TechnologyUK - Computing - Software Development - Event Driven Programming. 10. Event-Driven Programming — How to Think Like a Computer Scientist: Learning with Python 3. Most programs and devices like a cellphone respond to events — things that happen.
For example, you might move your mouse, and the computer responds. Or you click a button, and the program does something interesting. In this chapter we’ll touch very briefly on how event-driven programming works. 10.1. Keypress events Here’s a program with some new features. Here are some points to note: We need the call to the window’s listen method at line 31, otherwise it won’t notice our keypresses.We named our handler functions h1, h2 and so on, but we can choose better names. 10.2. Understanding Event-Driven Programming. With "traditional" programming languages (often referred to as procedural languages), the program itself fully dictates what code is executed and when it's executed.
When you start such a program, the first line of code in the program executes, and the code continues to execute in a completely predetermined path. The execution of code may, on occasion, branch and loop, but the execution path is completely controlled by the program. This often meant that a program was rather restricted in how it could respond to the user. For instance, the program might expect text to be entered into controls on the screen in a predetermined order, unlike in Windows, where a user can interact with different parts of the interface, often in any order the user chooses.
Triggering Events In the previous hour, you learned how a method is simply a function of an object. There are many types of events and many ways to trigger those events. Users can trigger events by interacting with your program. Object sender. TechnologyUK - Computing - Software Development - Event Driven Programming. Understanding Event-Driven Programming. Programming paradigm. This article is about classification of programming languages.
For definition of the term "programming model", see Programming model. Common programming paradigms include imperative which allows side effects, functional which does not allow side effects, declarative which does not state the order in which operations execute, object-oriented which groups code together with the state the code modifies, procedural which groups code into functions, logic which has a particular style of execution model coupled to a particular style of syntax and grammar, and symbolic programming which has a particular style of syntax and grammar. Overview Overview of the various programming paradigms according to Peter Van Roy:5. Event-driven programming. Event handlers Main article: Event handler A trivial event handler Because the code for checking for events and the main loop do not depend on the application, many programming frameworks take care of their implementation and expect the user to provide only the code for the event handlers.
In this simple example there may be a call to an event handler called OnKeyEnter() that includes an argument with a string of characters, corresponding to what the user typed before hitting the ENTER key. To add two numbers, storage outside the event handler must be used. Globally declare the counter K and the integer T. While keeping track of history is straightforward in a batch program, it requires special attention and planning in an event-driven program.
Exception handlers Event Driven Basics on Scratch. Event-Based Programming. Event based programming is programming in which the code is based on events, which are similar to broadcasts.
For example, a "when mouse moved" event can trigger all scripts when the mouse is moved. Events have their own attributes, called event attributes. For example, When mouse moved can have the attributes current mouse x position, previous mouse x position, distance moved, etc. Scratch Events An event block, called a Hat Block, are how Scratch events are portrayed.
This is demonstrated using Java's component hierarchies and event mechanism. Please select a subtopic to view its contents.