153 lines
9.5 KiB
HTML
153 lines
9.5 KiB
HTML
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<HTML><HEAD><TITLE>Using FrameWork and TextEdit</TITLE></HEAD>
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<BODY>
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<H1>Using FrameWork and TextEdit</H1>
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<HR>
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In this document we use the <CODE>FrameWork</CODE> and <CODE>TextEdit</CODE>
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modules to create a simple text editor. The functionality
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of the editor is very basic: you can open multiple files, type text and use
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cut/copy/paste. The main intention is to explain the use of FrameWork, really. <p>
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<H2>FrameWork</H2>
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The FrameWork module provides you with a skeleton application. It declares a
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number of classes suitable for subclassing in your application, thereby
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releaving you of the burden of doing all event handling, etc. yourself. For a
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real understanding you will have to browse the source. Here is a short overview
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of the classes and what functionality they provide.
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<dl>
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<dt> <CODE>Application</CODE>
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<dd>
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This is the toplevel class you will override. It maintains the menu bar and contains
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the main event handling code. Normal use is to override the <code>__init__</code> routine
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to do your own initializations and override <code>makeusermenus</code> to create your menus
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(your menu callback routines may be here too, but this is by no means necessary).
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The event handling code can be overridden at various levels, from very low-level (the
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<code>dispatch</code> method) to intermedeate level (<code>do_keyDown</code>, for instance)
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to high-level (<code>do_key</code>). The application class knows about the <code>Window</code>
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objects you create, and will forward events to the appropriate window (So, normally you
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would have a <code>do_key</code> method in your window object, not your application object).
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<dt> <CODE>MenuBar</CODE>, <CODE>Menu</CODE> and <CODE>MenuItem</CODE>
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<dd>
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These classes (and a few friends like <CODE>SubMenu</CODE>) handle your menus. You would not
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normally override them but use them as-is. The idiom for creating menus is a bit strange,
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see the test code at the bottom of FrameWork for sample use. The apple menu is handled for you
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by <CODE>MenuBar</CODE> and <CODE>Application</CODE>.
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<dt> <CODE>Window</CODE>
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<dd>
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The basic window. Again, a class that you normally subclass in your application, possibly
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multiple times if you have different types of windows. The init call instantiates the data
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structure but actually opening the window is delayed until you call <code>open</code>. Your
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open method should call <code>do_postopen</code> to let the base class handle linking in to
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the application object. Similarly with <code>close</code> and <code>do_postclose</code>. The
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rest of the code is mainly event-oriented: you override <code>do_postresize</code>,
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<code>do_contentclick</code>, <code>do_update</code>, <code>do_activate</code>
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and <code>do_key</code> to "do your thing". When these methods are called the relevant environment
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has been setup (like <code>BeginDrawing</code> has been called for updates, etc).
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<dt> <CODE>windowbounds</CODE>
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<dd>
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Not a class but a function: you pass it a width and height and it will return you a rectangle
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you can use to create your window. It will take care of staggering windows and it will try
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to fit the window on the screen (but the resulting rect will <em>always</em> have the size you
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specify).
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<dt> <CODE>ControlsWindow</CODE>
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<dd>
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A subclass of Window which automatically handles drawing and clicking for controls. You override
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the same methods as for Window (if you need to: control-related things are done automatically) and
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<code>do_controlhit</code>.
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<dt> <CODE>ScrolledWindow</CODE>
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<dd>
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A subclass of ControlsWindow, a window with optional scrollbars. If you override <code>do_activate</code>
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or <code>do_postresize</code> you must call the ScrolledWindow methods at the end of your override.
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You call <code>scrollbars</code> to enable/disable scrollbars and <code>updatescrollbars</code> to
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update them. You provide <code>getscrollbarvalues</code> to return the current x/y values (a helper
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method <code>scalebarvalues</code> is available) and <code>scrollbarcallback</code> to update your
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display after the user has used the scrollbars.
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<dt> <CODE>DialogWindow</CODE>
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<dd>
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A modeless dialog window initialized from a DLOG resource. See the
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<A HREF="example2.html">second Interslip example</A> for its useage.
