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;

使用Dart Extension方法修改@andyw的答案:

extension Precision on double {
    double toPrecision(int fractionDigits) {
        double mod = pow(10, fractionDigits.toDouble());
        return ((this * mod).round().toDouble() / mod);
    }
}

用法:

var latitude = 1.123456;
var latitudeWithFixedPrecision = latitude.toPrecision(3); // Outputs: 1.123

如果你想要使用特殊的舍入。您可以尝试这个函数(舍入)。

void main(List<String> arguments) {
list.map((e) {
 log('list1');
 rounding(e, 0.05);
 rounding(e, 0.1);
 rounding(e, 0.2);
 rounding(e, 0.25);
 rounding(e, 0.5);
 rounding(e, 1);
 rounding(e, 10);
}).toList();
list2.map((e) {
 log('list2');
 rounding(e, 0.05);
 rounding(e, 0.1);
 rounding(e, 0.2);
 rounding(e, 0.25);
 rounding(e, 0.5);
 rounding(e, 1);
 rounding(e, 10);
}).toList();
}

const list = [1.11, 1.22, 1.33, 1.44, 1.55, 1.66, 1.77, 1.88, 1.99];

const list2 = [2.19, 3.28, 4.37, 5.46, 6.55, 7.64, 8.73, 9.82, 10.91];

void rounding(double price, double count) {
log('-----------------------');
log('price: $price, count: $count');
double _priceRemainder = price % count;
double _someDiff = count / _priceRemainder;
log('_price: ${_priceRemainder.toStringAsFixed(2)}');
log('_pricePlus: ${_someDiff.toStringAsFixed(2)}');
if (_someDiff.toStringAsFixed(2) == '1.00') {
 log('_someDiff = 1');
} else if (_someDiff > 1 && _someDiff <= 2 ||
   _someDiff.toStringAsFixed(2) == '2.00') {
 log('_someDiff > 1 && _someDiff <= 2 || _someDiff.toStringAsFixed(2) == 2.00');
 log('ceilToDouble: $price: ${(price + (count - _priceRemainder)).toStringAsFixed(2)}');
 log('floorToDouble: $price: ${(price - _priceRemainder).toStringAsFixed(2)}');
 log('roundToDouble: $price: ${(price + (count - _priceRemainder)).toStringAsFixed(2)}');
} else if (_someDiff > 2) {
 log('_someDiff > 2');
 log('ceilToDouble: $price: ${(price + (count - _priceRemainder)).toStringAsFixed(2)}');
 log('floorToDouble: $price: ${(price - _priceRemainder).toStringAsFixed(2)}');
 log('roundToDouble: $price: ${(price - _priceRemainder).toStringAsFixed(2)}');
}
log('-----------------------');
}

调试控制台:

[log] price: 10.91, count: 0.05
[log] _price: 0.01
[log] _pricePlus: 5.00
[log] _someDiff > 2
[log] ceilToDouble: 10.91: 10.95
[log] floorToDouble: 10.91: 10.90
[log] roundToDouble: 10.91: 10.90
2
[log] -----------------------
[log] price: 10.91, count: 0.1
[log] _price: 0.01
[log] _pricePlus: 10.00
[log] _someDiff > 2
[log] ceilToDouble: 10.91: 11.00
[log] floorToDouble: 10.91: 10.90
[log] roundToDouble: 10.91: 10.90
2
[log] -----------------------
[log] price: 10.91, count: 0.2
[log] _price: 0.11
[log] _pricePlus: 1.82
[log] _someDiff > 1 && _someDiff <= 2 || _someDiff.toStringAsFixed(2) == 2.00
[log] ceilToDouble: 10.91: 11.00
[log] floorToDouble: 10.91: 10.80
[log] roundToDouble: 10.91: 11.00
2
[log] -----------------------
[log] price: 10.91, count: 0.25
[log] _price: 0.16
[log] _pricePlus: 1.56
[log] _someDiff > 1 && _someDiff <= 2 || _someDiff.toStringAsFixed(2) == 2.00
[log] ceilToDouble: 10.91: 11.00
[log] floorToDouble: 10.91: 10.75
[log] roundToDouble: 10.91: 11.00
2
[log] -----------------------
[log] price: 10.91, count: 0.5
[log] _price: 0.41
[log] _pricePlus: 1.22
[log] _someDiff > 1 && _someDiff <= 2 || _someDiff.toStringAsFixed(2) == 2.00
[log] ceilToDouble: 10.91: 11.00
[log] floorToDouble: 10.91: 10.50
[log] roundToDouble: 10.91: 11.00
2
[log] -----------------------
[log] price: 10.91, count: 1.0
[log] _price: 0.91
[log] _pricePlus: 1.10
[log] _someDiff > 1 && _someDiff <= 2 || _someDiff.toStringAsFixed(2) == 2.00
[log] ceilToDouble: 10.91: 11.00
[log] floorToDouble: 10.91: 10.00
[log] roundToDouble: 10.91: 11.00
2
[log] -----------------------
[log] price: 10.91, count: 10.0
[log] _price: 0.91
[log] _pricePlus: 10.99
[log] _someDiff > 2
[log] ceilToDouble: 10.91: 20.00
[log] floorToDouble: 10.91: 10.00
[log] roundToDouble: 10.91: 10.00

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

我使用toStringAsFixed()方法将一个数字四舍五入到小数点后的特定数字 例:

double num = 22.48132906

当我四舍五入到像这样的两个数字时:

print(num.toStringAsFixed(2)) ;

结果是22.48

当我四舍五入到一个数字时，它显示出22.5

要将Dart中的double整入到小数点后的给定精度，可以使用Dart toStringAsFixed()方法中的内置解决方案，但必须将其转换回double

void main() {
  double step1 = 1/3;  
  print(step1); // 0.3333333333333333
  
  String step2 = step1.toStringAsFixed(2); 
  print(step2); // 0.33 
  
  double step3 = double.parse(step2);
  print(step3); // 0.33
}