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SECTION 5 - Delphi VCL This document contains information that is most often provided to users of this section. There is a listing of common Technical Information Documents that can be downloaded from the libraries, and a listing of the most frequently asked questions and their answers. TI1171 Bug Report Form TI2711 How to Circumvent the "Index not found" Exception TI2776 List of Delphi books from Third-Party Publishers TI2779 Delphi Client/Server and PowerBuilder Compared TI2781 Step by Step Configuration of an ODBC Driver TI2841 Delphi Consultants and Training Centers Delphi FTP and WWW sites on Internet: ftp.borland.com ftp.netcom.com /pub/ic/ice-floe. http://www.Borland.com http://www.cybernetics.net/users/bstowers/delphi-bugs.html http://www.coriolis.com/coriolis/whatsnew/delphi.htm Zip files related to VCL components: VCLPATCH.ZIP Patch for the Visual Component Library source. DELCSPAT.ZIP Patch for Delphi Client Server. DELPATCH.ZIP Patch for Delphi Questions and answers: ------------------------------------------------------------------------ Q: "How can VCL components be created on the fly at run-time?" A: The following code will create a modal password form at runtime. The TPasswordForm type is a TForm descendent class defined either in the current unit or in a separate unit referenced by the current unit's uses clause. with TPasswordForm.Create(Application) do begin ( i.e TForm1, TPasswordForm etc. } ShowModal; { Display form as a modal window } Free; { Free the form when it is closed } end; The following are the general steps to add a component to a form at run-time: 1. Declare an instance variable of the component type that you wish to create {i.e. TButton }. Note: instance variables are used to point to an actual instance of an object. They are not objects themselves. 2. Use the component's Create constructor to create an instance of the component and assign the instance to the instance variable declared in step 1. All components' Create constructors take a parameter - the component's owner. Except in special circumstances, you should always pass the form as the owner parameter of the component's Create constructor. 3. Assign a parent to the component's Parent property (i.e. Form1, Panel1, etc). The Parent determines where the component will be displayed, and how the component's Top and Left coordinates are interpreted. To place a component in a groupbox, set the component's Parent property to the groupbox. For a component to be visible, it must have a parent to display itself within. 4. Set any other properties that are necessary (i.e. Width, Height). 5. Finally, make the component appear on the form by setting the component's Visible property to True. 6. If you created the component with an owner, you don't need to do anything to free the component - it will be freed when the owner is destroyed. If you did not give the component an owner when you created it, you are responsible for making sure the component is freed when it is no longer needed. The following demonstrates how to add a TButton component to the current form at run-time: var TempButton : TButton; { This is only a pointer to a TButton } begin TempButton := TButton.Create(Self); { Self refers to the form } TempButton.Parent := Self; { Must assign the Parent } TempButton.Caption := 'Run-time'; { Assign properties now } TempButton.Visible := True; { Show to button } end; Since the button was created with an owner, it will be freed automatically when its owner, the form, is freed. ------------------------------------------------------------------------ Q: "How can the event handler of a popup menu item determine which component was right-clicked upon to activate that menu? A: Use the PopupMenu.PopupComponent property to determine what control the menu was activated for. procedure TForm1.PopupItem1Click(Sender: TObject); begin Label1.Caption := PopupMenu1.PopupComponent.ClassName; end; The form's ActiveControl property can also be used, however, the active control may not necessarily be the control that caused the popup menu to appear. ------------------------------------------------------------------------ Q: "What are the capacity limits of the standard Delphi controls?" A: Any component that uses a TList to store information has an upper bound of 16368 items. For example, a TTabControl can contain up to 16368 tabs and the Delphi Component Palette can contain up to 16368 palette pages. Many of the Delphi standard components are wrappers around standard Windows controls. Windows 3.1 imposes its own limits on these components. For example: a TComboBox or TListbox can hold up to 5440 items and TMemo or TEdit (and related components) can hold up to 32k of text. Windows 3.1 resource space imposes a limit of 570 pages in a TNoteBook component. (It's difficult to get more than 500 window handles in any Windows application.) Note 1: Exceeding these limits will raise exceptions or cause Windows to behave strangely. Note 2: Many of the Windows-based capacity limits are much higher in the 16-bit WOW box of Windows NT and in Windows 95. In future 32 bit releases of