Return a query from inside a block - ios

Question

i hope NSlog outside of block can have value.
i don't know how to fix it. i hope loadPuppiesFromJSON can working.
could somebody help me!?THX!!
- (id)init
{
if((self = [super init]))
{
allPuppies=[self loadPuppiesFromJSON];
}
return self;
}
- (NSArray *)loadPuppiesFromJSON
{
PFQuery *query = [PFQuery queryWithClassName:#"Information"];
[query findObjectsInBackgroundWithBlock:^(NSArray *objects, NSError *error) {
if (!error) {
// The find succeeded.
// Do something with the found objects
for (PFObject *object in objects) {
Fish *fish = [[Fish alloc]init];
fish.price = object[#"price"];
fish.name = object[#"name"];
[object saveInBackground];
self.allFishes = objects;
NSLog(#"%#",allFishes);<-----here have some value
} else {
// Log details of the failure
NSLog(#"Error: %# %#", error, [error userInfo]);
}
}];
NSLog(#"%#",allFishes);<----here doesn't have value
}

Answer 1

The reason your NSLog(#"%#",allFishes); doesn't have a value is that it is being called before your query is complete. It's a Race Condition, and at run-time here is what the program thinks you want:
Start query
Call NSLog outside the block - no data yet, so it's empty
Call completion block when it is ready - this is when the data is generated so you get a populated NSLog here
Since you also want to have the value return, try this instead - just remove your NSLost from outside the block and call a second function with the return value to continue your logic:
- (void)loadPuppiesFromJSON
{
PFQuery *query = [PFQuery queryWithClassName:#"Information"];
[query findObjectsInBackgroundWithBlock:^(NSArray *objects, NSError *error) {
if (!error) {
// The find succeeded.
// Do something with the found objects
for (PFObject *object in objects) {
Fish *fish = [[Fish alloc]init];
fish.price = object[#"price"];
fish.name = object[#"name"];
[object saveInBackground];
}
self.allFishes = objects;
NSLog(#"%#",allFishes);<-----here have some value
[self processPuppiesArray:objects];
} else {
// Log details of the failure
NSLog(#"Error: %# %#", error, [error userInfo]);
}
}];
//No NSLog out here - it won't do anything
}
- (void)processPuppiesArray:(NSArray *)puppiesArray
{
//Continue processing here...
}

Answer 2

The NSLog where you are not getting any value is because block is called in background after it completes your function execution. Thats why before executing you block, it finishes your function execution and during that time allFishes variable is empty/nil. Once the block excution starts and assigns value to allFishes after that this variable gets the value.
If you need to execute some code after allFishes have value create a function and call it after blockexecution finishes like below:
- (NSArray *)loadPuppiesFromJSON
{
PFQuery *query = [PFQuery queryWithClassName:#"Information"];
[query findObjectsInBackgroundWithBlock:^(NSArray *objects, NSError *error) {
if (!error) {
// The find succeeded.
// Do something with the found objects
for (PFObject *object in objects) {
Fish *fish = [[Fish alloc]init];
fish.price = object[#"price"];
fish.name = object[#"name"];
[object saveInBackground];
self.allFishes = objects;
NSLog(#"%#",allFishes);<-----here have some value
[self dataLoadFinished];
} else {
// Log details of the failure
NSLog(#"Error: %# %#", error, [error userInfo]);
}
}];
NSLog(#"%#",allFishes);<----here doesn't have value
}
-(void) dataLoadFinished {
NSLog(#"%#",self.allFishes);<----here you will have value
}

Answer 3

The reason you aren't retrieving any data is because you are trying to retrieve an Array from a function but never return anything.
When you use the -(NSArray *)loadPuppiesFromJSON you actually have to return an Array which you are not doing.
For example:
-(NSArray *)loadPuppiesFromJson {
NSArray *allFishes;
allFishes = #[#"someinfo1",#"someinfo2",#"someinfo3"];
return allFishes; // this is where your getting your error and need for it to return anything
}
I would suggest butting your code into a void function like so:
-(void)loadPuppiesFromJSON {
PFQuery *query = [PFQuery queryWithClassName:#"Information"];
[query findObjectsInBackgroundWithBlock:^(NSArray *objects, NSError *error) {
if (!error) {
self.allFishes = objects;
for (PFObject *object in objects) {
Fish *fish = [[Fish alloc]init];
fish.price = object[#"price"];
fish.name = object[#"name"];
[object saveInBackground];
} else {
// Log details of the failure
NSLog(#"Error: %# %#", error, [error userInfo]);
}
}];
NSLog(#"%#",allFishes);<----here has value now
}
And call it in viewDidLoad or viewDidAppear or wherever you need it with:
[self loadPuppiesFromJSON]