By default, every Windows (Delphi) application you run has a corresponding button on the TaskBar (the Start button lies on it). You can use the Alt-Tab key combination when you want to switch to or from the running applications. When you press the Ctrl-Alt-Delete you get the "Close Program" window used to "End task" or to "Shut down" the system.
Have you ever wondered how to make your application invisible to the "Close Program" dialog that lists all the applications running in Windows xx? Suppose you're writing a utility that you want to run in the background so that the user doesn't notice it. How about disabling all task-switching/starting or stopping operations; coding "The Big Brother" Delphi application to prevent the user to work with any other (and I mean AnyOther) application but yours?
Code snippets will show you how to utilise the power of the Windows API to add special features to your Delphi applications.
Disable Task Switching
Using the SystemParametersInfo API function you can trick Windows into thinking that the screen saver is running. Doing so disables the Ctrl-Alt-Delete key sequence from displaying the "Close Program" dialog and rebooting the computer and Alt-Tab from switching to another application. It also stops Ctrl-Esc from opening the Start Menu.If you wish to disable those keys while your application is running call the following SystemKeys function (place it in the Implementation section of your unit's code - and call from any procedure in your application - where needed). When you call SystemKeys, if Disable is True, the keys will be disabled, False otherwise.
procedure SystemKeys(Disable: Boolean) ;
var
OldVal : LongInt;
begin
SystemParametersInfo(SPI_SCREENSAVERRUNNING, Word(Disable), @OldVal, 0) ;
end; Disable or Hide the Task Bar and Tray
Another thing we can do to prevent the user from working with anything else but our application is to disable or even hide the TaskBar. Since the Tray (down-right where the clock is) is on the TaskBar disabling the TaskBar will disable the Tray.The ShowTaskBar procedure displays or hides the TaskBar depending on the value of the bShow parameter passed to it.
procedure ShowTaskBar(bShow: Boolean) ;
begin
if bShow = True then
ShowWindow(FindWindow('Shell_TrayWnd', nil), SW_SHOWNA)
else
ShowWindow(FindWindow('Shell_TrayWnd', nil), SW_HIDE) ;
end;
procedure EnableTaskBar(bShow: Boolean) ;
begin
if bShow = True then
EnableWindow(FindWindow('Shell_TrayWnd', nil), TRUE)
else
EnableWindow(FindWindow('Shell_TrayWnd', nil), FALSE) ;
end; Hiding the Application's TaskBar Button
Suppose you want to remove/hide the button on the TaskBar that represents your application. The trick is simple: in the OnCreate handler for your main form, insert the following piece of code: procedure TMainForm.FormCreate(Sender: TObject) ;
begin
ShowWindow(Application.Handle, SW_HIDE) ;
SetWindowLong(Application.Handle, GWL_EXSTYLE, GetWindowLong(Application.Handle, GWL_EXSTYLE) or WS_EX_TOOLWINDOW ) ;
ShowWindow(Application.Handle, SW_SHOW) ;
end; Hide from "Close Program"
When you press the Ctrl-Alt-Del key combination the "Close Program" dialog box pops up. One simple way to hide your program from that dialog (the Task Manager dialog) is to clear the Application object's Title. If a program's main window does not have a title, Windows XX does not put the program in the "Close Program" dialog window. Remember that in Delphi the so called "main" window is not the Application window. The best place to clear the Title property is inside the Project's source code. To see the Project source select Project|View Source in the IDE. After the Application.Initialize add the bolded line: ...
Application.Initialize;
Application.Title := '';
Application.CreateForm(TForm1, Form1) ;
... I got the power...
As always, the beauty of Delphi and the ease of using the Win API has made "impossible" things to happen. All the API functions are available directly from the Windows unit which is automatically added to every new Delphi form unit - to call all the API function given in this article you do not need to do anything extra - just use them as described.If you know of any other way of "hiding a Delphi application from Windows" please, go to the Forum and gives us your solutions.
If you are interested in a Delphi component that does all the dirty work for you, check the: "The Big Brother" Delphi code toolkit - PART 2.
