There are many classes in mx.utils such as ArrayUtil,Base64Decoder,Base64Encoder and so on.
But if we are in an as project, when we type 'import mx.utils.' only NameUtil and StringUtil appeared.
Next,we copy the source of mx.utils from 'D:\Program Files\Adobe\Flex Builder 3\sdks\3.0.0\framework\src\mx' (Only if your flex builder 3 is installed in ''D:\Program Files\Adobe\Flex Builder 3' folder )to our as project's src folder.
Then type 'import mx.utils.' again,now you will see what happened.
But the same thing wonn't occur in flex project. So I am puzzled.
If you know why. Please leave a comment. Thanks!

要不你重新定位下你的库?