ios - 下载任务中的AFNetworking EXC_BAD_ACCESS(代码= 2，地址= 0x0)

Question

我有一个应用程序，可在登录后为客户编译客户特定报告的列表。这些报告正在显示，我已经放置了一个“查看”按钮，该按钮应该可以下载PDF文件，并在应用程序中显示它。

在此阶段，按下查看按钮时似乎出现了内存问题，并且我不确定如何找到问题所在。这是我的代码:

#import "reportsTestViewController.h"
#import "ReportsDataObject.h"
#import "Session.h"
#import "AFNetworking.h"
@interface reportsTestViewController ()

@end

@implementation reportsTestViewController

@synthesize response;

@synthesize myDataIvar;

@synthesize viewReportPressed;


- (id)initWithNibName:(NSString *)nibNameOrNil bundle:(NSBundle *)nibBundleOrNil
{
    self = [super initWithNibName:nibNameOrNil bundle:nibBundleOrNil];
    if (self) {
        // Custom initialization
    }
    return self;
}

- (void)viewDidLoad
{
    reportsTable.delegate = self;
    reportsTable.dataSource = self;
    self.sections = [[NSMutableDictionary alloc] init];

    [super viewDidLoad];
}

- (void)viewWillAppear:(BOOL)animated
{
    [super viewWillAppear:animated];

#pragma mark NSURLConnection Delegate Methods
//    

    //Create your request pointing to the test page
   NSURLRequest *request = [NSURLRequest requestWithURL:[NSURL URLWithString:@"http://www.tesg.com.au/allCustBuild.php"] cachePolicy:NSURLRequestUseProtocolCachePolicy timeoutInterval:15.0];


    NSURLConnection *connection = [[NSURLConnection alloc] initWithRequest:request delegate:self];

    //initialize it when you create your connection
    if (connection){
        self.myDataIvar = [[NSMutableData alloc] init];
    }
}

    -(void)connection:(NSURLConnection *)connection didReceiveResponse:(NSURLResponse *)response{
        [self.myDataIvar setLength:0];
    }

    -(void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data{
        [self.myDataIvar appendData:data];

    }

    -(void)connection:(NSURLConnection *)connection didFailWithError:(NSError *)error{
        NSLog(@"Connection Failed: %@", error.userInfo);
    }

-(void)connectionDidFinishLoading:(NSURLConnection *)connection{
    //this is where you would parse the data received back from the server
    NSString *responseString = [[NSString alloc] initWithData:self.myDataIvar encoding:NSUTF8StringEncoding];
    NSLog(@"Received Data: %@",responseString);
    [self setupReportsFromJSONArray:self.myDataIvar];

}

-(void)connectionWasASuccess:(NSData *)data{
    [self setupReportsFromJSONArray:data];

}



-(void)setupReportsFromJSONArray:(NSData*)dataFromReportsArray{
    BOOL found;
    NSError *error;
   // NSMutableArray *reportsArray = [[NSMutableArray alloc] init];
    NSArray *arrayFromServer = [NSJSONSerialization JSONObjectWithData:dataFromReportsArray options:0 error:&error];

    if(error){
        NSLog(@"error parsing the json data from server with error description - %@", [error localizedDescription]);
    }

    else {
        reportsArray = [[NSMutableArray alloc] init];
        for(NSDictionary *eachReport in arrayFromServer)
        {

            ReportsDataObject *report = [[ReportsDataObject alloc] initWithJSONData:eachReport];

            [reportsArray addObject:report];
            NSString *c = [[eachReport objectForKey:@"title"] substringToIndex:3];
                      found = NO;

            for (NSString *str in [self.sections allKeys])
            {
                if ([str isEqualToString:c])
                {
                    found = YES;
                }
            }

            if (!found)
            {
                [self.sections setValue:[[NSMutableArray alloc] init] forKey:c];
            }
        }

        }
        NSLog(@"Array Populated");
        NSLog(@"%u reports found",reportsArray.count);
        //Now you have your reportsArray filled up with all your data objects



for (NSDictionary *eachReport in arrayFromServer)
{
   [[self.sections objectForKey:[[eachReport objectForKey:@"title"] substringToIndex:3]] addObject:eachReport];
}

// Sort each section array
for (NSString *key in [self.sections allKeys])
{
    [[self.sections objectForKey:key] sortUsingDescriptors:[NSArray arrayWithObject:[NSSortDescriptor sortDescriptorWithKey:@"title" ascending:YES]]];


}

[reportsTable reloadData];
}


-(void)didReceiveMemoryWarning
{
    [super didReceiveMemoryWarning];
    // Dispose of any resources that can be recreated.
}

-(void)viewReportPressed:(UIButton*)button {

    NSLog(@"Button successfully Pressed");
    NSURLSessionConfiguration *configuration = [NSURLSessionConfiguration defaultSessionConfiguration];
    AFURLSessionManager *manager = [[AFURLSessionManager alloc] initWithSessionConfiguration:configuration];

    NSURL *URL = [NSURL URLWithString:@"http://tesg.com.au/portal/media/reports/1367365180_367 Collins Passive April 2013.pdf"];
    NSURLRequest *request = [NSURLRequest requestWithURL:URL];

