iOS：下载图像从网址和救设备

Question

我想下载的图象从网址 http://a3.twimg.com/profile_images/414797877/05052008321_bigger.jpg

我使用了下列代码，但像是不存在的装置。我想知道我在做什么错误的。

 NSURLRequest *request = [NSURLRequest requestWithURL:[NSURL URLWithString:@"http://a3.twimg.com/profile_images/414797877/05052008321_bigger.jpg"]];
 [NSURLConnection connectionWithRequest:request delegate:self];

 NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
 NSString *documentsDirectory = [paths objectAtIndex:0];
 NSString *localFilePath = [documentsDirectory stringByAppendingPathComponent:@"pkm.jpg"];
 NSData *thedata = NULL;
 [thedata writeToFile:localFilePath atomically:YES];

 UIImage *img = [[UIImage alloc] initWithData:thedata];

Answer 1

如果您设定theData到nil，你有什么期待它写入磁盘？

什么可以使用是NSData* theData = [NSData dataWithContentsOfURL:yourURLHere];从磁盘加载的数据，并然后将其保存使用writeToFile:atomically:。如果您需要更多的控制在装载过程中还是有它的背景，看看NSURLConnection的文件和相关指南。

Answer 2

我正好有你在寻找什么。

获取图像从网址

-(UIImage *) getImageFromURL:(NSString *)fileURL {
    UIImage * result;

    NSData * data = [NSData dataWithContentsOfURL:[NSURL URLWithString:fileURL]];
    result = [UIImage imageWithData:data];

    return result;
}

保存图片

-(void) saveImage:(UIImage *)image withFileName:(NSString *)imageName ofType:(NSString *)extension inDirectory:(NSString *)directoryPath {
    if ([[extension lowercaseString] isEqualToString:@"png"]) {
        [UIImagePNGRepresentation(image) writeToFile:[directoryPath stringByAppendingPathComponent:[NSString stringWithFormat:@"%@.%@", imageName, @"png"]] options:NSAtomicWrite error:nil];
    } else if ([[extension lowercaseString] isEqualToString:@"jpg"] || [[extension lowercaseString] isEqualToString:@"jpeg"]) {
        [UIImageJPEGRepresentation(image, 1.0) writeToFile:[directoryPath stringByAppendingPathComponent:[NSString stringWithFormat:@"%@.%@", imageName, @"jpg"]] options:NSAtomicWrite error:nil];
    } else {
        NSLog(@"Image Save Failed\nExtension: (%@) is not recognized, use (PNG/JPG)", extension);
    }
}

<强>加载图片

-(UIImage *) loadImage:(NSString *)fileName ofType:(NSString *)extension inDirectory:(NSString *)directoryPath {
    UIImage * result = [UIImage imageWithContentsOfFile:[NSString stringWithFormat:@"%@/%@.%@", directoryPath, fileName, extension]];

    return result;
}

如何对

//Definitions
NSString * documentsDirectoryPath = [NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES) objectAtIndex:0];

//Get Image From URL
UIImage * imageFromURL = [self getImageFromURL:@"http://www.yourdomain.com/yourImage.png"];

//Save Image to Directory
[self saveImage:imageFromURL withFileName:@"My Image" ofType:@"png" inDirectory:documentsDirectoryPath];

//Load Image From Directory
UIImage * imageFromWeb = [self loadImage:@"My Image" ofType:@"png" inDirectory:documentsDirectoryPath];

Answer 3

这是码下载的图象从网址和保存图像设备和 此 是的参考链接。

 NSURLRequest *request = [NSURLRequest requestWithURL:[NSURL URLWithString:@"http://a3.twimg.com/profile_images/414797877/05052008321_bigger.jpg"]];
 [NSURLConnection connectionWithRequest:request delegate:self];

 NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
 NSString *documentsDirectory = [paths objectAtIndex:0];
 NSString *localFilePath = [documentsDirectory stringByAppendingPathComponent:@"pkm.jpg"];
 NSData *thedata = [NSData dataWithContentsOfURL:[NSURL URLWithString:@"http://a3.twimg.com/profile_images/414797877/05052008321_bigger.jpg"]];
 [thedata writeToFile:localFilePath atomically:YES];

Answer 4

  

获取图像从URL

-(UIImage *) getImageFromURL:(NSString *)fileURL {
    UIImage * result;

    NSData * data = [NSData dataWithContentsOfURL:[NSURL URLWithString:fileURL]];
    result = [UIImage imageWithData:data];

    return result;
}

这为我工作不错，但我遇到了内存问题与CFData（店）。与autoreleasepool固定它：

 -(UIImage *) getImageFromURL:(NSString *)fileURL {
    @autoreleasepool {
     UIImage * result;

