Mac/Demo/example2.html

   1 <HTML><HEAD><TITLE>Using python to create Macintosh applications, part two</TITLE></HEAD>
   2 <BODY>
   3 <H1>Using python to create Macintosh applications, part two</H1>
   4 <HR>
   5
   6 In this document we rewrite the application of the <A
   7 HREF="example1.html">previous example</A> to use modeless dialogs. We
   8 will use an application framework, and we will have a look at creating
   9 applets, standalone applications written in Python.  <A
  10 HREF="example2/InterslipControl-2.py">Source</A> and resource file (in
  11 binary and <A HREF="example2/InterslipControl-2.rsrc.hqx">BinHex</A>
  12 form for downloading) are available in the folder <A
  13 HREF="example2">example2</A>.  If you want to run the program on your
  14 machine and you have Python 1.3 or earlier you will also need a new copy of <A
  15 HREF="update-to-1.3/FrameWork.py">FrameWork.py</A>, which has been
  16 updated since the 1.3 release. <p>
  17
  18 Again, we start with ResEdit to create our dialogs. Not only do we
  19 want a main dialog this time but also an "About" dialog, and we
  20 provide the <A NAME="bundle">BNDL resource</A> and related stuff that
  21 an application cannot be without. (Actually, a python applet can be
  22 without, <A HREF="#no-bundle">see below</A>). "Inside Mac" or various
  23 books on macintosh programming will help here. Also, you can refer to
  24 the resource files provided in the Python source distribution for some
  25 of the python-specific points of BNDL programming: the
  26 "appletbundle.rsrc" file is what is used for creating applets if you
  27 don't provide your own resource file. <p>
  28
  29 Let's have a look at InterslipControl-2.rsrc, our resource file. First
  30 off, there's the standard BNDL combo. I've picked 'PYTi' as signature
  31 for the application. I tend to pick PYT plus one lower-case letter for
  32 my signatures.  The finder gets confused if you have two applications
  33 with the same signature. This may be due to some incorrectness on the
  34 side of "mkapplet", I am not sure.  There is one case when you
  35 definitely need a unique signature: when you create an applet that has
  36 its own data files and you want the user to be able to start your
  37 applet by double-clicking one of the datafiles. <p>
  38
  39 There's little to tell about the BNDL stuff: I basically copied the
  40 generic Python applet icons and pasted in the symbol for
  41 InterSLIP. The two dialogs are equally unexciting: dialog 512 is our
  42 main window which has four static text fields (two of which we will be
  43 modifying during runtime, to show the status of the connection) and
  44 two buttons "connect" and "disconnect". The "quit" and "update status"
  45 buttons have disappeared, because they are handled by a menu choice
  46 and automatically, respectively. <p>
  47
  48 <H2>A modeless dialog application using FrameWork</H2>
  49
  50 On to the source code in <A
  51 HREF="example2/InterslipControl-2.py">InterslipControl-2.py</A>.  The
  52 start is similar to our previous example program <A
  53 HREF="example1/InterslipControl-1.py">InterSlipControl-1.py</A>, with
  54 one extra module being imported. To make life more simple we will use
  55 the <CODE>FrameWork</CODE> module, a nifty piece of code that handles
  56 all the gory mac details of event loop programming, menubar
  57 installation and all the other code that is the same for every mac
  58 program in the world.  Like most standard modules, FrameWork will run
  59 some sample test code when you invoke it as a main program, so try it
  60 now. It will create a menu bar with an Apple menu with the about box
  61 and a "File" menu with some pythonesque choices (which do nothing
  62 interesting, by the way) and a "Quit" command that works. <p>
  63
  64 <BLOCKQUOTE>
  65 If you have not used <code>FrameWork</code> before you may want to
  66 first take a look at the <A HREF="textedit.html">Pathetic EDitor</A>
  67 example, which builds a minimal text editor using FrameWork and TextEdit.
  68 On the other hand: we don't use many features of FrameWork, so you could
  69 also continue with this document.
