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Conditional Pub/Sub

The example demonstrates publishing a weather forecast message with headers which can be used to create a conditional subscriber. The subscriber uses a selector to get weather forecast messages for the Dallas area when the expected temperature is higher than 60F degrees. The message is published into the demo channel.

Subscriber

final Channel channel = Backendless.Messaging.subscribe( "demo" );
String selector = "city = 'Dallas' and temperature > 60";
channel.addMessageListener( selector, new AsyncCallback<String>()
{
  @Override
  public void handleResponse( String message )
  {
    Log.i( "MYAPP", "Received a message " + message );
  }

  @Override
  public void handleFault( BackendlessFault fault )
  {
    Log.e( "MYAPP", "Error processing a message " + fault );
  }
} );

Publisher

curl -X POST \
  https://api.backendless.com/APP-ID/REST-API-KEY/messaging/demo \
  -H 'content-type: application/json' \
  -d '{  "message": "Thunderstorms likely. High 62F. Winds NNW at 10 to 15 mph. Chance of rain 90%.", 
         "headers" : { 
             "city" : "Dallas",
             "state" : "Texas", 
             "temperature":62    
         }                  
      }'
var message = "Thunderstorms likely. High 62F. Winds NNW at 10 to 15 mph. Chance of rain 90%.";
var publishOptions = new Backendless.PublishOptions({
       headers: {
          "city": "Dallas",
          "state": "Texas",
          "temperature": 62
       }
   });

Backendless.Messaging.publish( "demo", message, publishOptions )
 .then( function( result ) {
    console.log( "message has been published" );
  })
 .catch( function( error ) {
    console.log( "error publishing the message - " + error );
  })
String message = "Thunderstorms likely. High 62F. Winds NNW at 10 to 15 mph. Chance of rain 90%.";
PublishOptions publishOptions = new PublishOptions();
publishOptions.putHeader( "city", "Dallas" );
publishOptions.putHeader( "state", "Texas" );
publishOptions.putHeader( "temperature", 62);

Backendless.Messaging.publish( "demo", 
                               message,
                               publishOptions, 
                               new AsyncCallback<MessageStatus>()
{
  @Override
  public void handleResponse( MessageStatus response )
  {
    Log.i( "MYAPP", "Message has been published" );  
  }

  @Override
  public void handleFault( BackendlessFault fault )
  {
    Log.e( "MYAPP", "Error publishing the message" );
  }
} );
let message = "Thunderstorms likely. High 62F. Winds NNW at 10 to 15 mph. Chance of rain 90%."

let publishOptions = PublishOptions()
publishOptions.addHeader(name: "city", value: "Dallas")
publishOptions.addHeader(name: "state", value: "Texas")
publishOptions.addHeader(name: "temperature", value: 62)

Backendless.shared.messaging.publish(channelName: "demo", message: message, publishOptions: publishOptions, responseHandler: { messageStatus in
    print("Message has been published")
}, errorHandler: { fault in
    print("Error: \(fault.message ?? "")")
})
NSString *message = @"Thunderstorms likely. High 62F. Winds NNW at 10 to 15 mph. Chance of rain 90%.";

PublishOptions *publishOptions = [PublishOptions new];
[publishOptions addHeaderWithName:@"city" value:@"Dallas"];
[publishOptions addHeaderWithName:@"state" value:@"Texas"];
[publishOptions addHeaderWithName:@"temperature" value:@62];

[Backendless.shared.messaging publishWithChannelName:@"demo" message:message publishOptions:publishOptions responseHandler:^(MessageStatus *messageStatus) {
    NSLog(@"Message has been published");
} errorHandler:^(Fault *fault) {
    NSLog(@"Error: %@", fault.message);
}];
AsyncCallback<MessageStatus> callback = new AsyncCallback<MessageStatus>(
   messageStatus =>
   {
     Console.WriteLine( $"message has been published {messageStatus.MessageId}"); 
   },
   fault =>
   {
     Console.WriteLine( $"error {fault.Message}");
   } 
);

PublishOptions publishOptions = new PublishOptions();
publishOptions.AddHeader( "city", "Dallas" );
publishOptions.AddHeader( "state", "Texas" );
publishOptions.AddHeader( "temperature", 62 );

string message = "Thunderstorms likely. High 62F. Winds NNW at 10 to 15 mph. Chance of rain 90%."
Backendless.Messaging.Publish( message,
                               "demo",
                               publishOptions,
                               callback );