检查省道中的字符串是否为数字

小开

最佳答案

这可以简化一点

void main(args) {
print(isNumeric(null));
print(isNumeric(''));
print(isNumeric('x'));
print(isNumeric('123x'));
print(isNumeric('123'));
print(isNumeric('+123'));
print(isNumeric('123.456'));
print(isNumeric('1,234.567'));
print(isNumeric('1.234,567'));
print(isNumeric('-123'));
print(isNumeric('INFINITY'));
print(isNumeric(double.INFINITY.toString())); // 'Infinity'
print(isNumeric(double.NAN.toString()));
print(isNumeric('0x123'));
}


bool isNumeric(String s) {
if(s == null) {
return false;
}
return double.parse(s, (e) => null) != null;
}

false   // null
false   // ''
false   // 'x'
false   // '123x'
true    // '123'
true    // '+123'
true    // '123.456'
false   // '1,234.567'
false   // '1.234,567' (would be a valid number in Austria/Germany/...)
true    // '-123'
false   // 'INFINITY'
true    // double.INFINITY.toString()
true    // double.NAN.toString()
false   // '0x123'

来自 double 解析 DartDoc

   * Examples of accepted strings:
*
*     "3.14"
*     "  3.14 \xA0"
*     "0."
*     ".0"
*     "-1.e3"
*     "1234E+7"
*     "+.12e-9"
*     "-NaN"

这个版本也接受十六进制数字

bool isNumeric(String s) {
if(s == null) {
return false;
}


// TODO according to DartDoc num.parse() includes both (double.parse and int.parse)
return double.parse(s, (e) => null) != null ||
int.parse(s, onError: (e) => null) != null;
}


print(int.parse('0xab'));

没错

更新

因为 {onError(String source)}已经被废弃了，所以你只需要使用 tryParse:

bool isNumeric(String s) {
if (s == null) {
return false;
}
return double.tryParse(s) != null;
}

小开

在 Dart 2中不推荐使用这种方法

int.parse(s, onError: (e) => null)

相反，使用

 bool _isNumeric(String str) {
if(str == null) {
return false;
}
return double.tryParse(str) != null;
}

小开

甚至更短。尽管事实上它将与 double一起工作，使用 num是更准确的。

isNumeric(string) => num.tryParse(string) != null;

内置 num.tryParse:

static num tryParse(String input) {
String source = input.trim();
return int.tryParse(source) ?? double.tryParse(source);
}

小开

对于任何想要使用正则表达式的非本地方式

RegExp _numeric = RegExp(r'^-?[0-9]+$');


/// check if the string contains only numbers
bool isNumeric(String str) {
return _numeric.hasMatch(str);
}

小开

if (int.tryParse(value) == null) {
return 'Only Number are allowed';
}

小开

是的，有一个更“复杂”的方式 * rsrs * 。

extension Numeric on String {
bool get isNumeric => num.tryParse(this) != null ? true : false;
}


main() {
print("1".isNumeric); // true
print("-1".isNumeric); // true
print("2.5".isNumeric); // true
print("-2.5".isNumeric); // true
print("0x14f".isNumeric); // true
print("2,5".isNumeric); // false
print("2a".isNumeric); // false
}

小开

import 'dart:convert';


void main() {
//------------------------allMatches Example---------------------------------
print('Example 1');


//We want to extract ages from the following string:
String str1 = 'Sara is 26 years old. Maria is 18 while Masood is 8.';


//Declaring a RegExp object with a pattern that matches sequences of digits
RegExp reg1 = new RegExp(r'(\d+)');


//Iterating over the matches returned from allMatches
Iterable allMatches = reg1.allMatches(str1);
var matchCount = 0;
allMatches.forEach((match) {
matchCount += 1;
print('Match ${matchCount}: ' + str1.substring(match.start, match.end));
});


//------------------------firstMatch Example---------------------------------
print('\nExample 2');


//We want to find the first sequence of word characters in the following string:
//Note: A word character is any single letter, number or underscore
String str2 = '#%^!_as22 d3*fg%';


//Declaring a RegExp object with a pattern that matches sequences of word
//characters
RegExp reg2 = new RegExp(r'(\w+)');


//Using the firstMatch function to display the first match found
Match firstMatch = reg2.firstMatch(str2) as Match;
print('First match: ${str2.substring(firstMatch.start, firstMatch.end)}');


//--------------------------hasMatch Example---------------------------------
print('\nExample 3');


//We want to check whether a following strings have white space or not
String str3 = 'Achoo!';
String str4 = 'Bless you.';


//Declaring a RegExp object with a pattern that matches whitespaces
RegExp reg3 = new RegExp(r'(\s)');


//Using the hasMatch method to check strings for whitespaces
print(
'The string "' + str3 + '" contains whitespaces: ${reg3.hasMatch(str3)}');
print(
'The string "' + str4 + '" contains whitespaces: ${reg3.hasMatch(str4)}');


//--------------------------stringMatch Example-------------------------------
print('\nExample 4');


//We want to print the first non-digit sequence in the following strings;
String str5 = '121413dog299toy01food';
String str6 = '00Tom1231frog';


//Declaring a RegExp object with a pattern that matches sequence of non-digit
//characters
RegExp reg4 = new RegExp(r'(\D+)');


//Using the stringMatch method to find the first non-digit match:
String? str5Match = reg4.stringMatch(str5);
String? str6Match = reg4.stringMatch(str6);
print('First match for "' + str5 + '": $str5Match');
print('First match for "' + str6 + '": $str6Match');


//--------------------------matchAsPrefix Example-----------------------------
print('\nExample 5');


//We want to check if the following strings start with the word "Hello" or not:
String str7 = 'Greetings, fellow human!';
String str8 = 'Hello! How are you today?';


//Declaring a RegExp object with a pattern that matches the word "Hello"
RegExp reg5 = new RegExp(r'Hello');


//Using the matchAsPrefix method to match "Hello" to the start of the strings
Match? str7Match = reg5.matchAsPrefix(str7);
Match? str8Match = reg5.matchAsPrefix(str8);
print('"' + str7 + '" starts with hello: ${str7Match != null}');
print('"' + str8 + '" starts with hello: ${str8Match != null}');
}