Question

My app needs to get data from a webpage that is in XML format. I am using XMLReader to do this and the function works great when there is internet access, however the specific line

NSArray *arr = [XMLReader objectsForXMLData:receivedData error:parseError]; 

crashes when there is no internet. I want the app to print out an error message when there is no internet. Thus i am using **parseError as an indicator. However, i am unsure why the app crashes when it executes this line. I posted the function below. Thank you for all of your help in advance.

NSDateFormatter *dateFmt = [[NSDateFormatter alloc] init];
dateFmt.timeStyle = NSDateFormatterNoStyle;
dateFmt.dateFormat = DATADATEFRMT; // @"yyyy-MM-dd";
NSMutableString *urlStr = [NSMutableString stringWithString:[DATASRCWCAT stringByAppendingString:cat]];
category = cat;
NSLog(@"cate = %@",cat);
[urlStr appendFormat:@"%@%@%@%@", DATAPRD, dataPeriod, DATASTDATE, [dateFmt stringFromDate:currDate]];
NSLog(@"dataPeriod = %@", [dateFmt stringFromDate:currDate]);
NSString *urlString = [urlStr stringByAddingPercentEscapesUsingEncoding:NSUTF8StringEncoding];

//NSLog(@"URL to obtain data: %@", urlString);

self.crimeid = cat;

// Get the data in xml format and parse
NSData *receivedData = [NSData dataWithContentsOfURL:[NSURL URLWithString:urlString]];
NSError **parseError = nil;
NSArray *arr = [XMLReader objectsForXMLData:receivedData error:parseError]; // <---- crashes here with no internet access.
//NSLog(@"array = %@", [arr objectAtIndex:1]);
self.crimeDataArray = arr;

Answer 1

Check for the presence of ‘receivedData’ before using.

// Get the data in xml format and parse

NSData *receivedData = [NSData dataWithContentsOfURL:[NSURL URLWithString:urlString]];

if ( receivedData )  // Will only get here if there's data
{
  NSError **parseError = nil;
  NSArray *arr = [XMLReader objectsForXMLData:receivedData error:parseError]; // <---- crashes here  with no internet access.
  //NSLog(@"array = %@", [arr objectAtIndex:1]);
  self.crimeDataArray = arr;
}