Publish Strings

The example demonstrates publishing a string value and creating a subscriber for string messages. The message is published into the demo channel.

Subscriber

Channel channel = await Backendless.messaging.subscribe("demo");
channel.addMessageListener((String message) {
  print("Received a message: $message");
});

Codeless Reference

where:

Argument	Description
id	The unique identifier of the event listener.
channel	Name of the channel to subscribe to.
selector	A selector is a query expressed in the SQL-92 syntax and formatted as the condition part of the SQL's WHERE clause. The condition references headers in the published messages.
message	When a listener gets triggered, it assigns data of the message matching the where clause condition to this variable(message).

This operation does not return a value.

The example below creates a message listener with id "1111-1111-1111-11111" for the "demo" channel. When a message is published to the "demo" channel the listener gets triggered and saves the message content to the message variable. Then the data stored in the message variable gets printed.

Publisher

RESTJavaScriptAndroidSwiftObjective-CC#Flutter

curl -X POST \
  https://api.backendless.com/APP-ID/REST-API-KEY/messaging/demo \
  -H 'content-type: application/json' \
  -d '{  "message": "It's a great day!" }'

Backendless.Messaging.publish( "demo", "It's a great day!" )
 .then( function( result ) {
    console.log( "message has been published" );
  })
 .catch( function( error ) {
    console.log( "error publishing the message - " + error );
  })

Backendless.Messaging.publish( "demo", 
                               "It is a great day!", 
                               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" );
  }
} );

Backendless.shared.messaging.publish(channelName: "demo", message: "It is a great day!", responseHandler: { messageStatus in
    print("Message has been published")
}, errorHandler: { fault in
    print("Error: \(fault.message ?? "")")
})

[Backendless.shared.messaging publishWithChannelName:@"demo" message:@"It is a great day!" 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}");
   } 
);

Backendless.Messaging.Publish( "demo", 
                               "It is a great day!", 
                               callback );

Backendless.messaging.publish("It is a great day!", channelName: "demo").then((response) {
  print("Message has been published");
});

Codeless Reference

where:

Argument	Description
channel name	Name of the channel where a message must be published to.
subtopic name	The subtopic of the message allows developers to designate and filter messages by subtopic name. For instance, if a messaging application has a group and a few subgroups, all messages sent to the main group can be marked with this subtopic name which can be used to route messages to the appropriate subgroups depending on the context.
message	The contents of the message that must be published to a channel.
headers	Message headers is a collection of name/value pairs. A subscriber can set a filter expressed as an SQL "where clause" query (called selector) which Backendless uses to determine whether a message should be delivered to the subscriber. When the query matches the published data in message headers, message is delivered to the corresponding subscriber. For more information see the Conditional Delivery section of this guide.
publish at	Must be a Unix Timestamp, which is the number of milliseconds since the Epoch (January 1st, 1970 at UTC).  Note that if you want to specify the number of seconds instead of milliseconds, you must multiply the number by 1000 or add three trailing zeroes to your number (e.g. (1681324179 * 1000) or 1681324179000.
return result	When this box is checked, the operation returns an object containing the status of the message delivery and a unique message identifier.

Returns an object containing the status of the message delivery and a unique message identifier:

// Sample object  

{  
    "errorMessage":null,  
    "messageId":"message:FCBD8BF1-A45D-4564-B449-3C91D4896987",  
    "status":"published"  
}

The example below publishes the message to the "demo" channel.