TWinControl.Update Method

Forces the control to update.

Pascal

procedure Update; override;

C++

virtual __fastcall Update();

Description

Update repaints any part of the control surface that is out of date. Normally, updates occur automatically, but an Update call may be necessary before lengthy processing that might interfere with automatic updates. Calling Update unnecessarily can increase overhead and cause screen flicker.

Update only repaints areas of the control the have been determined to be out of date. To force immediate repainting of the entire control, call the Repaint method. To notify a control that it is out of date (without forcing an immediate repaint), call the Invalidate method.

C++ Examples:

Copy Code

/*
StepBy, CreateForm, Run, Show, Update, Initialize example
This example shows progress of loading forms as an application starts up. The code example is placed in the project source (*.dpr) file. To see project source, select the View | Project Source menu item.  
You will need to set up your project with the following steps before using the code example:
o          Add four additional forms to a default project.
o          Place a TProgressBar on Form5
o          Take the Project|Options|Forms menu option and place Form5 on the available forms list.
o          Change the code of your project (*.dpr) file to look like the example.
*/
#include <vcl\vcl.h>
#include "Unit5.h"
#pragma hdrstop
//---------------------------------------------------------------------------
USEFORM("TAppCreateForm.cpp", Form1);
USERES("Project1.res");
USEFORM("Unit2.cpp", Form2);
USEFORM("Unit3.cpp", Form3);
USEFORM("Unit4.cpp", Form4);
USEFORM("Unit5.cpp", Form5);
//---------------------------------------------------------------------------
WINAPI WinMain(HINSTANCE, HINSTANCE, LPSTR, int)
{
  try
  {
    Application->Initialize();
    SetApplicationMainFormOnTaskBar(Application, true);
    Application->CreateForm(__classid(TForm5), &Form5);
    Form5->ProgressBar1->Max = 100;
    Form5->Show();   // show a splash screen contain ProgressBar control
    Form5->Update(); // force display of Form5
    Application->CreateForm(__classid(TForm1), &Form1);
    Form5->ProgressBar1->StepBy(25);
    Form5->Label1->Caption =  "Form1 loaded successfully.";
    Form5->Update(); // force display of Form5
    Sleep(3000);
    Application->CreateForm(__classid(TForm2), &Form2);
    Form5->ProgressBar1->StepBy(25);
    Form5->Label1->Caption =  "Form2 loaded successfully.";
    Form5->Update(); // force display of Form5
    Sleep(3000);
    Application->CreateForm(__classid(TForm3), &Form3);
    Form5->ProgressBar1->StepBy(25);
    Form5->Label1->Caption =  "Form3 loaded successfully.";
    Form5->Update(); // force display of Form5
    Sleep(3000);
    Application->CreateForm(__classid(TForm4), &Form4);
    Form5->ProgressBar1->StepBy(25);
    Form5->Label1->Caption =  "Form4 loaded successfully.";
    Form5->Update(); // force display of Form5
    Sleep(3000);
//  delete Form5;
    Application->Run();
  }
  catch (Exception &exception)
  {
    Application->ShowException(&exception);
  }
  return 0;
}

Delphi Examples:

Copy Code

{
This example shows progress of loading forms as an
application starts up. The code example is placed in the
project source (*.dpr) file.  To see project source, select
the View | Project Source menu item.
You will need to set up your project with the following steps
before using the code example:
    Add four additional forms to a default project. 
    Place a TProgressBar on Form5
    Take the Project|Options|Forms menu option and place 
          Form5 on the available forms list.
    Change the code of your project (*.dpr) file to look 
          like the example.
}
begin
  Application.Initialize;
  with TForm5.Create(nil) do
  try
    Application.MainFormOnTaskbar := True;
    ProgressBar1.Max := 100;
    Show;  // show a splash screen contain ProgressBar control
    Update; // force display of Form5
    Application.CreateForm(TForm1, Form1);
    ProgressBar1.StepBy(25);
    Label1.Caption :=  'Form1 loaded successfully.';
    Update; // force display of Form5
    Sleep(3000);
    Application.CreateForm(TForm2, Form2);
    ProgressBar1.StepBy(25);
    Label1.Caption :=  'Form2 loaded successfully.';
    Update; // force display of Form5
    Sleep(3000);
    Application.CreateForm(TForm3, Form3);
    ProgressBar1.StepBy(25);
    Label1.Caption :=  'Form3 loaded successfully.';
    Update; // force display of Form5
    Sleep(3000);
    Application.CreateForm(TForm4, Form4);
    ProgressBar1.StepBy(25);
    Label1.Caption :=  'Form4 loaded successfully.';
    Update; // force display of Form5
    Sleep(3000);
  finally
    Free;
  end;
  Application.Run;