All language subtitles for 25. A Brief Look Under The Hoodf

Now with our stateful widget added, it's important to have a brief first look. I'll later to have

a more detailed look but a brief first look at what Flutter actually does when set state is executed

here. Set state is a function that forces Flutter to re-render the user interface, however not the entire

user interface of the entire app,

instead what set state does in the end is it calls build again of this widget where you call set

state.

Now in our case, that is almost the entire app, MyApp,

this widget here with this build method that is basically our entire app

but later in this course, we'll have bigger applications with more widgets where we split that into more

custom widgets and therefore, it will really make a difference if you update the entire app or just that

widget with set state,

so set state updates this widget by calling its build method again.

Now the build method goes ahead and rebuilds this widget tree,

it basically goes through all these instructions again.

Now that might sound very inefficient because the majority of this user interface didn't change right,

all the buttons are still the same,

the appBar is the same,

only this text changed and therefore Flutter,

no worries, is pretty efficient about that. Internally, it has a lot of mechanism to go through that build

method again but to not really render the entire UI again, so it does not redraw every pixel again.

In the end, it just has its tools and its mechanisms to find out what changed on the screen and what

needs to be redrawn and therefore it will find out that text here changed, that this widget changed because

the text we passed to it changed and it will only update this text here

in the end. Now again, I'll dive deeper into how that works and how we can find out what Flutter changed

and so on, I'll dive into that throughout the course

once we are a bit more proficient with Flutter, it's just a brief first look which I wanted to give you

at this point, that build is getting called when you call set state and that is why you see the change

then and that is also why you didn't see anything without set state because then you changed the data

which is nice but Flutter never executed build again and therefore this widget tree never got rebuilt

and therefore this text with the updated text never made it onto what the user sees.