TProgressBar при помощи фонового потока

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TProgressBar при помощи фонового потока[править | править код]

{ 
  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;


Language: en
Source: Взято с сайта: http://www.swissdelphicenter.ch
ID: 00960