Swift class cast fails while casting AnyObject to NSMutableDictionary - class

Question

var fetchEachStory = Firebase(url: "\(self.individualStoryUrl)\(eachStory)")
// Read data and react to changes
fetchEachStory.observeEventType(.Value) {
snapshot in
let storyDetails = snapshot.value as NSMutableDictionary?
let score = storyDetails!["score"] as Int?
var thisStory = eachStory
if score? > self.minSetScore {
self.showStories[thisStory] = storyDetails
}
}
While Assigning Snapshot.value to story details, it fails some times saying:
error: Execution was interrupted, reason: EXC_BREAKPOINT (code=EXC_I386_BPT, subcode=0x0).
The process has been returned to the state before expression evaluation.
How can I handle this ?

Answer 1

This line of code:
let storyDetails = snapshot.value as NSMutableDictionary?
fails if snapshot.value is not an NSMutableDictionary. It is better to use a conditional cast as? along with optional binding if let to make sure you only proceed if snapshot.value is the type you expect. The same is true for score being an Int.
According to the Firebase Documentation:
value
Returns the contents of this data snapshot as native types.
#property (strong, readonly, nonatomic) id value Return Value The data
as a native object.
Discussion Returns the contents of this data snapshot as native types.
Data types returned: * NSDictionary * NSArray * NSNumber (also
includes booleans) * NSString
Declared In FDataSnapshot.h
So you should be checking for NSDictionary instead of NSMutableDictionary.
I recommend:
// Read data and react to changes
fetchEachStory.observeEventType(.Value) {
snapshot in
if let storyDetails = snapshot.value as? NSDictionary {
// We know snapshot.value was non-nil and it is an NSDictionary.
if let score = storyDetails["score"] as? Int {
// We know "score" is a valid key in the dictionary and that its
// type is Int.
var thisStory = eachStory
if score > self.minSetScore {
self.showStories[thisStory] = storyDetails
self.tableView.reloadData()
}
}
}
}

Answer 2

I found the bug , It's more to do with FireBase FDataSnapshot , Should check if snapshot is nil , with snapshot.exists()
var fetchEachStory = Firebase(url:"\(self.individualStoryUrl)\(eachStory)")
// Read data and react to changes
fetchEachStory.observeEventType(.Value, withBlock: {
snapshot in
if snapshot.exists(){
let storyDetails = snapshot.value as NSDictionary?
let score = storyDetails!["score"] as Int?
var thisStory = eachStory
if score? > self.minSetScore{
self.showStories[thisStory] = storyDetails
self.tableView.reloadData()
}
}
})