在iOS应用程序中下载多幅图像

Question

我想下载多个图片从URL到我的设备在iOS应用程序。

//
//  ImageDownload.m
//

#import "ImageDownload.h"

@implementation ImageDownload {
    int *position;
    NSArray *downloableImages;
}

- (void)start:(NSArray *)images delegate:(id)delegate
{
    position = 0;
    downloableImages = images;

    NSUInteger *count = ((NSUInteger *)[downloableImages count]);
    NSLog(@"%d", count);

    [self startDownload];
}

- (void)startDownload
{
    NSUInteger *imageDataCount;

    NSArray *image;
    NSString *filename;
    NSString *fileurl;

    NSURLRequest *imageUrlRequest;

    image = [downloableImages objectAtIndex:position];

    NSLog(@"%d", position);

    NSArray *imageData = [image valueForKey:@"image"];
    imageDataCount = ((NSUInteger *)[imageData count]);

    if (imageDataCount > 0) {
        filename = [imageData objectAtIndex:0];
        fileurl = [imageData objectAtIndex:1];

        NSLog(@"%@", fileurl);

        imageUrlRequest = [NSURLRequest requestWithURL:[NSURL URLWithString:fileurl]];
        NSURLConnection *imageUrlConnection = [[NSURLConnection alloc] initWithRequest:imageUrlRequest delegate:self startImmediately:TRUE];
    } else {
        NSUInteger *count = ((NSUInteger *)[downloableImages count]);

        if (((NSUInteger *)position) < ((NSUInteger *)count - 1)) {
            position = position + 1;

            [self startDownload];
        }
    }
}

- (void)connectionDidFinishLoading:(NSURLConnection *)connection
{
    NSLog(@"finish image...");
    NSUInteger *count = ((NSUInteger *)[downloableImages count]);

    if (((NSUInteger *)position) < ((NSUInteger *)count - 1)) {
        position = position + 1;

        [self startDownload];
    }
}

@end

现在..。我只检查下载的位置和当前的URL，存在27个文件供下载.但下载不是一个接一个..。检查此输出：

职位:0 http.fic海洛因00.jpg 完成下载位置:4 http.fic海洛因04.jpg 完成下载位置:8 http.fic海洛因08.jpg 完成下载

Answer 1

在您的NSOperationQueue *operationQueue;文件中创建一个ivar .h，并在您的.m文件中插入它：

operationQueue = [[NSOperationQueue alloc] init];
operationQueue.maxConcurrentOperationCount = 1;

要下载图像，创建一个获取图像URL并为每个图像调用它的方法：

-(void)downloadImageAtURL:(NSURL *)imageURL {

    [NSURLConnection sendAsynchronousRequest:[NSURLRequest requestWithURL:imageURL] queue:operationQueue completionHandler:^(NSURLResponse *response, NSData *data, NSError *error) {
        // Do something with your images here...
    };
}

Answer 2

你可以试试这段代码。它百分之百地为我工作

你可以在这里得到更多的参考资料

-(IBAction)startdownload
{
for (int i=0; i<[downloadarray count]; i++)   //download array have url links
{ 
NSURL *URL = [NSURL URLWithString:[downloadarray objectAtIndex:i]];
NSMutableURLRequest *urlRequest = [[NSMutableURLRequest alloc]initWithURL:URL];
NSOperationQueue *queue = [[NSOperationQueue alloc]init];
[NSURLConnection sendAsynchronousRequest:urlRequest queue:queue  completionHandler:^(NSURLResponse *response, NSData *data, NSError *error)
 {
  if([data length] > 0 && [[NSString stringWithFormat:@"%@",error] isEqualToString:@"(null)"])
{
 //make your image here from data.
 UIImage *imag = [[UIImage alloc] initWithData:[NSData dataWithData:data]];
 NSArray *array = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory,    NSUserDomainMask, YES);
 NSString *docDir = [array objectAtIndex:0];
 NSString *imgstr=[NSString stringWithFormat:@"%d",i];
 NSString *pngfilepath = [NSString stringWithFormat:@"%@sample%@.png",docDir,imgstr];
NSData *data1 = [NSData dataWithData:UIImagePNGRepresentation(imag)];
 [data1 writeToFile:pngfilepath atomically:YES];
  }
 else if ([data length] == 0 && [[NSString stringWithFormat:@"%@",error] isEqualToString:@"(null)"])
{
  NSLog(@"No Data!");
}
  else if (![[NSString stringWithFormat:@"%@",error] isEqualToString:@"(null)"]){
 NSLog(@"Error = %@", error);
 }
}];

 }

 -(IBAction)viewfile
 {
 NSMutableArray *arr=[[NSMutableArray alloc]init];

  NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory,   NSUserDomainMask, YES);
 NSString *documentsDirectory = [paths objectAtIndex:0];
 NSString *pngfilepath = [NSString stringWithFormat:@"%@",documentsDirectory];
 NSArray *filePathsArray = [[NSFileManager defaultManager] subpathsOfDirectoryAtPath:pngfilepath error:&error];
 for (int i=0; i<[filePathsArray count]; i++){
 NSString *pngfilepath = [NSString stringWithFormat:@"%@%@",documentsDirectory,  [filePathsArray objectAtIndex:i]];
 [arr addObject:[UIImage imageWithContentsOfFile:pngfilepath]];
 }
myimageview = [[UIImageView alloc] initWithImage:[arr objectAtIndex:0]]; //Here myimageview is UIImageView

 }

希望这会有帮助！

Answer 3

围绕NSOperationQueue工作，它允许您控制并发运行的操作数量。

创建：

NSOperationQueue *queue = [NSOperationQueue new];
queue.maxConcurrentOperationCount = 1;

然后添加操作：

NSBlockOperation *operation = [NSBlockOperation blockOperationWithBlock:^{
    ... here is you code with converting image to data and addition it to NSURLConnection
}];
[operation setCompletionBlock:^{
    ....something that you want to do, after operation completes
}];
[queue addOperation:operation];

更多关于NSOperation：参考文献/occ/cl/NSOperation的信息