在Dart中通过反射获取私有变量 [英] Get private variable by reflection in dart

问题描述

我想在dart中的对象中获取私有变量。

此变量没有吸气剂，因此我想通过反射来实现。

我尝试了很多方法，但对我无济于事。

例如，当我这样做时：

  var体现= reflect（this）; 
 InstanceMirror字段= Reflection.getField（new Symbol（fieldName））; 
  

我收到错误：

否字段名称的获取器。
这是正常现象，因为变量没有吸气剂。

如何获取此变量？

使用测试代码进行编辑：

这是我的反射测试（测试变量是reflectClass（MyClass））

< pre class = lang-dart prettyprint-override> reflectClass（Injector）.declarations.keys.forEach（（e）=> test.getField（e，test.type.owner））


我收到此错误：

类'_LocalInstanceMirror'没有实例方法'getField'具有
匹配的参数。

如果执行此操作：

  reflectClass（Injector）.declarations.keys.forEach（（e）=>测试.getField（e））
  

我得到：

类'DynamicInjector'没有实例获取器
'_PRIMITIVE_TYPES @ 0x1b5a3f8d'。

声明值相同

解决方案

您收到的错误消息实际上是正确的。该类对此领域有一个吸气剂。
Dart隐式地为所有非final / non-const字段创建getter，并为所有非final / non-const字段创建setter。

Dart2JS尚不支持私有成员。
请参阅 https://code.google.com/p/ dart / issues / detail？id = 13881

以下示例如何访问私有字段：
（来自 https://code.google.com/p/dart/issues/detail?id=16773 ）

  import'dart：mirrors'; 
 
类ClassWithPrivateField {
 
字符串_privateField; 
} 
 
 void main（）{
 
 ClassMirror classM = ReflectionClass（ClassWithPrivateField）; 
 Symbol privateFieldSymbol; 
符号构造器符号; 
用于（classM.declarations.values中的DeclarationMirror声明）{
 if（声明是VariableMirror）{
 privateFieldSymbol = clarification.simpleName; 
}否则，如果（声明是MethodMirror&& clarification.isConstructor）{
 constructorSymbol = clarification.constructorName; 
} 
} 
 
 //不必使用反射创建实例就可以
 //通过反射访问其成员
 InstanceMirror实例= classM.newInstance（constructorSymbol，[]）; 
 
 // var s = new Symbol（’_ privateField’）; //不适用于私有字段
 
 //要为私有字段创建符号，您需要使用库
 //如果该类位于主库
中/ / var s = MirrorSystem.getSymbol（'_ privateField'，currentMirrorSystem（）。isolate.rootLibrary）; 
 //或更简单的
 // var s = MirrorSystem.getSymbol（’_ privateField’，instance.type.owner）; 
 for（var i = 0; i< 1000; ++ i）{
 instance.setField（privateFieldSymbol，'test'）; 
 print（‘迭代$ {instance.getField（privateFieldSymbol）}’）； 
} 
} 
  

I would like to get private variable in an object in dart.

This variable has no getter so I want to do this with reflection.

I try many way but nothing works to me.

For exemple, when I do this:

var reflection = reflect(this);
InstanceMirror field = reflection.getField(new Symbol(fieldName));

I get an error:

No getter for fieldName. It's normal because the variable hasn't getter.

How can I get this variable ?

EDIT with a test code:

Here is my reflect test (test variable is a reflectClass(MyClass))

reflectClass(Injector).declarations.keys.forEach((e) => test.getField(e, test.type.owner))

I get this error:

Class '_LocalInstanceMirror' has no instance method 'getField' with matching arguments.

If I do this:

reflectClass(Injector).declarations.keys.forEach((e) => test.getField(e))

I get:

Class 'DynamicInjector' has no instance getter '_PRIMITIVE_TYPES@0x1b5a3f8d'.

Same thing with values of declarations.

解决方案

The error message you got is actually correct. The class has a getter for this field. Dart implicitly creates getters for all and setters for all non-final/non-const fields.

It seems access to private members isn't yet supported in Dart2JS. see https://code.google.com/p/dart/issues/detail?id=13881

Here an example how to access private fields: (example from https://code.google.com/p/dart/issues/detail?id=16773)

import 'dart:mirrors';

class ClassWithPrivateField {

  String _privateField;
}

void main() {

  ClassMirror classM = reflectClass(ClassWithPrivateField);
  Symbol privateFieldSymbol;
  Symbol constructorSymbol;
  for (DeclarationMirror declaration in classM.declarations.values) {
    if (declaration is VariableMirror) {
      privateFieldSymbol = declaration.simpleName;
    } else if (declaration is MethodMirror && declaration.isConstructor) {
      constructorSymbol = declaration.constructorName;
    }
  }

  // it is not necessary to create the instance using reflection to be able to
  // access its members with reflection
  InstanceMirror instance = classM.newInstance(constructorSymbol, []);

  // var s = new Symbol('_privateField'); // doesn't work for private fields

  // to create a symbol for a private field you need the library 
  // if the class is in the main library
  // var s = MirrorSystem.getSymbol('_privateField', currentMirrorSystem().isolate.rootLibrary);
  // or simpler
  // var s = MirrorSystem.getSymbol('_privateField', instance.type.owner); 
  for (var i=0; i<1000; ++i) {
    instance.setField(privateFieldSymbol, 'test');
    print('Iteration ${instance.getField(privateFieldSymbol)}');
  }
}

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