由于未捕获的异常“ NSInvalidArgumentException”而终止应用程序，原因：“数据参数为nil”

Question

I was developing apps using web services when I run the application it got responses but some time its crashes and show error like this:

NSInvalidArgumentException', reason: 'data parameter is nil'

Here is my coding:

NSMutableURLRequest *request=[NSMutableURLRequest requestWithURL:[NSURL URLWithString:@"http://api.espn.com/v1/sports/tennis/news/headlines?apikey=th98vzm67pufc36ka42xxxmy"]];
[request setHTTPMethod:@"GET"];
[request setValue:@"application/json;charset=UTF-8" forHTTPHeaderField:@"content-type"];

NSError *err;
NSURLResponse *response;

NSData *responseData = [NSURLConnection sendSynchronousRequest:request returningResponse:&response error:&err];
NSDictionary *jsonArray=[NSJSONSerialization JSONObjectWithData:responseData  options:NSJSONReadingMutableContainers error:&err];
NSArray *headlinetop=[jsonArray objectForKey:@"headlines"];

for (int i=0; i<[headlinetop count]; i++)
{
    NSString *headstr=[[headlinetop objectAtIndex:i]objectForKey:@"headline"];
    [loadingcell addObject:headstr];
}

Answer 1

I suspect the "headline" object isn't always available; guard against that using:

for (int i=0; i<[headlinetop count]; i++)
{
    NSString *headstr=[[headlinetop objectAtIndex:i]objectForKey:@"headline"];
    if (headstr)
        [loadingcell addObject:headstr];
}

If loadcell is an Objective-C collection class, it will object to headstr being nil as they cannot store NULL objects.

Answer 2

The problem is this code:

NSData *responseData = [NSURLConnection sendSynchronousRequest:request returningResponse:&response error:&err];
NSDictionary *jsonArray=[NSJSONSerialization JSONObjectWithData:responseData  options:NSJSONReadingMutableContainers error:&err];

Sending a URL request you should always expect that something went wrong. There are many reasons for it. In this case responseData is nil . NSJSONSerialization expects the data arg not to be nil : Error.

When receiving a response for a request you should always check it for being nil . Always.

So the code should look like this:

NSData *responseData = [NSURLConnection sendSynchronousRequest:request returningResponse:&response error:&err];
if (responseData == nil)
{
  //  Maybe logging. But getting nil as a response of a URL request isn't exciting.
  return; // or whatever you have to (not) do
}
NSDictionary *jsonArray=[NSJSONSerialization JSONObjectWithData:responseData  options:NSJSONReadingMutableContainers error:&err];

Answer 3

I think your problem is Url which you are using. Please check the following link: 'NSInvalidArgumentException', reason: 'data parameter is nil'