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Added safeguard against failure in __del__.
author Guido van Rossum <guido@python.org>
date Wed, 27 Nov 1996 19:39:58 +0000
parents 3b3870b9acf2
children 4722d37faa14
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1 <HTML><HEAD><TITLE>Using FrameWork and TextEdit</TITLE></HEAD>
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2 <BODY>
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3 <H1>Using FrameWork and TextEdit</H1>
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4 <HR>
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5
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6 In this document we use the <CODE>FrameWork</CODE> and <CODE>TextEdit</CODE>
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7 modules to create a simple text editor. The functionality
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8 of the editor is very basic: you can open multiple files, type text and use
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9 cut/copy/paste. The main intention is to explain the use of FrameWork, really. <p>
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10
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11 <H2>FrameWork</H2>
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12
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13 The FrameWork module provides you with a skeleton application. It declares a
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14 number of classes suitable for subclassing in your application, thereby
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15 releaving you of the burden of doing all event handling, etc. yourself. For a
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16 real understanding you will have to browse the source. Here is a short overview
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17 of the classes and what functionality they provide.
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18
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19 <dl>
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20 <dt> <CODE>Application</CODE>
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21 <dd>
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22 This is the toplevel class you will override. It maintains the menu bar and contains
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23 the main event handling code. Normal use is to override the <code>__init__</code> routine
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24 to do your own initializations and override <code>makeusermenus</code> to create your menus
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25 (your menu callback routines may be here too, but this is by no means necessary).
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26 The event handling code can be overridden at various levels, from very low-level (the
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27 <code>dispatch</code> method) to intermedeate level (<code>do_keyDown</code>, for instance)
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28 to high-level (<code>do_key</code>). The application class knows about the <code>Window</code>
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29 objects you create, and will forward events to the appropriate window (So, normally you
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30 would have a <code>do_key</code> method in your window object, not your application object).
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31
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32 <dt> <CODE>MenuBar</CODE>, <CODE>Menu</CODE> and <CODE>MenuItem</CODE>
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33 <dd>
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34 These classes (and a few friends like <CODE>SubMenu</CODE>) handle your menus. You would not
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35 normally override them but use them as-is. The idiom for creating menus is a bit strange,
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36 see the test code at the bottom of FrameWork for sample use. The apple menu is handled for you
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37 by <CODE>MenuBar</CODE> and <CODE>Application</CODE>.
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38
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39 <dt> <CODE>Window</CODE>
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40 <dd>
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41 The basic window. Again, a class that you normally subclass in your application, possibly
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42 multiple times if you have different types of windows. The init call instantiates the data
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43 structure but actually opening the window is delayed until you call <code>open</code>. Your
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44 open method should call <code>do_postopen</code> to let the base class handle linking in to
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45 the application object. Similarly with <code>close</code> and <code>do_postclose</code>. The
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46 rest of the code is mainly event-oriented: you override <code>do_postresize</code>,
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47 <code>do_contentclick</code>, <code>do_update</code>, <code>do_activate</code>
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48 and <code>do_key</code> to "do your thing". When these methods are called the relevant environment
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49 has been setup (like <code>BeginDrawing</code> has been called for updates, etc).
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50
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51 <dt> <CODE>windowbounds</CODE>
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52 <dd>
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53 Not a class but a function: you pass it a width and height and it will return you a rectangle
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54 you can use to create your window. It will take care of staggering windows and it will try
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55 to fit the window on the screen (but the resulting rect will <em>always</em> have the size you
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56 specify).
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57
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58 <dt> <CODE>ControlsWindow</CODE>
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59 <dd>
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60 A subclass of Window which automatically handles drawing and clicking for controls. You override
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61 the same methods as for Window (if you need to: control-related things are done automatically) and
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62 <code>do_controlhit</code>.
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63
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64 <dt> <CODE>ScrolledWindow</CODE>
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65 <dd>
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66 A subclass of ControlsWindow, a window with optional scrollbars. If you override <code>do_activate</code>
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67 or <code>do_postresize</code> you must call the ScrolledWindow methods at the end of your override.
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68 You call <code>scrollbars</code> to enable/disable scrollbars and <code>updatescrollbars</code> to
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69 update them. You provide <code>getscrollbarvalues</code> to return the current x/y values (a helper
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70 method <code>scalebarvalues</code> is available) and <code>scrollbarcallback</code> to update your
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71 display after the user has used the scrollbars.
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72
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73 <dt> <CODE>DialogWindow</CODE>
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74 <dd>
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75 A modeless dialog window initialized from a DLOG resource. See the
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76 <A HREF="example2.html">second Interslip example</A> for its useage.
