Mac/Demo/textedit.html

   1 <HTML><HEAD><TITLE>Using FrameWork and TextEdit</TITLE></HEAD>
   2 <BODY>
   3 <H1>Using FrameWork and TextEdit</H1>
   4 <HR>
   5
   6 In this document we use the <CODE>FrameWork</CODE> and <CODE>TextEdit</CODE>
   7 modules to create a simple text editor. The functionality
   8 of the editor is very basic: you can open multiple files, type text and use
   9 cut/copy/paste. The main intention is to explain the use of FrameWork, really. <p>
  10
  11 <H2>FrameWork</H2>
  12
  13 The FrameWork module provides you with a skeleton application. It declares a
  14 number of classes suitable for subclassing in your application, thereby
  15 releaving you of the burden of doing all event handling, etc. yourself. For a
  16 real understanding you will have to browse the source. Here is a short overview
  17 of the classes and what functionality they provide.
  18
  19 <dl>
  20 <dt> <CODE>Application</CODE>
  21 <dd>
  22 This is the toplevel class you will override. It maintains the menu bar and contains
  23 the main event handling code. Normal use is to override the <code>__init__</code> routine
  24 to do your own initializations and override <code>makeusermenus</code> to create your menus
  25 (your menu callback routines may be here too, but this is by no means necessary).
  26 The event handling code can be overridden at various levels, from very low-level (the
  27 <code>dispatch</code> method) to intermedeate level (<code>do_keyDown</code>, for instance)
  28 to high-level (<code>do_key</code>). The application class knows about the <code>Window</code>
  29 objects you create, and will forward events to the appropriate window (So, normally you
  30 would have a <code>do_key</code> method in your window object, not your application object).
  31
  32 <dt> <CODE>MenuBar</CODE>, <CODE>Menu</CODE> and <CODE>MenuItem</CODE>
  33 <dd>
  34 These classes (and a few friends like <CODE>SubMenu</CODE>) handle your menus. You would not
  35 normally override them but use them as-is. The idiom for creating menus is a bit strange,
  36 see the test code at the bottom of FrameWork for sample use. The apple menu is handled for you
  37 by <CODE>MenuBar</CODE> and <CODE>Application</CODE>.
  38
  39 <dt> <CODE>Window</CODE>
  40 <dd>
  41 The basic window. Again, a class that you normally subclass in your application, possibly
  42 multiple times if you have different types of windows. The init call instantiates the data
  43 structure but actually opening the window is delayed until you call <code>open</code>. Your
  44 open method should call <code>do_postopen</code> to let the base class handle linking in to
  45 the application object. Similarly with <code>close</code> and <code>do_postclose</code>. The
  46 rest of the code is mainly event-oriented: you override <code>do_postresize</code>,
  47 <code>do_contentclick</code>, <code>do_update</code>, <code>do_activate</code>
  48 and <code>do_key</code> to "do your thing". When these methods are called the relevant environment
  49 has been setup (like <code>BeginDrawing</code> has been called for updates, etc).
  50
  51 <dt> <CODE>windowbounds</CODE>
  52 <dd>
  53 Not a class but a function: you pass it a width and height and it will return you a rectangle
  54 you can use to create your window. It will take care of staggering windows and it will try
  55 to fit the window on the screen (but the resulting rect will <em>always</em> have the size you
  56 specify).
  57
  58 <dt> <CODE>ControlsWindow</CODE>
  59 <dd>
  60 A subclass of Window which automatically handles drawing and clicking for controls. You override
  61 the same methods as for Window (if you need to: control-related things are done automatically) and
  62 <code>do_controlhit</code>.
  63
  64 <dt> <CODE>ScrolledWindow</CODE>
  65 <dd>
  66 A subclass of ControlsWindow, a window with optional scrollbars. If you override <code>do_activate</code>
  67 or <code>do_postresize</code> you must call the ScrolledWindow methods at the end of your override.
  68 You call <code>scrollbars</code> to enable/disable scrollbars and <code>updatescrollbars</code> to
  69 update them. You provide <code>getscrollbarvalues</code> to return the current x/y values (a helper
  70 method <code>scalebarvalues</code> is available) and <code>scrollbarcallback</code> to update your
  71 display after the user has used the scrollbars.
  72
  73 <dt> <CODE>DialogWindow</CODE>
  74 <dd>
  75 A modeless dialog window initialized from a DLOG resource. See the
  76 <A HREF="example2.html">second Interslip example</A> for its useage.
