Subscribing to events
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A controller can subscribe to all OIDs it is interested in receiving notifications from by using the Subscription message.
Controllers always send the complete list of OIDs they want to hold active subscriptions for. Omitting a previously subscribed OID from the message’s subscriptions array signals that the controller wishes to unsubscribe from it.
Example message for subscribing to multiple OIDs.
{
"messageType": 3,
"subscriptions": [
1,
100,
111,
98119
]
}
Example SubscriptionResponse message received
{
"messageType": 4,
"subscriptions": [
1,
100,
98119
]
}
Note in this example, 111 was removed from the response subscriptions array because it was not a valid OID for subscribing.
Example message to unsubscribe all OIDs.
{
"messageType": 3,
"subscriptions": []
}
Example message to unsubscribe a single previously subscribed OID.
{
"messageType": 3,
"subscriptions": [
100,
111,
98119
]
}
Note in this example, 1 was removed from the requests subscriptions array because the controller no longer wanted to subscribe to it.
Example notification for the PropertyChanged event (1e1) when the userLabel property (1p6) changes on object with OID 98119
{
"messageType": 2,
"notifications": [
{
"oid": 98119,
"eventId": {
"level": 1,
"index": 1
},
"eventData": {
"propertyId": {
"level": 1,
"index": 6
},
"changeType": 0,
"value": "Input 1",
"sequenceItemIndex": null
}
}
]
}
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