Checking if the first letter of string is in uppercase in Dart - dart

Question

I want to check if the first letter of string is in uppercase in Dart language. How can I implement it? Thanks in advance.

Answer 1

The simplest way I can think of is to compare the first letter of the string with the uppercase equivalent of it. Something like:
bool isUpperCase(String string) {
if (string == null) {
return false;
}
if (string.isEmpty) {
return false;
}
if (string.trimLeft().isEmpty) {
return false;
}
String firstLetter = string.trimLeft().substring(0, 1);
if (double.tryParse(firstLetter) != null) {
return false;
}
return firstLetter.toUpperCase() == string.substring(0, 1);
}
Updated the answer to take in consideration digits.
Also #Saed Nabil is right, this solution will return true if the string starts with any character that is not a letter (except for digits).

Answer 2

You can use the validators library if you are not already using it.
Then use this method
isUppercase(String str) → bool
check if the string str is uppercase
Don't forget to import the dependency, see documentation, to the pubspec.yaml and to your code import 'package:validators/validators.dart';.
Example code:
if(isUppercase(value[0])){
... do some magic
}
You should check that the value is not empty and not null first for safety. Like this:
if(value != null && value.isNotEmpty && isUppercase(value[0])){
... do amazing things
}

Answer 3

check this code it will return the actual uppercase letter else will return null
void main(){
var myString = "1s you said";
var firstCapital = firstCapitalLetter(myString);
if( firstCapital != null){
print("First Capital Letter is ${firstCapital}");
}else{
print("Not found");
}
}
String firstCapitalLetter(String myString){
final allCapitals = "ABCDEFGHIJKLMNOPQRSTUVWXYZ"; //string.substring(0, 1).toUpperCase() == string.substring(0, 1) will not work with for ex. numbers;
if (myString == null) {
return null;
}
if (myString.isEmpty) {
return null;
}
if (myString.trimLeft().isEmpty) {
return null;
}
if( allCapitals.contains(myString[0])){
return myString[0];
}else{
return null;
}
}
this is a typical case for Optional type of Java language , please check this library if you prefer functional style code
optional package

Answer 4

bool isUppercase(String str){
return str == str.toUpperCase();
}
This seems to be elegant way for checking uppercase
String s='Hello';
bool isUpper = isUppercase(s[0]);
print(isUpper); //true
isUpper = isUppercase(s[1]);
print(isUpper); //false

Answer 5

Add this extension
extension Case on String{
// isuppercase
bool isUpperCase(){
int ascii = codeUnitAt(0);
return ascii >= 65 && ascii <= 90;
}
// islowercase
bool isLowerCase(){
int ascii = codeUnitAt(0);
return ascii >= 97 && ascii <= 122;
}
}
use it like this
String letter = 'A';
print(letter.isUpperCase()); // true