Opens a document asynchronously.
- iOS 5.0+
A block with code to execute after the open operation concludes. The block returns no value and has one parameter:
trueif the open operation succeeds, otherwise
The block is invoked on the main queue.
Call this method to begin the sequence of method calls that opens and reads a document asynchronously. The method obtains the file-system location of the document from the
file property. After the open operation concludes, the code in
completion is executed.
You can override this method if you want custom document-opening behavior, but if you do it is recommended that you call the superclass implementation first (
super). If you don’t call
super, you should use the
NSFile class to implement coordinated reading. The default implementation calls
perform to schedule the document-reading work for execution on a background queue and then, from the dispatched block, performs file coordination. The queued task then calls