Added background transfer example

examples/background_transfer.py

@@ -0,0 +1,107 @@
+# -*- coding: utf-8 -*-
+"""
+This class provides a Background Transfer Service for iOS. It requires iOS 8 or
+later.
+
+Note that downloading from non-https sources requires modifying the Info.plist
+file.
+
+http://stackoverflow.com/questions/32631184/the-resource-could-not-be-loaded-because-the-app-transport-security-policy-requi
+
+"""
+from pyobjus import autoclass, protocol, objc_str, selector, objc_b
+from pyobjus.dylib_manager import make_dylib, load_dylib
+from pyobjus.dylib_manager import load_framework, INCLUDE
+from kivy.app import App
+from kivy.uix.label import Label
+from kivy.logger import Logger
+from kivy.properties import ObjectProperty
+from kivy.logger import Logger
+
+
+class TestApp(App):
+    """ Our test app for background downloading """
+    bg_transfer = ObjectProperty()
+
+    def build(self):
+        return Label(text="Background Transfer Demo.\nFor iOS 8 or later.")
+
+
+class BackgroundTransfer(object):
+    """
+    Main worker class for handling background transfers
+    """
+    identifier = objc_str('Kivy Background Transfer')
+
+    def __init__(self):
+        super(BackgroundTransfer, self).__init__()
+        load_framework(INCLUDE.Foundation)
+
+        # Load the configuration required for background sessions
+        ns_config = autoclass('NSURLSessionConfiguration')
+        self.config = ns_config.backgroundSessionConfigurationWithIdentifier_(
+            self.identifier)
+
+        # Load the session using the config and this class as the delegate
+        session = autoclass('NSURLSession')
+        self.session = session.sessionWithConfiguration_delegate_delegateQueue_(
+            self.config, self, None)
+
+        self.task = None
+        # Note the policy restriction on HTTP as mentioned in the doc string
+        # Use HTTPS to make you life easier :-) 
+        self.download_file('http://kivy.org/logos/kivy-logo-black-256.png')
+
+    def download_file(self, url):
+        """ Download the specified file in place it in the destination. """
+        NSURL = autoclass('NSURL')
+        oc_url = NSURL.URLWithString_(objc_str(url))
+
+        # Tasks are intialised in a paused state
+        self.task = self.session.downloadTaskWithURL_(oc_url)
+        self.task.resume()
+
+    @protocol('NSURLSessionDownloadDelegate')
+    def URLSession_downloadTask_didWriteData_totalBytesWritten_totalBytesExpectedToWrite_(self, *args):
+        Logger.info(
+            "main.y: Protocol method "
+            "URLSession_downloadTask_didWriteData_totalBytesWritten_"
+            "totalBytesExpectedToWrite_ with {0}".format(args))
+
+    @protocol('NSURLSessionDownloadDelegate')
+    def URLSession_downloadTask_didFinishDownloadingToURL_(self, *args):
+        Logger.info(
+            "main.py: Protocol method "
+            "URLSession_downloadTask_didFinishDownloadingToURL_ "
+            "with {0}".format(args))
+        if len(args) > 2:
+            ns_url = args[2]
+            Logger.info(
+                'Downloaded file is {0}.\nYou need to move this before the '
+                'function returns.'.format(ns_url.fileSystemRepresentation))
+
+    @protocol('NSURLSessionDownloadDelegate')
+    def URLSession_downloadTask_didResumeAtOffset_expectedTotalBytes_(self,
+                                                                      *args):
+        Logger.info(
+            "main.py: Protocol method "
+            "URLSession_downloadTask_didResumeAtOffset_expectedTotalBytes_"
+            " with {0}".format(args))
+
+    @protocol('NSURLSessionTaskDelegate')
+    def URLSession_task_didCompleteWithError_(self, *args):
+        """
+        Although not technically part of the required delegate class, this
+        delegate catches errors preventing the main delegate from functioning.
+        """
+        Logger.info(
+            "main.py: Protocol method URLSession_task_didCompleteWithError_"
+            "with {0}".format(args))
+
+        if len(args) > 2:
+            ns_err = args[2]
+            if ns_err is not None:
+                Logger.info('Error {}'.format(ns_err.description().cString()))
+
+if __name__ == '__main__':
+    TestApp(bg_transfer=BackgroundTransfer()).run()