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77 </dl>
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78
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79 <H2>A sample text editor</H2>
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80
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81 Let us have a look at <A HREF="textedit/ped.py">ped.py</A> (in the Demo:textedit folder), the Pathetic
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82 EDitor. It has multiple windows, cut/copy/paste and keyboard input, but that is about all. It looks
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83 as if you can resize the window but it does not work. Still, it serves as an example. We will improve
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84 on ped later, in a <A HREF="waste.html">waste-based example</A>. <p>
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85
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86 Ped creates two classes, <code>TEWindow</code> and <code>Ped</code>. Let us start with the latter one,
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87 which is a subclass of <code>FrameWork.Application</code> and our main application. The init function
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88 has little to do aside from the standard init: it remembers a window sequence number (for untitled windows),
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89 and sets things up for menu disable to work. Remember, the <code>makeusermenus</code> is called
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90 automatically. <p>
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91
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92 <code>Makeusermenus</code> creates the <code>File</code> and <code>Edit</code> menus. It also initializes
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93 a couple of lists that are used later to correctly enable and disable menu items (and complete menus) depending
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94 on whether a window is open, text is selected, etc. The callback functions for the menu items are
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95 all methods of this class. <p>
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96
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97 <code>Updatemenubar</code> handles greying out (and re-enabling) of menu items depending on whether there
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98 is a current window and its state. <p>
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99
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100 The rest of the methods are all callbacks and simple to understand. They check whether there is an active
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101 window (and complain loudly if there is none: the corresponding menu entry should have been disabled
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102 in that case!) and call the appropriate window method. Only the <code>_open</code> method (the common code
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103 for <code>Open</code> and <code>New</code>) deserves some mention. It instantiates a <code>TEWindow</code>
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104 object and opens it with the title, filename and contents of the file to edit. Note that FrameWork takes
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105 care of remembering the window object. A minor note on opening the file in binary mode: this is because
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106 TextEdit expects MacOS style carriage-return terminated lines, not python/unix/C style newline-terminated
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107 lines. <p>
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108
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109 Oh yes: the <code>quit</code> callback does a little magic too. It closes all windows, and only if this
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110 succeeds it actually quits. This gives the user a chance to cancel the operation if some files are unsaved.
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111 <p>
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112
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113 Lastly, there is the <code>idle</code> method, called by the Application base class when no event
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114 is available. It is forwarded to the active window, so it can blink the text caret. <p>
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115
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116 The <code>TEWindow</code> object handles a single window. Due to this structuring it is absolutely no
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117 problem to have multiple windows open at the same time (although a real application should exercise care when
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118 two windows refer to the same document). TEWindow uses the standard init code inherited from
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119 <code>ScrolledWindow</code>, and sets itself up at the time of the <code>open</code> call. It obtains screen
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120 coordinates, opens the window, creates rectangles for TextEdit to work in (the magical number <code>15</code>
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121 here is the size of a normal scroll bar: unfortunately there is no symbolic constant for it),
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122 creates the TextEdit object and initializes it with our data. Finally, the scroll bars are created (the
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123 initial values will be obtained automatically through <code>getscrollbarvalues</code>) and we activate
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124 ourselves (this is unfortunately not done automatically by the MacOS event handling code). <p>
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125
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126 <code>Do_idle</code> simply calls the TextEdit routine that blinks the cursor. <code>Getscrollbarvalues</code>
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127 returns the current X and Y scrollbar values, scaled to <code>0..32767</code>. For X we return <code>None</code>,
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128 which means "no scrollbar, please", for Y we use the scaler provided by <code>ScrolledWindow</code>. <p>
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129
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130 <code>Scrollbar_callback</code> is called when the user uses the scrollbar. It is passed a string <code>'x'</code>
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131 or <code>'y'</code>, one of <code>'set', '-', '--', '+', '++'</code> and (for <code>set</code>) an absolute
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132 value. Note that the sign of the value passed to <code>TEPinScroll</code> is counter-intuitive. <p>
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133
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134 <code>do_activate</code> (de)activates the scrollbars and calls the relevant TextEdit routine. Moreover, it
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135 tells the application object if we are now the active window, and updates the menubar. The next few methods
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136 are update and menu callbacks, and pretty straightforward. Note that <code>do_close</code> can
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137 return without closing the window (if the document is changed and the users cancels out of the operation).
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138 Also note the "magic" in <code>menu_save_as</code>
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139 that set the correct window title. <p>
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140
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141 Things get moderately interesting again at the cut/copy/paste handling, since the TextEdit scrap is
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142 separate from the desktop scrap. For that reason there are various calls to routines that move the scrap
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143 back and forth. <code>Have_selection</code> is called by the menubar update code to determine whether cut and
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144 copy should be enabled. <p>
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145
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146 Understanding the main program is left as an exercise to the reader. <p>
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147
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148 <hr>
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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
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150 TextEdit compatible library with more functionality, to rebuild our editor. Or you can
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151 return to the <A HREF="index.html">table of contents</A> to pick another topic. <p>