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Отображать движение TProgressBar при помощи фонового потока



Оформил: DeeCo

{ 
  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;





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