您可以调用此函数来获得黑暗(颤振)的精确程度。 Double eval -> Double想要转换的 Int I ->返回的小数点。

double doubleToPrecision(double eval, int i) {
double step1 = eval;//1/3
print(step1); // 0.3333333333333333

String step2 = step1.toStringAsFixed(2);
print(step2); // 0.33

double step3 = double.parse(step2);
print(step3); // 0.33
eval = step3;
return eval; }

请参阅num.toStringAsFixed()的文档。

字符串磨损

返回this的小数字符串表示形式。

在计算字符串表示形式之前，将此转换为double。

如果this的绝对值大于或等于10^21，则该方法返回由this. tostringasexponential()计算的指数表示。

例子:

1000000000000000000000.toStringAsExponential(3); // 1.000e+21

否则，结果是与小数点后的fractionDigits位数最接近的字符串表示形式。如果fractionDigits等于0，则小数点将被省略。

参数fractionDigits必须是满足以下条件的整数:0 <= fractionDigits <= 20。

例子:

1.toStringAsFixed(3);  // 1.000
(4321.12345678).toStringAsFixed(3);  // 4321.123
(4321.12345678).toStringAsFixed(5);  // 4321.12346
123456789012345678901.toStringAsFixed(3);  // 123456789012345683968.000
1000000000000000000000.toStringAsFixed(3); // 1e+21
5.25.toStringAsFixed(0); // 5

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");
    });
  });
}

上述解决方案没有适当地四舍五入数字。我使用:

double dp(double val, int places){ 
   num mod = pow(10.0, places); 
   return ((val * mod).round().toDouble() / mod); 
}

如果你想在文本中舍入double值。

文本(“$ {carpetprice.toStringAsFixed(3)}”,),

您可以简单地将该值乘以100，然后四舍五入，然后再除以100。

(number * 100).round() / 100.0;