ch13.htm

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Editor and return to the Form Designer.</P>


<BLOCKQUOTE>
	<P>
<HR>
<strong>NOTE:</strong> When you modify the Panels property of a StatusBar component, the
	Form Designer automatically sets the SimplePanel property to False. The assumption
	is that if you are using multiple panels, you don't want to have a simple status
	bar. 
<HR>


</BLOCKQUOTE>

<H4>Changing Text in the Status Bar</H4>
<P>There are two ways to change text in a status bar:</P>

<UL>
	<LI>Manually modify the SimpleText property of the status bar (for simple status
	bars) or the Text property of an individual panel (for complex status bars).
	<P>
	<LI>Let VCL automatically supply the status bar text by setting the AutoHint property
	to True.
</UL>

<P>Manually changing the text in the status bar is simple, particularly if you have
a simple status bar. When the SimplePanel property is True, you can set the SimpleText
property to the text you want displayed in the status bar:</P>
<P>
<PRE>StatusBar.SimpleText := `This shows up in the status bar.';
</PRE>
<P>In the case of complex status bars, changing the text is only slightly more complicated.
If you want to change the text for the first panel of a complex status bar, you would
use something like this:</P>
<P>
<PRE>StatusBar.Panels[0].Text := `Status Bar Text';
</PRE>
<P>The Panels property of the StatusBar component has a property called Items that
is an array of panels in the status bar. Setting the Text property for an element
in the Items array changes the text for that panel (because Items is the default
array property for the Panels object, you don't have to specifically reference Items).
As you can see, the array is 0-based. The first panel in the status bar is array
element 0.</P>
<P>Automatic status bar hint text doesn't require much in the way of explanation.
All you have to do is set the AutoHint property to True. The rest is, as the property
name implies, automatic.</P>


<BLOCKQUOTE>
	<P>
<HR>
<strong>NOTE:</strong> You can still modify the status bar's text manually even when using
	AutoHint. There's nothing to stop you from changing the text manually, but remember
	that the text will be replaced the next time the mouse passes over a component with
	hint text. 
<HR>


</BLOCKQUOTE>

<H4>Owner-Drawn Status Bar Panels</H4>
<P>Earlier I said that a panel's Style property can be either psText or psOwnerDraw.
When you set a panel's style to psOwnerDraw, you must take the responsibility of
drawing anything in the panel that needs to be displayed there. It is unlikely that
you are going to go to the trouble of using an owner-drawn panel just to display
text. Usually it means you are going to display some sort of icon or bitmap in the
status bar. Regardless of what is being drawn on the panel, the steps are the same:</P>

<DL>
	<DD><B>1. </B>Set the panel's Style property to psOwnerDraw (usually via the StatusBar
	Panels Editor).
	<DT></DT>
	<DD><B>2. </B>Respond to the OnDrawPanel event.
	<P>
</DL>

<P>Obviously, the real work here is going to take place in the event handler for
the OnDrawPanel event. The declaration for the OnDrawPanel event handler looks like
this:</P>
<P>
<PRE>procedure TForm1.StatusBar1DrawPanel(StatusBar: TStatusBar;
  Panel: TStatusPanel; const Rect: TRect);
</PRE>
<P>The StatusBar parameter is a pointer to the status bar. Usually you have a pointer
to the status bar anyway (the Name property of the StatusBar component), so this
parameter is not all that useful unless you are using multiple owner-drawn status
bars. The Panel property is a pointer to the particular panel that currently needs
drawing. You can use this parameter to determine which panel needs drawing if you
have more than one owner-drawn panel in your status bar. The Rect parameter contains
the panel's size and position. The Rect parameter is important because it tells you
the exact dimensions of the drawing area.</P>
<P>The OnDrawPanel event handler is called once for each panel that has its Style
property set to psOwnerDraw. If you have only one panel to draw, you don't have to
worry about much except the Rect parameter. If you have multiple panels to draw,
you must first determine which panel to draw and then do your drawing. An illustration
might help to explain this. The book's code includes a program called StatBar that
illustrates some of the things you can do with status bars. Run the program and examine
its source for tips on implementing status bars in your applications. Figure 13.6
shows the StatBar program running.</P>
<P><A HREF="javascript:popUp('28671306.gif')"><B>FIGURE 13.6.</B></A><B> </B><I>The
StatBar program with owner-drawn status bar panels.</I></P>