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</dl>
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<H2>A sample text editor</H2>
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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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EDitor. It has multiple windows, cut/copy/paste and keyboard input, but that is about all. It looks
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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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on ped later, in a <A HREF="waste.html">waste-based example</A>. <p>
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Ped creates two classes, <code>TEWindow</code> and <code>Ped</code>. Let us start with the latter one,
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which is a subclass of <code>FrameWork.Application</code> and our main application. The init function
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has little to do aside from the standard init: it remembers a window sequence number (for untitled windows),
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and sets things up for menu disable to work. Remember, the <code>makeusermenus</code> is called
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automatically. <p>
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<code>Makeusermenus</code> creates the <code>File</code> and <code>Edit</code> menus. It also initializes
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a couple of lists that are used later to correctly enable and disable menu items (and complete menus) depending
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on whether a window is open, text is selected, etc. The callback functions for the menu items are
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all methods of this class. <p>
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<code>Updatemenubar</code> handles greying out (and re-enabling) of menu items depending on whether there
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is a current window and its state. <p>
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The rest of the methods are all callbacks and simple to understand. They check whether there is an active
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window (and complain loudly if there is none: the corresponding menu entry should have been disabled
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in that case!) and call the appropriate window method. Only the <code>_open</code> method (the common code
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for <code>Open</code> and <code>New</code>) deserves some mention. It instantiates a <code>TEWindow</code>
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object and opens it with the title, filename and contents of the file to edit. Note that FrameWork takes
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care of remembering the window object. A minor note on opening the file in binary mode: this is because
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TextEdit expects MacOS style carriage-return terminated lines, not python/unix/C style newline-terminated
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lines. <p>
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Oh yes: the <code>quit</code> callback does a little magic too. It closes all windows, and only if this
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succeeds it actually quits. This gives the user a chance to cancel the operation if some files are unsaved.
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Quitting itself is also a bit strange: you raise <code>self</code> to break out of the main loop. This bit
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of idiom was invented by Guido, so blame him:-). <p>
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Lastly, there is the <code>idle</code> method, called by the Application base class when no event
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is available. It is forwarded to the active window, so it can blink the text caret. <p>
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The <code>TEWindow</code> object handles a single window. Due to this structuring it is absolutely no
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problem to have multiple windows open at the same time (although a real application should exercise care when
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two windows refer to the same document). TEWindow uses the standard init code inherited from
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<code>ScrolledWindow</code>, and sets itself up at the time of the <code>open</code> call. It obtains screen
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coordinates, opens the window, creates rectangles for TextEdit to work in (the magical number <code>15</code>
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here is the size of a normal scroll bar: unfortunately there is no symbolic constant for it),
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creates the TextEdit object and initializes it with our data. Finally, the scroll bars are created (the
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initial values will be obtained automatically through <code>getscrollbarvalues</code>) and we activate
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ourselves (this is unfortunately not done automatically by the MacOS event handling code). <p>
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<code>Do_idle</code> simply calls the TextEdit routine that blinks the cursor. <code>Getscrollbarvalues</code>
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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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which means "no scrollbar, please", for Y we use the scaler provided by <code>ScrolledWindow</code>. <p>
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<code>Scrollbar_callback</code> is called when the user uses the scrollbar. It is passed a string <code>'x'</code>
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or <code>'y'</code>, one of <code>'set', '-', '--', '+', '++'</code> and (for <code>set</code>) an absolute
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value. Note that the sign of the value passed to <code>TEPinScroll</code> is counter-intuitive. <p>
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<code>do_activate</code> (de)activates the scrollbars and calls the relevant TextEdit routine. Moreover, it
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tells the application object if we are now the active window, and updates the menubar. The next few methods
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are update and menu callbacks, and pretty straightforward. Note that <code>do_close</code> can
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return without closing the window (if the document is changed and the users cancels out of the operation).
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Also note the "magic" in <code>menu_save_as</code>
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that set the correct window title. <p>
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Things get moderately interesting again at the cut/copy/paste handling, since the TextEdit scrap is
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separate from the desktop scrap. For that reason there are various calls to routines that move the scrap
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back and forth. <code>Have_selection</code> is called by the menubar update code to determine whether cut and
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copy should be enabled. <p>
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Understanding the main program is left as an exercise to the reader. <p>
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<hr>
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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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TextEdit compatible library with more functionality, to rebuild our editor. Or you can
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return to the <A HREF="index.html">table of contents</A> to pick another topic. <p>
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