how to display progress bar?

问题:

I created a steganography(hide text in bitmap) application and I want to add a progress bar to show how long the process works.

procedure TForm1.Button2Click(Sender: TObject);
var
   x,y,i,currentBit,bitInChar,currentChar,currentPixel,newPixelValue,pixelsToSkip,skippedPixels: integer;
   pixels: PByteArray;
   bmp: TBitmap;
   stringToHide: string;
begin
if Image1.Picture.Bitmap=nil then
showmessage('gambar belum dipilih')
else
   memo1.lines.clear;
   stringToHide := AntiKeyLoggerMemo1.text;

   stringToHide:= stringToHide + chr(terminator); // add terminator to indicate end of text
   Image2.Picture.Assign(Image1.Picture.Bitmap);
   bmp := Image2.Picture.Bitmap;
   x := 0;
   y := 0;
   pixels := bmp.ScanLine[y];

   // iterate over the chars in the string we want to hide
   for i := 1 to length(stringToHide) do
   begin
      currentChar := ord(stringToHide[i]);
      memo1.lines.append('');
      memo1.lines.append('Sembunyikan ' + stringToHide[i] + ' - Ascii ' + inttostr(currentChar) + ' (biner ' + toBinary(currentChar) + ')');
      // iterate over the bits in the current char
      for currentBit := 7 downto 0 do
      begin
         begin
            if (i = 1) and (currentBit = 7) then
               pixelsToSkip := 0
            else
               pixelsToSkip := 1;
         end;
         for skippedPixels := 1 to pixelsToSkip do
         begin
            inc(x);
            if x = bmp.width then
            begin
               x := 0;
               inc(y);
               if (y = bmp.height) and (i < length(stringToHide)) then raise Exception.create('gambar terlalu kecil');
               pixels := bmp.ScanLine[y];
            end;
         end;
         bitInChar := getBit(currentChar, currentBit);
         // get the value of the pixel at x,y
         currentPixel := pixels[x];
         // set the least significant bit of the pixel to the bit we read from the char
         newPixelValue := setBit(currentPixel, 0, bitInChar);
         pixels[x] := newPixelValue;
         memo1.lines.append('Bit karakter ' + inttostr(currentBit) + '=' + inttostr(bitInChar) +
            ', pixel ke ' + inttostr(x) + ',' + inttostr(y) + ' desimal ' + inttostr(currentPixel) + ' (biner ' + toBinary(currentPixel) + ') ' +
            ' desimal baru ' + inttostr(newPixelValue) + ' (biner ' + toBinary(newPixelValue) + ')');

            end;
         end;
   memo1.lines.append('All done!');
   Button4.Enabled :=True;
   Button2.Enabled:=False ;
   Button5.Enabled:=True;
   Button1.Enabled:=False;
   AntiKeyLoggerMemo1.ReadOnly:=True;
     end;   

how do I make a progress bar for the process? and where I have to put the command progress bar?

回答1:

First, you need to move the code to its own thread. Otherwise the GUI will not respond. You also have to make sure the code is thread-safe.

Anyhow, inside the thread, you need to update the progress bar every now and then. If it so happens that you have an outer loop and an inner loop, where the outer loop iterates once a second or so, you could update the progress bar at that place. If you only have one big loop, you might not want to update the progress bar at every iteration; for instance, a single iteration might perhaps be done in only a few milliseconds.

Instead, you can make sure to update the progress bar once every second, or so. To accomplish this, you can use GetTickCount:

tc := GetTickCount;
if Terminated then Exit;
if tc - oldtc > 1000 then
begin
  PostMessage(FProgressBarHandle, PBM_SETPOS, TheNewPosition, 0);
  oldtc := tc;
end;

This also shows a way to update the progress bar -- simply post it a message! You could also define your own message and send it to the main from.