Delphi, virtually all of these limits will disappear. ------------------------------------------------------------------------ Q: "How can I determine the Length in pixels of a string after a specific font has been aplied to it?" A: Use the Canvas methods TextHeight and TextWidth to determine the text height and width of a string in pixels. Be sure to assign the font into the Canvas before drawing or taking measurements. All visual components have a Canvas property, but usually this property is protected so that only direct descendents can draw on the Canvas. Since you write much of your code inside methods of a TForm descendent, you always have access to your form's inherited Canvas property. The TPaintBox component makes its Canvas property public so that you can draw on the component from OnPaint event methods in the form. If a component doesn't have a Canvas property you can use the following function to get the text width based on the font passed. function GetTextWidth(CanvasOwner: TForm; Text : String; TextFont : TFont): Integer; var OldFont : TFont; begin OldFont := TFont.Create; try OldFont.Assign( CanvasOWner.Font ); CanvasOWner.Font.Assign( TextFont ); Result := CanvasOwner.Canvas.TextWidth(Text); CanvasOWner.Font.Assign( OldFont ); finally OldFont.Free; end; end; ------------------------------------------------------------------------ Q: "Why do some visual components like TPanel and TEdit not have a Canvas property?" A: All descendents of TCustomControl have a Canvas property, however, most are protected to prevent 'outsiders' from drawing on the component. Descendents of a component can always access the protected properties they inherit from the component (such as Canvas), but users of the component cannot. type TCanvasPanel = class(TPanel) public property Canvas; end; If you want to draw on a component that doesn't have a public canvas property, consider using a different component that was intended for arbitrary drawing (TPaintBox), or layer components to achieve the desired result (client-align a TPaintBox inside a TPanel to get a bevelled, drawable area). ------------------------------------------------------------------------ Q: "How can I get a horizontal scrollbar on a list box?" A: Send a LB_SetHorizontalExtent message to the listbox's window handle. For example, the message could be sent in the form's OnCreate: procedure TForm1.FormCreate(Sender: TObject); begin SendMessage(Listbox1.Handle, LB_SetHorizontalExtent, 1000, Longint(0)); end; ------------------------------------------------------------------------ Q: "Does Delphi have a component that supports serial communications?" A: No. However, there are serial communications libraries (and soon Delphi components) for Delphi available from third party vendors such as TurboPower, SaxComm, and and others. ------------------------------------------------------------------------ Q: "How can the tab stops be set in a TMemo control?" A: To change the tab stops for a multiline edit control (i.e. a TMemo) send the EM_SetTabStops message to the component. The Tabs array indicates where the tab stops will be located. Since the WParam parameter to SendMessage is 1, then all tab stops will be set to the value passed in the Tabs array. Remember to set the WantTabs property of TMemo to True to enable the tabs. procedure TForm1.FormCreate( Sender : TObject ); const TabInc : LongInt = 10; begin SendMessage( Memo1.Handle, EM_SetTabStops, 1, Longint( @TabInc ) ); end; ------------------------------------------------------------------------ Q: "Where is the best place to open a splash screen on program start up?" A: The best place to open a splash screen is in the project source file after the first Application.FormCreate and before the Application.Run. This is accomplished by creating a form on the fly and then displaying it before the application is actual opened. program Project1; uses Forms, Unit1 in 'UNIT1.PAS' {Form1}, Splash; {$R *.RES} var SplashScreen : TSplashScreen; {in the Splash unit} begin Application.CreateForm(TForm1, Form1); SplashScreen := TSplashScreen.Create(Application); try SplashScreen.Show; SplashScreen.Update; {Process any pending Windows paint messages} { do other CreatForms or any other processing before the application is to be opened. If the start up processing is going to take a long time you may want to run Application.ProcessMessages periodically to allow Windows to respond to Windows messages. } finally {Make sure the splash screen gets released} SplashScreen.Free; end; Application.Run; end. ------------------------------------------------------------------------ Q: "Why does the OnExit event of a TEdit component not execute when the user clicks on a speed button? Is there a way to make a an OnExit event execute when a speed button is pressed?" A: A speed button never actually gets focus, so the active control never loses its focus, consequently the active control's OnExit event never occurs. One way to execute the active control's OnExit event is to explicitly call it in the OnClick event of the speedbutton. For example: procedure TForm1.SpeedButton1Click(Sender: TObject); begin If ActiveControl