可选对象参考 [英] Optional object reference

问题描述

spring.net配置出现问题：

I have a problem with my spring.net configuration:

<object id="O1">
    <constructor-arg ref="Dep1"/>
    <constructor-arg ref="Dep2"/>
</object>

这是所有应用程序使用的通用配置的一部分。有些应用程序在其配置中定义了Dep2，而有些则没有。当特定应用程序未定义Dep2时，是否可以使第二个构造函数arg返回空值（而不是报告错误）？

我想解决此问题而不覆盖特定于应用程序的配置中的O1定义。 em>

This is part of my generic configuration used by all applications. Some applications define Dep2 in their configuration and some don't. Can I make second constructor arg return null (instead of reporting error) when specific application doesn't define Dep2?
I would like to solve this without overriding O1 definition in app specific configuration.

谢谢。

推荐答案

您可以创建 IFactoryObject 返回null并在其中进行配置您的特定应用程序配置文件。参见以下相关问题：如何配置NULL对象在Spring.Net 中。

You can create an IFactoryObject that returns null and configure it in your "specific application" config file. See this related question: How do I configure a NULL object in Spring.Net.

此外，如果Dep2是可选依赖项（例如，它可以为null或具有合理的默认值），则可能会更好将其定义为属性并使用属性注入。

Furthermore, if Dep2 is an optional dependency (e.g it can be null or it has a sensible default) than it is probably better to define it as a property and use property injection.

编辑

我希望这样做可以，但实际上不起作用，因为弹簧容器将 IFactoryObject 返回null视为错误：

I expected this to work, but it actually doesn't, because an IFactoryObject that returns null is treated as an error by the spring container:

来自api文档 IFactoryObject.GetObject（）

如果在以下环境中调用此方法一个封闭的IoC
容器并返回，该IoC容器将
认为此工厂对象未完全初始化，并抛出
a相应的（并且很可能是致命的）异常。

If this method is being called in the context of an enclosing IoC container and returns , the IoC container will consider this factory object as not being fully initialized and throw a corresponding (and most probably fatal) exception.

类：

public class MyClass
{
    public MyOtherClass Prop { get; set; }

    public MyClass(MyOtherClass ref1)
    {
    }
}

public class MyOtherClass
{
}

public class NullFactoryObject : IFactoryObject
{
    public object GetObject()
    {
        return null;
    }

    public Type ObjectType
    {
        get { return typeof(MyOtherClass); }
    }

    public bool IsSingleton
    {
        get { return true; }
    }
}

在configfile1.xml中：

in configfile1.xml:

<object id="MyObject" type="q9292066_null_object_reference.MyClass, q9292066_null_object_reference">
  <constructor-arg name="ref1" ref="ref1" />
</object>

：

<object id="ref1" 
        type="q9292066_null_object_reference.NullFactoryObject, q9292066_null_object_reference" />

这篇关于可选对象参考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！