详解C#中访问私有成员

     首先我必须承认访问一个类的私有成员不是什么好做法。大家也都知道私有成员在外部是不能被访问的。而一个类中会存在很多私有成员：如私有字段、私有属性、私有方法。对于私有成员访问，可以套用下面这种非常好的方式去解决。

<span style="color: blue;">private string </span>name;
<span style="color: blue;">public string </span>Name
{
<span style="color: blue;">get
</span>{
<span style="color: blue;">return </span>name;
}
<span style="color: blue;">set
</span>{
name = <span style="color: blue;">value</span>;
}
}

<a href="http://11011.net/software/vspaste"></a>

但是有时候，源代码是别人的，你就不能修改源代码，只提供给你dll。或者你去维护别人的代码，源代码却有丢失。这样的情况如果你想知道私有成员的值，甚至去想直接调用类里面的私有方法。那怎么办呢？其实在.net中访问私有成员不是很难，这篇文章提供几个简单的方法让你如愿以偿。

为了让代码用起来优雅，使用扩展方法去实现。

1、得到私有字段的值：

<span style="color: blue;">public static </span>T GetPrivateField<T>(<span style="color: blue;">this object </span>instance, <span style="color: blue;">string </span>fieldname)
{
<span style="color: #2b91af;">BindingFlags </span>flag = <span style="color: #2b91af;">BindingFlags</span>.Instance | <span style="color: #2b91af;">BindingFlags</span>.NonPublic;
<span style="color: #2b91af;">Type </span>type = instance.GetType();
<span style="color: #2b91af;">FieldInfo </span>field = type.GetField(fieldname, flag);
<span style="color: blue;">return </span>(T)field.GetValue(instance);
}

2、得到私有属性的值：

<span style="color: blue;">public static </span>T GetPrivateProperty<T>(<span style="color: blue;">this object </span>instance, <span style="color: blue;">string </span>propertyname)
{
<span style="color: #2b91af;">BindingFlags </span>flag = <span style="color: #2b91af;">BindingFlags</span>.Instance | <span style="color: #2b91af;">BindingFlags</span>.NonPublic;
<span style="color: #2b91af;">Type </span>type = instance.GetType();
<span style="color: #2b91af;">PropertyInfo </span>field = type.GetProperty(propertyname, flag);
<span style="color: blue;">return </span>(T)field.GetValue(instance, <span style="color: blue;">null</span>);
}

3、设置私有成员的值：

<span style="color: blue;">public static void </span>SetPrivateField(<span style="color: blue;">this object </span>instance, <span style="color: blue;">string </span>fieldname, <span style="color: blue;">object </span>value) <br>{ <br><span style="color: #2b91af;">BindingFlags </span>flag = <span style="color: #2b91af;">BindingFlags</span>.Instance | <span style="color: #2b91af;">BindingFlags</span>.NonPublic; <br><span style="color: #2b91af;">Type </span>type = instance.GetType(); <br><span style="color: #2b91af;">FieldInfo </span>field = type.GetField(fieldname, flag); <br> field.SetValue(instance, value); <br>} <br>4、设置私有属性的值： <br><span style="color: blue;">public static void </span>SetPrivateProperty(<span style="color: blue;">this object </span>instance, <span style="color: blue;">string </span>propertyname, <span style="color: blue;">object </span>value) <br>{ <br><span style="color: #2b91af;">BindingFlags </span>flag = <span style="color: #2b91af;">BindingFlags</span>.Instance | <span style="color: #2b91af;">BindingFlags</span>.NonPublic; <br><span style="color: #2b91af;">Type </span>type = instance.GetType(); <br><span style="color: #2b91af;">PropertyInfo </span>field = type.GetProperty(propertyname, flag); <br> field.SetValue(instance, value, <span style="color: blue;">null</span>); <br>} <br><span style="font-family: Verdana;">5、调用私有方法：</span>

<span style="color: blue;">public static </span>T CallPrivateMethod<T>(<span style="color: blue;">this object </span>instance, <span style="color: blue;">string </span>name, <span style="color: blue;">params object</span>[] param)<br>{<br><span style="color: #2b91af;">BindingFlags </span>flag = <span style="color: #2b91af;">BindingFlags</span>.Instance | <span style="color: #2b91af;">BindingFlags</span>.NonPublic;<br><span style="color: #2b91af;">Type </span>type = instance.GetType();<br><span style="color: #2b91af;">MethodInfo </span>method = type.GetMethod(name, flag);<br><span style="color: blue;">return </span>(T)method.Invoke(instance, param);<br>}

