Detecting when the mouse is over a component

When the mouse enters the area of a component, Delphi sends the CM_MouseEnter message. When it leaves, Delphi sends a CM_MouseLeave message. Treating this two messages, you can detect if the mouse is over the component. The Fly-Over label component shows this technique.

Executing default action of an Ole Container

To execute the default action of an Ole Container (open a Word or Excel document or run a Powerpoint presentation), you can use this code:

procedure TForm1.Button1Click(Sender: TObject);

begin

  OleContainer1.DoVerb(ovprimary);

end;

Paradox Password in code

To give the password of a Paradox table in code, you can use this code:

procedure TForm1.FormCreate(Sender: TObject);

begin

  Session.AddPassWord('MyPass');

  Table1.Acive := True;

end;

Hiding and showing the Windows Taskbar

To hide the Windows Taskbar you must use a code like this:

procedure TForm1.Button1Click(Sender: TObject);

var

  hTaskBar :Thandle;

begin

  hTaskBar := FindWindow('Shell_TrayWnd',Nil);

  ShowWindow(hTaskBar,Sw_Hide);

end;

To Show the Windows Taskbar, you must use this code:

procedure TForm1.Button2Click(Sender: TObject);

var

  hTaskBar :Thandle;

begin

  hTaskBar := FindWindow('Shell_TrayWnd',Nil);

  ShowWindow(hTaskBar,Sw_Normal);

end;

Hiding Minimized MDI Child Windows

To hide minimized MDI child windows, you must trap its WM_Size message, like this:

type

  TForm1 = class(TForm)

  public

    procedure WMSize(var M : TWMSIZE);Message WM_Size;

  end;



implementation



procedure TForm1.WMSize(var M:TWMSIZE);

begin

  if M.SizeType=Size_Minimized then

    showwindow(Handle,Sw_Hide);

end;

Acessing Protected Members of an Object

Usually, you can't access protected members of an object. But Delphi let you access protected members if the object is defined in the same unit. So you can define a derived object and typecast where you want to use the protected member. It's something like this:

THackControl = class(TCustomEdit)

end;

After defining this class, you can access all protected members of TCustomEdit, with objects of derived classes with a code like this:

THackControl(MyEdit).Color := clBlack;

Calling Windows DialUp Connection Dialog

To call Windows DialUp Connection Dialog, you can use WinExec, like this:

procedure TForm1.Button1Click(Sender: TObject);

begin

  winexec(PChar('rundll32.exe rnaui.dll,RnaDial '+Edit1.Text),sw_show);

end;

Drawing with different line types

Windows allows to draw lines where each pixel is another shape or drawing with LineDDa function. It needs a callback function that is called when each pixel must be drawn. There you can put the drawing routines. This routine draws a rectangle every 4 pixels:



TForm1 = class(TForm)

  procedure FormCreate(Sender: TObject);

  procedure FormPaint(Sender: TObject);

public

  DrawNow : Integer;

end;



var

  Form1: TForm1;



procedure DrawPoint(x,y : Integer;lpData : LParam); stdcall;



implementation



{$R *.DFM}



procedure DrawPoint(x,y : Integer;lpData : LParam);

begin

  with TObject(lpData) as TForm1 do begin

    if DrawNow mod 4 = 0 then

      Canvas.Rectangle(x-2,y-2,x+3,y+3);

    Inc(DrawNow);

  end;

end;



procedure TForm1.FormCreate(Sender: TObject);

begin

  DrawNow := 0;

end;



procedure TForm1.FormPaint(Sender: TObject);

begin

  LineDDA(0,0,Width,Height,@DrawPoint,Integer(Self));

end;

Detecting Windows shutdown

When Windows is shutting down, it sends a WM_QueryEndSession to all open applications. To detect (and prevent shutdown), you must define a message handler to this message. Put this definition on the private section of the main form:

procedure WMQueryEndSession(var Msg : TWMQueryEndSession); message WM_QueryEndSession;

And put this method in the implementation section of the unit:

procedure TForm1.WMQueryEndSession(var Msg : TWMQueryEndSession);

begin

  if MessageDlg('Close Windows ?', mtConfirmation, [mbYes,mbNo], 0) = mrNo then

    Msg.Result := 0

  else

    Msg.Result := 1;

end;

Display and Change video resolutions

To display available video modes, you must use the API function EnumDisplaySettings: it gets all display setting modes available.