  77 </dl>
  78
  79 <H2>A sample text editor</H2>
  80
  81 Let us have a look at <A HREF="textedit/ped.py">ped.py</A> (in the Demo:textedit folder), the Pathetic
  82 EDitor. It has multiple windows, cut/copy/paste and keyboard input, but that is about all. It looks
  83 as if you can resize the window but it does not work. Still, it serves as an example. We will improve
  84 on ped later, in a <A HREF="waste.html">waste-based example</A>. <p>
  85
  86 Ped creates two classes, <code>TEWindow</code> and <code>Ped</code>. Let us start with the latter one,
  87 which is a subclass of <code>FrameWork.Application</code> and our main application. The init function
  88 has little to do aside from the standard init: it remembers a window sequence number (for untitled windows),
  89 and sets things up for menu disable to work. Remember, the <code>makeusermenus</code> is called
  90 automatically. <p>
  91
  92 <code>Makeusermenus</code> creates the <code>File</code> and <code>Edit</code> menus. It also initializes
  93 a couple of lists that are used later to correctly enable and disable menu items (and complete menus) depending
  94 on whether a window is open, text is selected, etc. The callback functions for the menu items are
  95 all methods of this class. <p>
  96
  97 <code>Updatemenubar</code> handles greying out (and re-enabling) of menu items depending on whether there
  98 is a current window and its state. <p>
  99
 100 The rest of the methods are all callbacks and simple to understand. They check whether there is an active
 101 window (and complain loudly if there is none: the corresponding menu entry should have been disabled
 102 in that case!) and call the appropriate window method. Only the <code>_open</code> method (the common code
 103 for <code>Open</code> and <code>New</code>) deserves some mention. It instantiates a <code>TEWindow</code>
 104 object and opens it with the title, filename and contents of the file to edit. Note that FrameWork takes
 105 care of remembering the window object. A minor note on opening the file in binary mode: this is because
 106 TextEdit expects MacOS style carriage-return terminated lines, not python/unix/C style newline-terminated
 107 lines. <p>
 108
 109 Oh yes: the <code>quit</code> callback does a little magic too. It closes all windows, and only if this
 110 succeeds it actually quits. This gives the user a chance to cancel the operation if some files are unsaved.
 111 <p>
 112
 113 Lastly, there is the <code>idle</code> method, called by the Application base class when no event
 114 is available. It is forwarded to the active window, so it can blink the text caret. <p>
 115
 116 The <code>TEWindow</code> object handles a single window. Due to this structuring it is absolutely no
 117 problem to have multiple windows open at the same time (although a real application should exercise care when
 118 two windows refer to the same document). TEWindow uses the standard init code inherited from
 119 <code>ScrolledWindow</code>, and sets itself up at the time of the <code>open</code> call. It obtains screen
 120 coordinates, opens the window, creates rectangles for TextEdit to work in (the magical number <code>15</code>
 121 here is the size of a normal scroll bar: unfortunately there is no symbolic constant for it),
 122 creates the TextEdit object and initializes it with our data. Finally, the scroll bars are created (the
 123 initial values will be obtained automatically through <code>getscrollbarvalues</code>) and we activate
 124 ourselves (this is unfortunately not done automatically by the MacOS event handling code). <p>
 125
 126 <code>Do_idle</code> simply calls the TextEdit routine that blinks the cursor. <code>Getscrollbarvalues</code>
 127 returns the current X and Y scrollbar values, scaled to <code>0..32767</code>. For X we return <code>None</code>,
 128 which means "no scrollbar, please", for Y we use the scaler provided by <code>ScrolledWindow</code>. <p>
 129
 130 <code>Scrollbar_callback</code> is called when the user uses the scrollbar. It is passed a string <code>'x'</code>
 131 or <code>'y'</code>, one of <code>'set', '-', '--', '+', '++'</code> and (for <code>set</code>) an absolute
 132 value. Note that the sign of the value passed to <code>TEPinScroll</code> is counter-intuitive. <p>
 133
 134 <code>do_activate</code> (de)activates the scrollbars and calls the relevant TextEdit routine. Moreover, it
 135 tells the application object if we are now the active window, and updates the menubar. The next few methods
 136 are update and menu callbacks, and pretty straightforward. Note that <code>do_close</code> can
 137 return without closing the window (if the document is changed and the users cancels out of the operation).
 138 Also note the "magic" in <code>menu_save_as</code>
 139 that set the correct window title. <p>
 140
 141 Things get moderately interesting again at the cut/copy/paste handling, since the TextEdit scrap is
 142 separate from the desktop scrap. For that reason there are various calls to routines that move the scrap
 143 back and forth. <code>Have_selection</code> is called by the menubar update code to determine whether cut and
 144 copy should be enabled. <p>
 145
 146 Understanding the main program is left as an exercise to the reader. <p>
 147
 148 <hr>
 149 That's all for this example, you could now continue with the <A HREF="waste.html">next example</A>, where we use WASTE, a more-or-less
 150 TextEdit compatible library with more functionality, to rebuild our editor. Or you can
 151 return to the <A HREF="index.html">table of contents</A> to pick another topic. <p>