Core: Implementing Events in UnfoldingMaps

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Из курса от партнера University of California San Diego

Object Oriented Programming in Java

3454 оценки

University of California San Diego

Object Oriented Programming in Java

3454 оценки

Курс 3 из 4 — Specialization Object Oriented Programming in Java

Welcome to our course on Object Oriented Programming in Java using data visualization. People come to this course with many different goals -- and we are really excited to work with all of you! Some of you want to be professional software developers, others want to improve your programming skills to implement that cool personal project that you’ve been thinking about, while others of you might not yet know why you’re here and are trying to figure out what this course is all about. This is an intermediate Java course. We recommend this course to learners who have previous experience in software development or a background in computer science. Our goal is that by the end of this course each and every one of you feels empowered to create a Java program that’s more advanced than any you have created in the past and that is personally interesting to you. In achieving this goal you will also learn the fundamentals of Object Oriented Programming, how to leverage the power of existing libraries, how to build graphical user interfaces, and how to use some core algorithms for searching and sorting data. And this course is project-based, so we’ll dive right into the project immediately! We are excited to be offering a unique course structure, designed to support learners of different backgrounds in succeeding at their own pace. The first module explains how this will work and if this course is right for you. We also recommend taking a few minutes to explore the course site. A good place to start is the navigation bar on the left. Click Course Content to see what material we’ll cover each week, as well preview the assignments you’ll need to complete to pass the course. Click Discussions to see forums where you can discuss the course material with fellow students taking the class. Be sure to introduce yourself to everyone in the Meet and Greet forum. This course should take about 6 weeks to complete. You can check out the recommended course schedule below to see a quick overview of the lessons and assignments you’ll complete each week. We’re excited you’re here learning with us. Let’s get started!

Из урока

GUIs: Responding to User Events

You’ve reached an exciting point in the project - in this week you’ll add interactivity to your map! You’ll be learning how to design event-driven programs, using a new and powerful programming paradigm. Your map will now respond to mouse hovers and clicks. As always, make sure you're writing code along with us as you watch the videos and work through the week. Also, feel free to dive into the programming assignment (project) whenever you are ready

Core: Introduction to Event-Driven Programming2:21

In the Real World: Events1:55

Core: Implementing Events in UnfoldingMaps4:50

Core: Implementing Buttons in UnfoldingMaps5:50

When I Struggled: Buttons and GUIs0:59

Core: Listener Hierarchy3:07

Познакомьтесь с преподавателями

Mia Minnes
Assistant Teaching Professor
Computer Science and Engineering
Leo Porter
Assistant Teaching Professor
Computer Science and Engineering
Christine Alvarado
Associate Teaching Professor
Computer Science and Engineering

[SOUND] In the previous video we introduced event driven programming.

And what we'll do now is trace through some code that uses events.

So by the end of this video you will have experience at tracing the execution of

a piece of code that has both some procedural elements to it and

also some event driven code.

Well I'd like to start with an example that should be completely familiar

at this point.

We've been playing a lot with maps and setting them up and displaying them.

And so when we have this piece of code remember that what we see is

a map with a border around it of grey in the canvas.

And when we think about how this piece of code is being executed,

we set up our canvas once, as so the setup method is executed once, and then

what our applet does is it continuously loops and runs the draw method.

Okay, now let's try to jazz it up a little bit and

add an additional method to our class.

So right after we've defined the draw method,

we're going to stick in these four lines of code and pause the video for

a second and think about what the impact of this new method is going to be.

One thing to think about is, when this method will be executed,

and the second thing to think about is what the effect of that execution will be.

So let's start with the second question because it's a little bit easier.

Let's think about what will happen if we were to run this method and what we notice

here is that the key part is the background color guest change.

So remember that the background method that we're calling inside key pressed.

Is the way that we have through processing to change the background color of our

canvas.

And what we're doing here is setting that background color to 255, 255 ,255 and

that's our code for all white.

Because the three color channels are set to their maximum.

R, G, and B are all at their maximum value, and

that means that we have a pure white color.

And so, if this method is executed,

what we expect to see is that the background of the canvas is all white.

Something like this picture that you see now.

But then we go back to the question of when this method actually gets executed.

And if we think back about our model of the setup method being run

once at the beginning of running the applet, and

then the drama method being continuously run.

Then it's not clear if keyPressed will ever be executed because we don't

call keyPressed explicitly from anywhere else in our application.

We don't call keyPressed for example from the draw method.

The thing is though that our application is acting as a listener.

Not only is it doing that flow of execution of running setup and

then continuously leaping through drop but it's also in the background listening for

user effects.

So it's trying to see if the user's trying to interact with the program in some way.

And the kind of events that it's looking for are keyboard presses,

mouse clicks, multi-touch actions.

And so the program is going to be able to react to any of those kinds of events.

However, we don't need to worry about handling all of those events ourselves.

In our unfolding maps library we already have a default EventDispatcher.

So just by including this line of code in our setup method what

we're telling our application is we'd like our application to be interactive and

so, do what I'm telling you.

Set up the canvas the way I'm saying, draw what I want, but also listen for

any of the default events that you have in mind.

And the default event functionality that the PApplet already works with and

UnfoldingMaps does.

Is for example if the user double-clicks somewhere inside our map we're going to

increase their zoom level by one and

so focus in on whatever is at the center of the map.

And we can also accomplish that zoom level changes by hitting some plus and

minus buttons.

So that means the map that we're drawing,

the application that we're running, is going to respond to certain user inputs,

but we could always customize the interactivity by adding additional methods

or modifying the methods like keypress, that we had before.

What we're doing when we're writing public void keypress It like we did before,

is we're overriding the key press method from the super class, PApplet.

And so, we're using the power of inheritance that you talked about

already with Leo in the previous module.

Well, what we'll do in the future videos is think about further interactivity and

how we want to indicate to the user what they can tell the map to do and

how to design a good user interface.

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