[size=medium;]测试：[/size]

下面我们使用一个测试类，进行测试。新建一个类库项目，测试的类代码如下：

<span style="color: blue;">public class </span><span style="color: #2b91af;">TestClass
</span>{
<span style="color: blue;">public </span>TestClass()
{
privatefield1 = 1;
privatefield2 = 99;
PrivateFieldA = <span style="color: #a31515;">"Lo"</span>;
PrivateFieldB = <span style="color: #a31515;">"ve"</span>;
}
<span style="color: blue;">private int </span>privatefield1;
<span style="color: blue;">private int </span>privatefield2;
<span style="color: blue;">private string </span>PrivateFieldA
{
<span style="color: blue;">get</span>;
<span style="color: blue;">set</span>;
}
<span style="color: blue;">private string </span>PrivateFieldB
{
<span style="color: blue;">get</span>;
<span style="color: blue;">set</span>;
}
<span style="color: blue;">private int </span>Add()
{
<span style="color: blue;">return </span>privatefield1 + privatefield2;
}
<span style="color: blue;">private string </span>Join()
{
<span style="color: blue;">return </span>PrivateFieldA + PrivateFieldB;
}
}

将上面类库的dll引入控制台项目中。使用下面代码去使用这个类的私有成员：

<span style="color: #2b91af;">TestClass </span>obj = <span style="color: blue;">new </span><span style="color: #2b91af;">TestClass</span>();
System.<span style="color: #2b91af;">Console</span>.WriteLine(<span style="color: #a31515;">"私有字段"</span>);
System.<span style="color: #2b91af;">Console</span>.WriteLine(obj.GetPrivateField<<span style="color: blue;">int</span>>(<span style="color: #a31515;">"privatefield1"</span>));
System.<span style="color: #2b91af;">Console</span>.WriteLine(obj.GetPrivateField<<span style="color: blue;">int</span>>(<span style="color: #a31515;">"privatefield2"</span>));
System.<span style="color: #2b91af;">Console</span>.WriteLine(<span style="color: #a31515;">"私有属性"</span>);
System.<span style="color: #2b91af;">Console</span>.WriteLine(obj.GetPrivateProperty<<span style="color: blue;">string</span>>(<span style="color: #a31515;">"PrivateFieldA"</span>));
System.<span style="color: #2b91af;">Console</span>.WriteLine(obj.GetPrivateProperty<<span style="color: blue;">string</span>>(<span style="color: #a31515;">"PrivateFieldB"</span>));
System.<span style="color: #2b91af;">Console</span>.WriteLine(<span style="color: #a31515;">"私有方法"</span>);
System.<span style="color: #2b91af;">Console</span>.WriteLine(obj.CallPrivateMethod<<span style="color: blue;">int</span>>(<span style="color: #a31515;">"Add"</span>,<span style="color: blue;">null</span>));
System.<span style="color: #2b91af;">Console</span>.WriteLine(obj.CallPrivateMethod<<span style="color: blue;">string</span>>(<span style="color: #a31515;">"Join"</span>, <span style="color: blue;">null</span>));
System.<span style="color: #2b91af;">Console</span>.WriteLine(<span style="color: #a31515;">"修改私有属性"</span>);
obj.SetPrivateProperty(<span style="color: #a31515;">"PrivateFieldA"</span>, <span style="color: #a31515;">"hello"</span>);
obj.SetPrivateProperty(<span style="color: #a31515;">"PrivateFieldB"</span>, <span style="color: #a31515;">"world"</span>);
System.<span style="color: #2b91af;">Console</span>.WriteLine(obj.CallPrivateMethod<<span style="color: blue;">string</span>>(<span style="color: #a31515;">"Join"</span>, <span style="color: blue;">null</span>));
System.<span style="color: #2b91af;">Console</span>.Read();

结果如下：

<img style="display: inline; border-width: 0px;" title="hhh" src="http://images.cnblogs.com/cnblogs_com/zhuqil/WindowsLiveWriter/C_13ACF/hhh_thumb.jpg" border="0" alt="hhh" width="611" height="398">

[size=small;]总结：[/size]实现对类私有成员的访问。