Have a look at the OnlineOffline Editing sample.
It should give you an idea of what to do. It uses JSON for the layer definition and data files.
Hi Rick,
Thanks for the reply. I tried to follow the concept in OnlineOffline sample , but no luck yet. I couldn't understand why there are multiple write and read function i.e, writeFeatureLayerDefinition, writeFeatureSet and writeAddedFeatures. I am very new to iOS development so can't everything in the sample. In my application I don't need to add or delete features, I just need update the features from textfile when get online.