下载大文件 - iPhone SDK

Question

我正在使用Erica Sadun的异步下载方法(此处链接到项目文件:下载),但是她的方法不适用于具有大尺寸(50 mb或更高)的文件.如果我尝试下载超过50 MB的文件,它通常会因内存崩溃而崩溃.无论如何我可以调整这段代码,以便它也适用于大文件？这是我在DownloadHelper类中的代码(已经在下载链接中):

.H

@protocol DownloadHelperDelegate <NSObject>
@optional
- (void) didReceiveData: (NSData *) theData;
- (void) didReceiveFilename: (NSString *) aName;
- (void) dataDownloadFailed: (NSString *) reason;
- (void) dataDownloadAtPercent: (NSNumber *) aPercent;
@end

@interface DownloadHelper : NSObject 
{
    NSURLResponse *response;
    NSMutableData *data;
    NSString *urlString;
    NSURLConnection *urlconnection;
    id <DownloadHelperDelegate> delegate;
    BOOL isDownloading;
}
@property (retain) NSURLResponse *response;
@property (retain) NSURLConnection *urlconnection;
@property (retain) NSMutableData *data;
@property (retain) NSString *urlString;
@property (retain) id delegate;
@property (assign) BOOL isDownloading;

+ (DownloadHelper *) sharedInstance;
+ (void) download:(NSString *) aURLString;
+ (void) cancel;
@end

.M

#define DELEGATE_CALLBACK(X, Y) if (sharedInstance.delegate && [sharedInstance.delegate respondsToSelector:@selector(X)]) [sharedInstance.delegate performSelector:@selector(X) withObject:Y];
#define NUMBER(X) [NSNumber numberWithFloat:X]

static DownloadHelper *sharedInstance = nil;

@implementation DownloadHelper
@synthesize response;
@synthesize data;
@synthesize delegate;
@synthesize urlString;
@synthesize urlconnection;
@synthesize isDownloading;

- (void) start
{
    self.isDownloading = NO;

    NSURL *url = [NSURL URLWithString:self.urlString];
    if (!url)
    {
        NSString *reason = [NSString stringWithFormat:@"Could not create URL from string %@", self.urlString];
        DELEGATE_CALLBACK(dataDownloadFailed:, reason);
        return;
    }

    NSMutableURLRequest *theRequest = [NSMutableURLRequest requestWithURL:url];
    if (!theRequest)
    {
        NSString *reason = [NSString stringWithFormat:@"Could not create URL request from string %@", self.urlString];
        DELEGATE_CALLBACK(dataDownloadFailed:, reason);
        return;
    }

    self.urlconnection = [[NSURLConnection alloc] initWithRequest:theRequest delegate:self];
    if (!self.urlconnection)
    {
        NSString *reason = [NSString stringWithFormat:@"URL connection failed for string %@", self.urlString];
        DELEGATE_CALLBACK(dataDownloadFailed:, reason);
        return;
    }

    self.isDownloading = YES;

    // Create the new data object
    self.data = [NSMutableData data];
    self.response = nil;

    [self.urlconnection scheduleInRunLoop:[NSRunLoop currentRunLoop] forMode:NSRunLoopCommonModes];
}

- (void) cleanup
{
    self.data = nil;
    self.response = nil;
    self.urlconnection = nil;
    self.urlString = nil;
    self.isDownloading = NO;
}

- (void)connection:(NSURLConnection *)connection didReceiveResponse:(NSURLResponse *)aResponse
{
    // store the response information
    self.response = aResponse;

    // Check for bad connection
    if ([aResponse expectedContentLength] < 0)
    {
        NSString *reason = [NSString stringWithFormat:@"Invalid URL [%@]", self.urlString];
        DELEGATE_CALLBACK(dataDownloadFailed:, reason);
        [connection cancel];
        [self cleanup];
        return;
    }

    if ([aResponse suggestedFilename])
        DELEGATE_CALLBACK(didReceiveFilename:, [aResponse suggestedFilename]);
}

- (void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)theData
{
    // append the new data and update the delegate
    [self.data appendData:theData];
    if (self.response)
    {
        float expectedLength = [self.response expectedContentLength];
        float currentLength = self.data.length;
        float percent = currentLength / expectedLength;
        DELEGATE_CALLBACK(dataDownloadAtPercent:, NUMBER(percent));
    }
}

- (void)connectionDidFinishLoading:(NSURLConnection *)connection
{
    // finished downloading the data, cleaning up
    self.response = nil;

    // Delegate is responsible for releasing data
    if (self.delegate)
    {
        NSData *theData = [self.data retain];
        DELEGATE_CALLBACK(didReceiveData:, theData);
    }
    [self.urlconnection unscheduleFromRunLoop:[NSRunLoop currentRunLoop] forMode:NSRunLoopCommonModes];
    [self cleanup];
}

- (void)connection:(NSURLConnection *)connection didFailWithError:(NSError *)error
{
    self.isDownloading = NO;
    NSLog(@"Error: Failed connection, %@", [error localizedDescription]);
    DELEGATE_CALLBACK(dataDownloadFailed:, @"Failed Connection");
    [self cleanup];
}

+ (DownloadHelper *) sharedInstance
{
    if(!sharedInstance) sharedInstance = [[self alloc] init];
    return sharedInstance;
}

+ (void) download:(NSString *) aURLString
{
    if (sharedInstance.isDownloading)
    {
        NSLog(@"Error: Cannot start new download until current download finishes");
        DELEGATE_CALLBACK(dataDownloadFailed:, @"");
        return;
    }

    sharedInstance.urlString = aURLString;
    [sharedInstance start];
}

+ (void) cancel
{
    if (sharedInstance.isDownloading) [sharedInstance.urlconnection cancel];
}
@end

最后这就是我用它上面的两个类编写文件的方式:

- (void) didReceiveData: (NSData *) theData
{
    if (![theData writeToFile:self.savePath atomically:YES])
        [self doLog:@"Error writing data to file"];

    [theData release];

}

如果有人可以帮助我,我会很高兴的!

谢谢,

凯文

Answer 1

更换内存NSData *data用NSOutputStream *stream.在-start创建要追加并打开它的流中:

stream = [[NSOutputStream alloc] initToFileAtPath:path append:YES];
[stream open];

当数据进入时,将其写入流:

NSUInteger left = [theData length];
NSUInteger nwr = 0;
do {
    nwr = [stream write:[theData bytes] maxLength:left];
    if (-1 == nwr) break;
    left -= nwr;
} while (left > 0);
if (left) {
    NSLog(@"stream error: %@", [stream streamError]);
}

完成后,关闭流:

[stream close];

更好的方法是在数据ivar之外添加流,将帮助程序设置为流的委托,缓冲数据ivar中的传入数据,然后每当流向辅助程序发送其空间时,将数据ivar的内容转储给帮助程序 - 可用事件并将其从数据ivar中清除.