Assign function to a variable in Dart/Flutter

Question

I'm trying to use a function(returning String) to a Text Widget. If I use getName() directly it works fine.

But if assign the function through a dynamic variable like below, It throws a error. I want to update the name on Button Press.

Text(title, style:kText20White),
Button(
 title: 'Change Name',
 onPressed: (){
   setState((){
     value = 1;
   });
 {
)

dynamic title;
int value = 0;

@override
void initState() {
 super.initState();
 title = getName;
}

String getName(){
 if(name == 0){
   return 'Taarak';
 } else {
   return 'Harshad';
 }

Error: type '() => String' is not a subtype of type 'String'

Is it possible to assign String by function through a variable?

Text(title(), ...) instead? The Text widget doesn't want a function, it wants a string. — Ben Butterworth
– Ben Butterworth, Commented Mar 18, 2021 at 9:37
I don't understand what you're saying ("until it returns?), can you reword it? Oh, you want to await a network request, asynchronous event or Future? Then use FutureBuilder — Ben Butterworth
– Ben Butterworth, Commented Mar 18, 2021 at 9:39
Sorry for my English. I meant 'as long as it returns' String from the function. I don't need to use FutureBuilder since my Strings are static. Check getName() for reference. — VipiN Negi
– VipiN Negi, Commented Mar 18, 2021 at 9:49
You only want to show Text widget when text exists? You can make getName return nullable, and use conditional render: inside build, var name = getName() and if (name) Text(name) — Ben Butterworth
– Ben Butterworth, Commented Mar 18, 2021 at 9:51

KuKu · Accepted Answer · 2021-03-18 09:27:57Z

2

Finally I understood what you want to do.

You need to check title's variable type and divide calling by type.

Here is final solution!!!

Text(title is String ? title : title(), style:kText20White),
Button(
 title: 'Change Name',
 onPressed: (){
   setState((){
     value = 1;
   });
 {
)

dynamic title;
int value = 0;

@override
void initState() {
 super.initState();
 title = getName;
}

String getName(){
 if(name == 0){
   return 'Taarak';
 } else {
   return 'Harshad';
 }

edited Mar 18, 2021 at 9:27

answered Mar 18, 2021 at 7:52

KuKu

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4 Comments

VipiN Negi Over a year ago

This will not help my use case. I've edited my question for better understanding of my usecase.

VipiN Negi Over a year ago

I want to assign title with String variable later, but providing () to title will not let me do that. Is it not possible to pass function directly via variable without () to mention on Text widget?

KuKu Over a year ago

I updated content after understood what you want to do.

KuKu Over a year ago

Enjoy your coding~!

Kishan Dhankecha · Accepted Answer · 2021-03-18 10:33:21Z

0

You are referencing a function, You have to call function there

String title;

String getName(){
 return 'First Name';
}

title = getName; //Here you are referencing a function, You have to call function here

Text(title, style:kText20White)

Solution:

title = getName();

Try this.

edited Mar 18, 2021 at 10:33

answered Mar 18, 2021 at 7:45

Kishan Dhankecha

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2 Comments

VipiN Negi Over a year ago

This will assign the output of getName() to the title, which is non-updatable later. I've edited my question for better understanding of my usecase.

Kishan Dhankecha Over a year ago

@VipiNNegi in this case you just have to give variable type annotation as a String, Use String instead of dynamic.

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