<P>As you can see, the status bar in this program has multiple panels. The middle
three panels are owner-drawn. The panels marked OVR and EXT simulate the status bar
on a word processing program or code editor. In those types of programs, the Overtype
or Extended Selection modes might be on or off. If the mode is on, the text in the
status bar panel shows in black. If the mode is off, the text has a 3D disabled-text
appearance. The third owner-drawn panel displays a stock Windows icon to illustrate
the use of a graphic on a status bar. Run the program and experiment with it to learn
how it works.</P>
<P>Listing 13.1 shows the OnDrawPanel event handler from the StatBar program. Examine
it and read the comments to understand what is going on in the code.</P>
<P>
<H4>LISTING 13.1. THE StatusBarDrawPanel METHOD OF THE StatBar PROGRAM.</H4>
<PRE>procedure TMainForm.StatusBarDrawPanel(StatusBar: TStatusBar;
  Panel: TStatusPanel; const Rect: TRect);
var
  R : TRect;
  Icon : HIcon;
begin
  with StatusBar.Canvas do begin
    { Create a temporary TRect object. The Rect parameter
    { is const so we can't change it. }
    R := Rect;
    { Check to see if panel 3 is the panel which needs
    { to be drawn. If so, draw an icon in the panel. }
    if Panel.Index = 3 then begin
        { Load one of the stock Windows icons. This time
        { using the API is easier than using VCL. }
        Icon := LoadIcon(0, IDI_HAND);
        { Draw the icon and shrink it down to 15 x 15 pixels. }
        { Center it in the panel, too. }
        DrawIconEx(Handle, Rect.Left + 6, 3,
          Icon, 15, 15, 0, 0, DI_NORMAL);
        { Nothing more to do. }
        Exit;
    end;
    { This rather lengthy if statement checks to see if
    { either the Overtype Mode or Extended Selection
    { check boxes are checked. If so, then what we need
    { to do is to draw the text twice. First, we draw it
    { in white. Then we draw it again, offset by 1 pixel,
    { in gray. The effect is a 3D disabled-text look. }
    if ((Panel.Index = 1) and (OvrMode.Checked = False)) or
      ((Panel.Index = 2) and (ExtendedSel.Checked = False))
        then begin
      { Move over and down one pixel for the offset. }
      Inc(R.Left);
      Inc(R.Top, 2);
      { Change the text color to white. }
      Font.Color := clWhite;
      { Set the backround mode to transparent so the
      { text appears hollow and so that the white
      { text can be seen under the gray. }
      Brush.Style := bsClear;
      { Draw the text using the API function DrawText. }
      { I use DrawText because it allows me to center
      { the text both horizontally and vertically within
      { the given rectangle. }
      DrawText(Handle, PChar(Panel.Text), -1,
        R, DT_CENTER or DT_VCENTER or DT_SINGLELINE);
      { Set the color to gray because we're going to
      { draw the text in gray in a moment. }
      Font.Color := clGray;
</PRE>
<PRE>      { Set the rect back to the original size. }
</PRE>
<PRE>      Dec(R.Left);
      Dec(R.Top, 2);
    end;
    { Display the text. If the item is not disabled then
    { the default color (black) is used to draw the text. }
    { If the item is disabled, then the text color has
    { been set to gray by the code above. }
    DrawText(Handle, PChar(Panel.Text), -1,
      R, DT_CENTER or DT_VCENTER or DT_SINGLELINE);
  end;
end;
</PRE>
<P>This code might seem intimidating, but most of it is comment lines. The code itself
is relatively simple. The comment lines explain what is happening at each step: The
3D appearance for the disabled text is accomplished by drawing the text once in white
and then drawing it again in gray with a slight offset. The result is that the text
looks recessed. The icon is displayed using the Windows API functions LoadIcon and
DrawIconEx.</P>
<P>Owner drawing of status bar panels is daunting at first, but you'll soon find
out that it's not all that bad. You might write Windows applications for a long time
and never need owner-drawn panels in your status bar. If you ever need them, however,
you'll know that's not impossible to accomplish.</P>
<P>
<H2><A NAME="Heading7"></A>Adding Functionality with Command Enabling</H2>
<P><I>Command enabling</I> is the process of enabling or disabling buttons depending
on current conditions. For example, there's not much point of having the Cut or Copy
button or menu item enabled for a text editor when no text is currently selected.
Likewise, if there is no text in the Clipboard, the Paste button should be disabled.</P>
<P>Command enabling isn't difficult, especially with Delphi's new TActionList component.
Still, it takes time to get right. It takes time because you have to pay attention
to detail. (Sometimes it is attention to detail that separates the great applications
from the mediocre applications.)</P>
<P>
<H3><A NAME="Heading8"></A>Command Enabling with TActionList and TAction</H3>
<P>The TAction class provides a convenient way of performing command enabling. TActionList,
the nonvisual component that manages actions, is found on the Additional tab of the
Component palette. TActionList, as its name implies, contains a list of TAction objects.
You create an action and then assign that action to any controls that need to be
enabled or disabled based on that action. By controls I mean menu items, toolbar
buttons, context menu items, and so on.</P>
<P>Let's take the Edit|Cut menu item, for example. You could have at least three
objects associated with this particular task:</P>

