Flutter Crash Course #6 - Widgets

Summary

This Flutter tutorial introduces the fundamental concept of widgets, which are the building blocks of any Flutter application. It explains that everything in Flutter is a widget, with the root widget being the starting point passed to the runApp function. The script delves into the distinction between stateless and stateful widgets, the importance of the build method in defining widget behavior, and the structure of a widget tree. It also touches on the use of pre-built widgets for UI elements and the creation of custom widgets for specific functionalities, like the example of a 'Footer' widget. The lesson aims to clarify the basics of widget-based UI development in Flutter.

Takeaways

• 📚 Flutter apps are primarily built using widgets, which form a widget tree.
• 🌟 The root widget is the main entry point of the application, passed into the runApp function.
• 🔄 Widgets can be either stateless or stateful, with stateless widgets not containing any changing state or data.
• 🏗️ The 'build' method in a widget class is responsible for constructing and returning the widget or widget tree.
• 🎨 Flutter provides a wide range of pre-built UI widgets for common elements like text, images, and layout features.
• 🛠️ Developers can create custom widgets by defining a class with a build method that returns a widget tree.
• 📦 Custom widgets allow for reusability, similar to components in React, and can be inserted into any widget tree.
• 📝 The 'Material App' widget is a built-in widget used for building the app's structure, which will be explored in more detail in subsequent lessons.
• 🔑 Understanding the concept of widgets is fundamental to developing in Flutter, as most UI elements are represented as widgets.
• 🔍 The script provides an example of a 'My App' widget and a 'Footer' widget to illustrate the creation and use of custom widgets.
• 🚀 The lesson emphasizes the importance of recognizing that widgets in Flutter are essentially classes that can be instantiated as needed.

Q & A

What is the fundamental concept discussed in the Flutter lesson?

The fundamental concept discussed in the Flutter lesson is the idea of widgets, which are the building blocks for most things in Flutter.

What is the root widget in a Flutter application?

The root widget is the top-level widget in a Flutter application that is passed into the runApp function. It is the starting point of the widget tree.

What does the term 'stateless' in 'StatelessWidget' signify in Flutter?

The term 'stateless' in 'StatelessWidget' signifies that the widget does not contain any state or data that changes over time or in response to user interactions.

What is the purpose of the 'build' method in a Flutter widget class?

The 'build' method in a Flutter widget class is responsible for constructing the widget and defining what is displayed on the screen. It must return a widget or a widget tree.

What is a widget tree in the context of Flutter?

A widget tree in Flutter is a hierarchical structure where widgets are nested within each other, forming the user interface of the application.

How are built-in widgets different from custom widgets in Flutter?

Built-in widgets are pre-made widgets provided by the Flutter framework for common UI elements, while custom widgets are created by developers using a class with a build method that returns a widget tree for specific needs.

Why might a developer create a custom widget in Flutter?

A developer might create a custom widget in Flutter to encapsulate a specific UI pattern or component that can be reused across the application, providing consistency and reducing code duplication.

Can you provide an example of a built-in Flutter widget mentioned in the script?

Examples of built-in Flutter widgets mentioned in the script include the Text widget for displaying text, the Image widget for displaying images, and the Container widget for layout purposes.

What is the relationship between the 'MyApp' widget and the 'MaterialApp' widget in the script?

In the script, the 'MyApp' widget is a custom widget that extends 'StatelessWidget' and its build method returns a 'MaterialApp' widget, which is a built-in Flutter widget used for the application's material design scaffolding.

How does the script relate the concept of widgets to a previous lesson?

The script relates the concept of widgets to a previous lesson by mentioning that the argument passed into the 'runApp' function, which is the 'MyApp' widget, was discussed as the root widget in the previous lesson.

What is the significance of the 'Column' and 'Row' widgets in the script's explanation of widget trees?

The 'Column' and 'Row' widgets are used in the script to demonstrate how widgets can be nested within each other to create a vertical or horizontal layout, contributing to the overall structure of the widget tree.

