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Lecture 3.1 - Graphic User Interface

Course video 38 of 40

In this module we describe how to communicate with devices through the pins of the Raspberry Pi. We examine the RPi.GPIO library which provides Python functions used to access the pins. We discuss how to set up the pins, apply digital voltages, and generate Pulse Width Modulated signals. We also describe the Tkinter Python library and show how it can be used to access pins through a graphic user interface.

The Raspberry Pi Platform and Python Programming for the Raspberry Pi

Калифорнийский университет в Ирвайне

Курс 4 из 6 — Введение в программирование интернета вещей (IOT) Специализация

The Raspberry Pi is a small, affordable single-board computer that you will use to design and develop fun and practical IoT devices while learning programming and computer hardware. In addition, you will learn how to set up up the Raspberry Pi environment, get a Linux operating system running, and write and execute some basic Python code on the Raspberry Pi. You will also learn how to use Python-based IDE (integrated development environments) for the Raspberry Pi and how to trace and debug Python code on the device. Please note that this course does not include discussion forums.

Просмотреть программу курса

Получаемые навыки

Computer Programming, Python Programming, Internet Of Things (IOT), Raspberry Pi

Преподаватели

Ian Harris
Professor

Текст видео

[MUSIC]

This lecture will talk about making a program, a Python program that actually

has a graphic user interface so the user can interact with the hardware.

Directly through some nice graphic user interface and this is interesting because

it's something you can do on Raspberry Pi that is interesting,

and you can't do it with something like an Arduino, not easily anyway.

So graphic user interface is basically,

a user interface that uses pictures somehow, all right.

And we've all seen graphic interfaces, point and click, buttons, pull downs,

that sort of thing.

So you would like to be able to use a graphic user interface to, you might like

to be able to use a graphic user interface to access the general purpose I/O pins.

Now, of course you're going to have to write some code,

write some pifying code for that.

But then once you've written that code, the user can interact with the pins,

make things happen on the pins,

and communicate with other devices by interacting with a graphic user interface.

So they'll see something on the screen, some kind of user interface, and click and

point and type and stuff like that and make something happen.

So that's the goal here to define some program that has a graphic user interface.

Now Raspberry Pi does it, Arduino doesn't.

So this is one of those things that's different,

that distinguishes Raspberry Pi from Arduino.

So the stuff we've seen for the last few lectures talking about accessing GPIO and

making pins high and low and pulse with modulation, and so on, all those

are things that the Arduino can do just as well, maybe better in a lot of cases.

But they don't really leverage the operating system at all.

So GUIs, graphic user interfaces, that's one of the things,

one of the advantages you get from having an operating system.

The operating system supports, you can talk to the HDMI, talk to the keyboard,

talk to the mouse and it can provide you with this graphic user interface, right?

And Linux allows that, right?

It supports that, so why not use that?

Right? So this is one of those things

that you can do with Raspberry Pi because it has this operating system support

that you couldn't do with regular or Arduino.

Not easily, when you're making a graphic user interface,

the user interacts with widgets.

Widgets are some kind of visual entities, something the user can interact with

what these are intuitively, you've seen these before buttons, menus, sliders,

scroll bars all those things you see on the screen that a user can mess with.

A drawing surface for drawing, you can put a drawing surface, and

a person can draw into that.

Any kind of graphic way User interacts with the screen.

Those are called widgets, so lots of different widgets, and

what you want to be able to do.

Well, for one thing, is to put these widgets on the screen in a Python program.

So write a Python program that puts widgets on the screen for you, and

allows users to interact.

Now, the execution of the code,

when you're talking about one of these graphic user interface programs it's

typically not completely controlled by the programmer but by the user, instead.

So what that means is the programmer writes code and

the code lists a bunch of lines of code that execute in a certain sequence.

Right, and with a regular Python program, everything, the order is completely

controlled by the programmer and the data the programmer receives.

But the programmer writes the sequence of instructions and

determines in what sequence they will execute, right?

And there are options, if-then statements, might execute this sequence or that.

But the programmer is in control of that by the way they write the code.

Now with a graphic user interface what happens is that the code that gets

executed is determined by what the user does in the interface.

That is if the user clicks on one button and then function gets called and

if user clicks on another button then another function get called.

So which function gets called isn't completely under

the control of the programmer.

In a regular Python program, you can have an if statement,

if this is true call function one else call function two.

Then the program determines one of these two things is gonna happen, but

with a graphic user interface these functions their

execution is controlled by the user and what they do.

Maybe they move a slider and then this function gets executed and so on.

That actually makes coding somewhat harder for

the programmer because you can't predict the control flow sequence as well, right?

You don't know exactly,

maybe the program's gonna press this button 100 times, right?

You don't know what random sequence they're gonna press, and

you have to accommodate all possible sequences.

So in general, it makes programming more difficult,

but you get a graphic user interface, and that's a good thing.

Okay, so often,

graphic user interface based programs are written as one big event loop, okay?

And this is simpler than it sounds, typically the program waits.

[LAUGH] It just sits there waiting for the user to interact with a widget, okay?

So it doesn't do anything it just sits there statically,

maybe it does some initial stuff.

But it puts a screen out there and it sits there and waits.

Until the user does something, type something and when the user isn't typing

anything, click anything, the code's not doing anything often.

So the user pushes a button or selects a menu item or

something, draws something, grabs a slider, does some event, okay.

Now when the event happens you do something in response to that event.

So when that event happens a function is called.

So when you say do something in response you typically mean execute a function.

So this so

in some place in your code in your Python code you're gonna have to associate

these events that the user could do with functions that you want to execute, right?

So somebody clicks on this button this function's executed.

They move this slider this function's executed and so on.

So you do something in response you call this function, and

you execute the function.

Then after your done executing the function, the function completes, and

then you wait for something else to do.

So you again wait until the user interacts again, and

then when the user interacts again you do the appropriate function.

So, that's the event loop.

You sit there, you wait for an event.

When the event happens you execute the appropriate function,

and then you wait for the next exam, okay.

[MUSIC]

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