To change modes, you must use ChangeDisplaySettings, that changes the video resolution and color depth.

procedure TForm1.FormCreate(Sender: TObject);
var
 i       : Integer;
 DevMode : TDevMode;
begin
 i:=0;
 while EnumDisplaySettings(nil,i,DevMode) do begin
   with Devmode do
    ListBox1.Items.Add
     (Format('%dx%d %d Colors',
     [dmPelsWidth,dmPelsHeight,Int64(1) shl dmBitsperPel]));
   Inc(i);
 end;
end;

procedure TForm1.Button1Click(Sender: TObject);
var
  DevMode    : TDeviceMode;
  liRetValue : Longint;
begin
 if EnumDisplaySettings
    (nil,Listbox1.ItemIndex,Devmode) then
  liRetValue := ChangeDisplaySettings
                  (DevMode, CDS_UPDATEREGISTRY);

  SendMessage(HWND_BROADCAST,
              WM_DISPLAYCHANGE,
              SPI_SETNONCLIENTMETRICS,
              0);
end;

Right justifying menu items

To justify menu items on the right side of the main menu bar, you must do like this:

{It will right justify all menu items to the right of the one selected}



procedure SetJustify(Menu: TMenu; MenuItem: TMenuItem; Justify: Byte);

{$IFDEF WIN32}

var

  ItemInfo: TMenuItemInfo;

  Buffer: array[0..80] of Char;

{$ENDIF}

begin

{$IFDEF VER80}

  MenuItem.Caption := Chr(8) + MenuItem.Caption;

{$ELSE}

  ItemInfo.cbSize := SizeOf(TMenuItemInfo);

  ItemInfo.fMask := MIIM_TYPE;

  ItemInfo.dwTypeData := Buffer;

  ItemInfo.cch := SizeOf(Buffer);

  GetMenuItemInfo(Menu.Handle, MenuItem.Command, False, ItemInfo);

  if Justify = 1 then

    ItemInfo.fType := ItemInfo.fType or MFT_RIGHTJUSTIFY;

  SetMenuItemInfo(Menu.Handle, MenuItem.Command, False, ItemInfo);

{$ENDIF}

end;

Moving forms with no caption

To move a form with no caption, you must override WM_NCHITTEST message, like this:

type

  TForm1 = class(TForm)

  public

    procedure WMNCHitTest(var M: TWMNCHitTest); message WM_NCHitTest;

  end;



var

  Form1: TForm1;



implementation

{$R *.DFM}



procedure TForm1.WMNCHitTest(var M: TWMNCHitTest);

begin

  inherited;

  if M.Result = htClient then {if the mouse clicked on the form}

    M.Result := htCaption; {make windows think that mouse has been clicked on caption}

end;

Positioning the caret in a line in a memo or RichEdit

To position the caret in a line in a Memo or RichEdit you must use this:







With Memo1 do

  SelStart := Perform(EM_LINEINDEX, Line, 0);

Moving the mouse pointer

To move the Mouse pointer with no user's action, you can use a timer and put the following code in it's OnTimer event:

procedure TForm1.Timer1Timer(Sender: TObject);

var

   pt:tpoint;

begin

  getcursorpos(pt);

  pt.x := pt.x + 1;

  pt.y := pt.y + 1;

  if pt.x>=screen.width-1 then setcursorpos(0,pt.y);

  if pt.y>=screen.height-1 then setcursorpos(pt.x,0);

end;

Detecting Windows Shutdown

To detect Windows Shutdown, you must trap WM_EndSession message. These steps should be taken:

Declare a message handling procedure in your Form's Private section:

procedure WMEndSession(var Msg : TWMEndSession); message WM_ENDSESSION;