is TEdit then (ActiveControl as TEdit).OnExit(ActiveControl); end; ------------------------------------------------------------------------ Q: "When I open the child windows at run-time each one is positioned slightly down and to the right of the previous window. My problem is that if I then close some of the child windows and then open a new one, the new one is placed down and to the right of where the last child window was before I closed it, even though it is no longer there! Is this as designed?" A: That's how MDI windows works. VCL doesn't override Windows default behavior in this situation. Untested suggestion: In the FormCreate procedure try setting the Top, Left, Width & Height properties to the values that you require. The MDI child form's FormCreate is called before the window is displayed. ------------------------------------------------------------------------ Q: "Why can't my program find any of the resources that I put in a .RES file if that .RES file is the same name as my form's unit name?" A: If the name of an included .RES file is the same as the name of a .DPR file Delphi wll overwrite it with it's own .RES file. In addition, the project RES file is for the Delphi project manager only; don't edit or add resources to this RES file. ------------------------------------------------------------------------ Q: "How can you do scrolling functions in a TForm component using keyboard commands? For example, scrolling the form up and down with the PgUp and PgDn keys. A: Form scrolling is accomplished by modifying the VertScrollbar or HorzScrollbar Postion properties of the form. The following code demonstrates how to do this: procedure TForm1.FormKeyDown(Sender: TObject; var Key: Word; Shift: TShiftState); const PageDelta = 10; begin With VertScrollbar do if Key = VK_NEXT then Position := Position+PageDelta else if Key = VK_PRIOR then Position := Position-PageDelta; end; Note: This may not work well if the active control uses PgUp & PgDn, too, like a TMemo. ------------------------------------------------------------------------ Q: "Is there a way to fill a TListbox or TMemo in one shot?" A: To fill multiple lines of a TListbox or TMemo component the SetText method can be used. The null terminated string passed to the SetText method is a concatination of each line of text delimeted by a carriage return character #13 in between. For example, the follow statement: Listbox1.Items.SetText('aaaaa'#13'bbbbb'#13'ccccc') will display the following in a listbox window: aaaaa bbbbb ccccc Note: The preferred method of filling a listbox or memo is with the Add method of their Items and Lines properties, respectfully. ------------------------------------------------------------------------ Q: "Is it possible to create something like the Control Array in Visual Basic? For example, I want a group of buttons with a common event handler whereby the event handler picks up an integer value for the particular button. In Visual Basic this would be done via the Control Array index." A: One way do to this is to set the Tag field for each button to a different number and then create a common OnClick event handler that looks at the Sender's Tag field. Assign the same OnClick event handler to all the buttons in the group. And then the OnClick event handler would look something like this: procedure TForm1.Button1Click(Sender: TObject); var cap: string; begin case TButton(sender).Tag of 1: ShowMessage('1st Button Pressed'); 2: ShowMessage('2nd Button Pressed'); 3: ShowMessage('3rd Button Pressed'); end; end; ------------------------------------------------------------------------ Q: "How can a new component be added to a page of a TTabbedNoteBook at run time? How do I determine what the parent will be for the new component?" A: To add a component to a TabbedNotebook page at run-time a pointer to the desired page must be assigned to the new component's Parent property before it can be shown. The way to access all the pages of a TTabbedNotebook at run-time is with the Objects array property of the TabbedNotebook's Pages property. In other words, the page components are stored as objects attached to the page names in the Pages string list property. The follow demonstrates the creation of a button on the second page of TabbedNotebook1: var NewButton : TButton; begin NewButton := TButton.Create(Self); NewButton.Parent := TWinControl(TabbedNotebook1.Pages.Objects[1]) ... This is how a TNotebook page would be used as a parent to a newly created component on that page: NewButton.Parent := TWinControl(Notebook1.Pages.Objects[1]) This is how a TTabSet tab page would be used as a parent to a newly created component on that tab page: NewButton.Parent := TWinControl(TabSet1.Tabs.Objects[1]) ------------------------------------------------------------------------ Q: "Are there any vertical ( side of the page ) tab components available, commercial, shareware or freeware." A: TurboPower's Orpheus product will support this. GO TURBOPOWER for more information. ------------------------------------------------------------------------ Q: "Is there an easy way to get CopyToClipboard, CutToClipboard etc. to know to use the