frequently asked questions (FAQ)

Desktop > top of page

Hiding the taskbar

Q: How can I hide or show the windows taskbar?

A: By retrieving the taskbar's handle and using ShowWindow() you can completely hide the bar from Desktop.

function ShowBar(Show: boolean): boolean;
var hWnd: THandle;
begin
  hWnd:= FindWindow('Shell_TrayWnd', nil);
  if Show = false then
    Result:= ShowWindow(hWnd, sw_Hide)
  else
    Result:= ShowWindow(hWnd, sw_Show);
end;

Registering an own application as taskbar

Q: How can I register my application as a taskbar?

A: Use SHAppBarMessage() to register your form as an AppBar with proper Desktop metrics.

procedure RegisterTaskBarH(FormHandle: THandle; Metrics: TRect;
  Align: byte; UnRegister: boolean);
var AppStruct: TAppBarData;
begin
  // ... fill AppStruct fields, then:
  SHAppBarMessage(ABM_New, AppStruct);
  SHAppBarMessage(ABM_SetPos, AppStruct);
  SHAppBarMessage(ABM_Activate, AppStruct);
  SHAppBarMessage(ABM_WindowPosChanged, AppStruct);
end;

Animating forms and controls

Q: How can I apply window animation fx to my forms?

A: Use DrawAnimatedRects() to create trace/wipe effects on open/close.

procedure ShowWindowH(Show: boolean; Win: TWinControl);
var StartPos, EndPos: TRect; MPos: TPoint;
begin
  GetCursorPos(MPos);
  if Show = false then begin
    with Win do begin
      Hide;
      StartPos:= Rect(Left, Top, Left+Width, Top+Height);
      EndPos:= Rect(MPos.X, MPos.Y, MPos.X, MPos.Y);
      DrawAnimatedRects(Handle, 3, StartPos, EndPos);
    end;
  end else begin
    with Win do begin
      Hide;
      EndPos:= Rect(Left, Top, Left+Width, Top+Height);
      StartPos:= Rect(MPos.X, MPos.Y, 0, 0);
      DrawAnimatedRects(Handle, 3, StartPos, EndPos);
      Show;
    end;
  end;
end;

Setting screen resolution

Q: How can I set another screen resolution?

A: Use ChangeDisplaySettings() with a TDevMode record specifying width, height, color depth and refresh rate.

Closing windows from other apps

Q: How can I close windows from other applications?

A: Get the window handle via FindWindow() and send WM_Quit:

procedure ExitOtherWindowH(Caption: string);
var WinHandle: THandle;
begin
  WinHandle:= FindWindow(nil, PChar(Caption));
  if WinHandle <> 0 then
    PostMessage(WinHandle, WM_Quit, 0, 0);
end;

Graphics / DirectX > top of page

Creating icons from bitmaps

Q: How can I create icons within my Delphi app?

A: Use CreateIconIndirect() with a color bitmap and a mask bitmap. Helper functions handle color replacement to create the transparency mask.

DirectX: where to get units

Q: Where do I get DirectX conversion units for Delphi?

A: Hori's DelphiX (VCL, good for beginners) or Erik Unger's 1:1 C++ header conversions on Delphi JEDI. Get the DirectX SDK from Microsoft for docs.

DirectX: initializing devices

Q: How to create DirectDraw and Direct3DRM devices?

A: Use DirectDrawCreate, QueryInterface for IDirectDraw2, SetCooperativeLevel, CreateSurface for primary/back/zbuffer, then Direct3DRMCreate and CreateDeviceFromSurface.

DirectX: enumerating display devices

Q: How to enumerate DirectDraw devices?

A: Use DirectDrawEnumerate() with a callback that stores device GUIDs in a TStringList via AddObject().

DirectX: enumerating display modes

Q: How to enumerate video modes?

A: Create a temp DirectDraw2 object and call EnumDisplayModes() with a callback storing width, height, and bit depth.

File related > top of page

Getting a list of all installed drives

Q: How to get a list of all drives?

