イベント

Event is a piece of application-level information from the underlying framework, typically the GUI toolkit. Event loop is a programming construct that waits for and dispatches events or messages in a program. The event loop repeatedly looks for events to process. A dispatcher is a process which maps events to event handlers. Event handlers are methods that react to events.

Event object is an object associated with the event. It is usually a window. Event type is a unique event, that has been generated. Event binder is an object, that binds an event type with an event handler.

In the following section we will describe a simple event. We will talk about a move event.

A move event is generated, when we move a window to a new position. The event type is wx.MoveEvent. The event binder for this event is wx.EVT_MOVE.

#! /usr/bin/env python

# moveevent.py

import wx

class MoveEvent(wx.Frame):
    def __init__(self, parent, id, title):
        wx.Frame.__init__(self, parent, id, title, size=(250, 180))

        wx.StaticText(self, -1, 'x:', (10, 10))
        wx.StaticText(self, -1, 'y:', (10, 30))
        self.st1 = wx.StaticText(self, -1, '', (30, 10))
        self.st2 = wx.StaticText(self, -1, '', (30, 30))

        self.Bind(wx.EVT_MOVE, self.OnMove)
        self.Centre()
        self.Show(True)

    def OnMove(self, event):
        x, y = event.GetPosition()
        self.st1.SetLabel(str(x))
        self.st2.SetLabel(str(y))

app = wx.App()
MoveEvent(None, -1, 'moveevent.py')
app.MainLoop()

The example displays the current position of the window.

self.Bind(wx.EVT_MOVE, self.OnMove)

Here we bind the wx.EVT_MOVE event binder to the OnMove() method.

def OnMove(self, event):
    x, y = event.GetPosition()

The event parameter in the OnMove() method is an object specific to a particular event type. In our case it is the instance of a wx.MoveEvent class. This object holds information about the event. For example the Event object or the position of the window. In our case the Event object is the wx.Frame widget. We can find out the current position by calling the GetPosition() method of the event.

Working with events is straightforward in wxPython. There are three steps:

• Identify the event binder name: wx.EVT_SIZE, wx.EVT_CLOSE etc
• Create an event handler. It is a method, that is called, when an event is generated
• Bind an event to an event handler.

In wxPython we say to bind a method to an event. Sometimes a word hook is used. You bind an event by calling the Bind() method. The method has the following parameters:

Bind(event, handler, source=None, id=wx.ID_ANY, id2=wx.ID_ANY)

• event is one of EVT_* objects. It specifies the type of the event.
• handler is an object to be called. In other words, it is a method, that a programmer binds to an event.
• source parameter is used when we want to differentiate between the same event type from different widgets.
• id parameter is used, when we have multiple buttons, menu items etc. The id is used to differentiate among them.
• id2 is used when it is desirable to bind a handler to a range of ids, such as with EVT_MENURANGE.

Note that method Bind() is defined in class EvtHandler. It is the class, from which wx.Window inherits. wx.Window is a base class for most widgets in wxPython. There is also a reverse process. If we want to unbind a method from an event, we call the Unbind() method. It has the same paremeters as the above one.

Sometimes we need to stop processing an event. To do this, we call the method Veto().

#! /usr/bin/env python

# veto.py

import wx

class Veto(wx.Frame):
    def __init__(self, parent, id, title):
        wx.Frame.__init__(self, parent, id, title, size=(250, 200))

        self.Bind(wx.EVT_CLOSE, self.OnClose)
        self.Centre()
        self.Show(True)

    def OnClose(self, event):
        dial = wx.MessageDialog(None, 'Are you sure to quit?', 'Question',
                                wx.YES_NO | wx.NO_DEFAULT | wx.ICON_QUESTION)

        ret = dial.ShowModal()
        if ret == wx.ID_YES:
            self.Destroy()
        else:
            event.Veto()

app = wx.App()
Veto(None, -1, 'veto.py')
app.MainLoop()

In our example, we process a wx.CloseEvent. This event is called, when we click the X button on the titlebar, press Alt + F4 or select close from the system menu. In many applications, we want to prevent from accidentally closing the window, if we made some changes. To do this, we must bind the wx.EVT_CLOSE event binder.

dial = wx.MessageDialog(None, 'Are you sure to quit?', 'Question',
    wx.YES_NO | wx.NO_DEFAULT | wx.ICON_QUESTION)
ret = dial.ShowModal()

During the close event, we show a message dialog.

if ret == wx.ID_YES:
    self.Destroy()
else:
    event.Veto()

Depending on the return value, we destroy the window, or veto the event. Notice that to close the window, we must call the Destroy() method. By calling the Close() method, we would end up in an endless cycle.