TEdit that has focus? A: Simply check to see if the ActiveControl is of type TEdit and then do the desired cut, copy or paste operation. For example: if (ActiveControl is TEdit) then TEdit(ActiveControl).CopyToClipboard; ------------------------------------------------------------------------ Q: "Does a TDBGrid component have an OnMouseDown, OnMouseUp and OnMouseMove events?" A: The events are there, but they aren't published. You could create a simple decendant of TDBGrid and publish them. ------------------------------------------------------------------------ Q: "Does Delphi grab system resources when displaying and closing modal dialogs? For example, the following code decreases the system resources every time it is used to show a modal dialog." ModalForm1 := TModalForm1.Create(Self); ModalForm1.ShowModal; A: Without an OnClose event handler that sets Action parameter to caFree, your code is creating a new form with each call to TModalForm1.Create(Self), but the previously created form is never destroyed. All previous instances of the "ModalForm1" forms are floating around in Windows. The Free method of a form can also be used to free its resources. This is demonstrated below: try ModalForm1.ShowModal; { other stuff here } finally ModalForm1.Free; end; ------------------------------------------------------------------------ Q: "What is the best way to create a radio button group and place radio buttons on it? It seems that you can create a Radio Group then drop Radio Buttons on it or you can create the group and enter values into the Items properties for the titles (captions) of the radio buttons and have Delphi place them in the group?" A: If you're going to use a radio group, you need to create your radio buttons using the Items string list. Radio buttons don't have to be in a group, which is why the plain radio button component is available. ------------------------------------------------------------------------ Q: "Is there a way to make sure the window that is holding a form or an image component is byte-aligned?" A: Override the CreateParams method: procedure TMyForm.CreateParams(var Params:TCreateParams); begin inherited CreateParams(Params); Style := Style or CS_BYTEALIGNWINDOW; end; Note: Byte alignment is less of a big deal than the Windows docs imply. It is only significant on monochrome, EGA, and 16 color VGA video modes. All higher video modes are always byte-aligned. ------------------------------------------------------------------------ Q: What is the order of event handlers when a form is created and shown? A: When a form is created the event handlers are executed in the following order: OnCreate, OnShow, OnPaint, OnActivate, OnResize and OnPaint again. ------------------------------------------------------------------------ Q: "Why does the error 'Cannot change Visible in OnShow or OnHide' occur when the FormStyle property of a form is changed in the OnActivate event? A: The FormStyle property defines how the window gets created and is usually set in the OnCreate event, however, it can changed after the window handle has been created, just not during the OnActivate, OnShow or OnHide events. The issue here is with the mode that the system is in during OnShow and OnHide events. ------------------------------------------------------------------------ Q: "How can I make components look sunken and raised? A: To make a component look raised or lowered place it on a TBevel or TPanel component which both have properties to raise or lower their frames. ------------------------------------------------------------------------ Q: Where is the source code for the tabbed controls (i.e. TTabbedNotebook)? A: The source code files shipped with Delphi does not contain the source for the tabbed controls because of legal reasons. However, the interface source for the tabbed controls is provided in the DELPHI\DOC directory with an INT extension. Note: Registered owners of the Delphi RTL source code can request the TTabSet and TTabbedNotebook source code from Borland Corporate Affairs. Instructions are in the RTL source readme. ------------------------------------------------------------------------ Q: "What is the memo field size in Delphi?" A: Microsoft's edit control that is built-in to Windows and used by Delphi's TEdit and TMemo wrapper classes has a maximum capacity of 32k. The Delphi wrapper classes do some special things to allow every edit and memo control on a form to contain up to 32k each. Normally all edit controls in an application would be limited to 32k collectively. ------------------------------------------------------------------------ Q: "How can I make a field in the TGrid component not show up?" A: This can be accomplished by either removing the field entirely from the Fields Editor's field list or by setting the Visible property of the field to False. ------------------------------------------------------------------------ Q: "Is there a way to put a wallpaper background on an MDI application?" A: There is a sample application that demostrates this in the VCL section (5) of the Delphi forum under the name of MDI_BGRD.ZIP. ------------------------------------------------------------------------ Q: "Does Delphi have a currency/money component?" A: No, bu there is a currency edit component in the VCL section of the Delphi forum under the name of CURREDIT.ZIP. ------------------------------------------------------------------------ Q: "Where can I find out about VBX datatypes (i.e. TBasicString) and the functions to manipulate these datatypes?" A: First off, all VBX related datatypes and functions are in the VBXCtrls unit which is Borland propriatary unit. Delphi does, however, provide the interface section of this unit is in the \DELPHI\DOC directory under the name of VBXCTRLS.INT. This is the only real source of information on the contents of the VBXCtrls unit. ------------------------------------------------------------------------ Q: "What issues do I need to be aware of when developing applications that will be ran on different screen resolutions (form scaling)?" A: The following are issue to bear in mind when scaling Delphi applications (forms) on different screen resolutions? * Decide early on in the form design stage whether you're going to allow the form to be scaled or not. The advantage of not scaling is that nothing changes at runtime. The disadvantage of not scaling is that nothing changes at runtime (your form may be far too small or too large to read on some systems if it is not scaled). * If you're NOT going to scale the form, set Scaled to False. * Otherwise, set the Form's Scaled property to True. * Set AutoScroll to False. AutoScroll = True means 'don't change the form's frame size at runtime' which doesn't look good when the form's contents do change size. * Set the form's font to a scaleable TrueType font, like Arial. MS San Serif is an ok alternate, but remember that it is still a bitmapped font. Only Arial will give you a font within a pixel of the desired height. NOTE: If the font used in an application is not installed on the target computer, then Windows will select an alternative font within the same font family to use instead. This font may not match the same size of the original font any may cause problems. * Set the form's Position property to something other than poDesigned. poDesigned leaves the form where you left it at design time, which for me always winds up way off to the left on my 1280x1024 screen - and completely off the 640x480 screen. * Don't crowd controls on the form - leave at least 4 pixels between controls, so that a one pixel change in border locations (due to scaling) won't show up as ugly overlapping controls. * For single line labels that are alLeft or alRight aligned, set AutoSize to True. Otherwise, set AutoSize to False. * Make sure there is enough blank space in a label component to allow for font width changes - a blank space that is 25% of the length of the current string display length is a little too much, but safe. (You'll need at least 30% expansion space for string labels if you plan to translate your app into other languages) If AutoSize is False, make sure you actually set the label width appropriately. If AutoSize is True, make sure there is enough room for the label to grow on its own. * In multi-line, word-wrapped labels, leave at least one line of blank space at the bottom. You'll need this to catch the overflow when the text wraps differently when the font width changes with scaling. Don't assume that because you're using large fonts, you don't have to allow for text overflow - somebody else's large fonts may be larger than yours! * Be careful about opening a project in the IDE at different resolutions. The form's PixelsPerInch property will be modified as soon as the form is opened, and will be saved to the DFM if you save the project. It's best to test the app by running it standalone, and edit the form at only one resolution. Editing at varying resolutions and font sizes invites component drift and sizing problems. * Speaking of component drift, don't rescale a form multiple times, at design time or a runtime. Each rescaling introduces roundoff errors which accumulate very quickly since coordinates are strictly integral. As fractional amounts are truncated off control's origins and sizes with each successive rescaling, the controls will appear to creep northwest and get smaller. If you want to allow your users to rescale the form any number of times, start with a freshly loaded/created form before each scaling, so that scaling errors do not accumulate. * Don't change the PixelsPerInch property of the form, period. * In general, it is not necessary to design forms at any particular resolution, but it is crucial that you review their appearance at 640x480 with small fonts and large, and at a high-resolution with small fonts and large before releasing your app. This should be part of your regular system compatibility testing checklist. * Pay close attention to any components that are essentially single-line TMemos - things like TDBLookupCombo. The Windows multi-line edit control always shows only whole lines of text - if the control is too short for its font, a TMemo will show nothing at all (a TEdit will show clipped text). For such components, it's better to make them