奇怪的错误 - 可以访问 NSURLConnection 和 NSMutableData 的描述方法，但不能访问它们的 ivars答案

【问题标题】：Weird bug - can access NSURLConnection & NSMutableData's description method, but not their ivars奇怪的错误 - 可以访问 NSURLConnection 和 NSMutableData 的描述方法，但不能访问它们的 ivars
【发布时间】：2011-07-27 18:22:39
【问题描述】：

所以我上课了：
DataFetcher.h

#import <Foundation/Foundation.h>

@interface DataFetcher : NSObject 
{
    NSURLConnection *networkConnection;
    NSMutableData *recievedData;
    BOOL isFetchingFinished;
}

@property (nonatomic, retain) NSMutableData *recievedData;
@property (nonatomic, retain) NSURLConnection *networkConnection;

- (void)fetchDataWithRequest:(NSMutableURLRequest *)request;

DataFetcher.m:

#import "DataFetcher.h"

@implementation DataFetcher

@synthesize recievedData;
@synthesize networkConnection;

- (id)init
{
    self = [super init];
    if (self) {
        NSMutableData *data = [[NSMutableData alloc] initWithLength:0];
        self.recievedData = data;
        [data release];
    }

    return self;
}

- (void)connection:(NSURLConnection *)connection didFailWithError:(NSError *)error
{
    NSLog(@"Connection Error:%@\n Failure Reason:%@", [error localizedDescription], [error localizedFailureReason]);
    [networkConnection release];
}

- (void)connection:(NSURLConnection *)connection didReceiveResponse:(NSURLResponse *)response
{
}

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

- (void)connectionDidFinishLoading:(NSURLConnection *)connection
{
    [networkConnection release];
    NSLog(@"%@", self.recievedData.length);
    [self processData];
}

- (void)fetchDataWithRequest:(NSMutableURLRequest *)request
{
    NSURLConnection *aConnection = [[NSURLConnection alloc] initWithRequest:request delegate:self startImmediately:NO];
    self.networkConnection = aConnection;
    [aConnection release];
    [self.networkConnection start];
    if( !self.networkConnection )
    {
        NSLog(@"Connection failed! recieved nil at alloc point");
    }
}

- (void)dealloc
{
    [super dealloc];
    [recievedData release];
}

@end

通常它会因为 EXC_BAD_ACCESS 而崩溃（NSZombie 不会检测到任何东西）。我注意到，如果您将connectionDidFinishLoading 和self.recievedData.length 切换为self.recievedData，它不会崩溃并且看起来里面有一些数据。 self.networkConnection 得到的结果相同 - 如果我只打印 self.networkConnection，没关系，但如果我打印 self.networkConnection.retainCount（例如，任何 ivar 都可以），它会因相同的信号而崩溃。

我似乎无法理解问题出在哪里，我已经安静地寻找了一段时间，我将不胜感激：)
天呐！

哦，我用这个代码调用它：
DataFetcher *fetcher = [[DataFetcher alloc] init]; NSMutableURLRequest *request = [[NSMutableURLRequest alloc] initWithURL:[NSURL URLWithString:@"http://www.google.com"]]; [fetcher fetchDataWithRequest:request]; [fetcher release]; [request release];

【问题讨论】：

标签： nsurlconnection exc-bad-access nsmutabledata

【解决方案1】：

NSLog(@"%@", self.recievedData.length);

这里的 %@ 格式说明符意味着您将记录 Objective-c 对象，而您实际上将纯整数传递给它 - 这会使您的应用程序崩溃。将您的日志更改为

 NSLog(@"%d", self.recievedData.length);

【讨论】：