Add the procedure to the implementation section of your Unit:

procedure TForm1.WMEndSession(var Msg : TWMEndSession);

begin

  if Msg.EndSession = TRUE then

    ShowMessage('Windows is shutting down ' + #13 + 'at ' +

      FormatDateTime('c', Now));

  inherited;

end;

Creating non rectangular windows (D2/D3)

To create a non rectangular window, you must create a Windows Region and use the API function SetWindowRgn, like this (this works only in D2/D3):

var

  hR : THandle;

begin

  {creates an Elliptic Region}

  hR := CreateEllipticRgn(0,0,100,200);

  SetWindowRgn(Handle,hR,True);

end;

Doing incremental search in a Query

To do incremental search in a Query, using a TEdit, you must put this code in the TEdit's OnChange Event (this works only in D2/D3):

procedure TForm1.Edit1Change(Sender: TObject);

begin

  With Edit1 do

    if Text <> '' then begin

      Query1.Filter := 'code = '''+Edit1.Text+'''';

      Query1.FindFirst;

    end;

end;

Another way could be

procedure TForm1.Edit1Change(Sender: TObject);

begin

  With Edit1 do

    if Text <> '' then

      Query1.Locate('code',Edit1.Text,[loPartialKey]);

end;

Doing incremental search in a Table

To do incremental search on a table, using a TEdit, you must put this code in the TEdit's OnChange Event:

procedure TForm1.Edit1Change(Sender: TObject);

begin

  With Edit1 do

    if Text <> '' then

      Table1.FindNearest([Text]);

end;

Converting the first letter of an EditBox to uppercase

To convert the first letter of an EditBox to uppercase this code can be used:

procedure TForm1.Edit1Change(Sender: TObject);

var

  OldStart : Integer;

begin

  With Edit1 do

    if Text <> '' then begin

      OnChange := NIL;

      OldStart := SelStart;

      Text := UpperCase(Copy(Text,1,1))+LowerCase(Copy(Text,2,Length(Text)));

      SelStart := OldStart;

      OnChange := Edit1Change;

    end;

end;

Listing all open windows

To list (get) all open windows, you must use EnumWindows API function. It uses a callback function, that receives 2 parameters: a Window handle and a Pointer.
You can use it with a code like this (this code lists all open windows, even invisible ones in a listbox):

function EnumWindowsProc(Wnd : HWnd;Form : TForm1) : Boolean; Export;
{$ifdef Win32} StdCall; {$endif}

var

  Buffer : Array[0..99] of char;

begin

  GetWindowText(Wnd,Buffer,100);

  if StrLen(Buffer) <> 0 then

    Form.ListBox1.Items.Add(StrPas(Buffer));

  Result := True;

end;



procedure TForm1.Button1Click(Sender: TObject);

begin

  EnumWindows(@EnumWindowsProc,LongInt(Self));

end;

Working with multiselect grids

Delphi 2.0 multiselect grids have an undocumented SelectedRows property, a TBookmark list.
You can use it with a code like this:

With DbGrid1 do begin

  for i := 0 to Pred(SelectedRows.Count) do begin

    DataSource.DataSet.Bookmark := SelectedRows[i];

    {the dataset is positioned on the selection. Do your stuff}

  end;

end;

Packing tables

To pack (remove phisically all deleted records) from a Paradox table you must use this code





procedure ParadoxPack(Table : TTable);

var

  TBDesc : CRTblDesc;

  hDb: hDbiDb;

  TablePath: array[0..dbiMaxPathLen] of char;

begin

  FillChar(TBDesc,Sizeof(TBDesc),0);

  with TBDesc do begin

    StrPCopy(szTblName,Table.TableName);

    StrPCopy(szTblType,szParadox);

    bPack := True;

  end;

  Table.Open;

  hDb := nil;

  Check(DbiGetDirectory(Table.DBHandle, True, TablePath));

  Table.Close;

  Check(DbiOpenDatabase(nil, 'STANDARD', dbiReadWrite,

    dbiOpenExcl,nil,0, nil, nil, hDb));

  Check(DbiSetDirectory(hDb, TablePath));

  Check(DBIDoRestructure(hDb,1,@TBDesc,nil,nil,nil,False));