a few pixels too large than to be one pixel too small and show not text at all. * Keep in mind that all scaling is proportional to the difference in the font height between runtime and design time, NOT the pixel resolution or screen size. Remember also that the origins of your controls will be changed when the form is scaled - you can't very well make components bigger without also moving them over a bit. ------------------------------------------------------------------------ Q: "How can I get rid of the ReportSmith about box splash screen when I run a report." A: Add the following line in [RS_RunTime] section of the RS_RUN.INI file to not have the ReportSmith about box appear when a report is ran. ShowAboutBox=0 ------------------------------------------------------------------------ Q: "How do you make a moveable multi-split window?" A: The following steps and code demonstrate how to make a simple splitter window. 1) Put a memo on a form and set its Align property to alTop. 2) Place a panel on the form and set its Align property to alTop. 3) Set the panel's Height property to 6 or 7. 4) Set the panel's DragMode property to dmAutomatic. 5) Set the panel's DragCursor property to crVSplit. 6) Set the panel's Cursor property to crVSplit. 7) Add another memo on the form and set its Align property to alClient. 8) Now select both memos and the panel, and connect them all to this OnDragOver handler: procedure TForm1.Memo1DragOver(Sender, Source: TObject; X, Y: Integer; State: TDragState; var Accept: Boolean); begin Accept := False; if Source = Panel1 then begin Accept := True; Memo1.Height := Y + (Sender as TControl).Top; end; end; ------------------------------------------------------------------------ Q: "How can I determine the current row and column position of the caret in a TMemo component? A: You can use the Windows API messages EM_LINEFROMCHAR and EM_LINEINDEX to determine the current line and offset within that line (starting from SelStart). var LineNum: longint; CharsBeforeLine: longint; begin LineNum := SendMessage(Memo1.Handle, EM_LINEFROMCHAR, Memo1.SelStart,0); CharsBeforeLine := SendMessage(Memo1.Handle, EM_LINEINDEX, LineNum, 0); Label1.Caption := 'Line ' + IntToStr(LineNum +1) Lebel2.Caption := 'Position ' + IntToStr((Memo1.SelStart - CharsBeforeLine) + 1); end; ------------------------------------------------------------------------ Q: How can I get the pixels per inch of the printer? A: If you want the value in pixels you can use the API function GetDeviceCaps(). For example: VertPixelsPerInch := GetDeviceCaps(Printer.Handle, LogPixelsX); HorzPixelsPerInch := GetDeviceCaps(Printer.Handle, LogPixelsY); ------------------------------------------------------------------------ Q: "Is there a way to store an integer value along with a string value in a TString list object or property?" A: Yes, but it requires some type conversions. The TString component has an Objects array along with the string array that can be utilized for the purpose of storing integer datA: The data type that the Objects array holds is TObject. In essence it holds a 4 byte pointer value. So to put an integer value in it you would need to type cast that value. For example, the following is adding a string and an integer value of 100 to an items property (TString object) of a Listbox: Listbox1.Items.AddObject('Text string', TObject(100)); To get the value out do the following: Result := LongInt( Listbox1.Items.Objects[0] ); This assumes that Result is of type Longint and that the value that were after is at index position 0. Note: Though this works it is never wise to rely on the internal workings of an object. This is trick code and should be well commented. If you want to keep track of more than one value then a new class can be derived from the TObject base class to hold these values. type ManyValues = class(TObject) Value1 : Integer; Value2 : Integer; end; ... ------------------------------------------------------------------------ Q: Is it possible to access components by their name property (i.e. 'SpeedButton' + IntToStr(i) ) A: Yes it's possible. The following example uses the FindComponent method of Form1 to disable the first 10 SpeedButtons by name. for I := 1 to 10 do with Form1.FindComponent('SpeedButton' + IntToStr(i)) as TSpeedButton do Enabled := False; ------------------------------------------------------------------------ Q: How do you create a 'modal' form in an MDI application? When my application calls the ShowModal method I get an error "Can't Show Modal when Visible is set true". When I try to set Visible to False, I get the error, can't set Visible to False on an MDI Child. A: Normally, the first form of a project (the main form) is created with its Visible property set to True, and all of the other forms are created with their Visible properties set to False. An MDI child form, on the other hand, can't be invisible, so its Visible property is set to True. When you change its form style back to fsNormal, the Visible property stays True, so you need to set it to False manually. ------------------------------------------------------------------------ Q: Is there a way to change the