Objective-C - Firebase retrieving data from database and populate in table - ios

Question

Database structure
I have a Firebase database setup (please refer to the picture).
I have a "FeedViewController" to display the contents of each post in the database. A user may post one or more posts.
When retrieving these posts from the Firebase snapshot and storing them onto a dictionary, I find that this dictionary's values are not accessible outside of the Firebase's observeEventType function.
My idea was to retrieve these key-value pairs, store them onto a NSObject custom class object (Post *post) and use this object to load the table view for my "FeedViewController". Inside the observeEventType function, I am able to access the object's values, but outside, I'm not. As a result, I don't know how to use these values to populate the table view in my FeedViewController. I understand that this observeEventType function is an asynchronous callback, but I don't know how to access the values of the object and populate my table. I don't have a clue what the dispatch_async(dispatch_get_main_queue() function is doing here. Any help would be highly appreciated. Thanks!
FeedViewController.m
#import "FeedViewController.h"
#import "Post.h"
#import "BackgroundLayer.h"
#import "SimpleTableCell.h"
#import "FBSDKCoreKit/FBSDKCoreKit.h"
#import "FBSDKLoginKit/FBSDKLoginKit.h"
#import "FBSDKCoreKit/FBSDKGraphRequest.h"
#import Firebase;
#import FirebaseAuth;
#import FirebaseStorage;
#import FirebaseDatabase;
#interface FeedViewController()
#property (strong, nonatomic) Post *post;
#end
#implementation FeedViewController
-(void) viewDidLoad {
[super viewDidLoad];
_ref = [[FIRDatabase database] reference];
self.post = [[Post alloc] init];
/*
_idArr = [[NSMutableArray alloc] init];
_postDict = [[NSMutableDictionary alloc] init];
_idDict = [[NSMutableDictionary alloc] init];
_postID = [[NSMutableArray alloc] init];
_userName = [[NSMutableArray alloc] init];
_placeName = [[NSMutableArray alloc] init];
_addressLine1 = [[NSMutableArray alloc] init];
_addressLine2 = [[NSMutableArray alloc] init];
_ratings = [[NSMutableArray alloc] init];
_desc = [[NSMutableArray alloc] init];
_userEmail = [[NSMutableArray alloc] init];
_userIDArray = [[NSMutableArray alloc] init];
*/
[self fetchData];
NSLog(#"Emails: %#", _post.userID);
}
-(void) viewWillAppear:(BOOL)animated {
[super viewWillAppear:animated];
CAGradientLayer *bgLayer = [BackgroundLayer blueGradient];
bgLayer.frame = self.view.bounds;
[self.view.layer insertSublayer:bgLayer atIndex:0];
FIRUser *user = [FIRAuth auth].currentUser;
if (user != nil)
{
//fbFirstName.text = user.displayName;
//fbEmail.text = user.email;
NSURL *photoUrl = user.photoURL;
NSString *userID = user.uid;
//NSString *uploadPath = [userID stringByAppendingString:#"/profile_pic.jpg"];
//NSData *data = [NSData dataWithContentsOfURL:photoUrl];
//ProfilePic.image = [UIImage imageWithData:data];
FIRStorage *storage = [FIRStorage storage];
FIRStorageReference *storageRef = [storage referenceForURL:#"gs://foodsteps-cee33.appspot.com"];
NSString *access_token = [[NSUserDefaults standardUserDefaults] objectForKey:#"fb_token"];
FBSDKGraphRequest *friendList = [[FBSDKGraphRequest alloc]
initWithGraphPath:#"me?fields=friends"
parameters:nil
tokenString: access_token
version:nil
HTTPMethod:#"GET"];
[friendList startWithCompletionHandler:^(FBSDKGraphRequestConnection *connection,
id result,
NSError *error) {
if(error == nil)
{
//NSLog(#"%#", result);
NSDictionary *dictionary = (NSDictionary *)result;
NSDictionary *dict = [dictionary objectForKey:#"friends"];
_idArray = [[NSMutableArray alloc] init];
for(int i = 0; i < [[dict objectForKey:#"data"] count]; i++) {
[_idArray addObject:[[[dict objectForKey:#"data"] objectAtIndex:i] valueForKey:#"id"]];
}
//NSLog(#"%#", idArray);
}
else {
NSLog(#"%#",error);
}
}];
}
}
-(void) fetchData {
_refHandle = [[_ref child:#"users"] observeEventType:FIRDataEventTypeValue
withBlock:^(FIRDataSnapshot * _Nonnull snapshot)
{
NSDictionary *postDict = snapshot.value;
NSLog(#"%#", postDict);
for( NSString *aKey in [postDict allKeys] )
{
// do something like a log:
_post.userID = aKey;
}
//_post.
//[_post setValuesForKeysWithDictionary:postDict];
[self.tableView reloadData];
}];
NSLog(#"Emails: %#", _post.userID);
dispatch_async(dispatch_get_main_queue(), ^{
[self.tableView reloadData];
});
}
-(void) viewWillDisappear:(BOOL)animated
{
[super viewWillDisappear:animated];
[[_ref child:#"users"] removeObserverWithHandle:_refHandle];
}
#end
Post.m
#import "Post.h"
#implementation Post
- (instancetype)init {
return [self initWithUid:#""
andPostid:#""
andUsername:#""
andDesc:#""
andRatings:#""
andPlacename:#""
andAddressLine1:#""
andAddressLine2:#""
andEmail:#""];
}
- (instancetype)initWithUid:(NSString *)userID
andPostid:(NSString *)postID
andUsername: (NSString *)userName
andDesc:(NSString *)desc
andRatings:(NSString *)ratings
andPlacename: (NSString *)placeName
andAddressLine1: (NSString *)addressLine1
andAddressLine2: (NSString *)addressLine2
andEmail: (NSString *)userEmail {
self = [super init];
if(self) {
self.userID = userID;
self.postID = postID;
self.userName = userName;
self.desc = desc;
self.ratings = ratings;
self.placeName = placeName;
self.addressLine1 = addressLine1;
self.addressLine2 = addressLine2;
self.userEmail = userEmail;
}
return self;
}
#end

Answer 1

Your approach is what I tried to do initially. But I had problems accessing it in cellforrowatindexpath. the thing that works for me is.
- (void)configureDatabase :(NSUInteger)postsAmount{
_ref = [[FIRDatabase database] reference];
// Listen for new messages in the Firebase database
_refHandle = [[[[_ref child:#"posts"]queryOrderedByKey] queryLimitedToLast:postsAmount]observeEventType:FIRDataEventTypeChildAdded withBlock:^(FIRDataSnapshot *snapshot) {
[_posts insertObject:snapshot atIndex:0];
}];
}
Then in viewdidappear
[self configureDatabase:_numberOfPosts];
then lastly
- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
FIRDataSnapshot *postsSnapshot = _posts[indexPath.section];
NSDictionary *post = postsSnapshot.value;
//use key values to create your views.
}
also include
#property (strong, nonatomic) NSMutableArray<FIRDataSnapshot *> *posts;
What this does is queries firebase for your values and receives snapshots. those snapshots are then placed in your _posts array and then you can access them in other methods.