Null value causing crash even with if/else statement? - ios

Question

I'm having the strangest issue. I'm using the below code to display the profile photo of a logged in user (I'm retrieving the image from a field in my Drupal database).
.m
//USER PHOTO
NSDictionary *user = [[DIOSSession sharedSession] user];
NSString *secondLink = user[#"field_photo_path"][#"und"][0][#"safe_value"];
NSLog(#"This is second link %#", secondLink);
if([secondLink length]>0) {
NSString *ImageURL = secondLink;
NSData *imageData = [NSData dataWithContentsOfURL:[NSURL URLWithString:ImageURL]];
// self.imageView.image = [UIImage imageWithData:imageData];
self.imageView.image = [[UIImage alloc] initWithData:imageData];
} else {
NSString *ImageURL = #"http://url.com/default.png";
NSData *imageData = [NSData dataWithContentsOfURL:[NSURL URLWithString:ImageURL]];
self.imageView.image = [UIImage imageWithData:imageData];
}
Naturally, if secondLink is null (or empty, e.g. no photo has been uploaded), I receive the following error:
*** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-[__NSArray0
objectForKeyedSubscript:]: unrecognized selector sent to instance
0x14f602fe0'
I thought I solved this issue with the if/else statement, but apparently not. How can I fix this?
Cheers!

Answer 1

NSString *secondLink = user[#"field_photo_path"][#"und"][0][#"safe_value"];
You need to verify that the user dictionary is valid before reading that far into it.
if (user[#"field_photo_path"]) {
// you can look for [#"und"] here
// providing it is a dictionary and not an array
if([user[#"field_photo_path"] isKindOfClass:[NSDictionary class]]){
if (user[#"field_photo_path"][#"und"]) {
// etc
}
}
}
You can reduce this nested code by modelling a User class as an NSObject subclass and include methods in that class to parse this data safely, allowing you to only write this validation code in one place.
Edit
As mentioned in a comment:
If the data in user[#"field_photo_path"][#"und"] is an NSDictionary and not an NSArray you cannot access it with [0] and will get your crash. You access NSArray's with an index (array[0], array[1] etc) and an NSDictionary with a key (dict[#"name"], dict[#"und"] etc)

Answer 2

Solution is to put check on on your key's
//USER PHOTO
NSDictionary *user = [[DIOSSession sharedSession] user];
if (user[#"field_photo_path"]) {
if ([user[#"field_photo_path"] isKindOfClass:[NSDictionary class]]) {
if (user[#"field_photo_path"][#"und"]) {
if ([user[#"field_photo_path"][#"und"]isKindOfClass:[NSArray class]]) {
if ([user[#"field_photo_path"][#"und"] count]>0) {
if (user[#"field_photo_path"][#"und"][0][#"safe_value"]) {
if ([user[#"field_photo_path"][#"und"][0][#"safe_value"] isKindOfClass:[NSDictionary class]]){
NSString *secondLink = user[#"field_photo_path"][#"und"][0][#"safe_value"];
NSLog(#"This is second link %#", secondLink);
if([secondLink length]>0) {
NSString *ImageURL = secondLink;
NSData *imageData = [NSData dataWithContentsOfURL:[NSURL URLWithString:ImageURL]];
// self.imageView.image = [UIImage imageWithData:imageData];
self.imageView.image = [[UIImage alloc] initWithData:imageData];
} else {
NSString *ImageURL = #"http://url.com/default.png";
NSData *imageData = [NSData dataWithContentsOfURL:[NSURL URLWithString:ImageURL]];
self.imageView.image = [UIImage imageWithData:imageData];
}
}
}
}
}
}
}
}
You can also use try catch block to avoid crashing
#try {
//USER PHOTO
NSDictionary *user = [[DIOSSession sharedSession] user];
NSString *secondLink = user[#"field_photo_path"][#"und"][0][#"safe_value"];
NSLog(#"This is second link %#", secondLink);
if([secondLink length]>0) {
NSString *ImageURL = secondLink;
NSData *imageData = [NSData dataWithContentsOfURL:[NSURL URLWithString:ImageURL]];
// self.imageView.image = [UIImage imageWithData:imageData];
self.imageView.image = [[UIImage alloc] initWithData:imageData];
} else {
NSString *ImageURL = #"http://url.com/default.png";
NSData *imageData = [NSData dataWithContentsOfURL:[NSURL URLWithString:ImageURL]];
self.imageView.image = [UIImage imageWithData:imageData];
}
}
#catch (NSException *exception) {
//Handle expecption
}
#finally {
}