    NSURLSessionDownloadTask *downloadTask = [manager downloadTaskWithRequest:request progress:nil destination:^NSURL *(NSURL *targetPath, NSURLResponse *theResponse) {
        NSURL *documentsDirectoryPath = [NSURL fileURLWithPath:[NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES) firstObject]];
        return [documentsDirectoryPath URLByAppendingPathComponent:[theResponse suggestedFilename]];
    } completionHandler:^(NSURLResponse *response, NSURL *filePath, NSError *error) {
        NSLog(@"File downloaded to: %@", filePath);
    }];
    [downloadTask resume];

                                              }


- (NSInteger)numberOfSectionsInTableView:(UITableView *)tableView
{

    NSUInteger count = [[self.sections allKeys] count];
    NSLog(@"Number of sections: %d", count);
    return count;
}




- (NSString *)tableView:(UITableView *)tableView titleForHeaderInSection:(NSInteger)section
{
    return [[[self.sections allKeys] sortedArrayUsingSelector:@selector(localizedCaseInsensitiveCompare:)] objectAtIndex:section];
}


- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section{
    //We check against table to make sure we are displaying the right number of cells
    // for the appropriate table. This is so that things will work even if one day you
    //decide that you want to have two tables instead of one.

    {
        NSUInteger count = [[self.sections valueForKey:[[[self.sections allKeys] sortedArrayUsingSelector:@selector(localizedCaseInsensitiveCompare:)] objectAtIndex:section]] count];
        NSLog(@"Number of rows in section: %d", count);
        return count;
    }
}
//- (NSArray *)sectionIndexTitlesForTableView:(UITableView *)tableView {
        //return [[self.sections allKeys] sortedArrayUsingSelector:@selector(localizedCaseInsensitiveCompare:)];
   // }





-(UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath

{


    static NSString *cellIdentifier = @"Cell";



    UITableViewCell *cell =[tableView dequeueReusableCellWithIdentifier:cellIdentifier];
    if (!cell)
    {


        cell = [[UITableViewCell alloc] initWithStyle:UITableViewCellStyleSubtitle reuseIdentifier:cellIdentifier];

    }

        //The beauty of this is that you have all your data in one object and grab WHATEVER you like
    //This way in the future you can add another field without doing much.
    NSUInteger count = [[self.sections allKeys] count];
    if(count == 0){
        cell.textLabel.text = @"no reports to show";
    }
    else{
        NSDictionary *Reports = [[self.sections valueForKey:[[[self.sections allKeys] sortedArrayUsingSelector:@selector(localizedCaseInsensitiveCompare:)] objectAtIndex:indexPath.section]] objectAtIndex:indexPath.row];

        cell.textLabel.text = [Reports objectForKey:@"title"];
        cell.detailTextLabel.text = [Reports objectForKey:@"building"];








        UIButton *button = [UIButton buttonWithType:UIButtonTypeRoundedRect];
        [button addTarget:self action:@selector(viewReportPressed:) forControlEvents:UIControlEventTouchUpInside];
        [button setTitle:@"View" forState:UIControlStateNormal];

        button.frame = CGRectMake(180.0f, 5.0f, 150.0f, 30.0f);
        [cell addSubview:button];


        // in the future you can grab whatever data you need like this
        //[currentReport buildingName], or [currentReport reportName];
    }


    return(cell);

        }




@end

当在任何一个单元格中按下查看按钮时，我得到NSLog说“按钮成功按下”，但是在出现错误后立即崩溃

[downloadTask resume];             Thread 1:EXC_BAD_ACCESS (code=2, address=0x0)

任何想法如何解决这一问题？

Answer 1

如果获得地址为EXC_BAD_ACCESS的0x0，通常意味着在不允许nil的上下文中使用了nil值。

在这种情况下，这是因为您的URL字符串无效。不允许使用空格。因此，所得的URL变量为nil，这将导致您描述的行为。您可能希望对URL字符串进行转义，例如:

NSString *URLString = @"http://tesg.com.au/portal/media/reports/1367365180_367 Collins Passive April 2013.pdf";
NSURL *URL = [NSURL URLWithString:[URLString stringByAddingPercentEscapesUsingEncoding:NSUTF8StringEncoding]];

要在将来识别这种异常，可以使用 exception breakpoints，它通常可以帮助识别有问题的代码行。或者只是仔细检查您的代码，以防可能无意中将 nil值传递给了不接受它的方法。

但是，如果您得到的 EXC_BAD_ACCESS的值不是 0x0，则通常是尝试使用先前释放的对象的结果。 (并非总是如此，但经常出现。幸运的是，ARC使这种问题变得不那么普遍了。)显然，这里不是这种情况，但是您询问了如何识别试图使用先前释放的对象的情况。

要诊断这种情况，通常可以打开“僵尸”(请参阅​​ Running Your Application with Diagnostics)。顺便说一句，一旦完成了对僵尸的诊断，请确保将其关闭，因为您不想让僵尸保持打开状态(尤其是在生产应用程序中)。

无论如何，在这种情况下，由于地址是 0x0，所以它不是对象释放的结果，而是问题在于无效URL导致的 nil值使用不正确。