如何使用Dart中的compute()方法为一个函数传递多个命名参数

Question

如何将compute((方法与只接受多个命名参数的顶级函数一起使用？

我尝试使用函数助手进行命名参数转换，但我得到了一个异常：

出现异常。ArgumentError(无效参数：隔离消息中的非法参数：(对象是闭包-函数"helper"：.(

我该怎么做？

下面是Flutter小部件的一些示例代码。

import 'dart:convert';
import 'dart:math';
import 'package:flutter/foundation.dart';
import 'package:flutter/material.dart';
class Sampler extends StatefulWidget {
@override
_SamplerState createState() => _SamplerState();
}
class _SamplerState extends State<Sampler> {
String result = 'No Samples Yet!';
@override
Widget build(BuildContext context) {
return Container(
child: Column(
children: <Widget>[
Text(result),
RaisedButton(
child: Text('Sample!'),
onPressed: _generateSample,
)
],
),
);
}
Future<void> _generateSample() async {
Map<Symbol, dynamic> symbolizeKeys(Map<String, dynamic> map) {
final result = new Map<Symbol, dynamic>();
map.forEach((String k, v) {
result[new Symbol(k)] = v;
});
return result;
}
Map<String, int> helper(Map<String, Object> params) {
final paramsConverted = symbolizeKeys(params);
return Function.apply(sampleDistribution, [], paramsConverted);
}
var _samples = await compute(helper, {
'strings': ['a', 'b'],
'probaDistribution': [0.4, 0.6],
'numSamples': 10000
});
setState(() {
result = json.encode(_samples);
});
}
}
Map<String, int> sampleDistribution(
{List<String> strings, List<double> probaDistribution, int numSamples}) {
// assert(strings.length == probaDistribution.length);
// assert(probaDistribution.reduce((a, b) => a + b) == 1.0);
List<double> cdf = [];
List<double> probas = generateUniformProbas(numSamples: numSamples);
Map<String, int> result =
Map.fromIterable(strings, key: (s) => s, value: (s) => 0);
double tmp = 0;
for (double i in probaDistribution) {
tmp += i;
cdf.add(tmp);
}
for (double proba in probas) {
var stringIndex = cdf.indexWhere((p) => p > proba);
var selectedString = strings[stringIndex];
result[selectedString] = result[selectedString] + 1;
}
return result;
}
List<double> generateUniformProbas({int numSamples = 1}) {
var randomGenerator = new Random();
List<double> result = [];
for (int i = 0; i < numSamples; i++) {
result.add(randomGenerator.nextDouble());
}
return result;
}

Answer 1

Oops，计算函数只接受顶级函数。只要把它移出去就会得到一个有效的结果。

import 'dart:convert';
import 'dart:math';
import 'package:flutter/foundation.dart';
import 'package:flutter/material.dart';
class Sampler extends StatefulWidget {
@override
_SamplerState createState() => _SamplerState();
}
class _SamplerState extends State<Sampler> {
String result = 'No Samples Yet!';
@override
Widget build(BuildContext context) {
return Container(
child: Column(
children: <Widget>[
Text(result),
RaisedButton(
child: Text('Sample!'),
onPressed: _generateSample,
)
],
),
);
}
Future<void> _generateSample() async {
var _samples = await compute(helper, {
'strings': ['a', 'b'],
'probaDistribution': [0.4, 0.6],
'numSamples': 100000
});
setState(() {
result = json.encode(_samples);
});
}
}
Map<Symbol, dynamic> symbolizeKeys(Map<String, dynamic> map) {
final result = new Map<Symbol, dynamic>();
map.forEach((String k, v) {
result[new Symbol(k)] = v;
});
return result;
}
Map<String, int> helper(Map<String, Object> params) {
final paramsConverted = symbolizeKeys(params);
return Function.apply(sampleDistribution, [], paramsConverted);
}
Map<String, int> sampleDistribution(
{List<String> strings, List<double> probaDistribution, int numSamples}) {
// assert(strings.length == probaDistribution.length);
// assert(probaDistribution.reduce((a, b) => a + b) == 1.0);
List<double> cdf = [];
List<double> probas = generateUniformProbas(numSamples: numSamples);
Map<String, int> result =
Map.fromIterable(strings, key: (s) => s, value: (s) => 0);
double tmp = 0;
for (double i in probaDistribution) {
tmp += i;
cdf.add(tmp);
}
for (double proba in probas) {
var stringIndex = cdf.indexWhere((p) => p > proba);
var selectedString = strings[stringIndex];
result[selectedString] = result[selectedString] + 1;
}
return result;
}
List<double> generateUniformProbas({int numSamples = 1}) {
var randomGenerator = new Random();
List<double> result = [];
for (int i = 0; i < numSamples; i++) {
result.add(randomGenerator.nextDouble());
}
return result;
}