A: Call GetLogicalDrives() and loop through 26 letters:

procedure GetDrivesH(Drives: TStrings);
var DI: DWord; i: integer;
begin
  DI:= GetLogicalDrives;
  Drives.BeginUpdate;
  for i:= 0 to 25 do
    if (DI and (1 shl i)) <> 0 then
      Drives.Add(Char(Ord('A') + i) + ':\');
  Drives.EndUpdate;
end;

Check if a disk is inserted

Q: How to check if a disk is in a drive?

A: Suppress error dialogs with SetErrorMode(), then try ChDir(). If IoResult <> 0, the drive is not ready.

Delete running executable

Q: How to delete a running executable?

A: Write a command to the Registry RunOnce key. Windows executes it on next boot and removes the entry.

Network / Internet > top of page

Check if computer is online

Q: How to check if the machine is online?

A: Call InternetGetConnectedState() from WinInet.pas.

function IsOnlineH: boolean;
const Internet_Connection_Modem = 1;
      Internet_Connection_LAN = 2;
      Internet_Connection_Proxy = 4;
var dwConnectionTypes: dWord;
begin
  dwConnectionTypes:= Internet_Connection_Modem +
    Internet_Connection_LAN + Internet_Connection_Proxy;
  Result:= InternetGetConnectedState(@dwConnectionTypes, 0);
end;

Check if connected to LAN

Q: How to check for LAN connection?

A: Use GetSystemMetrics(SM_Network):

function IsNetConnectedH: boolean;
begin
  Result:= (GetSystemMetrics(SM_Network) and $01) = $01;
end;

Miscellaneous > top of page

Execute and wait

Q: How to execute an app and wait until finished?

A: Use CreateProcess() with WaitForSingleObject():

function ExecAndWaitH(Filename, Parameter: string;
  nCmdShow: integer): longword;
var StartupInfo: TStartupInfo;
    ProcessInfo: TProcessInformation;
begin
  FillChar(StartupInfo, SizeOf(StartupInfo), #0);
  StartupInfo.cb:= SizeOf(StartupInfo);
  StartupInfo.dwFlags:= StartF_UseShowWindow;
  StartupInfo.wShowWindow:= nCmdShow;
  if not CreateProcess(PChar(Filename), PChar(Parameter),
    nil, nil, false,
    Create_New_Console or Normal_Priority_Class,
    nil, nil, StartupInfo, ProcessInfo)
  then Result:= 0
  else begin
    WaitForSingleObject(ProcessInfo.hProcess, Infinite);
    GetExitCodeProcess(ProcessInfo.hProcess, Result);
  end;
end;

Detect math coprocessor

Q: How to check for a math coprocessor?

A: Most machines since 80486 have it built in. Check the Registry key HKEY_LOCAL_MACHINE\HARDWARE\DESCRIPTION\System\FloatingPointProcessor.

Compress data

Q: How to compress files?

A: Use ZLib (included since Delphi 3) which works on a stream base, or download Zip components from the Delphi Super Page.

Exit / reboot Windows

Q: How to shutdown or reboot?

A: Call ExitWindows() or ExitWindowsEx() with flags like ewx_Reboot, ewx_Shutdown, ewx_PowerOff, ewx_Force.

Delay code progress

Q: How to pause code like Delay() in TurboPascal?

A: Use GetTickCount() in a loop:

procedure DelayH(App: TApplication; ms: longint);
var xTime: longint;
begin
  xTime:= GetTickCount + ms;
  while GetTickCount < xTime do
    Application.ProcessMessages;
end;

Monitor suspend mode

Q: How to send the monitor to sleep?

A: Send SC_MonitorPower via SendMessage:

procedure MonitorPowerH(AppHandle: THandle; PowerOn: boolean);
begin
  if PowerOn then
    SendMessage(AppHandle, WM_SysCommand, SC_MonitorPower, -1)
  else
    SendMessage(AppHandle, WM_SysCommand, SC_MonitorPower, 0);
end;