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Kivy Cookbook

By : Hugo Solis, Solis

2.5 (2)

Kivy Cookbook

2.5 (2)

By: Hugo Solis, Solis

Overview of this book

Kivy is an open-source Python library for rapid development of applications that make use of innovative user interfaces, such as multi-touch apps. It is a promising Python framework to develop UI and UX apps in a cross-platform environment, under the Python philosophy. Kivy Cookbook is a practical book that will guide you through the Kivy framework to develop apps and get your apps ready for distribution in App Store and Android devices. You will start off with installing Kivy and building your interfaces. You will learn how to work the accelerometer and create custom events. Then, you will understand how to use the basics, buttons, labels and text inputs and manipulate the widget tree. Next, you will be able to work with manipulating instructions, create an atlas and layouts. Moving on, you will learn packing for Windows and packing for iOS, and use TestDrive. By the end of the book, you will have learnt in detail the relevant features and tools in Kivy and how to create portable packages to distribute your apps in the most used platforms.

Preface

Preface

What this book covers

What you need for this book

Who this book is for

Sections

Conventions

Reader feedback

Customer support

Free Chapter

1. Kivy and the Kv Language

1. Kivy and the Kv Language

Introduction

Installing Kivy

Building your interfaces

Declaring properties within a class

Relating Python code and the Kv language

Referencing widgets

Accessing widgets defined inside the Kv language in your Python code

Reusing styles in multiple widgets

Designing with the Kv language

Running your code

Using Kivy garden

2. Input, Motion, and Touch

2. Input, Motion, and Touch

Introduction

Using the mouse

Evolving to the touchscreen

Working with the accelerometer

Using the gyroscope

The differences between the touch and motion events

Recognizing touch shapes

Detecting multitapping

Grabbing touch events

Recording gestures

3. Events

3. Events

Introduction

Scheduling a one-time event

Scheduling a repetitive event

Triggering events

Defining widget events

Creating custom events

Attaching callbacks

Declaring a property

Compounding properties

4. Widgets

4. Widgets

Introduction

Using the basics: buttons, labels, and text inputs

Manipulating the widget tree

Traversing the tree

Using swappable widgets

Organizing with layouts

Using FloatLayout

Using BoxLayout

Using GridLayout

Using StackLayout

Using RelativeLayout

Using AnchorLayout

Working with ActionBar

5. Graphics – Canvas and Instructions

5. Graphics – Canvas and Instructions

Introduction

Separating with the screen manager

Using drawing instructions

Using context instructions

Working with manipulating instructions

Rotating, translating, and scaling the canvas

Modifying with multitouching

Storing and retrieving the coordinate space context

Introducing animations

6. Advanced Graphics – Shaders and Rendering

6. Advanced Graphics – Shaders and Rendering

Introduction

Using Carousel

Creating and using Atlas

Creating layouts

Editing shaders

Creating widgets

Creating your own shader

Rendering in a Framebuffer

Optimizing graphics

7. The API in Detail

7. The API in Detail

Introduction

Getting to know the API

Using the asynchronous data loader

Logging objects

Parsing

Applying utils

Leveraging the factory object

Working with audio

Working with video

Working with a camera

Using spelling

Adding effects

Advanced text manipulation

8. Packaging our Apps for PC

8. Packaging our Apps for PC

Introduction

Packaging for Windows

Including multimedia for Windows

Running apps in Windows

Packaging for Mac OS

Including multimedia for Mac OS

Running apps in Mac OS

Packaging for Linux

Including multimedia for Linux

Running apps in Linux

9. Kivy for Mobile Devices

9. Kivy for Mobile Devices

Introduction

Packaging for iOS

Resizing the screen into iOS

Leveraging mobile features in iOS

Preparing for the App Store

Packaging for Android

Resizing the screen into Android

Leveraging mobile features in Android

Index

Index

Customer Reviews

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Referencing widgets

Sometimes, it is necessary to access or reference other widgets in a specific widget tree. In the Kv language, there is a way to do it using IDs.

Getting ready

This recipe will use two common widgets just for reference. The Button and TextInput fields are very common widgets.

How to do it…

This recipe is as follows:

Make a rule
Establish the ID

Call the ID:

<MyWidget>:
    Button: 
        id: f_but 
    TextInput: 
        text: f_but.state

How it works…

Let's see the code; this is the first line:

<MyWidget>:

This is the name of the widget we will use, which is a clickable text input. The second line is:

Button:

This defines the button. The third line is:

id: f_but

This gives the button an ID of f_but, which we will use to reference the button. The fourth line is:

TextInput:

This defines the text input. The fifth line is:

text: f_but.state

This is the definition of the text that is in the text input where we are referencing the state of the button. It says that if you do not click the button, the text in the text input is normal, and if you click the button, the text in the text input is shown.

There's more…

An ID is limited in scope to the rule it is declared in, so in the preceding code, f_but cannot be accessed outside the <MyWidget> rule; that is, if we have a second <MyWidget2>, we are not able to reference f_but in <MyWidget2>.

Also ID is a weakref module for the widget and not the widget itself. As a consequence, storing the ID is not sufficient to keep the widget from being garbage collected. To demonstrate:

<MyWidget>:
    label_widget: label_widget.__self__ 
    Button: 
        text: 'Add Button' 
        on_press: root.add_widget(label_widget) 
    Button: 
        text: 'Remove Button' 
        on_press: root.remove_widget(label_widget) 
    Label: 
        id: label_widget 
        text: 'widget'

If we do not use ID.__self__ or in this case label_widget.__self__ just label_widget, we are going to get an error: ReferenceError: weakly-referenced object no longer exists.

See also

If you want to get more details about widgets, see the recipes in Chapter 4, Widgets.

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