NSMutableArray下载时for循环崩溃

Question

在我的NSMutableArray中有4个元素，我用下面的代码下载文件，在UITextView中显示文件数据，如果不加for循环，运行正常，但是问题出在这个函数中：

- (void)complexDownload {
    int i;
    for (i=0; i < downloadArray.count; i++) {
        if (isBusy == NO) {
            [[UIApplication sharedApplication] setNetworkActivityIndicatorVisible:YES];
            downloadURL = [downloadArray objectAtIndex:i];
            NSLog(@"URL is %@", downloadURL);
            NSLog(@"Downloading object at index %i", i);
            NSURL *url = downloadURL;
            NSURLRequest *theRequest=[NSURLRequest requestWithURL:url
                                                      cachePolicy:NSURLRequestUseProtocolCachePolicy
                                                  timeoutInterval:60.0];

            NSURLConnection *theConnection = [NSURLConnection connectionWithRequest:theRequest delegate:self];

                if (theConnection) {
                    self.downloadData = [NSMutableData data];
                    isBusy = YES;
                    NSLog(@"Busy value in download cycle equals %i, downloading", isBusy);
                } else {
                    [[UIApplication sharedApplication] setNetworkActivityIndicatorVisible:NO];
                    NSLog(@"Connection failed");
                    isBusy = NO;
                }
        }
    }
}

我最初以为是isBusyBOOL的问题，但是去掉if条件之后还是会崩溃。
余下的函数如下：

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

- (void)connectionDidFinishLoading:(NSURLConnection *)connection {
    NSString *dataString = [[NSString alloc] initWithData:downloadData encoding:NSASCIIStringEncoding];
    self.dataTextView.text = dataString;
    [[UIApplication sharedApplication] setNetworkActivityIndicatorVisible:NO];
    NSLog(@"Download finished!");
    isBusy = NO;
}

- (void)connection:(NSURLConnection *)connection didFailWithError:(NSError *)error {
    NSLog(@"%@", error);
    [[UIApplication sharedApplication] setNetworkActivityIndicatorVisible:NO];
}

所有的NSLogged值都正常，array中的数组链接也正确。

编译屏幕截图点击这里

Answer 1

我猜测应该某些点的downloadArray[i]出了问题，或者因为它不是NSUrl。代码是在[NSURLRequest requestWithURL...]调用CFURLCopyAbsoluteURL()时崩溃的。