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The OPCUA node listens for subscription callbacks
January 13, 2021
13:04, EET
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Forum Posts: 1
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January 13, 2021
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i use Opcua client listener for data change through the nodeID. function ondataRange callback is triggered when first time the client connected, the prevValue is always null
but i do not want to trigger the ondataRange callback that is first time to connect,how should i do,thanks!

January 14, 2021
9:13, EET
Matti Siponen

Forum Posts: 79
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February 11, 2020
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I’m assuming that you’re talking about onDataChange method of the DataChangeListener interface. Please, tell if that assumption is incorrect.

There is no way to avoid triggering onDataChange of a DataChangeListener in specific situations such as when the Client is connected to the Server for the first time. This applies to listeners in general as well. Instead, if you need to use prevValue in your code, you should add a null check to it to handle it being null when there are no previous values.

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