Outlines

00:00

📚 Introduction to Widgets in Flutter

This paragraph introduces the fundamental concept of widgets in Flutter, emphasizing that everything in Flutter is considered a widget. The root widget, passed into the runApp function, is explained as the starting point of the application. It is a class that extends StatelessWidget, which means it doesn't contain any changing state. The paragraph also touches on the build method, crucial for constructing the widget and defining the UI. Additionally, it mentions the existence of both pre-built and custom widgets, which can be nested to form a widget tree that represents the user interface.

05:00

🏭 Building Custom Widgets and Widget Trees

The second paragraph delves into the process of creating custom widgets by packaging built-in Flutter widgets into reusable components. It draws a parallel to React's reusable components, highlighting the modularity and reusability of widgets in Flutter. The paragraph explains that while most widgets are pre-made for common UI elements, developers can also create custom widgets using a class with a build method that returns a widget tree. The example of a 'Footer' widget is given to illustrate this concept. The paragraph concludes by reinforcing the idea that Flutter apps are constructed from a combination of pre-built and custom widgets, which are instantiated as needed.

Keywords

💡Widgets

Widgets in the context of Flutter are the fundamental building blocks of the user interface. They are classes that represent different elements on the screen, such as text, images, and layout structures. The script emphasizes that most things in Flutter are considered widgets, and they can be either pre-built or custom-created by developers. The main theme of the video revolves around the concept of widgets, as they form the basis of any Flutter application.

💡Root Widget

The Root Widget is a specific widget that is passed into the runApp function in a Flutter application. It sits at the very top of the widget tree and is the entry point for the app's UI structure. In the script, the 'MyApp' class is mentioned as an example of a root widget, which extends the 'StatelessWidget' class and returns a 'MaterialApp' widget tree in its 'build' method.

💡StatelessWidget

StatelessWidget is a type of widget in Flutter that does not contain any state or data that changes over time. It is used when the part of the UI does not need to respond to user interactions or other changes. The script explains that the 'MyApp' class extends 'StatelessWidget', indicating that it is a widget without any mutable state.

💡Stateful Widget

Stateful Widget is another type of widget in Flutter that is used when there is a need to represent a UI that changes over time or in response to user interactions. Although not deeply explored in the script, it is mentioned as a counterpart to 'StatelessWidget' for scenarios where state management is necessary.

💡Build Method

The 'build' method is a function within a widget class that is responsible for returning the widget's content. It is overridden in custom widget classes to define what the widget will look like on the screen. The script uses the 'build' method in the context of the 'MyApp' widget to return a 'MaterialApp' widget, illustrating how widgets are constructed.

💡Widget Tree

A Widget Tree is the hierarchical structure formed by widgets nested within each other in a Flutter application. It represents the entire UI of the app, starting from the root widget down to the individual UI elements like text or images. The script describes the widget tree as a series of nested widgets, such as a 'Container' widget with a 'Column' widget inside it, which in turn contains 'Text' and 'Image' widgets.

💡Custom Widget

A Custom Widget is a widget created by the developer using a class that extends either 'StatelessWidget' or 'StatefulWidget'. It allows for the creation of reusable components that can be inserted into the widget tree wherever needed. The script gives an example of a 'Footer' widget, which is a custom widget made up of a 'Row' with 'Text', 'Image', and a 'Logo' widget as its children.

💡Pre-built Widgets

Pre-built Widgets are the ready-made widgets provided by the Flutter framework for common UI elements such as 'Text', 'Image', 'Container', 'Column', 'Row', etc. The script mentions these widgets as the primary components used to construct the UI of a Flutter application, emphasizing their ease of use and the variety available.

💡Flutter Framework

The Flutter Framework is the set of tools, widgets, and libraries provided by Flutter for building natively compiled applications for mobile, web, and desktop from a single codebase. The script refers to the built-in widgets and the overall structure of a Flutter application, which are part of this framework.

💡Material App

Material App is a pre-built widget in Flutter that provides an implementation of the Material Design guidelines. It is used as the root widget in many Flutter applications to ensure a consistent look and feel across platforms. The script mentions 'Material App' as the widget returned by the 'build' method of the 'MyApp' widget.