  70 </BLOCKQUOTE>
  71
  72 After the imports we get the definitions of resource-IDs in our
  73 resource file, slightly changed from the previous version of our
  74 program, and the state to string mapping. The main program is also
  75 similar to our previous version, with one important exception: we
  76 first check to see whether our resource is available before opening
  77 the resource file. Why is this? Because later, when we will have
  78 converted the script to an applet, our resources will be available in
  79 the applet file and we don't need the separate resource file
  80 anymore. <p>
  81
  82 Next comes the definition of our main class,
  83 <CODE>InterslipControl</CODE>, which inherits
  84 <CODE>FrameWork.Application</CODE>. The Application class handles the
  85 menu bar and the main event loop and event dispatching. In the
  86 <CODE>__init__</CODE> routine we first let the base class initialize
  87 itself, then we create our modeless dialog and finally we jump into
  88 the main loop. The main loop continues until <CODE>self</CODE> is
  89 raised, which we will do when the user selects "quit". When we create
  90 the instance of <CODE>MyDialog</CODE> (which inherits
  91 <CODE>DialogWindow</CODE>, which inherits <CODE>Window</CODE>) we pass
  92 a reference to the application object, this reference is used to tell
  93 Application about our new window.  This enables the event loop to keep
  94 track of all windows and dispatch things like update events and mouse
  95 clicks. <p>
  96
  97 The <CODE>makeusermenus()</CODE> method (which is called sometime
  98 during the Application <CODE>__init__</CODE> routine) creates a File
  99 menu with a Quit command (shortcut command-Q), which will callback to
 100 our quit() method. <CODE>Quit()</CODE>, in turn, raises 'self' which
 101 causes the mainloop to terminate. <p>
 102
 103 Application provides a standard about box, but we override this by
 104 providing our own <CODE>do_about()</CODE> method which shows an about
 105 box from a resource as a modal dialog. This piece of code should look
 106 familiar to you from the previous example program. That do_about is
 107 called when the user selects About from the Apple menu is, again,
 108 taken care of by the __init__ routine of Application. <p>
 109
 110 Our main object finally overrides <CODE>idle()</CODE>, the method
 111 called when no event is available. It passes the call on to our dialog
 112 object to give it a chance to update the status fields, if needed. <p>
 113
 114 The <CODE>MyDialog</CODE> class is the container for our main
 115 window. Initialization is again done by first calling the base class
 116 <CODE>__init__</CODE> function and finally setting two local variables
 117 that are used by <CODE>updatestatus()</CODE> later. <p>
 118
 119 <CODE>Do_itemhit()</CODE> is called when an item is selected in this
 120 dialog by the user. We are passed the item number (and the original
 121 event structure, which we normally ignore). The code is similar to the
 122 main loop of our previous example program: a switch depending on the
 123 item selected.  <CODE>Connect()</CODE> and <CODE>disconnect()</CODE>
 124 are again quite similar to our previous example. <p>
 125
 126 <CODE>Updatestatus()</CODE> is different, however. It is now
 127 potentially called many times per second instead of only when the
 128 user presses a button we don't want to update the display every time
 129 since that would cause some quite horrible flashing. Luckily,
 130 <CODE>interslip.status()</CODE> not only provides us with a state and
 131 a message but also with a message sequence number. If neither state
 132 nor message sequence number has changed since the last call there is
 133 no need to update the display, so we just return. For the rest,
 134 nothing has changed. <p>
 135
 136 <H2><IMG SRC="html.icons/mkapplet.gif"><A NAME="applets">Creating applets</A></H2>
 137
 138 Now, if you have a PowerPC Macintosh, let us try to turn the python
 139 script into an applet, a standalone application.  Actually,
 140 "standalone" is probably not the correct term here, since an applet
 141 does still depend on a lot of the python environment: the PythonCore
 142 shared library, the Python Preferences file, the python Lib folder and
 143 any other modules that the main module depends on. It is possible to
 144 get rid of all these dependencies except for the dependency on
 145 PythonCore, but at the moment that is still quite difficult so we will
 146 ignore that possibility for now. By standalone we mean here that the
 147 script has the look-and-feel of an application, including the ability
 148 to have its own document types, be droppable, etc. <p>
 149
 150 The easiest way to create an applet is to take your source file and
 151 drop it onto "mkapplet" (normally located in the Python home
 152 folder). This will create an applet with the same name as your python
 153 source with the ".py" stripped. Also, if a resource file with the same
 154 name as your source but with ".rsrc" extension is available the
 155 resources from that file will be copied to your applet too. If there
 156 is no resource file for your script a set of default resources will be
 157 used, and the applet will have the default creator 'PYTa'. The latter
 158 also happens if you do have a resource file but without the BNDL
 159 combo. <A NAME="no-bundle">Actually</A>, for our example that would
 160 have been the most logical solution, since our applet does not have
 161 its own data files.  It would have saved us hunting for an unused
 162 creator code. The only reason for using the BNDL in this case is
 163 having the custom icon, but that could have been done by pasting an
 164 icon on the finder Info window, or by providing an custon icon in your
 165 resource file and setting the "custom icon" finder bit. <p>
 166
 167 If you need slightly more control over the mkapplet process you can
 168 double-click mkapplet, and you will get dialogs for source and
 169 destination of the applet. The rest of the process, including locating
 170 the resource file, remains the same. <p>
 171
 172 Note that though our example application completely bypasses the
 173 normal python user interface this is by no means necessary. Any python
 174 script can be turned into an applet, and all the usual features of the
 175 interpreter still work. <p>
 176
 177 That's all for this example, you may now return to the <A HREF="index.html">
 178 table of contents</A> to pick another topic. <p>