Event-driven programming (EDP) is changing the world of software development services and becoming part and parcel of today’s development. Its spread was stimulated by Windows and the dissemination of visual RAD environments. As its name suggests, the programming approach focuses on events. The latter may be user-initiated, systemic, and program-generated. The most common areas of EDP application today include the creation of GUIs, server apps, and multi-player game development.
Unlike old-style programs controlling the user’s options and predetermining the flow of events, more adaptive and innovative programming came up with a graphical user interface (GUI). The GUI changed the human-computer interaction by giving users multiple options in the form of drop-down menus, windows, buttons, and checkboxes. Thus, instead of following the predetermined order of actions set by the computer, users became able to choose one of many available commands on their own.
What is event-driven programming? How is it implemented today? What pros and cons does it offer to coders, businesses, and end-users? What examples of this software development approach are available?
Read this comprehensive guide that we have created in association with LitsLink to find all you might be interested in.
What Is Event-Driven Programming?
While traditional programming is linear and based on the flow of execution, with operations running for a fixed span or until reaching pre-written decision points, event-driven programming progresses as triggered by certain events (e.g., clicking on the mouse, pressing some keys on the keyboard, selecting an option from a drop-down menu). This type of programming is most common for programs with graphical user interfaces (GUIs). In case it is used, the program waits for events to occur and then responds.
Let’s deal with some introductory terminology for a better idea of EDP.
- Event: An event is a condition arising during the program’s lifetime and requiring some actions by the run-time system. Events are different by nature. Some of them require the program to retrieve and display certain information. Others initiate some computations and change state.
- Message: A message is a data structure representing an event at run-time. It gives information about the event type and parameters needed from the program to handle it.
- Event handler: An Event handler is a certain unit in the program activated to react to the event.
- Message loop: It is a polling algorithm used for EDP implementation via continuous examination of the message queue and routing traffic to event handlers.
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Event Handling as the Core of EDP
Event handling forms the basis of EDP and distinguishes this programming paradigm from others. Program actions following the EDP fundamentals are initiated by scheduled events, hardware events, operating system events, language run-time events, and events triggered by the user’s instructions provided through interaction with the program’s GUI. The programmers specify these actions during software development in the form of event handlers. In the simplest sense, coders have to answer the question, “what should happen when a specific event takes place?”
The most basic EDP model is the hardware model. It presupposes that the central processing unit’s operation is interrupted by any external stimulus requiring its response. In such conditions, little processing of the event is done by a primitive interrupt handler, while higher-level functions of the operating system remain intact. However, this model is quite primitive, devoid of the message queue, while the modern ODP systems function differently.
One of the oldest event handling tools in software engineering is the callback function. It is an EDP procedural model based on the interrupt vector table model. Callback functions have predetermined interfaces, which may differ slightly depending on the event type. Event types are small integers at run-time computing the event’s position in the callback table. The message loop invokes the callback function upon discovering the message at the head of the queue corresponding to that event type. For the function to be executed in the EDP process, the programming language in which this is done should provide a method of associating events with specific callback functions.
Features of Event-Driven Applications
Event-based apps differ from one another, depending on their purposes and functionality. Nevertheless, they all have to possess a universal set of features, such as:
- The event’s abstraction often provided explicitly as a monad;
- The event synchronization ability;
- A continuation-passing style implementation in the form of callback;
- Sources of primitive events.
Event-Driven Programming Languages
It is possible to create event-driven programs in any modern programming language, while Visual Basic, Visual C++, and Java are specifically suited for this purpose. For instance, the visual programming languages Visual C++ and Visual Basic are equipped with an Integrated Development Environment (IDE) suite with numerous standard control options, events, and event-handler code templates. Python is also used as a suitable EDP tool.
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Advantages of Event-Driven Programming
This approach to software coding possesses numerous advantages for all stakeholders. It requires fewer coded decisions than console applications. Many events are determined by user actions instead of advance coding of all possible scenarios. While console-based apps act, event-driven apps react. Second, it removes the possibility of invalid value entry. A console-based app asks a question and allows the user to type the answer. Event-Based apps commonly offer a set of options either as buttons or as a drop-down menu.
ODP is perfectly suited for the recent software engineering trends, such as cloud computing, microservices, and the need for enhanced scalability with flexible, distributed systems. The use of ODP removes the need to correct and adjust the existing code when adding or removing some module. The ODP system continues working flawlessly regardless of any adjustments of such kinds. Thus, programmers praise the ODP paradigm for being intuitive and well-suited to applications with control flows based on a complex of internal and external events rather than on structure. Other benefits of ODP include:
- Use of object-oriented programming as its basis;
- Better software design outcomes;
- Better responsiveness and flexibility of resulting programs;
- Quicker processing due to data dissemination across multiple processors and event handlers;
- Improved app scalability;
- Better loose coupling.
Disadvantages of Event-Driven Programming
One of the most commonly cited cons of event-based programming is the complex control flow and manual stack management. Because of these downfalls, this coding approach is not the best option for simple, small apps as the efforts are not reasonable.
Besides, one should keep in mind that event-driven programming doesn’t replace the traditional structured programming, while only supplementing it. The conventional programming techniques are still critical for writing the actual program, while event-driven coding elements may aid in designing the GUI.
The ODP flexibility, its indisputable advantage, also turns into a con in certain scenarios. One of such manifestations is the unpredictability of an ODP program in case of changes and weaker control over the system overall. While coders like ODP for frictionless adjustments, e.g., the deletion or addition of some functional modules, these adjustments may cause unexpected alterations in functionality. In traditional programming, the system detects such functionality abnormalities immediately and provides a report to the coder about their causes, in the ODP environment, the detection of such dysfunctions is slower and more complex.
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Event-Driven Programming Examples
Event-driven programs have become highly commonplace today. The most popular examples include word processing, drawing toolkits, spreadsheets, etc. The majority of modern messaging systems also follow the event-driven patterns, while large-scale websites use the scalable, event-driven architectures of distributed nature. ODP has also claimed a solid spot in the modern multi-tasking OSs and a variety of programming frameworks. With such benefits and a high degree of intuitive and flexible adjustment, ODP is sure to remain a highly popular coding option in the consumer community wishing more customization and individualization from the software they consume.