<UL>
	<LI>A main menu item
	<P>
	<LI>A toolbar button
	<P>
	<LI>A pop-up menu item
</UL>

<P>You create actions with the ActionList Editor. Given the Edit|Cut example, you
would create an action for Cut called, say, CutAction. Then, using the Object Inspector,
you assign CutAction to the Action property of each of the objects that correspond
to the cut operation (toolbar buttons and menus, for example). At runtime, when you
need to enable the Cut option, you can do so with just one line of code:</P>
<P>
<PRE>CutAction.Enabled := True;
</PRE>
<P>This will enable all components with their Action properties set to CutAction.
Disabling the Cut items is as simple as assigning False to the Enabled property of
the action. The OnUpdate event of TAction and TActionList provides a convenient place
to put your command-enabling code.</P>
<P>Command enabling with TAction is something that you have to experience to fully
appreciate. You add command enabling to ScratchPad in the next section.</P>
<P>
<H3><A NAME="Heading9"></A>Implementing Command Enabling</H3>
<P>In this section you implement command enabling for the ScratchPad program. First
you set up the ActionList component, and then you hook up the various components
to the action list.</P>
<P>
<H4>Creating an ActionList</H4>
<P>It all starts with the ActionList component, which is the heart of the command-enabling
system in VCL. First you add the actions for the Edit menu items. After that, you
add an action for the File menu's Save and Save As menu items. The following steps
will take you through the ActionList setup process.</P>
<P><B>Creating the Edit Menu Actions</B></P>
<P>The following steps show you how to create actions for the Edit menu's Cut, Copy,
and Paste items. Perform these steps:</P>

<DL>
	<DT></DT>
	<DD><B>1. </B>Place an ActionList component on the form and change the Name property
	to ActionList.
	<P>
	<DT></DT>
	<DD><B>2. </B>Double-click the ActionList icon to invoke the ActionList Editor.
	<P>
	<DT></DT>
	<DD><B>3. </B>Right-click on the ActionList Editor and choose New Standard Action
	from the context menu. Choose the TEditCopy action and click OK. Notice that the
	Object Inspector changes to show the properties of the TEditCopy action class.
	<P>
	<DT></DT>
	<DD>I want to pause for a moment here and explain more about how actions work. Examine
	the Object Inspector at this point. Notice that the TEditCopy action has several
	familiar properties and that those properties all have values. In particular, notice
	that the Caption, Hint, ImageIndex, and ShortCut properties already have values that
	correspond to an Edit menu's Copy item. These properties will be transferred to any
	control that you assign this action to, which means that you must set any properties
	of the action to the values that you want the corresponding components to acquire.
	That won't make much sense until you attach the action to components in the next
	section, but it will be clear at that time. Let's continue with the action creation
	process.
	<P>
	<DT></DT>
	<DD><B>4. </B>Change the new action's Name property to CopyAction, the Hint property
	to Copy|Copy to Clipboard, and the ImageIndex property to 3.
	<P>
	<DT></DT>
	<DD><B>5. </B>Create another standard action, this time a TEditCut action. Change
	the Name to CutAction, the Hint property to Cut|Cut to Clipboard, and the ImageIndex
	property to 4.
	<P>
	<DT></DT>
	<DD><B>6. </B>Create a third action, a TEditPaste action. Change the Name property
	to PasteAction, the Hint property to Paste|Paste from Clipboard, and the ImageIndex
	property to 5.
	<P>
</DL>

<P>You have now created the actions for the primary Edit menu items.</P>
<P><B>Creating the File Menu Actions</B></P>
<P>Next you need to create the actions for the File menu's Save and Save As menu