💡Constructor

In the context of the script, a Constructor refers to the process of creating an instance of a class in Flutter, which in turn creates a widget. When named arguments are passed to a widget class, its constructor is invoked, and an instance of that widget is created. This is how pre-built widgets are utilized in the script's example of creating a UI with 'AppBar', 'Center', 'Column', 'Text', and 'Icon' widgets.

Highlights

Flutter apps are built using the concept of widgets, which can be thought of as the building blocks of the user interface.

The 'runApp' function's argument is known as the root widget, which is the topmost widget in the widget tree.

Widgets in Flutter are essentially classes that inherit functionality from either 'StatelessWidget' or 'StatefulWidget'.

Stateless widgets do not contain any state or data that changes over time, unlike stateful widgets.

The 'build' method within a widget class is responsible for constructing the widget and its content.

The 'build' method returns a widget or a widget tree, which is a nested structure of widgets.

Flutter has pre-built widgets for various content and layout features, such as text, image, container, column, and row.

Custom widgets can be created when pre-built widgets do not meet specific requirements.

A widget tree is a hierarchical structure where widgets are nested within other widgets.

The root widget can have child widgets, which can in turn have their own children, forming a complex structure.

Built-in widgets like 'Container', 'Text', 'Image', 'Column', 'Row', etc., are used to create the UI.

Custom widgets are created by defining a class with a 'build' method that returns a widget tree.

Custom widgets can encapsulate multiple built-in widgets to create reusable components.

The 'MaterialApp' widget is a built-in widget used for building the overall app structure.

Understanding the widget tree is crucial for creating complex and dynamic Flutter applications.

The process of creating custom widgets involves packaging built-in widgets into a new structure.

Flutter's widget system is similar to React's reusable components, allowing for modular UI development.

The 'MyApp' widget in the example is a custom widget that returns a 'MaterialApp' widget tree.

Pre-built UI widgets are instances of classes created by passing named arguments to their constructors.

The fundamental concept of Flutter apps is the use of widgets, which are instantiated classes for UI elements.

