arcengine中，如何在一条线上增加一个点

<P>在arcengine中，想在一条线上增加一个点需要调用AddPoint函数，帮助中说可以省略后面两个参数，调用函数时省略参数出了问题，大家看看怎么办；</P>
<P>IPointCollection pPC;</P>
<P>IPolyline pPolyline = new PolylineClass();</P>
<P>pPC =(IPointCollection)pPolyline;</P>
<P>IPoint pAddP = new PointClass();</P>
<P>pPC.AddPoint( pAddP，null,null );//用null表示忽略参数</P>

<DIV>[C#]
<P><B>Optional Values</B></P>
<DIV><I>before</I>   To indicate that this parameter is undefined, first define a variable <B>object Missing = Type.Missing;</B> then pass this in as <B>ref Missing</B>.</DIV>
<DIV><I>after</I>   To indicate that this parameter is undefined, first define a variable <B>object Missing = Type.Missing;</B> then pass this in as <B>ref Missing</B>.</DIV>
<DIV> </DIV>
<DIV>null?OY-</DIV></DIV>

<P>谢谢上面的朋友，问题解决了，看来我的基本功还有待加强，以后多多指教</P>