All language subtitles for 15. Using String Interpolation

With that, back to our application here and before we continue working on the user interface where we

of course still have lots of work left to do,

let me actually first work on the data we're outputting.

With that, I mean this price here which doesn't really look like a price,

there is no dollar sign in front of it for example

and I also mean the date, I want to change the formatting or the content of these two pieces

of data which were outputting here. Now for that, let's start with the price, with the amount we're

outputting

and there I have a special syntax or I want to show you a special syntax you can use in Dart, not just

in Flutter, to output values in a text or as a text.

Right now I'm outputting the amount here with the help of to string and that is the perfectly fine way

of doing that

and this is actually all we need

if all we want to output is the amount value here as a string.

But if I want to add a dollar sign in front of that, I actually can also concatenate this string together

with another string,

I can add dollars sign here and then add a plus to combine these two strings.

And normally this would work, here

however, Dart doesn't like this for some reason.

Now let's first of all try an alternative which will work if I add simply a colon for amount or whatever,

so a colon and then a whitespace

and then I have the plus and then the amount to string and I save this and here we see a colon empty amount.

Now that's nice but I don't want to show a colon but a dollar sign.

So what's special about the dollar sign? For this, let's first of all understand how we could shorten

this here. Concatenating strings like this with a plus is perfectly fine

but Dart actually has a more concise and shorter syntax for that. Instead of combining strings with a

plus, which gets especially cumbersome if you have very long strings with a lot of different segments,

you can use a special syntax where you use the dollar sign, which actually has a special meaning in Dart

strings, which is why we had this error before and after the dollar sign, you can reference a variable

or a property name to output that here.

So here we could type tx and now it would try to inject the value of tx here in that place.

So if we now save that and we go back, we see some strange error here on the right,

that simply is shown because we're exceeding the boundaries here,

let's ignore it for now.

More interesting is that we see instance of transactions, so indeed we are outputting our transaction

here.

An instance of transaction is simply what you see when you call tx to string

and that's called for you here automatically.

Now the more interesting thing is that of course here I don't want I'll put my entire transaction but

my amount and therefore we can also use .amount here,

however if you are trying to inject or to interpolate as it's called more, than just the variable itself,

so if you use more than just a variable name, like here where I also use the dot notation, then you have

to wrap that expression which you're trying to interpolate into curly braces.

So then you have dollar sign and then curly braces and between the curly braces, you have your expression

which should resolve to a string or to something where to string can be called on, which will then be

called automatically by Dart

so that this string gets now added in this place here.

So now I've actually remove txAmount to string here at the end and I just have this syntax,

if we now go back, we indeed see our amount here again but now using a feature called string interpolation

and that's a very handy feature since this is obviously shorter than combining multiple pieces of text

together with a plus.

We also don't have to call to string here because Dart does this for us when we use this string interpolation

syntax.

Now that's all nice

but of course I wanted to add a dollar sign here and not a colon and a whitespace.

However the dollar sign as you can tell is a reserved character,

the dollar assigned to Dart means that

you plan on interpolating some value

but what if you want the dollar sign as a character?

Well you can do something which we already did earlier when we wanted to output a quote.

Then you might remember we added a backslash in front of it to escape it,

so to tell Dart that this should not be treated as a language feature, to close a string but instead

as a normal character and you can do exactly the same with a dollar sign. If you don't want the special

meaning it has to Dart but you want the character dollar sign, then you add a backslash in front

of it and you simply add the dollar sign after the backslash.

So now this dollar sign after the backslash here will just be output as text,

this dollar sign here however, since there is no backslash directly in front of it, will be treated as

the beginning of a string interpolation

and with that if we save this, we have the dollar sign in front of the amount. That was a lot of talking just

to add a dollar sign

but the core takeaway of course is not just that you can escape it but that it has a special meaning

and that you can use it in string interpolation.