给定一个double，我希望将它四舍五入到小数点后的给定精度点数，类似于PHP的round()函数。
我能在Dart文档中找到的最接近的东西是double.toStringAsPrecision()，但这不是我所需要的，因为它包括了精度总分中小数点前的数字。
例如，使用toStringAsPrecision(3):
0.123456789 rounds to 0.123
9.123456789 rounds to 9.12
98.123456789 rounds to 98.1
987.123456789 rounds to 987
9876.123456789 rounds to 9.88e+3
随着数字大小的增加，小数点后的精度也相应降低。
当前回答
你可以创建一个可重用的函数，接受你想格式化的numberOfDecimal，并利用toStringAsFixed()方法来格式化数字并将其转换回double。
供参考，toStringAsFixed方法不会四舍五入以5结尾的数字(例如:toStringAsFixed四舍五入2.275到2.27而不是2.28)。这是dart toStringAsFixed方法的默认行为(类似于Javascript的toFixed)
作为一种变通方法，我们可以在现有数字的最后一个十进制数后面加上1(例如:将0.0001加到2.275变成2.2751，而2.2751将正确舍入为2.28)
double roundOffToXDecimal(double number, {int numberOfDecimal = 2}) {
// To prevent number that ends with 5 not round up correctly in Dart (eg: 2.275 round off to 2.27 instead of 2.28)
String numbersAfterDecimal = number.toString().split('.')[1];
if (numbersAfterDecimal != '0') {
int existingNumberOfDecimal = numbersAfterDecimal.length;
number += 1 / (10 * pow(10, existingNumberOfDecimal));
}
return double.parse(number.toStringAsFixed(numberOfDecimal));
}
// Example of usage:
var price = roundOffToXDecimal(2.275, numberOfDecimal: 2)
print(price); // 2.28
其他回答
把这个扩展写在double上
extension Round on double {
double roundToPrecision(int n) {
int fac = pow(10, n).toInt();
return (this * fac).round() / fac;
}
}
如果使用动态类型的数据。你可以使用它。
typeDecimal(data) => num.parse(data.toString()).toStringAsFixed(2);
我在double上做了这个扩展
import 'dart:math';
extension DoubleExtension on double {
/// rounds the double to a specific decimal place
double roundedPrecision(int places) {
double mod = pow(10.0, places) as double;
return ((this * mod).round().toDouble() / mod);
}
/// good for string output because it can remove trailing zeros
/// and sometimes periods. Or optionally display the exact number of trailing
/// zeros
String roundedPrecisionToString(
int places, {
bool trailingZeros = false,
}) {
double mod = pow(10.0, places) as double;
double round = ((this * mod).round().toDouble() / mod);
String doubleToString =
trailingZeros ? round.toStringAsFixed(places) : round.toString();
if (!trailingZeros) {
RegExp trailingZeros = RegExp(r'^[0-9]+.0+$');
if (trailingZeros.hasMatch(doubleToString)) {
doubleToString = doubleToString.split('.')[0];
}
}
return doubleToString;
}
String toStringNoTrailingZeros() {
String doubleToString = toString();
RegExp trailingZeros = RegExp(r'^[0-9]+.0+$');
if (trailingZeros.hasMatch(doubleToString)) {
doubleToString = doubleToString.split('.')[0];
}
return doubleToString;
}
}
这是通过的测试。
import 'package:flutter_test/flutter_test.dart';
import 'package:project_name/utils/double_extension.dart';
void main() {
group("rounded precision", () {
test("rounding to 0 place results in an int", () {
double num = 5.1234;
double num2 = 5.8234;
expect(num.roundedPrecision(0), 5);
expect(num2.roundedPrecision(0), 6);
});
test("rounding to 1 place rounds correctly to 1 place", () {
double num = 5.12;
double num2 = 5.15;
expect(num.roundedPrecision(1), 5.1);
expect(num2.roundedPrecision(1), 5.2);
});
test(
"rounding a number to a precision that is more accurate than the origional",
() {
double num = 5;
expect(num.roundedPrecision(5), 5);
});
});
group("rounded precision returns the correct string", () {
test("rounding to 0 place results in an int", () {
double num = 5.1234;
double num2 = 5.8234;
expect(num.roundedPrecisionToString(0), "5");
expect(num2.roundedPrecisionToString(0), "6");
});
test("rounding to 1 place rounds correct", () {
double num = 5.12;
double num2 = 5.15;
expect(num.roundedPrecisionToString(1), "5.1");
expect(num2.roundedPrecisionToString(1), "5.2");
});
test("rounding to 2 places rounds correct", () {
double num = 5.123;
double num2 = 5.156;
expect(num.roundedPrecisionToString(2), "5.12");
expect(num2.roundedPrecisionToString(2), "5.16");
});
test("cut off all trailing zeros (and periods)", () {
double num = 5;
double num2 = 5.03000;
expect(num.roundedPrecisionToString(5), "5");
expect(num2.roundedPrecisionToString(5), "5.03");
});
});
}
我永远转换我像这样=> ｀
num.tryParse("23.123456789")!.toDouble().roundToDouble()
`
您可以使用toStringAsFixed来显示小数点后的有限数字。toStringAsFixed返回一个小数字符串表示形式。toStringAsFixed接受一个名为fraction Digits的参数，它表示我们想要显示的小数后面的位数。下面是如何使用它。
double pi = 3.1415926;
const val = pi.toStringAsFixed(2); // 3.14
