProgressDialog，让用户可以取消长时间运行的查询：
Recordset Execute(HWND parenthWnd, String caption, Connection connection, String commandText)
{
//[pseudo-code]
//Construct a progressDialog and show it
IProgressDialog pd = new ProgressDialog();
pd.SetTitle(caption); //e.g. "Annual Funding Report"
pd.SetCancelMsg("Please wait while the operation is cancelled");
pd.StartProgressDialog(parenthWnd, null, PROGDLG_MODAL | PROGDLG_NOTIME | PROGDLG_NOMINIMIZE, null);
pd.SetLine(1, "Querying server", False, null);
try
{
//Query the server
Recordset rs = new Recordset();
rs.Open(commandText, connection,
adOpenForwardOnly, //CursorType
adLockReadOnly, //LockType
adCmdText | adAsyncExecute);
while (rs.State and (adStateConnecting+adStateExecuting+adStateFetching) <> 0)
{
if pd.HasUserCancelled()
throw new EUserCancelledOperationException();
Sleep(100);
};
finally
{
//Hide and destroy the progress dialog
pd.StopProgressDialog();
pd = null;
}
//Now we have our results for the client
return rs;
}
检查用户是否已取消操作的方法是，如果用户按下取消按钮，则定期询问进度对话框：
pd.HasUserCancelled(); //returns true if user has clicked Cancel
现在我面临着如何定期检查用户是否已取消（以及知道查询是否已完成，或者是否已发生错误）以及如何成为一名优秀的程序员而无需轮询的情况。
知道错误发生的唯一方法是在Recordset的FetchCompleteEvent上设置一个处理程序：
pError
一个Error对象。它描述了adStatus的值为adStatusErrorsOccurred时发生的错误;否则它没有设置。
adStatus
EventStatusEnum状态值。调用此事件时，如果导致事件的操作成功，则将此参数设置为adStatusOK;如果操作失败，则将此参数设置为adStatusErrorsOccurred。在此事件返回之前，请将此参数设置为adStatusUnwantedEvent以防止后续通知。
pRecordset
一个Recordset对象。检索记录的对象。
所以这意味着我将不得不让我的函数构造一个辅助对象，所以我可以有一个FetchComplete处理程序。但是我必须立即阻止我的同步功能。然后我们进入MsgWaitForSingleObject，这是非常难以正确使用的。
所以我要求帮助或罐装代码。
我应该更明确：我正在寻找使用此方法签名的函数实现：
Recordset ExecuteWithCancelOption(Connection connection, String commandText)
显示一个带有取消按钮的对话框。
挑战在于，该功能现在必须创建实现该功能所需的一切。如果这涉及一个隐藏的形式，它有一个计时器，等等 - 好吧。
但我正在寻找一个显示取消按钮的同步功能。
该功能将成为
的近乎（或确切）替代品Recordset Execute(Connection connection, String commandText)
考虑到Windows的实际考虑因素，我需要为该函数提供一个父窗口句柄，它将对话框的父对象：
Recordset ExecuteWithCancelOption(HWND parentHwnd, Connection connection, String commandText)
鉴于这将是一个可重用的函数，我将让调用者提供将要显示的文本：
Recordset ExecuteWithCancelOption(HWND parenthWnd, String caption, Connection connection, String commandText)
鉴于这些都是我的TADOHelper类中的类函数，我可以给它们相同的名称，让它们相互重载：
Recordset Execute(HWND parenthWnd, String caption, Connection connection, String commandText)
我认为在Delphi以外的语言中，匿名代表是有帮助的。但我仍然害怕必须处理MsgWaitForMultipleObjects。
答案 0 :(得分：1)
答案 1 :(得分：1)
为了使GUI响应按钮点击，您应该将控制权返回到窗口的消息循环。 while循环 while（rs.State和（adStateConnecting + adStateExecuting + adStateFetching）＆lt;＆gt; 0）不会将控制权返回给消息循环，从而阻止GUI。
以下是使用异步ADO查询的Delphi代码的摘录。此代码不允许非模态提取数据，但可确保在获取数据期间重新绘制主窗体，并允许取消查询。
通过设置：
实现异步执行和提取
FOpeningDataSet.ExecuteOptions := [eoAsyncExecute, eoAsyncFetchNonBlocking];
通过调用
取消执行查询
DataSet.Recordset.Cancel;
在FetchProgress事件中。
任何TADODataSet都应通过以下方法打开：
OpenDataSetInBackground(DataSourceData.DataSet as TADODataSet);
