CSE445_M4L5 Events and Delegates

Events and Delegates

• Introduction to event-driven programming and its significance in software development.

• Overview of the framework used by the Ira A. Fulton Schools of ASU Engineering at Arizona State University.

Lecture Outline

| Topics Covered| Event-driven Paradigm| Delegates and Events| General Event-driven Programming

Control Flow-Based Programming (Polling)

• Polling: A method to control the program flow based on certain conditions.

• Main Operations:

  • Temperature measurement.

  • Breaking news updates.

  • Exchange rate methods and services.

• CPU Utilization: Control flow is active when the processor is available.

Event-Drive Programming

• Application of Event-Driven Models:

  • Controlling motors based on events.

  • Receiving and processing information from a base station.

  • Using sensors (e.g., sonar sensor, temperature sensor).

• Process Details:

  • Image processing – involves decompression and compression tasks.

  • Sending processed information back to the base station.

  • Implementations of event boards, alert boards, sensor notifications, and handling multiple threads for parallel activities.

Need for Event-Driven Programming

• Comparison of polling for different sensors:

  • Sonar sensor can be polled once per second with alerts for distances shorter than 5 feet.

  • Touch sensor values must be polled every millisecond to avoid missing inputs.

• Importance of writing efficient event-driven programs to manage frequent events without overwhelming the system.

Understanding Events and Event Handling

• Design Components:

  • Events are generated and handled by different classes.

  • Delegates define the signatures for event handling.

  • Class A serves as an event service, while Class B and Class C act as event clients subscribing to events.

• Callbacks: Allows flexibility in event handling, enabling a one-to-many relationship for subscriptions.

Example: 911 Call Center System

• Structure of a simulated 911 call center to handle emergency calls.

• Registration of phone numbers and processing of emergencies effectively using event-driven concepts.

Advanced Events and Event Handling Design

• Utilizing delegates and subscription lists for effective event handling.

• Detailing event generation and orchestration for sensor inputs and actions.

• Discussion of built-in support for events in programming frameworks.

C# Delegate for Events and Event Handling

• Definition of a Delegate:

  • A design pattern to encapsulate methods with specific signatures.

  • Functions as a type-safe function pointer similar to C++.

  • Enables dynamic method invocation and subscription to callback methods through delegates.

• Examples of Delegate Use:

  • Delegate declarations and instantiations to invoke methods.

  • Program example illustrating delegate usage with methods Pi_Plus and E_Plus.

Defining Events Using Delegates

• Requirements for defining an event:

  • Creation of a container for subscriptions using delegates.

  • Implementation of an event emitter function to notify subscribers of events.

  • Example structures demonstrating the event definition process, including event declarations in C#.

Implementation Example: Event-Driven Programming in C#

• Event Handlers:

  • Definitions for various sensor events (Touch and Motion sensors).

  • Implementation details including adding and removing event handlers, notifying subscribers with emitted events.

• Main Class Execution:

  • Demonstrates creation of an event class and interactions with event handlers.

• Concept Application: Shows practical implementation of event-driven programming as applied to sensor inputs.

Closing Remarks

• Recap of key concepts covered in the sections and their implications for programming.

• Introduction to upcoming lectures that will expand on these concepts with further detailed examples.

Coordination events in C# are used for

defining the order of execution among the threads.