检查是否存在财产(Check if property exists)

 要求很简单。 
 
 您需要从每个客户端生成gcm令牌。 
 
 客户端A安装您的应用程序，并在启动/登录时（无论它适合您的业务逻辑），您将尝试生成此gcm令牌（让我们说10000是生成的令牌）。 并且您需要将此令牌发送到您的服务器以存储以便在将来的通信中使用它。 当你想与这个客户端A通信时，你需要告诉gcm服务器， 
 
Hey Gcm server, send mobile with gcm token 10000 the following message "Event time updated"
 
 因此，如果客户端b安装，它将生成其gcm令牌并以相同方式将其发送到服务器。 
 
 如果您有用户登录或某种方式可以唯一标识每个用户，建议将其与用户详细信息一起存储。 （以及名称，唯一ID等...）如果您没有登录，您仍然可以将令牌发送到服务器和商店，但是您放弃的是您希望向客户端A而不是B发送更新的情况。 
 
 来代码吧。 
 
 客户代码： 
 
 用于生成gcm令牌： 
 
 https://github.com/googlesamples/google-services/tree/master/android/gcm 
 
 生成后，您需要将此令牌发送到服务器 
 
 服务器代码： 
 
 服务器接收令牌并存储。 
 
 如果要在以后的某个时间点发送特定消息，可以将json数据或纯文本消息发送给客户端。 例如，以下是python示例。 
 
import gcm
response = gcm.json_request(registration_ids=reg_ids, data=in_data, delay_while_idle=False)
 
 希望这可以帮助。 

The requirement is simple.
 
You need to generate gcm token from each of your client.
 
Client A installs your application and upon launch/login(wherever it fits in your business logic) you will try to generate this gcm token(let us say 10000 is the generated token) . And you need to send this token to your server to store for using it in future communication. when you want to communicate with this client A, you need to tell gcm server, 
 
Hey Gcm server, send mobile with gcm token 10000 the following message "Event time updated"
 
So if client b installs, it will generate its gcm token and send it to server in same way.
 
In case you have user login or some way where each user can be identified uniquely, it is recommended to store it along with user details. (along with name, unique id, etc... ) If you do not have login, you can still send token to server and store but what you loose out is the cases where You want to send update to Client A but not B.
 
Coming to code point of it. 
 
Client code:
 
For generating gcm token:
 
https://github.com/googlesamples/google-services/tree/master/android/gcm
 
after you generate you need to send this token to server
 
Server code:
 
server receives the token and stores.
 
When you want to send a particular message in later point of time, you can send json data or plain message to client. For example, Following is the python example.
 
import gcm
response = gcm.json_request(registration_ids=reg_ids, data=in_data, delay_while_idle=False)
 
Hope this helps.