writeToFile如何判断何时完成。

I'm doing some writing of data to my documents directory and I was wondering if there is a way to tell when my writeToFile method completes and the file I am creating has be fully created. Thanks in advance here is the method I am calling I am just looking for a way wether it is a delegate method or some other way to tell when this completes.I'm doing some writing of data to my documents