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    <p>In order to make GUI to respond to button clicks you should return control to the message loop of the window. While loop <strong>while (rs.State and (adStateConnecting+adStateExecuting+adStateFetching) &lt;> 0)</strong> does not return control back to the message loop thus blocking GUI.</p> <hr> <p>Below is an excerpt from a working Delphi code that uses asyncronous ADO queries. This code does not allow for non-modal fetching of data, but ensures that the main form is repainted during data fetch and also allows cancelling the query.</p> <p>Asynchronous execution and fetching is achieved by setting:<br> <code>FOpeningDataSet.ExecuteOptions := [eoAsyncExecute, eoAsyncFetchNonBlocking];</code> execution of query is cancelled by calling<br> <code>DataSet.Recordset.Cancel;</code><br> in <code>FetchProgress</code> event.</p> <p>Any TADODataSet shall be opened via the method:</p> <pre><code>OpenDataSetInBackground(DataSourceData.DataSet as TADODataSet); </code></pre> <p>Supporting code in the main form:</p> <pre><code>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 &gt; 0 then if Bof then Recordset.MoveFirst else if Eof then Recordset.MoveLast; CursorPosChanged; Resync([]); end; end; if Assigned(FAfterScroll) then FAfterScroll(DataSet); end; </code></pre> <p>Progress form:</p> <pre><code>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. </code></pre> <p>and dfm</p> <pre><code>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 </code></pre>
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    1. POADO: How to execute query synchronously with the ability to cancel?
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    1. USandrius
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      1. VTUpMod
    1. COThat's everything i want - and i've already done stuff like that. But now i want it in a form of a function that does not return (i.e. synchronous). Not to worry about the "progress dialog" not updating though - the Windows ProgressDialog component runs on a separate thread.
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      1. USIan Boyd
    2. CO@Ian: after reading your updated question – what I wanted to stress is that at least in Delphi VCL if you want GUI to be responsive and display a clickable cancel button, you should give control back to the message loop. In Delphi you can resolve this by calling ProgressForm.ShowModal that contains a message loop inside, as shown in my example above. And exactly function OpenDataSetInBackground is synchronous: it does not return until ADODataSet is fetched or cancelled.
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