iphone - 如何在 iPhone 操作系统上直接将文件下载到磁盘？

Question

我想在 iPhone 操作系统上使用 Objective-c 直接从 URL 下载文件到磁盘。

目前我正在使用 NSURLConnection 发送同步请求，将返回的 NSData 写入文件。

如何更改下载处理（仍然有同步的请求，它已经在后台线程中）以将数据直接写入磁盘，而不是使用内存变量来存储完整的内容（只有小部分）？

示例代码将不胜感激。

提前感谢大家的回复！

Answer 1

您可以这样做，但设置起来有点复杂。这是我的做法：

警告：以下代码是在浏览器中输入并在我脑海中编译的。此外，没有太多的错误处理。警告实施者。

//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;
}

基本思想是您创建一个标准的NSURLConnection，通常是异步的，但只需通过自己旋转 runloop 来阻止线程，直到连接完成。您还可以使用自定义 url 连接委托将连接接收到的任何数据直接通过管道传输到文件。

您现在可以执行以下操作：

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);
}