     NSData * data = [NSData dataWithContentsOfURL:[NSURL URLWithString:fileURL]];
     result = [UIImage imageWithData:data];

     return result;
    }
 }

Answer 5

由于我们正在IOS6现在，你不再需要编写的图像，来一盘.
由于iOS5你现在可以设定"允许外部储存"一coredata二进制的属性。根据苹果释放注意到这意味着如下：

小小的数据的价值观图像可以略图有效地存储在一个 数据库，但laarge照片或其他媒体是最好的处理直接通过 本文件系统。你现在可以指定该价值的管理 目属性可能被储存作为外部的记录看看 setAllowsExternalBinaryDataStorage: 在启用时，核心数据的试探性地决定对每价值的基础上，如果 它应保存的数据直接的数据库或存储URI 单独的文件，该文件管理用于你。你不能查询的基础上 内容的二进制数据的财产，如果使用这个选项。

Answer 6

喜很显然，你正在写NULL数据到您的文件。

在您的代码语句的NSData *海图= NULL;表明您分配NULL值给您的数据。

您正在编写NULL数据到您的文件中。

请再次检查你的代码。

Answer 7

-(IBAction)BtnDwn:(id)sender
{
  [self.actvityIndicator startAnimating];

  NSURL *URL = [NSURL URLWithString:self.dataaArray];
  NSURLRequest *request = [NSURLRequest requestWithURL:URL];
  NSURLSession *session = [NSURLSession sharedSession];

  NSURLSessionDownloadTask *downloadTask = [session downloadTaskWithRequest:request completionHandler:^(NSURL *location, NSURLResponse *response, NSError *error)
   {

      NSString *documentsPath = [NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES) firstObject];
      NSURL *documentsDirectoryURL = [NSURL fileURLWithPath:documentsPath];
      NSURL *documentURL = [documentsDirectoryURL URLByAppendingPathComponent:[response suggestedFilename]];
      BOOL exists = [[NSFileManager defaultManager] fileExistsAtPath:[documentURL path]];

      if (exists)
      {
         NSLog(@"not created");
         UIAlertView *alert = [[UIAlertView alloc] initWithTitle:@"Download"
                                                    message:@"sory,file already exists"
                                                   delegate:nil
                                          cancelButtonTitle:@"cancel"
                                          otherButtonTitles:nil];
         [alert show];
      }
      else
      { 
         [[NSFileManager defaultManager] moveItemAtURL:location toURL:documentURL error:nil];
         UIAlertView *alert = [[UIAlertView alloc] initWithTitle:@"Download"
                                                    message:@"Succesfully downloaded"
                                                   delegate:nil
                                          cancelButtonTitle:@"OK"
                                          otherButtonTitles:nil];
         [self.actvityIndicator stopAnimating];
         NSLog(@"wait downloading......");
         [alert show];
     }
  }];

    [downloadTask resume];    
}

Answer 8

下面是如何在异步斯威夫特保存图像：

requestImage("http://www.asdf.com/89asdf.gif") { (image) -> Void in
    let myImage = image
}

func requestImage(url: String, success: (UIImage?) -> Void) {
    requestURL(url, success: { (data) -> Void in
        if let d = data {
            success(UIImage(data: d))
        }
    })
}

func requestURL(url: String, success: (NSData?) -> Void, error: ((NSError) -> Void)? = nil) {
    NSURLConnection.sendAsynchronousRequest(
        NSURLRequest(URL: NSURL (string: url)!),
        queue: NSOperationQueue.mainQueue(),
        completionHandler: { response, data, err in
            if let e = err {
                error?(e)
            } else {
                success(data)
            }
    })
}

其包括在如我的回购的标准功能：

https://github.com/goktugyil/EZSwiftExtensions

Answer 9

下面是我如何下载横幅我的应用程序的例子。我在后台下载的图像，然后我的大多数应用程序不使用引用计数，所以我释放的对象。

- (void)viewDidLoad {
    [super viewDidLoad];

    [NSThread detachNewThreadSelector:@selector(loadImageInBackground) toTarget:self withObject:nil];

}

- (void) loadImageInBackground {
    NSURL *url = [[NSURL alloc] initWithString:@"http://yourImagePath.png"];
    NSData *data = [[NSData alloc] initWithContentsOfURL:url];
    [url release];
    UIImage *result = [[UIImage alloc] initWithData:data];
    [data release];

    UIImageView *banner_ImageView = [[UIImageView alloc] initWithFrame:CGRectMake(0, 0, 320, 50)];
    [self.view addSubview:banner_ImageView];
    banner_ImageView.image = result;
    [result release];
}