Question

我的应用需要从XML格式的网页获取数据。我正在使用XMLReader来执行此操作，并且当有Internet访问时，该功能很有用，但是具体的行

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

没有互联网时

崩溃。我希望应用程序在没有互联网时打印出错误信息。因此我使用** parseError作为指标。但是，我不确定为什么应用程序在执行此行时崩溃。我发布了以下功能。感谢您提前提供的所有帮助。

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

使用前检查是否存在'receivedData'。

// 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;
}

Answer 2

您可以使用try / catch处理异常，如果没有互联网连接，您将收到异常。我认为这是正确的方法

@try {
            NSData *data= [NSData dataWithContentsOfURL:[NSURL URLWithString:urlString]];
            NSDictionary *dict=[NSJSONSerialization JSONObjectWithData:data options:0 error:nil];

            UIAlertView *alert = [[UIAlertView alloc] initWithTitle:NSLocalizedString(@"Conection found",nil) message:@"Conection found" delegate:nil cancelButtonTitle:NSLocalizedString(@"Ok",nil) otherButtonTitles:nil ,nil];
            [alert show];
        }
        @catch (NSException *exception) {
            UIAlertView *alert = [[UIAlertView alloc] initWithTitle:@"NO Conection found" message:@"No Conection found"  delegate:nil cancelButtonTitle:NSLocalizedString(@"Ok",nil) otherButtonTitles:nil ,nil];
            [alert show];
        }

没有互联网连接时，XMLReader崩溃

2 个答案: