TProgressBar

Code:

{

Question:

I am trying query to display records in a dbgrid.however, due to size

of tables and joins takes a while for the query to Execute.is

there any way to Show a prorgess bar with a timer that increments

position but continues to work while the query is being executed.BTW,

using access so BDE is not used.

Answer:

A progress bar would not be an ideal choice since you cannot determine up

front how long the query will take, so you do not know the range the progress

bar has to cover.A simple kind of animation that tells the user basically

only that the application is not hung would be more appropriate.One could do

such a thing in a secondary thread but it would have to be done using the

plain Windows API and * no * Synchronize calls (since the main thread is

blocked in the BDE call).Here is an example: unit anithread;

}

interface

uses

  Classes, Windows, Controls, Graphics;

type

  TAnimationThread = class(TThread)

  private

    { Private declarations }

    FWnd: HWND;

    FPaintRect: TRect;

    FbkColor, FfgColor: TColor;

    FInterval: integer;

  protected

    procedure Execute; override;

  public

    constructor Create(paintsurface : TWinControl; {Control to paint on }

      paintrect : TRect;          {area for animation bar }

      bkColor, barcolor : TColor; {colors to use }

      interval : integer);       {wait in msecs between

paints}

  end;

implementation

constructor TAnimationThread.Create(paintsurface : TWinControl;

  paintrect : TRect; bkColor, barcolor : TColor; interval : integer);

begin

  inherited Create(True);

  FWnd := paintsurface.Handle;

  FPaintRect := paintrect;

  FbkColor := bkColor;

  FfgColor := barColor;

  FInterval := interval;

  FreeOnterminate := True;

  Resume;

end; { TAnimationThread.Create }

procedure TAnimationThread.Execute;

var

  image : TBitmap;

  DC : HDC;

  left, right : integer;

  increment : integer;

  imagerect : TRect;

  state : (incRight, incLeft, decLeft, decRight);

begin

  Image := TBitmap.Create;

  try

    with Image do

     begin

      Width := FPaintRect.Right - FPaintRect.Left;

      Height := FPaintRect.Bottom - FPaintRect.Top;

      imagerect := Rect(0, 0, Width, Height);

    end; { with }

    left := 0;

    right := 0;

    increment := imagerect.right div 50;

    state := Low(State);

    while not Terminated do

     begin

      with Image.Canvas do

       begin

        Brush.Color := FbkColor;

        FillRect(imagerect);

        case state of

          incRight:

           begin

            Inc(right, increment);

            if right > imagerect.right then

             begin

              right := imagerect.right;

              Inc(state);

            end; { if }

          end; { Case incRight }

          incLeft:

           begin

            Inc(left, increment);

            if left >= right then

             begin

              left := right;

              Inc(state);

            end; { if }

          end; { Case incLeft }

          decLeft:

           begin

            Dec(left, increment);

            if left <= 0 then

             begin

              left := 0;

              Inc(state);

            end; { if }

          end; { Case decLeft }

          decRight:

           begin

            Dec(right, increment);

            if right <= 0 then

             begin

              right := 0;

              state := incRight;

            end; { if }

          end; { Case decLeft }

        end; { Case }

        Brush.Color := FfgColor;

        FillRect(Rect(left, imagerect.top, right, imagerect.bottom));

      end; { with }

      DC := GetDC(FWnd);

      if DC <> 0 then

        try

          BitBlt(DC,

            FPaintRect.Left,

            FPaintRect.Top,

            imagerect.right,

            imagerect.bottom,

            Image.Canvas.handle,

            0, 0,

            SRCCOPY);

        finally

          ReleaseDC(FWnd, DC);

        end;

      Sleep(FInterval);

    end; { While }

  finally

    Image.Free;

  end;

  InvalidateRect(FWnd, nil, True);

end; { TAnimationThread.Execute }

end.

{Usage:

Place a TPanel on a form, size it as appropriate.Create an instance of the

TanimationThread call like this: procedure TForm1.Button1Click(Sender : TObject);

}

var

  ani : TAnimationThread;

  r : TRect;

  begin

    r := panel1.clientrect;

  InflateRect(r, - panel1.bevelwidth, - panel1.bevelwidth);

  ani := TanimationThread.Create(panel1, r, panel1.color, clBlue, 25);

  Button1.Enabled := False;

  Application.ProcessMessages;

  Sleep(30000);  // replace with query.Open or such

Button1.Enabled := True;

  ani.Terminate;

  ShowMessage('Done');

end;