使用dart：mirrors反射检索getter值 [英] Retrieving getter values with dart:mirrors reflection

问题描述

我有以下代码（简化），它使用反射来迭代类的字段和getter并输出值。 ContainsGetter 类包含getter， ContainsField 类包含一个简单字段。

使用 dart：mirrors 库，我可以通过使用 $ b>

$ b>

$
$ b

以下Dart脚本（使用build 17463）提供以下输出：

应用脚本 p>

  import'dart：mirrors' 
 
 class ContainsGetter {//引发一个错误
 String get aGetter => 我是吸气者; 
} 
 
 class ContainsField {//工作正常
 String aField =我是字段; 
} 
 
 void main（）{
 printFieldValues（reflect（new ContainsField（）））; 
 printGetterValues（reflect（new ContainsGetter（）））; 
} 
 
 void printFieldValues（instanceMirror）{
 var classMirror = instanceMirror.type; 
 classMirror.variables.keys.forEach（（key）{
 var futureField = instanceMirror.getField（key）; //<  -  works ok 
 futureField.then（（imField）= > print（Field：$ key = $ {imField.reflectee}））; 
}）; 
} 
 
 void printGetterValues（instanceMirror）{
 var classMirror = instanceMirror.type; 
 classMirror.getters.keys.forEach（（key）{
 var futureValue = instanceMirror.invoke（key，[]）; //<  -  failed 
 futureValue.then（（imValue ）=> print（Field：$ key = $ {imValue.reflectee}））; 
}）; 
} 
  

输出

字段：aField =我是字段
未捕获错误：在镜像执行期间的编译时错误：< Dart_Invoke：没有找到实例方法'ContainsGetter .aGetter'。
堆栈跟踪：
＃0 _LocalObjectMirrorImpl._invoke（dart：mirrors-patch：163：3）
＃1 _LocalObjectMirrorImpl.invoke（dart：mirrors-patch：125：33）


（可接受的可能是此位尚未写入！）

解决方案

Aah，我刚刚解决了。虽然 aGetter 在实现中类似于一个方法，但您可以使用 getField（）而不是调用以检索其值。

  void printGetterValues（instanceMirror）{ 
 var classMirror = instanceMirror.type; 
 classMirror.getters.keys.forEach（（key）{
 var futureValue = instanceMirror.getField（key）; //<  -  now works ok 
 futureValue.then（（imValue） => print（Field：$ key = $ {imValue.reflectee}））; 
}）; 
} 
  

I have the following code (simplified), that uses reflection to iterate a class's fields and getters and output the values. The ContainsGetter class contains a getter, and the ContainsField class contains a simple field.

Using dart:mirrors library, I can get the value of the field by using instanceMirror.getField(fieldName)), but not the getter by using instanceMirror.invoke(fieldName,[]).

The following Dart script (using the build 17463) gives the output below:

app script

import 'dart:mirrors';

class ContainsGetter { // raises an error
  String get aGetter => "I am a getter";
}

class ContainsField { // works fine
  String aField = "I am a field";
}

void main() {
  printFieldValues(reflect(new ContainsField()));
  printGetterValues(reflect(new ContainsGetter()));
}

void printFieldValues(instanceMirror) {
  var classMirror = instanceMirror.type;
  classMirror.variables.keys.forEach((key) {
    var futureField = instanceMirror.getField(key); // <-- works ok
    futureField.then((imField) => print("Field: $key=${imField.reflectee}"));
  });
}

void printGetterValues(instanceMirror) {
  var classMirror = instanceMirror.type;
  classMirror.getters.keys.forEach((key) {
    var futureValue = instanceMirror.invoke(key,[]); // <-- fails
    futureValue.then((imValue) => print("Field: $key=${imValue.reflectee}"));
  });
}

output

Field: aField=I am a field
Uncaught Error: Compile-time error during mirrored execution: <Dart_Invoke: did not find instance method 'ContainsGetter.aGetter'.>
Stack Trace:
#0      _LocalObjectMirrorImpl._invoke (dart:mirrors-patch:163:3)
#1      _LocalObjectMirrorImpl.invoke (dart:mirrors-patch:125:33)

(An acceptable could be that "this bit just hasn't been written yet!")

解决方案

Aah, I've just worked it out. Although aGetter is like a method in its implementation, you use the getField() rather than invoke to retrieve its value.

void printGetterValues(instanceMirror) {
  var classMirror = instanceMirror.type;
  classMirror.getters.keys.forEach((key) {
    var futureValue = instanceMirror.getField(key); // <-- now works ok
    futureValue.then((imValue) => print("Field: $key=${imValue.reflectee}"));
  });
}

这篇关于使用dart：mirrors反射检索getter值的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！