I would like to download files directly from an URL to the disk using objective-c on the iPhone os.
Currently I am using NSURLConnection to send a synchronousRequest, writing the returned NSData into a file.
How can I change the download handling (still having the request beeing synchronous, it i开发者_Go百科s already in a background thread) to write the data directly to disk, not using memory variables to store the complete content (only small parts)?
A sample code would be appreciated.
Thank you all in advance for your responses!
You can do this, but it's a bit complicated to set up. Here's how I'd do it:
warning: the following code was typed in a browser and compiled in my head. Also, there's not a lot of error handling. Caveat Implementor.
//NSURLConnection+DirectDownload.h
@interface NSURLConnection (DirectDownload)
+ (BOOL) downloadItemAtURL:(NSURL *)url toFile:(NSString *)localPath error:(NSError **)error;
@end
//NSURLConnection+DirectDownload.m
@implementation NSURLConnection (DirectDownload)
+ (BOOL) downloadItemAtURL:(NSURL *)url toFile:(NSString *)localPath error:(NSError **)error {
NSMutableURLRequest * request = [[NSMutableURLRequest alloc] initWithURL:url];
//configure the request, or leave it as-is
DirectDownloadDelegate * delegate = [[DirectDownloadDelegate alloc] initWithFilePath:localPath];
NSURLConnection * connection = [[NSURLConnection alloc] initWithRequest:request delegate:delegate];
[delegate autorelease];
[request release];
while ([delegate isDone] == NO) {
[[NSRunLoop currentRunLoop] runUntilDate:[NSDate dateWithTimeIntervalSinceNow:1.0]];
}
[connection release];
NSError * downloadError = [delegate error];
if (downloadError != nil) {
if (error != nil) { *error = [[downloadError retain] autorelease]; }
return NO;
}
return YES;
}
//DirectDownloadDelegate.h
@interface DirectDownloadDelegate : NSObject {
NSError *error;
NSURLResponse * response;
BOOL done;
NSFileHandle * outputHandle;
}
@property (readonly, getter=isDone) BOOL done;
@property (readonly) NSError *error;
@property (readonly) NSURLResponse * response;
@end
//DirectDownloadDelegate.m
@implementation DirectDownloadDelegate
@synthesize error, request, done;
- (id) initWithFilePath:(NSString *)path {
if (self = [super init]) {
if ([[NSFileManager defaultManager] fileExistsAtPath:path]) {
[[NSFileManager defaultManager] removeItemAtPath:path error:nil];
}
[[NSFileManager defaultManager] createFileAtPath:path contents:nil attributes:nil];
outputHandle = [[NSFileHandle fileHandleForWritingAtPath:path] retain];
}
return self;
}
- (void) dealloc {
[error release];
[response release];
[outputHandle closeFile];
[outputHandle release];
[super dealloc];
}
- (void) connection:(NSURLConnection *)connection didFailWithError:(NSError *)anError {
error = [anError retain];
[self connectionDidFinishLoading:connection];
}
- (void) connection:(NSURLConnection *)connection didReceiveData:(NSData *)someData {
[outputHandle writeData:someData];
}
- (void) connection:(NSURLConnection *)connection didReceiveResponse:(NSURLResponse *)aResponse {
response = [aResponse retain];
}
- (void) connectionDidFinishLoading:(NSURLConnection *)connection {
done = YES;
}
The basic idea is that you create a standard NSURLConnection
, which is normally asynchronous, but just block the thread by spinning the runloop yourself until the connection is done. You also use a custom url connection delegate to just pipe any data the connection receives directly to a file.
You can now do:
NSError * downloadError = nil;
BOOL ok = [NSURLConnection downloadItemAtURL:someURL toFile:someFile error:&downloadError];
if (!ok) {
NSLog(@"ack there was an error: %@", error);
} else {
NSLog(@"file downloaded to: %@", someFile);
}
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