下载大文件 - iPhone SDK [英] Downloading a Large File - iPhone SDK
问题描述
我正在使用Erica Sadun的异步下载方法（链接到项目文件：下载）然而，她的方法不适用于具有大尺寸（50 mb或以上）的大文件。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。有没有办法我可以调整这个代码，以便它与大文件一起使用？以下是我在DownloadHelper类中的代码（已经在下载链接中）：
I am using Erica Sadun's method of Asynchronous Downloads (link here for the project file: download), however her method does not work with files that have a big size (50 mb or above). If I try to download a file above 50 mb, it will usually crash due to a memory crash. Is there anyway I can tweak this code so that it works with large files as well? Here is the code I have in the DownloadHelper Classes (which is already in the download link):
.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
最后这是我如何写文件上面的两个类：
And finally this is how I write the file with the two classes above it:
- (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！
If someone could help me out I would be so glad!
谢谢，
凯文
推荐答案
使用 NSOutputStream * stream 替换内存中的 NSData *数据。在 -start 中创建流以追加并打开它：
Replace the in-memory NSData *data with an NSOutputStream *stream. In -start create the stream to append and open it:
stream = [[NSOutputStream alloc] initToFileAtPath:path append:YES];
[stream open];
随着数据的输入，写入流：
As data comes in, write it to the stream:
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];
除了数据ivar之外，更好的方法是添加流，将助手设置为流的代表，缓冲数据ivar中的传入数据，然后将数据ivar的内容转储到帮助器，每当流发送帮助者其空间可用事件并将其从数据ivar中清除。
A better approach would be to add the stream in addition to the data ivar, set the helper as the stream's delegate, buffer incoming data in the data ivar, then dump the data ivar's contents to the helper whenever the stream sends the helper its space-available event and clear it out of the data ivar.
这篇关于下载大文件 - iPhone SDK的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！
