因为你在插入元素之前没有对araylist赋chu初值,在元素为空的情况下是不允许引用该元素的,如果改成这样就可以了.
ArrayList al = new ArrayList();
al.Add("test0");
al.Add("test1");
al.Add("test2");
al.Insert(1,"mytest");
ArrayList al = new ArrayList();
al.Add("test0");
al.Add("test1");
al.Add("test2");
al.Insert(1,"mytest");
al.Insert(2,"mytest");
al.Insert(4,"test");
仍出错,WHY?
↓ ↓ ↓ ↓
"0" , "1" , "2"