default font size for components when they are placed on a form? A: Just add a form with it's Font property set to your desired font to the gallery. Since, by default, components reflect the parent's font any components you add to your form will take on that font. In addition, you can set your new form as the Default Main Form and Default New Form from the gallery (Options | Gallery...). ------------------------------------------------------------------------ Q: How can I determine the directory that my program was executed from? A: The following function extracts the path from the ExeName property of the global Application object. function GetExePath : String; var LastBackSlashPos, Index : Integer; begin Result := Application.ExeName; for Index := 1 to length(Result) do if Result[Index] = '\' then LastBackSlashPos := Index; { subtract 1 so that the last backslash is not included } Result[0] := chr(LastBackSlashPos - 1); end; ------------------------------------------------------------------------ Q: How can I change Font.Style back to normal after calling Canvas.Font.Style := [fsBold]? The online help shows ([fsBold],[fsItalic] etc] but does not mention normal style. A: You simply specify an empty set for no style at all: Canvas.Font.Style := []; or, you might just want to exclude the fsBold style like this: Canvas.Font.Style := Canvas.Font.Style - [fsBold]; ------------------------------------------------------------------------ Q: How can I get some actions to happen after a form is showing normally? It seems that all the form events (OnCreate, OnPaint, etc.) happen before the form is show. A: You can add "Visible := True" inside OnCreate event, and then do whatever you wish. ------------------------------------------------------------------------ Q: How much GDI resource does each built-in components use? A: The TGraphicControl descendants like TLabel and TBevel don't use free system resources at all. On the other hand, TWinControl descendants like TEdit and TPanel do. Also each radio button in a TRadioGroup is a window, i.e. has a window handle. ------------------------------------------------------------------------ Q: Why does a TTabbedNotebook use so much of the system resources when only one page is showing at a time? A: Even though only one page is showing at a time each pages' components have already been created thus taking resources. One solution to this is instead of using a notebook you use a separate form for each page and when the user clicks on a tab, the existing page is destroyed and the new one created. The basic steps to set this is is as follows: First, each child form needs its creation parameters setup in a certain way: ... private { Private declarations } PROCEDURE CreateParams(VAR Params: TCreateParams); override; ... procedure TForm2.CreateParams(VAR Params: TCreateParams); begin Inherited CreateParams(Params); with Params do begin WndParent := Application.MainForm.Handle; Style := (Style OR WS_CHILD) AND NOT (WS_POPUP); end; end; The child form's BorderStyle must be set to bsNone. In the main form, create a private data field Child of type TForm. Initialize it in the OnActivate event, NOT OnCreate. And each time the tab is clicked to change "pages", free the existing Child and initialize a new one of the desired type. E.g. in OnActivate do: Child := TForm2.Create(Self); with Child do begin Parent := Self; Align := alClient; Visible := True; end; When you create a child page due to a tab change, do it in the same way just shown. Of course you'll need to use the main form to store any data about the state of the controls in a given child window, because the data will go bye-bye when the child is freed. ------------------------------------------------------------------------ Q. How do you deselect one or more items in a listbox or combobox? A. Listbox1.ItemIndex := -1; ------------------------------------------------------------------------ Q. Why is it that when I call a dialog window such as MessageBox() from within an event handler such as OnExit that the blinking cursor (the caret) disappears upon closing the dialog? A. This is a Windows behavior. Forcing an additional focus change (e.g., with ShowMessage) during an event associated with a focus change (e.g., OnExit) will cause Windows to become confused. It is Windows that is controlling the focus change, and it is Windows that becomes confused when you force a focus change in the middle of that process. ------------------------------------------------------------------------ Q. Why do I get the exception 'EInvalidOperation: Cannot make a visalbe window modal' when I try to open a form with Showmodal? The form is not open yet. A. Make sure the form's Visible property is not being set to Ture at design-time or run-time. ------------------------------------------------------------------------ Q. Why do I get the message 'Unable to load RPTSMITH.EXE' when I double click on the TReport componet on the form? It should bring up ReportSmith. A. Either the [ReportSmith] section is missing or incorrect in the DELPHI.INI file. Make sure that it specifies the correct path. e.g. [ReportSmith] ExePath=C:\RPTSMITH