怎样触发delphi 中的progressbar

使用max,step,stepby等属性,大致如下(step : integer):
step := 9000;
progressbar1.Max := step;
progressbar1.Step :=1;
progressbar1.StepBy(250);
delphi帮助有例子(传输文件):
procedure TForm1.Button2Click(Sender: TObject);

const
// On Windows replace, myfile with a pathname such as c:\autoexec.bat
FName = 'MyFile';
var
F: File;
MyData: array[1..2048] of byte;
BytesRead: LongInt;
begin
AssignFile(F, FName);
try
Reset(F);
ProgressBar1.Max := FileSize(F);
if (ProgressBar1.Max > 10) then
ProgressBar1.Step := ProgressBar1.Max div 10
else
ProgressBar1.Step := ProgressBar1.Max;
while (ProgressBar1.Position < ProgressBar1.Max) do
begin
// read one Step size chunk of data to buffer
BlockRead(F, MyData, ProgressBar1.Step, BytesRead);
// move the ProgressBar Position using StepIt