支持主要表格中的代码：
procedure TOperatorForm.OpenDataSetInBackground(DataSet: TADODataSet);
begin
if DataSet.Active then Exit;
FOpeningDataSet := DataSet;
if not FAsyncDataFetch then
begin
FOpeningDataSet.Open;
Exit;
end;
FFetchCancel := False;
FExecuteOptions := FOpeningDataSet.ExecuteOptions;
FFetchProgress := FOpeningDataSet.OnFetchProgress;
FFetchComplete := FOpeningDataSet.OnFetchComplete;
FRecordsetCreate := FOpeningDataSet.OnRecordsetCreate;
FAfterScroll := FOpeningDataSet.AfterScroll;
FOpeningDataSet.ExecuteOptions := [eoAsyncExecute, eoAsyncFetchNonBlocking];
FOpeningDataSet.OnFetchProgress := DataSetFetchProgress;
FOpeningDataSet.OnFetchComplete := DataSetFetchComplete;
FOpeningDataSet.OnRecordsetCreate := DataSetRecordsetCreate;
FOpeningDataSet.AfterScroll := DataSetAfterScroll;
FOpeningDataSet.CursorLocation := clUseClient;
FOpeningDataSet.DisableControls;
try
DataSetProgressForm.Left := Left + (Width - DataSetProgressForm.Width) div 2;
DataSetProgressForm.Top := Top + (Height - DataSetProgressForm.Height) div 2;
DataSetProgressForm.cxButton1.OnClick := DataSetProgressClick;
DataSetProgressForm.cxButton1.Visible := FShowProgressCancelButton;
FOpeningDataSet.Open;
DataSetProgressForm.ShowModal;
finally
FOpeningDataSet.EnableControls;
FOpeningDataSet.ExecuteOptions := FExecuteOptions;
FOpeningDataSet.OnFetchProgress := FFetchProgress;
FOpeningDataSet.OnFetchComplete := FFetchComplete;
FOpeningDataSet.OnRecordsetCreate := FRecordsetCreate;
FOpeningDataSet.AfterScroll := FAfterScroll;
end;
end;
procedure TOperatorForm.DataSetProgressClick(Sender: TObject);
begin
FFetchCancel := True;
end;
procedure TOperatorForm.DataSetFetchProgress(DataSet: TCustomADODataSet; Progress, MaxProgress: Integer; var EventStatus: TEventStatus);
begin
if FFetchCancel then
DataSet.Recordset.Cancel;
end;
procedure TOperatorForm.DataSetFetchComplete(DataSet: TCustomADODataSet; const Error: Error; var EventStatus: TEventStatus);
begin
PostMessage(DataSetProgressForm.Handle, WM_CLOSE, 0, 0);
MessageBeep(MB_ICONEXCLAMATION);
end;
procedure TOperatorForm.DataSetFetchComplete(DataSet: TCustomADODataSet; const Error: Error; var EventStatus: TEventStatus);
begin
PostMessage(DataSetProgressForm.Handle, WM_CLOSE, 0, 0);
MessageBeep(MB_ICONEXCLAMATION);
end;
procedure TOperatorForm.DataSetRecordsetCreate(DataSet: TCustomADODataSet; const Recordset: _Recordset);
begin
if Assigned(FRecordsetCreate) then FRecordsetCreate(DataSet, Recordset);
end;
procedure TOperatorForm.DataSetAfterScroll(DataSet: TDataSet);
begin
// From TBetterADODataSet 4.04
// Ole Willy Tuv's fix 03-10-00 for missing first record
with TADODataSet(DataSet) do
begin
if (eoAsyncFetchNonBlocking in ExecuteOptions) and
(Bof or Eof) and
(CursorLocation = clUseClient) and
(stFetching in RecordSetState) then
begin
if Recordset.RecordCount > 0 then
