10.4. Layout Container
The Layout container is similar to the Fixed container except that it implements an infinite (where infinity is less than 2^32) scrolling area. The X window system has a limitation where windows can be at most 32767 pixels wide or tall. The Layout container gets around this limitation by doing some exotic stuff using window and bit gravities, so that you can have smooth scrolling even when you have many child widgets in your scrolling area.A Layout container is created using:
layout = GtkLayout() layout = GtkLayout(hadjustment, vadjustment) |
As you can see, you can optionally specify the Adjustment objects that the Layout widget will use for its scrolling. If you don't specify the Adjustment objects, new ones will be created.
You can add and move widgets in the Layout
container using the following two methods:
layout.put(widget, x, y) layout.move(widget, x, y) |
The size of the Layout container can be
set using the next method:
layout.set_size(width, height) |
Layout containers are one of the very few widgets in the GTK widget set that actively repaint themselves on screen as they are changed using the above methods (the vast majority of widgets queue requests which are then processed when control returns to the mainloop() function).
When you want to make a large number of
changes to a Layout container, you can use the following two methods to
disable and re-enable this repainting functionality:
layout.freeze() layout.thaw() |
The final four methods for use with Layout
widgets are for manipulating the horizontal and vertical adjustment widgets:
hadj = layout.get_hadjustment() vadj = layout.get_vadjustment() layout.set_hadjustment(adjustment) layout.set_vadjustment(adjustment) |
The layout.py example program creates three buttons and puts them in a layout widget. when a button is clicked, it is moved to a random location in the layout. Figure 10.3 illustrates the starting display of the program:
Figure 10.3 Layout Example
1 #!/usr/bin/env python
2
3 # example layout.py
4
5 import gtk
6 import whrandom
7
8 class LayoutExample:
9 def OnWindowDeleteEvent(self, widget, event):
10 # return false so that window will be destroyed
11 return gtk.FALSE
12
13 def OnWindowDestroy(self, widget, *data):
14 # exit main loop
15 gtk.mainquit()
16
17 def OnButtonClicked(self, button):
18 # move the button
19 # Note: it probably isn't necessary to freeze the layout widget here,
20 # but better safe than sorry
21 self.layout.freeze()
22 self.layout.move(button, whrandom.randint(0,500),
23 whrandom.randint(0,500))
24 self.layout.thaw()
25
26 def __init__(self):
27 # create the top level window
28 window = gtk.GtkWindow(gtk.WINDOW_TOPLEVEL)
29 window.set_title("Layout Example")
30 window.set_default_size(300, 300)
31 window.connect("delete-event", self.OnWindowDeleteEvent)
32 window.connect("destroy", self.OnWindowDestroy)
33 # create the table and pack into the window
34 table = gtk.GtkTable(2, 2, gtk.FALSE)
35 window.add(table)
36 # create the layout widget and pack into the table
37 self.layout = gtk.GtkLayout(None, None)
38 self.layout.set_size(600, 600)
39 table.attach(self.layout, 0, 1, 0, 1, gtk.FILL|gtk.EXPAND,
40 gtk.FILL|gtk.EXPAND, 0, 0)
41 # create the scrollbars and pack into the table
42 vScrollbar = gtk.GtkVScrollbar(None)
43 table.attach(vScrollbar, 1, 2, 0, 1, gtk.FILL|gtk.SHRINK,
44 gtk.FILL|gtk.SHRINK, 0, 0)
45 hScrollbar = gtk.GtkHScrollbar(None)
46 table.attach(hScrollbar, 0, 1, 1, 2, gtk.FILL|gtk.SHRINK,
47 gtk.FILL|gtk.SHRINK, 0, 0)
48 # tell the scrollbars to use the layout widget's adjustments
49 vAdjust = self.layout.get_vadjustment()
50 vScrollbar.set_adjustment(vAdjust)
51 hAdjust = self.layout.get_hadjustment()
52 hScrollbar.set_adjustment(hAdjust)
53 # create 3 buttons and put them into the layout widget
54 button = gtk.GtkButton("Press Me")
55 button.connect("clicked", self.OnButtonClicked)
56 self.layout.put(button, 0, 0)
57 button = gtk.GtkButton("Press Me")
58 button.connect("clicked", self.OnButtonClicked)
59 self.layout.put(button, 100, 0)
60 button = gtk.GtkButton("Press Me")
61 button.connect("clicked", self.OnButtonClicked)
62 self.layout.put(button, 200, 0)
63 # show all the widgets
64 window.show_all()
65
66 def main():
67 # enter the main loop
68 gtk.mainloop()
69 return 0
70
71 if __name__ == "__main__":
72 LayoutExample()
73 main()
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