应用程序未从Firebase检索数据

Question

I cant seem to retrieve any information from my firebase database. I created a table with both author and title available.

This is the code i ran in my ios app, but the app just keeps crashing.

// Get a reference to our posts
Firebase *ref = [[Firebase alloc] initWithUrl: @"**********"];

[ref observeEventType:FEventTypeChildAdded withBlock:^(FDataSnapshot *snapshot) {
    NSLog(@"%@", snapshot.value[@"author"]);
    NSLog(@"%@", snapshot.value[@"title"]);
}];

}

I cant tell whats going wrong, any help with this i will be appreciated.

Thank you

Answer 1

change event type to

[ref observeEventType:FEventTypeValue withBlock:^(FDataSnapshot *snapshot) {
     NSLog(@"%@", snapshot.value[@"author"]);
      NSLog(@"%@", snapshot.value[@"title"]);
 }];

Answer 2

You would generally not store data like that right under your root node - it would generally be a child node(s) stored under the root node, like this:

sizzling-inferno-255
  book_node_0
    author: test_author
    title: test title
  book_node_1
    author: another author
    title: another title title


Firebase *ref = [[Firebase alloc] initWithUrl: @"sizzling-inferno-255"];

[ref observeEventType:FEventTypeChildAdded withBlock:^(FDataSnapshot *snapshot) {
    NSLog(@"%@", snapshot.value[@"author"]);
    NSLog(@"%@", snapshot.value[@"title"]);
}];

will iterate over each book node and return a snapshot of that node. So the first time a snapshot is returned, it will be

  book_node_0
    author: test_author
    title: test title

and the second time a snapshot is returned will be

  book_node_1
    author: another author
    title: another title title

the book_node keys are generated with childByAutoId.

ChildAdded reads in each child node one at a time as a snapshot.

Value reads in everything in the node; all child nodes, those children etc and can be a large amount of data. If the ref node contains children, like in this answer, all of the nodes are returned and they need to be iterated over to get the child data, so within the observe block...

for child in snapshot.children {
   NSLog(@"%@", child.value[@"author"]);
}

Edit - and to specifically answer the OP question, here's how you do it with the Firebase structure in the question:

self.myRootRef = [[Firebase alloc] initWithUrl:@"https://**********"];
[ref observeEventType:FEventTypeChildAdded withBlock:^(FDataSnapshot *snapshot) { 
    NSString *key = snapshot.key;
    NSString *value = snapshot.value;

    if ( [key isEqualToString:@"author"] ) {
        NSLog(@"author = %@", value);
    } else if ([snapshot.key isEqualToString:@"title"] ) {
        NSLog(@"title = %@", value);
    }
}];