错误：

解决方法：

A) Set the new port for dev server 
User command react-native start --port=8088 
or 
yourproject\node_modules\react-native\local-cli\server\server.js to set the the available port say 8080
now use react-native start to start server on 8080 

B) Now to establish communication between emulator and dev server, use below command
adb -s emulator -5554 reverse tcp:8088 tcp:8088
i) 5554 =>emulator port (adb devices command will tell you emulator port but if this command is not working then set the path C:/../android-sdk/platform-tools in Path environemnt variable )
ii) 8088 =>server port 

C) run the command react-native run-android

D) Follow below steps updating Dev server path in emulator

i) Ctrl + M for windows to open your dev menu for the emulator. 
ii) Click Dev Settings 
III) Under Debugging select Debug server host & port for device 
IV) Enter the url and port for your application as 10.0.2.2:8088 

参考：https://stackoverflow.com/questions/37376512/dev-server-returned-error-code-403-react-native