There are two types of events. Basic events and command events. They differ in propagation. Event propagation is travelling of events from child widgets to parent widgets and grand parent widgets etc. Basic events do not propagate. Command events do propagate. For example wx.CloseEvent is a basic event. It does not make sense for this event to propagate to parent widgets.

By default, the event that is catched in a event handler stops propagating. To continue propagation, we must call the Skip() method.

#! /usr/bin/env python

# propagate.py

import wx
            
class MyPanel(wx.Panel):
    def __init__(self, parent, id):
        wx.Panel.__init__(self, parent, id)
        self.Bind(wx.EVT_BUTTON, self.OnClicked)

    def OnClicked(self, event):
        print 'event reached panel class'
        event.Skip()

class MyButton(wx.Button):
    def __init__(self, parent, id, label, pos):
        wx.Button.__init__(self, parent, id, label, pos)
        self.Bind(wx.EVT_BUTTON, self.OnClicked)

    def OnClicked(self, event):
        print 'event reached button class'
        event.Skip()

class Propagate(wx.Frame):
    def __init__(self, parent, id, title):
        wx.Frame.__init__(self, parent, id, title, size=(250, 150))
        panel = MyPanel(self, -1)
        MyButton(panel, -1, 'Ok', (15, 15))
        self.Bind(wx.EVT_BUTTON, self.OnClicked)

        self.Centre()
        self.Show(True)

    def OnClicked(self, event):
        print 'event reached frame class'
        event.Skip()

app = wx.App()
Propagate(None, -1, 'propagate.py')
app.MainLoop()

In our example, we have a button on a panel. The panel is placed in a frame widget. We define a handler for all widgets.

event reached button class
event reached panel class
event reached frame class

We get this, when we click on the button. The event travels from the button to panel and to frame.

Try to omit some Skip() methods and see, what hapens.

Window identifiers are integers that uniquely determine the window identity in the event system. There are three ways to create window id's.

• let the system automatically create an id
• use standard identifiers
• create your own id

Each widget has an id parameter. This is a unique number in the event system. If we work with multiple widgets, we must differantiate among them.

wx.Button(parent, -1)
wx.Button(parent, wx.ID_ANY)

If we provide -1 or wx.ID_ANY for the id parameter, we let the wxPython automatically create an id for us. The automatically created id's are always negative, whereas user specified id's must always be positive. We usually use this option when we do not need to change the widget state. For example a static text, that will never be changed during the life of the application. We can still get the id, if we want. There is a method GetId(), which will determine the id for us.

#! /usr/bin/env python

# automaticids.py

import wx

class AuIds(wx.Frame):
    def __init__(self, parent, id, title):
        wx.Frame.__init__(self, parent, id, title, size=(170, 100))
        panel = wx.Panel(self, -1)
        exit = wx.Button(panel, -1, 'Exit', (10, 10))
        self.Bind(wx.EVT_BUTTON, self.OnExit, id=exit.GetId())
        self.Centre()
        self.Show(True)

    def OnExit(self, event):
        self.Close()

app = wx.App()
AuIds(None, -1, 'automaticids.py')
app.MainLoop()

In this example, we do not care about the actual id value.

self.Bind(wx.EVT_BUTTON,  self.OnExit, id=exit.GetId())

We get the automatically generated id by calling the GetId() method.

Standard identifiers should be used whenever possible. The identifiers can provide some standard graphics or behaviour on some platforms.

#! /usr/bin/env python

# identifiers.py

import wx

class Identifiers(wx.Frame):
    def __init__(self, parent, id, title):
        wx.Frame.__init__(self, parent, id, title, size=(250, 150))

        panel = wx.Panel(self, -1)
        grid = wx.GridSizer(3, 2)

        grid.AddMany([(wx.Button(panel, wx.ID_CANCEL), 0, wx.TOP | wx.LEFT, 9),
                      (wx.Button(panel, wx.ID_DELETE), 0, wx.TOP, 9),
                      (wx.Button(panel, wx.ID_SAVE), 0, wx.LEFT, 9),
                      (wx.Button(panel, wx.ID_EXIT)),
                      (wx.Button(panel, wx.ID_STOP), 0, wx.LEFT, 9),
                      (wx.Button(panel, wx.ID_NEW))])

        self.Bind(wx.EVT_BUTTON, self.OnQuit, id=wx.ID_EXIT)

        panel.SetSizer(grid)
        self.Centre()
        self.Show(True)

    def OnQuit(self, event):
        self.Close()

app = wx.App()
Identifiers(None, -1, 'identifiers.py')
app.MainLoop()

In our example we use standard identifiers on buttons. On linux, the buttons have small icons.

