delsec05.txt

《Delphi开发人员指南》配书原码

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