Using Events and Callbacks

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You can enhance the power and flexibility of your OPC application by using event callbacks. An event is a specific occurrence that can happen while an OPC Data Access client object (opcda client object) is connected to an OPC server. The toolbox defines a set of events that include starting, stopping, or acquiring records during a logging task, as well as events for asynchronous reads and writes, data changes, and server shutdown notification.

When a particular event occurs, the toolbox can execute a function that you specify. This is called a callback. Certain events can result in one or more callbacks. You can use callbacks to perform processing tasks while your client object is connected. For example, you can display a message, analyze data, or perform other tasks. Callbacks are controlled through OPC Toolbox object properties. Each event type has an associated property. You specify the function that you want executed as the value of that property.

• Example: Using the Default Callback Function

• Event Types

• Retrieving Event Information

• Creating and Executing Callback Functions

Working with Different Data Types

Example: Using the Default Callback Function

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