0

在我的应用程序中，我尝试下载数千张图像（每个图像大小最大为 3mb）和 10 个视频（每个视频大小最大为 100mb）并将其保存在文档目录中。

为了实现这一点，我正在使用 AFNetworking

在这里，我的问题是，当我使用慢速 wifi（大约 4mbps）时，我成功获取了所有数据，但是如果我在100mbps的 wifi 下进行相同的下载，则应用程序在下载图像和内存时收到内存警告下载视频时出现压力问题，然后应用程序崩溃。

-(void) AddVideoIntoDocument :(NSString *)name :(NSString *)urlAddress{

    NSMutableURLRequest *theRequest=[NSMutableURLRequest requestWithURL:[NSURL URLWithString:urlAddress]];
    [theRequest setTimeoutInterval:1000.0];

    AFHTTPRequestOperation *operation = [[AFHTTPRequestOperation alloc] initWithRequest:theRequest];

    NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
    NSString *path = [[paths objectAtIndex:0] stringByAppendingPathComponent:name];
    operation.outputStream = [NSOutputStream outputStreamToFileAtPath:path append:NO];

    [operation setCompletionBlockWithSuccess:^(AFHTTPRequestOperation *operation, id responseObject) {
        NSLog(@"Successfully downloaded file to %@", path);
    } failure:^(AFHTTPRequestOperation *operation, NSError *error) {
        NSLog(@"Error: %@", error);
    }];
    [operation setDownloadProgressBlock:^(NSUInteger bytesRead, long long totalBytesRead, long long totalBytesExpectedToRead) {

        //NSLog(@"Download = %f", (float)totalBytesRead / totalBytesExpectedToRead);

    }];
    [operation start];
}

-(void)downloadRequestedImage : (NSString *)imageURL :(NSInteger) type :(NSString *)imgName{

    NSMutableURLRequest *theRequest=[NSMutableURLRequest requestWithURL:[NSURL URLWithString:imageURL]];
    [theRequest setTimeoutInterval:10000.0];
    AFHTTPRequestOperation *posterOperation = [[AFHTTPRequestOperation alloc] initWithRequest:theRequest];
    posterOperation.responseSerializer = [AFImageResponseSerializer serializer];
    [posterOperation setCompletionBlockWithSuccess:^(AFHTTPRequestOperation *operation, id responseObject) {
        //NSLog(@"Response: %@", responseObject);

        UIImage *secImg = responseObject;
        if(type == 1) { // Delete the image from DB
            [self removeImage:imgName];
        }
        [self AddImageIntoDocument:secImg :imgName];
    } failure:^(AFHTTPRequestOperation *operation, NSError *error) {
        NSLog(@"Image request failed with error: %@", error);
    }];

    [posterOperation start];
}

上面的代码我根据我必须下载的视频和图像的数量循环

这种行为背后的原因是什么

我什至有两种场景的内存分配屏幕截图

请帮忙

添加用于保存下载图像的代码

-(void)AddImageIntoDocument :(UIImage *)img :(NSString *)str{

    if(img) {
        NSData *pngData = UIImageJPEGRepresentation(img, 0.4);
        NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);

        NSString *filePathName =[[paths objectAtIndex:0]stringByAppendingPathComponent:str];
        [pngData writeToFile:filePathName atomically:YES];
    }
    else {
        NSLog(@"Network Error while downloading the image!!! Please try again.");
    }
}
4

2 回答 2

1

这种行为的原因是您将大文件加载到内存中（并且可能它发生得足够快，以至于您的应用程序没有机会响应内存压力通知）。

您可以通过不将这些下载加载到内存中来控制峰值内存使用量来缓解这种情况。下载大文件时，通常最好将它们直接流式传输到持久存储。要使用 AFNetworking 执行此操作，您可以设置 的outputStream，AFURLConnectionOperation它应该将内容直接流式传输到该文件，例如

AFHTTPRequestOperation *operation = [[AFHTTPRequestOperation alloc] initWithRequest:request];

NSString *documentsPath = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES)[0];
NSString *path          = [documentsPath stringByAppendingPathComponent:[url lastPathComponent]]; // use whatever path is appropriate for your app

operation.outputStream = [[NSOutputStream alloc] initToFileAtPath:path append:NO];

[operation setCompletionBlockWithSuccess:^(AFHTTPRequestOperation *operation, id responseObject) {
    NSLog(@"successful");
} failure:^(AFHTTPRequestOperation *operation, NSError *error) {
    NSLog(@"failure: %@", error);
}];

[self.downloadQueue addOperation:operation];

顺便说一句，你会注意到我不只是呼吁start这些请求。就个人而言，我总是将它们添加到我指定了最大并发操作数的队列中：

self.downloadQueue = [[NSOperationQueue alloc] init];
self.downloadQueue.maxConcurrentOperationCount = 4;
self.downloadQueue.name = @"com.domain.app.downloadQueue";

我认为这对于内存使用而言不如将结果直接流式传输到outputStream使用持久存储的关键，但我发现这是在启动许多并发请求时管理系统资源的另一种机制。

于 2014-10-22T16:17:15.710 回答
0

您可以开始使用NSURLSession的 downloadTask。

我认为这将解决您的问题。 

NSURLRequest *request = [NSURLRequest requestWithURL:[NSURL URLWithString:@"http://someSite.com/somefile.zip"]];
[[NSURLSession sharedSession] downloadTaskWithRequest:request
                                        completionHandler:^(NSURL *location, NSURLResponse *response, NSError *error)
     {
         // Use location (it's file URL in your system)
     }];
于 2014-10-22T15:03:04.887 回答