if Bof then
Recordset.MoveFirst
else if Eof then
Recordset.MoveLast;
CursorPosChanged;
Resync([]);
end;
end;
if Assigned(FAfterScroll) then
FAfterScroll(DataSet);
end;
进度表：
unit uDataSetProgressForm;
interface
uses
Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
Dialogs, ComCtrls, ExtCtrls, StdCtrls;
type
TDataSetProgressForm = class(TForm)
AnimateProgress: TAnimate;
Label1: TLabel;
Bevel1: TBevel;
Bevel2: TBevel;
Button1: TButton;
Shape1: TShape;
procedure FormCreate(Sender: TObject);
procedure FormShow(Sender: TObject);
procedure FormHide(Sender: TObject);
private
{ Private declarations }
public
{ Public declarations }
end;
var
DataSetProgressForm: TDataSetProgressForm;
implementation
{$R *.dfm}
{$R servertimeout.res} // contains IDR_SERVAVI animation resource
procedure TDataSetProgressForm.FormCreate(Sender: TObject);
begin
AnimateProgress.ResName := 'IDR_SERVAVI';
end;
procedure TDataSetProgressForm.FormShow(Sender: TObject);
begin
AnimateProgress.Active := True;
end;
procedure TDataSetProgressForm.FormHide(Sender: TObject);
begin
AnimateProgress.Active := False;
end;
end.
和dfm
object DataSetProgressForm: TDataSetProgressForm
Left = 590
Top = 497
BorderStyle = bsNone
ClientHeight = 104
ClientWidth = 205
Font.Charset = DEFAULT_CHARSET
Font.Color = clWindowText
Font.Height = -11
Font.Name = 'MS Sans Serif'
Font.Style = []
FormStyle = fsStayOnTop
OldCreateOrder = False
Position = poDefaultSizeOnly
OnCreate = FormCreate
OnHide = FormHide
OnShow = FormShow
DesignSize = (
205
104)
PixelsPerInch = 96
TextHeight = 13
object Bevel1: TBevel
Left = 0
Top = 0
Width = 205
Height = 104
Align = alClient
Style = bsRaised
end
object Bevel2: TBevel
Left = 12
Top = 12
Width = 181
Height = 80
Anchors = [akLeft, akTop, akRight, akBottom]
end
object Shape1: TShape
Left = 1
Top = 1
Width = 203
Height = 102
Anchors = [akLeft, akTop, akRight, akBottom]
Brush.Style = bsClear
Pen.Color = clWindowFrame
end
object AnimateProgress: TAnimate
Left = 25
Top = 23
Width = 32
Height = 32
end
object Label1: TLabel
Left = 70
Top = 31
Width = 106
Height = 17
Hint = 'Selecting data...'
Caption = 'Selecting data...'
TabOrder = 1
end
object Button1: TButton
Left = 63
Top = 64
Width = 80
Height = 23
Caption = 'Cancel'
Default = True
TabOrder = 2
end
end
答案 2 :(得分：0)
如果是Delphi，您可以删除TTimer组件并使用它来检查HasUserCancelled值是否为True。我没有在我面前使用Delphi所以我以后必须发布一个例子。
编辑：
这是一个TTimer OnTimer事件的示例，它检查当前时间和最后一个活动时间，以确定如果程序保持“Up”状态如何处理表单：
procedure TForm_Main.Timer1Timer(Sender: TObject);
begin
// return to opening screen if no activity for a while:
if Now - LastActivity > TimeOut
then
begin
Form_Select.SBtn_Defendant.Down:= False;
Form_Select.SBtn_Officer.Down:= False;
Form_Select.SBtn_Attorney.Down:= False;
Form_Main.ModalResult:= mrCancel;
Exit;
end;
Form_Main.Caption:= FormatDateTime('dddd mmmm d, yyyy h:nn:ss AM/PM', Now);
end;