The last option is to use own identifiers. We define our own global ids.

#! /usr/bin/env python

# focusevent.py

import wx

class MyWindow(wx.Panel):
    def __init__(self, parent):
        wx.Panel.__init__(self, parent, -1)

        self.color = '#b3b3b3'
        
        self.Bind(wx.EVT_PAINT, self.OnPaint)
        self.Bind(wx.EVT_SIZE, self.OnSize)
        self.Bind(wx.EVT_SET_FOCUS, self.OnSetFocus)
        self.Bind(wx.EVT_KILL_FOCUS, self.OnKillFocus)

    def OnPaint(self, event):
        dc = wx.PaintDC(self)

        dc.SetPen(wx.Pen(self.color))
        x, y = self.GetSize()
        dc.DrawRectangle(0, 0, x, y)

    def OnSize(self, event):
        self.Refresh()

    def OnSetFocus(self, event):
        self.color = '#0099f7'
        self.Refresh()

    def OnKillFocus(self, event):
        self.color = '#b3b3b3'
        self.Refresh()

class FocusEvent(wx.Frame):
    def __init__(self, parent, id, title):
        wx.Frame.__init__(self, parent, id, title, size=(400, 250))

        grid = wx.GridSizer(2, 2, 10, 10)
        grid.AddMany([(MyWindow(self), 1, wx.EXPAND | wx.TOP | wx.LEFT, 9),
                      (MyWindow(self), 1, wx.EXPAND | wx.TOP | wx.RIGHT, 9),
                      (MyWindow(self), 1, wx.EXPAND | wx.BOTTOM | wx.LEFT, 9),
                      (MyWindow(self), 1, wx.EXPAND | wx.BOTTOM | wx.RIGHT, 9)])

        self.SetSizer(grid)
        self.Centre()
        self.Show(True)

app = wx.App()
FocusEvent(None, -1, 'focusevent.py')
app.MainLoop()

#! /usr/bin/env python

# myscrollwinevent.py

import wx

class ScrollWinEvent(wx.Frame):
    def __init__(self, parent, id, title):
        wx.Frame.__init__(self, parent, id, title)

        panel = wx.Panel(self, -1)
        self.st = wx.StaticText(panel, -1, '0', (30, 0))
        panel.Bind(wx.EVT_SCROLLWIN, self.OnScroll)
        panel.SetScrollbar(wx.VERTICAL, 0, 6, 50)
        self.Centre()
        self.Show(True)

    def OnScroll(self, event):
        y = event.GetPosition()
        self.st.SetLabel(str(y))

app = wx.App()
ScrollWinEvent(None, -1, 'myscrollwinevent.py')
app.MainLoop()

#! /usr/bin/env python

# sizeevent.py

import wx

class SizeEvent(wx.Frame):
    def __init__(self, parent, id, title):
        wx.Frame.__init__(self, parent, id, title)

        self.Bind(wx.EVT_SIZE, self.OnSize)
        self.Centre()
        self.Show(True)

    def OnSize(self, event):
        self.SetTitle(str(event.GetSize()))

app = wx.App()
SizeEvent(None, -1, 'sizeevent.py')
app.MainLoop()

self.SetTitle(str(event.GetSize()))

#! /usr/bin/env python

# paintevent.py

import wx

class PaintEvent(wx.Frame):
    def __init__(self, parent, id, title):
        wx.Frame.__init__(self, parent, id, title)

        self.count = 0
        self.Bind(wx.EVT_PAINT, self.OnPaint)
        self.Centre()
        self.Show(True)

    def OnPaint(self, event):
        self.count = self.count + 1
        print self.count

app = wx.App()
PaintEvent(None, -1, 'paintevent.py')
app.MainLoop()

#! /usr/bin/env python

# keyevent.py

import wx

class KeyEvent(wx.Frame):
    def __init__(self, parent, id, title):
        wx.Frame.__init__(self, parent, id, title)

        panel = wx.Panel(self, -1)
        panel.Bind(wx.EVT_KEY_DOWN, self.OnKeyDown)
        panel.SetFocus()

        self.Centre()
        self.Show(True)

    def OnKeyDown(self, event):
        keycode = event.GetKeyCode()
        if keycode == wx.WXK_ESCAPE:
            ret = wx.MessageBox('Are you sure to quit?', 'Question',
                                wx.YES_NO | wx.NO_DEFAULT, self)
            if ret == wx.YES:
                self.Close()
        event.Skip()

app = wx.App()
KeyEvent(None, -1, 'keyevent.py')
app.MainLoop()

keycode = event.GetKeyCode()

if keycode == wx.WXK_ESCAPE: