Parsing RSS in Obj-C? - ios

Question

I'm trying to parse RSS date to view in my app, following this tutorial. I have a JSON file to retrieve information from and display on the screen.
Here's the code
//
// ViewController.m
// JSONyt
//
// Created by yo_291 on 3/16/15.
// Copyright (c) 2015 yo_291. All rights reserved.
//
#import "ViewController.h"
#interface ViewController ()
{
NSMutableData *webData;
NSURLConnection *connection;
NSMutableArray *array;
}
#end
#implementation ViewController
- (void)viewDidLoad {
[[self myView]setDelegate:self];
[[self myView]setDataSource:self];
array = [[NSMutableArray alloc]init];
[super viewDidLoad];
// Do any additional setup after loading the view, typically from a nib.
}
- (void)didReceiveMemoryWarning {
[super didReceiveMemoryWarning];
// Dispose of any resources that can be recreated.
}
-(void)connection:(NSURLConnection *)connection didReceiveResponse:(NSURLResponse *)response
{
[webData setLength:0];
}
-(void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data
{
[webData appendData:data];
}
-(void)connection:(NSURLConnection *)connection didFailWithError:(NSError *)error
{
NSLog(#"fail with error");
}
-(void)connectionDidFinishLoading:(NSURLConnection *)connection
{
NSDictionary *allDataDictionary = [NSJSONSerialization JSONObjectWithData:webData options:0 error:nil];
NSDictionary *rd = [allDataDictionary objectForKey:#"responseData"];
NSDictionary *feed = [rd objectForKey:#"feed"];
NSArray *aoe = [feed objectForKey:#"entries"];
for(NSDictionary *diction in aoe)
{
NSDictionary *numb = [diction objectForKey:#"0"];
NSString *title = [numb objectForKey:#"title"];
[array addObject:title];
}
[[self myView] reloadData];
}
- (IBAction)getFeed:(id)sender {
NSURL *url = [NSURL URLWithString:#"http://ajax.googleapis.com/ajax/services/feed/load?v=2.0&q=http://www.britannica.com/feeds/tdih.rss&num="];
NSURLRequest *request = [NSURLRequest requestWithURL:url];
connection = [NSURLConnection connectionWithRequest:request delegate:self];
if(connection)
{
webData = [[NSMutableData alloc]init];
}
}
-(NSInteger)numberOfSectionsInTableView:(UITableView *)tableView
{
return 1;
}
-(NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section
{
return [array count];
}
-(UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
static NSString *cellI = #"Cell";
UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:cellI];
if(!cell)
{
cell = [[UITableViewCell alloc]initWithStyle:UITableViewCellStyleDefault reuseIdentifier:cellI];
}
cell.textLabel.text = [array objectAtIndex:indexPath.row];
return cell;
}
#end
The application crashes on the line [array addObject:title];.
Error Stack trace:
2015-03-16 22:32:51.650 JSONyt[8195:547408] *** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '*** -[__NSArrayM insertObject:atIndex:]: object cannot be nil'
*** First throw call stack:
(
0 CoreFoundation 0x000000010ba28a75 __exceptionPreprocess + 165
1 libobjc.A.dylib 0x000000010b6c1bb7 objc_exception_throw + 45
2 CoreFoundation 0x000000010b8f70ca -[__NSArrayM insertObject:atIndex:] + 954
3 JSONyt 0x000000010b18da5f -[ViewController connectionDidFinishLoading:] + 735
4 CFNetwork 0x000000010d85998c __65-[NSURLConnectionInternal _withConnectionAndDelegate:onlyActive:]_block_invoke + 69
5 CFNetwork 0x000000010d859930 -[NSURLConnectionInternal _withConnectionAndDelegate:onlyActive:] + 199
6 CFNetwork 0x000000010d859a97 -[NSURLConnectionInternal _withActiveConnectionAndDelegate:] + 48
7 CFNetwork 0x000000010d729937 ___ZN27URLConnectionClient_Classic26_delegate_didFinishLoadingEU13block_pointerFvvE_block_invoke + 107
8 CFNetwork 0x000000010d7f6a31 ___ZN27URLConnectionClient_Classic18_withDelegateAsyncEPKcU13block_pointerFvP16_CFURLConnectionPK33CFURLConnectionClientCurrent_VMaxE_block_invoke_2 + 273
9 CFNetwork 0x000000010d714d16 _ZN19RunloopBlockContext13_invoke_blockEPKvPv + 72
10 CoreFoundation 0x000000010b930b44 CFArrayApplyFunction + 68
11 CFNetwork 0x000000010d714bd7 _ZN19RunloopBlockContext7performEv + 133
12 CFNetwork 0x000000010d714a16 _ZN17MultiplexerSource7performEv + 256
13 CFNetwork 0x000000010d71482c _ZN17MultiplexerSource8_performEPv + 72
14 CoreFoundation 0x000000010b95dc91 __CFRUNLOOP_IS_CALLING_OUT_TO_A_SOURCE0_PERFORM_FUNCTION__ + 17
15 CoreFoundation 0x000000010b953b5d __CFRunLoopDoSources0 + 269
16 CoreFoundation 0x000000010b953194 __CFRunLoopRun + 868
17 CoreFoundation 0x000000010b952bc6 CFRunLoopRunSpecific + 470
18 GraphicsServices 0x000000010f005a58 GSEventRunModal + 161
19 UIKit 0x000000010be18580 UIApplicationMain + 1282
20 JSONyt 0x000000010b18e483 main + 115
21 libdyld.dylib 0x000000010dfd6145 start + 1
22 ??? 0x0000000000000001 0x0 + 1
)
libc++abi.dylib: terminating with uncaught exception of type NSException
but I have no idea how to go about fixing it. To my eyes I'm searching the JSON file correctly but I may be wrong. The JSON file is also an RSS feed that I've used a google tool to "turn" into a JSON database, so I'm unsure if complications are from there.
Let me know any/all information that is needed, this is my first post so I don't know if I'm delivering enough context.

Answer 1

The error indicates that the object to be inserted is nil. The problem lies in the following lines:
NSDictionary *numb = [diction objectForKey:#"0"];
NSString *title = [numb objectForKey:#"title"];
[array addObject:title];
You never check whether title is nil or not before adding object to array. You can always use NSLog() to debug the values and check for nil values using techniques similar as follow:
if([numb objectForKey:#"title"] != nil) {
[array addObject:[numb objectForKey:#"title"]];
}
p.s. assigning the value to title is useless, as the title just used once (wasting memory).
Also, using libraries like AFNetworking will make your codes simpler, and provides extra error handling.