string[] to arraylist<string>:
eg:
string[] str; arraylist<string> arr;

for(int i=0;i<str.lenght;i++)
{
  arr.add(str[i]);
}

arraylist<string> to string[]:
eg:
string[] str; arraylist<string> arr;

str = new string[arr.size()];
str = arr.toarray(str);

http://blog.csdn.net/brave_heart_lxl/article/details/6178909