Transcripts

okay then gangs so in this lesson I

mainly want to talk about a key Concept

in flutter before we actually start

coding anything and that is the idea of

widgets and you can think of most things

in flutter as being a widget now I

mentioned in the last lesson that the

argument we pass into the run app

function this my app thing is a widget

and this widget whatever it might be

that we pass into the runapp function is

known as the root widget of the

application so if we take a look at that

my app widg where we Define it down here

we can see that it's actually just a

class and that's all widgets are in

flutter at the end of the day they're

just classes and you can see that this

class extends the stateless widgets

class meaning that it inherits all of

the special functionality that a widget

in flutter should have the stateless

part basically means that this widget

won't contain any state or data which

changes over time or in response to

something like user clicking on a button

for that we have stateful widgets but

we're going to talk more about those

later in the course

anyway you can see also that we have a

method in this class called build and

we're overriding this method because

it's also defined in the stateless

widget class we inherit from but this

build method is what's responsible for

building this widget and is ultimately

also responsible for what we see on the

screen because inside this build method

we have to return some kind of template

or content in the form of a widget or a

widget tree meaning a bunch of widgets

nested within each other now this widget

or widget tree that we return is the

material app widget in this case which

we're going to learn about in the next

lesson but built into flutter there's

also widgets for pretty much any kind of

content or layout feature that we might

need to display on the screen so if we

want to Output some text we could use a

pre-built text widget if we want to

Output an image we'd use an image widget

if we need a container for a layout then

we'd use a container widget or we'd use

a column widget if we wanted to Output a

bunch of stuff in a column so pretty

much anything we ever want to display to

the screen there's going to be a widget

for it and if there's not one already

built into flutter for something you can

just make your own custom widget as well

so then a flutter application is

primarily built from a bunch of these

different widgets which come together to

form a widget tree right now the root

widget is the one that sits at the very

top of this tree it's the one that we

pass into that run app function that we

just saw in the main do file now the

root widget could be called whatever you

want for example my app like it's named

in the start project but it could be

something else and that root widget will

have a child widget which could be a

container widget for layout purposes

maybe within that we might have a column

widget as a child to display a column of

different things on a screen now a

column widget can have multiple children

and they could be a text widget to

display some text an image widget to

display an image and maybe a row widget

to display a row of other things so the

row widget just like the column widget

can also have multiple children which

all widgets themselves so for example

another text widget and maybe a text

button widget and then finally we might

have a fo widget at the bottom of the

column as well so you can see now

following this pattern of widgets within

widgets we're building up a tree likee

structure of widget so in other words a

widget tree all right and on on a screen

this widget tree might look something

like this we have the root widget my app

then inside that a container widget with

some padding maybe around it the column

with text and image widgets inside it

and then we have a row widget below that

with some more text and a button and

then finally a footer widget at the

bottom of the column so when you're

making a flutter app you're essentially

going to be making a widget tree like

this made up of a bunch of different UI

widgets now most of the those widgets

are going to be pre-made widgets built

into the flutter framework like the

container Widget the text Widget the

image widget column row Etc there's

loads and loads of built-in widgets like

this that we can use but sometimes

you'll also need to make your own custom

widgets which themselves will probably

return a widget tree for example this

root widget my app isn't a built-in

widget it's a custom widget that we

create by using a class that inherits

the stateless widget class and that

class contain contains a build function

which returns a widget tree made up of a

few different widgets nested within each

other also in our example here we have a

footer widget now that's not a built-in

flutter widget that's just something I

made up for this example and I would

made that widget in my code using a

class much like the my app widget we saw

before and that class for the footer

widget is going to have a build method

that returns another widget tree that

might look something like this it could

be a row widget with three children

text an image and maybe a logo widget as

well so all I'm really doing is kind of

packaging three built-in flutter widgets

into my own custom widget and then I can

just drop that widget into any other

widget tree where I need it does that

make

sense if you've ever used react before I

guess this is a little bit like making a

reusable component right that can be

then dropped into the template wherever

we need it so we're just making these

kind of custom widgets anyway the

takeaway points here are that one we

make flutter apps by using widgets which

form a widget tree okay two most of

those widgets will be built-in pre-made

widgets for things like text images form

fields and layout features like

containers rows and columns and three

some of the widgets might be customade

widgets that we create by using a class

with a build method which also returns

its own widget tree okay now don't worry

too much if that third point is a little

bit foggy for now we're going to be

looking at that in more detail as we go

forward but just know that we can make

these custom widgets using a class when

we need to all right so now we know a

little bit more about what widgets are

let's have a quick look at this St code

again just to see if we can spot any

widgets in action so first up we've got

this root widget being passed into the

Runa function we've seen that already

and we can see that this root widget is

actually a custom widget because we're

making it right here using a class that

extends stateless widget and it also has

a build method which returns a widget

itself and this is the way that custom

widgets are made right using a class

with a build method that returns a

widget or a widget Tree in this case it

returns a widget called material app now

this is a built-in widget and we're

going to learn a little bit more about

that in the next lesson but if we scroll

down the file a little bit you're going

to see that we also have another widget

called my homepage nested within it

right here and again we can see that

this is a custom widget because we're

using a class to make it which contains

a build method again to build and return

another widget tree now we don't want to

go through every single bit of code in

this data project because in the next

lesson we're actually going to be

stripping this right back and starting

from scratch because I think it's much

easier to introduce and practice new

Concepts and new features that way but

just very quickly if we scroll right

down we're going to see a bunch of

built-in UI widgets like the appar

widget for example the center widget we

also have a column widget text widgets

an icon widget

Etc so all of these widgets are

pre-built widgets that we can just drop

into The Code by the way these pre-made

widgets are all originally made using

classes right just like the custom ones

that we make and each of these widgets

is just us making an instance of that

class and passing in some named

arguments right in turn that class runs

its Constructor takes in those arguments

and it makes us an instance of that

class that widget right and that's all

there is to it so if you remember just

one thing from this lesson it should be

that flut apps are made using widgets

which are just dark classes which we can

instanciate whenever we need them