**extractDouble() to the Rescue: How to Get Double Only from String in Flutter**
When working with user input or data retrieved from an API, you often need to convert strings into more usable formats – like numbers. In Flutter, you may encounter strings that contain only numbers, but also strings with non-numeric characters, like commas or decimal points. In this post, we’ll explore how to extract the double value from a string in Flutter using the `double.parse()` and `double.tryParse()` methods.
**Why Not Just Use `int.parse()`?**
First, let’s clarify why we’re using `double` instead of `int`. Suppose you have a string like `”12.50″`, which represents a decimal value. You’d want to convert it to a `double` rather than an `int` to preserve the decimal part. `double.parse()` can handle this conversion, while `int.parse()` would simply truncate the decimal part, resulting in an incorrect value.
**Using `double.parse()`**
To extract a double value from a string using `double.parse()`, you can simply pass the string as an argument. For example:
“`dart
String str = “123.45”;
double doubleValue = double.parse(str);
print(doubleValue); // Output: 123.45
“`
However, be aware that `double.parse()` will throw a `FormatException` if the input string cannot be parsed as a double value.
**Using `double.tryParse()`**
To handle the possibility of a invalid input, you can use `double.tryParse()`, which returns a nullable `double` value if the parsing fails. Here’s how to use it:
“`dart
String str = “invalid input”;
double? doubleValue = double.tryParse(str);
print(doubleValue); // Output: null
“`
In this example, `double.tryParse()` returns `null` because the input string cannot be parsed as a double value.
**How to Use `extractDouble()`**
In Flutter, you can create a handy extension method, called `extractDouble()`, to simplify the process of extracting a double value from a string. Here’s an example implementation:
“`dart
extension StringExtensions on String {
double? extractDouble() {
return double.tryParse(this);
}
}
“`
Now, you can use this extension method to extract a double value from a string:
“`dart
String str = “12.50”;
double? doubleValue = str.extractDouble();
print(doubleValue); // Output: 12.5
“`
**Conclusion**
In this post, we’ve explored how to extract a double value from a string in Flutter using `double.parse()` and `double.tryParse()` methods. We also created a handy extension method, `extractDouble()`, to simplify the process. By using these techniques, you can confidently handle user input and API data in your Flutter app, even when dealing with decimal values.
