How to convert Double to String or String to double in Dart| Flutter By Example

How to convert Double to String or String to double in Dart| Flutter By Example

This tutorial shows multiple ways to convert double to String or string to double in Dart and flutter programming languages.

  • Convert Double to String in Dart:

    • Double.parse method takes string number and returns adouble value. double.parse("111.12") returns 111.12. Throws FormatException if given string is non-numeric.

  • Double.tryParse method takes string number and returns double value. double.tryParse("111.12") returns 111.12. Does not throw exception and returns null if the string is non-numeric.

  • Convert String to Double in Dart: -Double toString() method returns the string version of a double number. 123.11.toString() returns 123.11.

  • toRadixString() convert string to double.

  • Append string with interpolation ${} syntax.'${number}' where number is a double number.

Let’s explore the String and Double types in Dart and Flutter.

A string is a sequence of characters enclosed in either double quotes or single quotes. It can consist of numbers, letters, symbols, or a combination of these. Example string is ‘1.123’.

On the other hand, a double is a primitive data type representing a floating-point number in Dart programming. Example double is ‘1.123’.

Both types are distinct, and automatic conversions between them are not possible. Therefore, manual conversion is required when converting from a String to a double or vice versa.

Here are some examples illustrating how to perform these conversions.

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How to parse String to double in Dart programming example

There are multiple ways to perform this conversion. One common approach is to use the parse method in the double class.

  • use the parse method in a double class

    The double class provides a static parse() method, which takes an input string and converts it into a double type.

    Syntax:

    double parse(String str)

    The argument is a string representation of a number. If the string contains non-numeric characters, it throws a Uncaught Error: FormatException: Invalid double.

    Here is an example

    void main() {
  var str = '123.10';
  var number = double.parse(str);
  print(number); // 123.1
  print(number.runtimeType); // double
  print(number == 123.10); // true
}

    The parse method throws an error for invalid string representations of floating-point numbers, such as those containing non-numeric characters or null values.

    For example, attempting to parse the string 123.1a0d will result in a Uncaught Error: FormatException: Invalid double 123.10d.

    void main() {
  var str='123.1a0d';
  var number = double.parse(str);
  print(number.runtimeType); // double
  print(number==123.10); // true
}

  • Double tryParse Method

    The tryParse method in the double class provides a more robust alternative to the parse method.

    It efficiently handles runtime exceptions and returns null if the provided string is invalid or contains non-numeric characters.

    Here is a double tryParse method example for successful usecase

    void main() {
  var str = '123.10';
  var number = double.tryParse(str);
  print(number); // 123.1
  print(number.runtimeType); // double
  print(number == 123.10); // true
}

    The above example demonstrates the successful parsing of a valid string into a double.

    The below example returns null and handles invalid string floating values

    void main() {
  var str = '123a.10';
  var number = double.tryParse(str);
  print(number); // null
  print(number.runtimeType); // Null
  print(number == 123.10); // false
}

    In this example, the tryParse method returns null when the input string contains invalid floating-point values, ensuring smooth error handling without raising exceptions.

parse and tryParse() both methods can be used in flutter programming for Converting strings to double.

How to Convert Double to String in Dart or flutter for example?

There are multiple ways to convert double to String in dart.

  • toString() method

  • toRadixString() method

  • Append string with interpolation syntax

  • using toString() method

    In Dart, every class provides the toString() method, which returns a string representation of the object.

    The double class also provides the toString() method, which converts a floating-point number into its string representation.

    void main() {
  double number = 12.11;
  String str = number.toString();
  print(str); // 12.11
  print(str.runtimeType); // String
  print(str == '12.11'); // true
}

    In this example, the toString() method is used to convert the double number 12.11 into its string representation. The resulting string is then printed along with its type information.

  • Appending a String with Interpolation Syntax

    String appending can be achieved using interpolation syntax, denoted by ${} within single or double quotes. This allows for dynamic inclusion of variables or expressions within a string.

    You can append strings or plain numbers using interpolation syntax.

    Here is an example

    void main() {
  double number = 12.11;
  String str = '${number}';
  print(str); // 12.11
  print(str.runtimeType);// String
  print(str == "12.11"); // true
}

    In this example, the interpolation syntax ${number}is used within the string to dynamically append the value of the variable number.

    The resulting string is then printed along with its type information.

Convert Long Double to String without Scientific Notation in Dart and Flutter

Sometimes, you may encounter a double floating-point number with an extended floating value that needs to be converted to a string without scientific notation.

Let’s explore various methods to achieve this in Dart and Flutter.

  • Using toString() and String Interpolation Syntax

    The toString() method and string interpolation syntax can be used to convert a long double to a string. However, by default, they may output the string with scientific notation.

    void main() {
  double number = 0.00000000124211113245266;
  String numToString = number.toString();

  String str = '${number}';
  print(str); // 1.24211113245266e-9
  print(numToString); // 1.24211113245266e-9
}

    Output:

    1.24211113245266e-9
1.24211113245266e-9

To convert a string without scientific notation, You can do it with toStringAsFixed() method or decimal parse method

  • Using toStringAsFixed() Method

    To avoid scientific notation and retain precision, you can utilize the toStringAsFixed() method, which allows specifying the number of fraction digits.

    String toStringAsFixed(int fractionDigits)

    Here is a toStringAsFixed example

    void main() {
  double number = 0.00000000124211113245266;
  String numToString = number.toStringAsFixed(20);
  print(numToString); // 0.00000000124211113245
}

The limitation of toStringAsFixed() is that it only supports up to 20 fraction digits. Attempting to use more than 20 digits will result in a below error.

Uncaught Error: RangeError (fractionDigits): Invalid value: Not in inclusive range 0..20: 23

Next, use a decimal package

  • Using the Decimal Package

    For more robust handling of numbers, you can utilize the decimal package.

    • Import decimal package
    • Convert to Decimal from double using Decimal.parse() method
    • Finally, Convert decimal to String with append syntax

    Here is an example code

    import 'package:decimal/decimal.dart';

void main() {
  double number = 0.00000000124211113245266;
  Decimal decimal = Decimal.parse(number.toString());
  String str = '${number}';
  print(str); // 0.00000000124211113245266

}

Conclusion

In this tutorial, we’ve learned various methods to convert strings to doubles and vice versa in Dart. Additionally, we explored techniques to convert long double fractions into strings without scientific notation, ensuring precision and clarity in our numeric representations.