Kivy UrlRequest 作为一个类调用 - 方法未执行？

Question

尝试尝试并构建一个解决使用 UrlRequest 的类，以检查给定的 URL 是否有效。结果比预期的要困难一些！

问题是定义为类的一部分的 on_success 和 on_failure/error 方法永远不会被调用。该脚本抛出以下输出（基于打印命令）：

http://www.google.com
request sent
URL doesn't work

现在我怀疑我是从 test_connection 方法获取返回码（“None”），而不是 connectionSuccess 或 connectionFailure。我怎样才能让电话等待后者之一给予回报？欢迎任何建议。谢谢。

from kivy.app import App
from kivy.uix.floatlayout import FloatLayout
from kivy.network.urlrequest import UrlRequest

class WebExplorer():      
    def test_connection(self, path):
        self.path = path
        print (self.path)
        req = UrlRequest(self.path,on_failure=self.connectionFailure,on_error=self.connectionFailure,on_success=self.connectionSuccess)
        print ("request sent")

    def connectionSuccess(self,*args):
        print ("connectionSuccess")
        return 0

    def connectionFailure(self,*args):
        print ("connectionFailure")
        return 1


class MainScreen(FloatLayout):
    def __init__(self, **kwargs):
        super(MainScreen, self).__init__(**kwargs)
        self.address = 'http://www.google.com'

        if WebExplorer().test_connection(self.address) == 0:
            print ("URL works")
        else:
            print ("URL doesn't work")

class App(App):
    def build(self):
        return MainScreen()


if __name__ == "__main__": 
    App().run() 

更新 2016-09-27 我改变了我的代码，我花了几个小时试图找出问题所在。先上代码：

from kivy.app import App
from kivy.uix.floatlayout import FloatLayout
from kivy.network.urlrequest import UrlRequest

class WebExplorer():

    def test_connection(self, path):
        self.path = path
        req = UrlRequest(self.path,on_failure=self.connectionFailure,on_error=self.connectionFailure,on_success=self.connectionSuccess)
        req.wait()
        return (self._return_value)

    def connectionSuccess(self, req, results):
        print ("Success")
        self._return_value = [0,results]

    def connectionFailure(self, req, results):
        print ("Failure")
        self._return_value = [1,results]


class MainScreen(FloatLayout):
    def __init__(self, **kwargs):
        super(MainScreen, self).__init__(**kwargs)
        self.URLtest = ['http://www.ikea.com/','https://www.google.com','https://www.sdfwrgaeh.com']
        for URL in self.URLtest:
            self.returnCode = WebExplorer().test_connection(URL)
            if self.returnCode[0] == 0:
                print ("Correct URL")
            else:
                print ("Wrong URL")

class App(App):
    def build(self):
        return MainScreen()

if __name__ == "__main__": 
    App().run() 

为什么是 3 个网址？因为一个是“正确的”（宜家），一个是重定向（谷歌），一个是完全伪造的。事实证明，该代码仅适用于第一个。当结果是失败/错误时，req.wait 不起作用（顺便说一句，我不知道这两者之间有什么区别）。

所以问题是如何使 req.wait 进程失败，或者如何使用正确的错误代码退出类。我考虑使用 Clock.schedule_interval 定期检查状态，但是由于 URL 不正确时甚至不执行事件方法，所以我无处设置变量-_-

Answer 1

UrlRequest 是一个异步的，这意味着实际请求在您的应用程序进行时在后台处理。 on_failure 等函数是回调，即它们将在请求完成时被调用——但这意味着返回值是“丢失”。你得到的返回值确实来自test_connection函数。

您在邮件列表中提到要调用根 URL，对返回的内容进行一些处理，然后根据内容和用户交互向子 URL 发出新请求。

以下内容应该为您正在尝试做的事情提供一个框架。

class WebExplorer

    def __init__(self, gui):
        self._visited_urls = [] # to prevent endless redirect loops
        self._visiting = set() # to check if we are still doing something
        self.gui = gui # used to display buttons in process_result

    def get_url(self, url):
        self._visited_urls.append(url)
        self._visiting.add(url)
        UrlRequest(url, 
            on_success=self.process_result,
            on_failure=self.failure,
            on_error=self.failure, # what is the difference between failure and error?
            on_redirect=self.redirect)

    def redirect(self, req):
        self._visiting.discard(req.url)
        self.get_url(req.req_headers["Location"]) # check if correct handling of 3xx

    def process_result(self, req):
        self._visiting.discard(req.url)
        #TODO process the body to extract urls you want to visit

        box = BoxLayout()
        for url in urls_you_want_to_visit:
            button = Button()
            button.text = url
            # I'm not sure if the following works due to some scoping oddities
            # if - no matter which button is pressed - the same url is called
            # this line is probably at fault
            button.bind(on_press=lambda: self.get_url(url)) 
            box.add_widget(button)

        gui.add_widget(box)

当然还有很多需要改进的地方。它也未经过测试，因此可能包含错误。