Merge pull request #1140 from secretrobotron/device-absent-error-hand…

…ling

Device absent error handling

airtest/core/error.py

@@ -70,6 +70,12 @@ class DeviceConnectionError(BaseError):
     DEVICE_CONNECTION_ERROR = r"error:\s*((device \'\S+\' not found)|(cannot connect to daemon at [\w\:\s\.]+ Connection timed out))"
     pass
 
+class NoDeviceError(BaseError):
+    """
+        When no device is connected
+    """
+    pass
+
 
 class ICmdError(Exception):
     """

airtest/core/helper.py

@@ -1,21 +1,37 @@
 # -*- coding: utf-8 -*-
-import time
-import sys
+import functools
 import os
 import six
+import sys
+import time
 import traceback
 from airtest.core.settings import Settings as ST
-from airtest.utils.logwraper import Logwrap, AirtestLogger
 from airtest.utils.logger import get_logger
+from airtest.utils.logwraper import Logwrap, AirtestLogger
+from airtest.core.error import NoDeviceError
+
+
+class DeviceMetaProperty(type):
+
+    @property
+    def DEVICE(cls):
+        if G._DEVICE is None:
+            raise NoDeviceError("No devices added.")
+        return G._DEVICE
+
+    @DEVICE.setter
+    def DEVICE(self, dev):
+        self._DEVICE = dev
+        self.LOGGING.debug("Set current device to: %s" % dev)
 
 
-class G(object):
+class G(object, metaclass=DeviceMetaProperty):
     """Represent the globals variables"""
     BASEDIR = []
     LOGGER = AirtestLogger(None)
     LOGGING = get_logger("airtest.core.api")
     SCREEN = None
-    DEVICE = None
+    _DEVICE = None
     DEVICE_LIST = []
     RECENT_CAPTURE = None
     RECENT_CAPTURE_PATH = None