  Table.Open;

end;




To pack Dbase tables use this command




  DBIPackTable(Table1.DBHandle,Table1.Handle,nil,nil,True);

Making Enter key act as Tab

To make the Enter key act as Tab key is a 3 step procedure:



1) Set the form's KeyPreview property to True

2) Set all form's buttons property Default to False

3) Create an OnKeyPress event for the form like this:





procedure TForm1.FormKeyPress(Sender: TObject; var Key: Char);

begin

  if Key = #13 then begin

    Key := #0;

    if (Sender is TDBGrid) then

      TDBGrid(Sender).Perform(WM_KeyDown,VK_Tab,0)

    else

      Perform(Wm_NextDlgCtl,0,0);

  end;

end;



Tip collaboration by: Antonio Carlos Maduro

Accessing DBNavigator buttons

The DBNavigator has a protected Buttons array that acesses its buttons. An inherited Navigator can acess them and change their properties. TBSNavigator does this to change their Enabled state or Glyph.

Filtering and sorting tables in Delphi 1.0

To filter and sort a table in Delphi 1.0 you can use a QBE (Query by Example) file as the TableName TTable's property. This is useful to filter, sort or join tables, while still using the TTable component. QBE files can be created in Database Desktop.

Extracting icons from an executable

To extract icons from an executable, you must use ExtractIcon API function. It gets 3 parameters:





Instance - Instance of the application


FileName - Name of the executable. Must be a PChar


NumIcon - Number of the icon to be retreaved. If it's Word(-1), the function returns the number of icons in the executable.



Download an example.

How to Get Dos Environment

To get DOS Environment, you must use GetDosEnvironment API Function.It returns a PChar that can be parsed. Download an example.

International settings

By default, Delphi gets its date/time, currency and numeric format from Control Panel's International settings.
This can lead to errors, when parsing dates, numbers or lists. To avoid these errors, you can set the constants defined in Delphi,
like DecimalSeparator, ShortDateFormat and others like this:







DecimalSeparator := '.';

ShortDateFormat := 'mm/dd/yy';



This will override the default settings assuring the correct values. To a complete list of these variables, look at Currency Formatting Variables in Delphi Help

Changing a menu font

To change a menu font, you must forget using Delphi's menu designer.
You must create the menu items using Api function AppendMenu, with flag
MF_OWNERDRAW, in the Form's OnCreate Event. Then you must use WM_MEASUREITEM
and WM_DRAWITEM to draw your menu options. Download
an example.

Getting current line and column from a memo

To get the current line and column from a memo you must use this:







With Memo1 do begin

  Line := Perform(EM_LINEFROMCHAR,SelStart, 0);

  Column := SelStart - Perform(EM_LINEINDEX, Line, 0);

end;

Shrinking the executable

In Delphi 1.0, sometimes checking the Optimize for size and load
time checkbox, in Options/Project/Linker doesn't work (you get
a Disk full message, even with plenty of space). Delphi 1.0 comes with
a Dos program, W8LOSS, that does the same. To use, it you must type:







W8LOSS program.exe







It will shrink your executable in about 20%, and will speed up loading
time.

Changing a TEdit text in its OnChange event

If you want to change a TEdit text in its OnChange event, it will fire
the event recursively until stack exhausts. To do this, you must set it
to NIL before changing its text and reassigning it after, like this:

procedure Edit1Change(Sender : TObject);

begin

  Edit1.OnChange := NIL;

  if Edit1.Text = 'Some Text' then

    Edit1.Text := 'New Text';

  Edit1.OnChange := Edit1Change;

end;







This tip works also with OnValidate events.

Running a DOS program and closing its window after running it

When you run a DOS program in Windows95, its window remains open until
closed by the user. To run a Dos program that closes its windows after
running, you must specify "command.com /c program" in the
command line. Using WinExec API function to run a program named progdos.exe,
the call should be:







WinExec("command.com /c progdos.exe",sw_ShowNormal);







If you wish that the program is run hidden from the user, the second
parameter must be sw_Hide. You must specify the .com extension, or the program will not run.