如何在情节提要中使用 NSURLConnection 下载文件

Question

我是NSURLConnection 的菜鸟。我搜索了谷歌并找到了这个网站，但我不明白。

请朋友们解释一下我从文档文件夹中的url下载的代码。

这是我的代码：

- (void)viewDidLoad
{
    [super viewDidLoad];
    NSURL *url =[NSURL URLWithString:@"http://cdn.arstechnica.net/wp-content/uploads/2012/09/iphone5-intro.jpg"];
    NSURLRequest *request = [NSURLRequest requestWithURL:url];
    NSURLConnection *con  = [[NSURLConnection alloc]initWithRequest:request delegate:self];
    [con start];}
- (void)connection:(NSURLConnection *)connection didReceiveResponse:(NSURLResponse *)response
{
    //I dont know what thing put here
}

- (void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)theData
{
    //I dont know what thing put here
}


- (void)connectionDidFinishLoading:(NSURLConnection *)connection
{
    //I dont know what thing put here
}
- (void)connection:(NSURLConnection *)connection didFailWithError:(NSError *)error
{
    UIAlertView *errorView = [[UIAlertView alloc]initWithTitle:@"Error" message:@"The Connection has been LOST" delegate:self cancelButtonTitle:@"OK" otherButtonTitles: nil];
    [errorView show];
    [UIApplication sharedApplication].networkActivityIndicatorVisible = NO;
}

Answer 1

使用 NSURLConnection ，试试这个

// Create the request.
NSURLRequest *theRequest=[NSURLRequest requestWithURL:[NSURL URLWithString:@"http://cdn.cultofmac.com/wp-content/uploads/2013/03/colorware-iphone-5-xl.jpg"]
                        cachePolicy:NSURLRequestUseProtocolCachePolicy
                    timeoutInterval:60.0];
// create the connection with the request
// and start loading the data
NSURLConnection *theConnection=[[NSURLConnection alloc] initWithRequest:theRequest delegate:self];
if (theConnection) {
    // Create the NSMutableData to hold the received data.
    // receivedData is an instance variable declared elsewhere.
    receivedData = [[NSMutableData data] retain];
} else {
    // Inform the user that the connection failed.
}

有关 NSURLConnection 的更多信息，请参阅：URL Loading System Programming Guide

编辑

这里recievedData是NSMutableData类型的实例变量

-(void)downloadWithNsurlconnection
{

    NSURL *url = [NSURL URLWithString:currentURL];
    NSURLRequest *theRequest = [NSURLRequest requestWithURL:url         cachePolicy:NSURLRequestReloadIgnoringLocalCacheData timeoutInterval:60];
    receivedData = [[NSMutableData alloc] initWithLength:0];
    NSURLConnection * connection = [[NSURLConnection alloc] initWithRequest:theRequest delegate:self     startImmediately:YES];


}


- (void) connection:(NSURLConnection *)connection didReceiveResponse:(NSURLResponse *)response {
    [UIApplication sharedApplication].networkActivityIndicatorVisible = YES;
    [receivedData setLength:0];
}

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


}

- (void) connectionDidFinishLoading:(NSURLConnection *)connection {
    NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);

    NSString *documentsDirectory = [paths objectAtIndex:0];
    NSString *pdfPath = [documentsDirectory stringByAppendingPathComponent:[currentURL stringByAppendingString:@".jpg"]];
    NSLog(@"Succeeded! Received %d bytes of data",[receivedData length]);
    [UIApplication sharedApplication].networkActivityIndicatorVisible = NO;
    [receivedData writeToFile:pdfPath atomically:YES];
}

Answer 2

最好使用带有块的 NSURLConnection 异步执行此操作。

- (NSString *)documentsDirectoryPath{
    NSArray *directories = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory,
                                                               NSUserDomainMask,
                                                               YES);
    return directories[0];
}

- (void)downloadImage{

    NSString *urlPath = @"http://cdn.arstechnica.net/wp-content/uploads/2012/09/iphone5-intro.jpg";
    NSURL *url = [NSURL URLWithString:urlPath];
    NSURLRequest *urlRequest = [NSURLRequest requestWithURL:url];
    [NSURLConnection sendAsynchronousRequest:urlRequest
                                       queue:[NSOperationQueue mainQueue]
                           completionHandler:^(NSURLResponse * response, NSData *responseData, NSError *error) {

                               if (responseData) {
                                   NSString *imageName = [urlPath lastPathComponent];
                                   NSString *imagePath = [[self documentsDirectoryPath]stringByAppendingPathComponent:imageName];

                                   [responseData writeToFile:imagePath atomically:YES];
                               }

    }];
}

Answer 3

不使用NSURLConnection，您可以轻松下载文件，无需额外调用委托。试试这个。

NSString *url = @"http://cdn.cultofmac.com/wp-content/uploads/2013/03/colorware-iphone-5-xl.jpg";
NSArray *path               = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
NSString *documentdirectory = [path objectAtIndex:0];
NSString *dataPath          = [documentdirectory stringByAppendingPathComponent:@"Pictures"];
NSString *localFileURL      = [NSString stringWithFormat:@"%@/%@",dataPath,[url lastPathComponent]];

if (![[NSFileManager defaultManager] fileExistsAtPath:dataPath])
[[NSFileManager defaultManager] createDirectoryAtPath:dataPath withIntermediateDirectories:NO attributes:nil error:nil];

NSData   *data         = [NSData dataWithContentsOfURL:[NSURL URLWithString:url]];
if([data writeToFile:localFileURL atomically:YES])
{
    NSLog(@"Downloaded File");
}