projects / OpenSPARC-T2-SAM / blame
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| 55 | <H3><A NAME="SECTION0018167000000000000000"> | |
| 56 | 16.1.6.7 Bindings and Events</A> | |
| 57 | </H3> | |
| 58 | <P> | |
| 59 | <a id='l2h-4840' xml:id='l2h-4840'></a> | |
| 60 | ||
| 61 | <P> | |
| 62 | The bind method from the widget command allows you to watch for | |
| 63 | certain events and to have a callback function trigger when that event | |
| 64 | type occurs. The form of the bind method is: | |
| 65 | ||
| 66 | <P> | |
| 67 | <div class="verbatim"><pre> | |
| 68 | def bind(self, sequence, func, add=''): | |
| 69 | </pre></div> | |
| 70 | where: | |
| 71 | ||
| 72 | <P> | |
| 73 | <DL> | |
| 74 | <DT><STRONG>sequence</STRONG></DT> | |
| 75 | <DD>is a string that denotes the target kind of event. (See the bind | |
| 76 | man page and page 201 of John Ousterhout's book for details). | |
| 77 | ||
| 78 | <P> | |
| 79 | </DD> | |
| 80 | <DT><STRONG>func</STRONG></DT> | |
| 81 | <DD>is a Python function, taking one argument, to be invoked when the | |
| 82 | event occurs. An Event instance will be passed as the argument. | |
| 83 | (Functions deployed this way are commonly known as <var>callbacks</var>.) | |
| 84 | ||
| 85 | <P> | |
| 86 | </DD> | |
| 87 | <DT><STRONG>add</STRONG></DT> | |
| 88 | <DD>is optional, either "<tt class="samp"></tt>" or "<tt class="samp">+</tt>". Passing an empty string | |
| 89 | denotes that this binding is to replace any other bindings that this | |
| 90 | event is associated with. Preceeding with a "<tt class="samp">+</tt>" means that this | |
| 91 | function is to be added to the list of functions bound to this event type. | |
| 92 | </DD> | |
| 93 | </DL> | |
| 94 | ||
| 95 | <P> | |
| 96 | For example: | |
| 97 | <div class="verbatim"><pre> | |
| 98 | def turnRed(self, event): | |
| 99 | event.widget["activeforeground"] = "red" | |
| 100 | ||
| 101 | self.button.bind("<Enter>", self.turnRed) | |
| 102 | </pre></div> | |
| 103 | ||
| 104 | <P> | |
| 105 | Notice how the widget field of the event is being accessed in the | |
| 106 | <tt class="method">turnRed()</tt> callback. This field contains the widget that | |
| 107 | caught the X event. The following table lists the other event fields | |
| 108 | you can access, and how they are denoted in Tk, which can be useful | |
| 109 | when referring to the Tk man pages. | |
| 110 | ||
| 111 | <P> | |
| 112 | <div class="verbatim"><pre> | |
| 113 | Tk Tkinter Event Field Tk Tkinter Event Field | |
| 114 | -- ------------------- -- ------------------- | |
| 115 | %f focus %A char | |
| 116 | %h height %E send_event | |
| 117 | %k keycode %K keysym | |
| 118 | %s state %N keysym_num | |
| 119 | %t time %T type | |
| 120 | %w width %W widget | |
| 121 | %x x %X x_root | |
| 122 | %y y %Y y_root | |
| 123 | </pre></div> | |
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