开罗上下文和持久性？

我刚开始使用pycairo，并遇到以下有趣的错误。我编写的程序创建一个简单的gtk窗口，在其上绘制一个矩形，然后有一个回调在任何类型的键盘输入上绘制一条随机线。但是，似乎每个键盘输入都必须创建一个新的上下文，否则在程序收到第一个键盘输入（特别是在.stroke（）行）时出现错误。错误如下，如果重要。 'BadDrawable（无效的Pixmap或Window参数）'。（详情：serial 230 error_code 9 request_code 53 minor_code 0）开罗上下文和持久性？

#! /usr/bin/env python 
import pygtk 
pygtk.require('2.0') 
import gtk, gobject, cairo, math, random 
# Create a GTK+ widget on which we will draw using Cairo 
class Screen(gtk.DrawingArea): 
# Draw in response to an expose-event 
    __gsignals__ = { "expose-event": "override" } 

    # Handle the expose-event by drawing 
    def do_expose_event(self, event): 
    # Create the cairo context 
    self.cr = self.window.cairo_create() 
    # Restrict Cairo to the exposed area; avoid extra work 
    self.cr.rectangle(event.area.x, event.area.y, event.area.width, event.area.height) 
    self.cr.clip() 

    self.draw(*self.window.get_size()) 

    def key_press_event(self, *args): 
    # print args 
    self.cr = self.window.cairo_create() # This is the line I have to add 
    # in order to make this function not throw the error. Note that cr is only 
    # given as attribute of self in order to stop it going out of scope when this line 
    # doesn't exist 
    self.cr.set_source_rgb(random.random(), random.random(), random.random()) 
    self.cr.move_to(*[z/2.0 for z in self.window.get_size()]) 
    self.cr.line_to(*[z*random.random() for z in self.window.get_size()]) 
    self.cr.stroke() 

    def draw(self, width, height): 
    # Fill the background with gray 
    self.cr.set_source_rgb(.5,.5,.5) 
    self.cr.rectangle(0, 0, width,height) 
    self.cr.fill() 

    self.cr.set_source_rgb(1,0,0) 
    self.cr.arc(width/2.0, height/2.0, min(width,height)/2.0 - 20.0, 0.0, 2.0*math.pi) 
    self.cr.stroke() 

#create a gtk window, attach to exit button, and whatever is passed as arg becomes the body of the window. AWESOME 
def run(Widget): 
    window = gtk.Window() 
    widget = Widget() 
    window.connect("delete-event", gtk.main_quit) 
    window.connect('key-press-event',widget.key_press_event) 
    widget.show() 
    window.add(widget) 
    window.present() 
    gtk.main() 

if __name__ == "__main__": 
    run(Screen)

感谢您的帮助！

（更新：我打过来，我实现了以下内容：当我调整窗口的大小，添加的所有新对象被删除（或者至少不会再出现）？）

来源

2010-08-18 Kurt Spindler

您可能对http://wiki.github.com/tbaugis/hamster_experiments/感兴趣 - 它在开罗之上提供了一个相当有用的抽象。即使你不使用完整的库，包含的tweener当然值得关注。 – 2010-08-19 12:41:13