Groovy：从类内部方法动态添加Groovy类的属性 [英] Groovy: dynamically add properties to groovy classes from inside class methods

问题描述

我有以下代码：

  class MyClass {
 def myMethod（）{
 variable =我是一个变量
} 
 
 def propertyMissing（String name）{
 println缺少属性$ name
} 
} 
 
 MyClass myClass = new MyClass（）; 
 myClass.myProperty 
 myClass.myMethod（）; 
  

在myClass.myProperty中，缺少属性myProperty 然后在 myClass.myMethod（）中，groovy不会尝试去到 propertyMissing ，而只是抛出一个

  groovy.lang.MissingPropertyException：没有这样的属性：类的变量：MyClass 
  

一些在线搜索表明它是因为 myClass.myProperty 调用getter方法，该方法重定向到propertyMissing。

我猜测在类方法中，groovy不会去通过getter方法的变量，这就是为什么propertyMissing没有被调用？

有没有办法实现我想要做的动态 propertyMissing 或 getProperty 或类似的东西？

PS我不想在myMethod中执行 def variable = ... 或字符串变量= ... 。我希望 myMethod 中的语法保持为 variable = ... ，但在该方法之外添加任何内容是可以接受的。

解决方案

你可以让你的类扩展Expando a href =http://groovy.codehaus.org/api/groovy/util/Expando.html =noreferrer> Expando在这里描述）

  class MyClass extends Expando {
 def myMethod（）{
 variable =我是一个变量
} 
 
 def propertyMissing（String name）{
 printlnMissing property $ name
} 
} 
 
 MyClass myClass = new MyClass（）
 myClass .myProperty 
 myClass.myMethod（）
 println myClass.variable 
  

您可以通过为变量创建自己的备份映射并自己编写 get / setProperty 方法来手动执行类似的功能，即：

  class MyClass {
 
 de f myMethod（）{
 variable =我是一个变量
} 
 
 def propertyMissing（String name）{
 printlnMissing property $ name
 
 $ b $ def backingMap = [：] 
 
 Object getProperty（String property）{
 if（backingMap [property] == null）{
 propertyMissing（property）
} 
 else {
 backingMap [property] 
} 
} 
 
 void setProperty（String property，Object value ）{
 backingMap [property] = value 
} 
} 
 
 MyClass myClass = new MyClass（）
 myClass.myProperty 
 myClass。 myMethod（）
 println myClass.variable 
  

虽然您可以从 Expando的源代码，this手卷版本的检查少了很多，我相信它少了; - ）

I have the following code:

class MyClass {
    def myMethod() {
        variable = "I am a variable"
    }

    def propertyMissing(String name) {
        println "Missing property $name"
    }
}

MyClass myClass = new MyClass();
myClass.myProperty
myClass.myMethod();

At myClass.myProperty, Missing property myProperty was printed out to the console.

But then in myClass.myMethod(), groovy makes no attempt to go to propertyMissing but instead just throws a

groovy.lang.MissingPropertyException: No such property: variable for class: MyClass

Some search online indicates that it is because myClass.myProperty calls a getter method, which redirects to propertyMissing.

I am guessing that within class methods, groovy doesn't go through getter methods for variables and that's why propertyMissing is not getting called?

Is there a way to achieve what I want to do using the dynamic propertyMissing, or getProperty, or anything like that?

P.S. I don't want to do def variable = ... or String variable = ... in myMethod. I am hoping that the syntax within myMethod will stay as variable = ..., but adding anything outside of that method is acceptable.

解决方案

You can make your class extend Expando (Expando is described here)

class MyClass extends Expando {
    def myMethod() {
        variable = "I am a variable"
    }

    def propertyMissing(String name) {
        println "Missing property $name"
    }
}

MyClass myClass = new MyClass()
myClass.myProperty
myClass.myMethod()
println myClass.variable

You can hand-roll a similar functionality by creating your own backing map for variables, and writing the get/setProperty methods yourself, ie:

class MyClass {

    def myMethod() {
        variable = "I am a variable"
    }

    def propertyMissing(String name) {
        println "Missing property $name"
    }

    def backingMap = [:]

    Object getProperty( String property ) {
      if( backingMap[ property ] == null ) {
        propertyMissing( property )
      }
      else {
        backingMap[ property ]
      }
    }

    void setProperty( String property, Object value ) {
      backingMap[ property ] = value
    }
}

MyClass myClass = new MyClass()
myClass.myProperty
myClass.myMethod()
println myClass.variable

Though as you can see from the source code for Expando, this hand-rolled version does a lot less checks and I'd trust it less ;-)

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