Question

我正在实现一个代码，用于下载图像并将其保存在应用程序的数据库中，

我有一个对象数组，每个对象包含图像url和一些其他信息。要下载图像，我正在使用类库AFImageRequestOperation.h AFNetworking。

我的代码下载并保存数据库中的数据，但需要通知用户下载了哪个图像，例如：如果我有一个包含5个对象的数组（在每个对象的上方引用），则必须下载数组中的顺序相同，但是当AFImageRequestOperation使异步下载时，可以在第一个项目之前下载第4项。

简而言之，我想拥有控制权，只有在完成上一次下载后才能下次下载。

我有一个for通过对象数组运行并为每个位置调用一个函数，该函数具有以下代码：

NSURLRequest *request = [NSURLRequest requestWithURL:[NSURL URLWithString:[arrImagem valueForKey:@"urlimagem"]]];
    AFImageRequestOperation *operation = [AFImageRequestOperation imageRequestOperationWithRequest:request imageProcessingBlock:nil success:^(NSURLRequest *request, NSHTTPURLResponse *response, UIImage *image){

        Imagens *imagem = (Imagens *)[NSEntityDescription insertNewObjectForEntityForName:@"IMAGENS" inManagedObjectContext:managedObjectContext];

        // Save Image
        NSData *imageData = UIImageJPEGRepresentation(image, 90);
        [imagem setCategoria:cat];
        [imagem setTitulo:[arrImagem valueForKey:@"titulo"]];
        [imagem setDescricao:[arrImagem valueForKey:@"descricao"]];
        [imagem setImagem:imageData];



        NSError *error;
        if(![managedObjectContext save:&error]){
            NSLog(@"houve um erro muito grave");
            //return false;
        }else{
            NSLog(@"Salvou imagem");
        }

    }failure:^(NSURLRequest *request, NSHTTPURLResponse *response, NSError *error){
        NSLog(@"%@", [error localizedDescription]);

    }];

    [operation start];

我不知道我的问题是否非常清楚，但基本上我的问题与此类似link

Answer 1

AFImageRequestOperation是NSOperation的子类，因此您可以使用：

- (void) addDependency: (NSOperation*) operation

确保一个操作在另一个操作之前完成。

例如：

NSOperation *op1 = [[NSOperation alloc]init];
NSOperation *op2 = [[NSOperation alloc]init];

[op1 addDependency: op2];

这样 op1 就会在 op2 完成之前启动。

Answer 2

您可以在类中创建一个方法，您可以在其中调用下载代码并添加一个块作为参数，该块接收下载的UIImage，图像URL（以及您需要的其他信息），或者您可以使用相同的参数实现委托来自街区。它可以锁定类似的东西：

-(void)downloadImageWithSuccess:(void (^)(UIImage *image, NSString *url, OtherParms here))success 
                       failure:(void (^)(NSError *error)failure {
NSURLRequest *request = [NSURLRequest requestWithURL:[NSURL URLWithString:[arrImagem valueForKey:@"urlimagem"]]];

    AFImageRequestOperation *operation = [AFImageRequestOperation imageRequestOperationWithRequest:request imageProcessingBlock:nil success:^(NSURLRequest *request, NSHTTPURLResponse *response, UIImage *image){
        Imagens *imagem = (Imagens *)[NSEntityDescription insertNewObjectForEntityForName:@"IMAGENS" inManagedObjectContext:managedObjectContext];

        // Save Image
        NSData *imageData = UIImageJPEGRepresentation(image, 90);
        [imagem setCategoria:cat];
        [imagem setTitulo:[arrImagem valueForKey:@"titulo"]];
        [imagem setDescricao:[arrImagem valueForKey:@"descricao"]];
        [imagem setImagem:imageData];

        NSError *error;
        if(![managedObjectContext save:&error]){
            NSLog(@"houve um erro muito grave");
            //return false;
        }else{
            NSLog(@"Salvou imagem");
        }
      success(imagem, [request.URL absoluteString], otherParams);

    }failure:^(NSURLRequest *request, NSHTTPURLResponse *response, NSError *error){
        NSLog(@"%@", [error localizedDescription]);
        failure(error);

    }];

    [operation start];
}

}

当你从代码中调用方法时，你可以做一些事情（使用块）：

[catalog downloadImageWithSuccess:^(UIImage *image, NSString *url, OtherParms here) {
                //NOTIFY USER THAT THE IMAGE WITH URL HAS BEEN DOWNLOADED
            }
            failure:^(NSError *error) {
                //NTOFIY USER THAT THE IMAGE FAILED
            }

];

Answer 3

设法解决了我的问题，抱歉发布解决方案的延迟，请按照以下代码：

dispatch_group_t group = dispatch_group_create();

        dispatch_group_enter(group);

        NSURLRequest *request = [NSURLRequest requestWithURL:[NSURL URLWithString:strUrl]];

        AFImageRequestOperation *operation = [AFImageRequestOperation imageRequestOperationWithRequest:request imageProcessingBlock:nil success:^(NSURLRequest *request, NSHTTPURLResponse *response, UIImage *image){

            //your implementation        

            dispatch_group_leave(group);     //<== NOTICE THIS

        }failure:^(NSURLRequest *request, NSHTTPURLResponse *response, NSError *error){
           //your implementation

            NSLog(@"%@", [error localizedDescription]);

        }];

        [operation start];

        dispatch_group_wait(group, DISPATCH_TIME_FOREVER);

因此按顺序下载ocorerão，如果此代码在一个case中，则只有在方法成功^：或者失败^：被调用时才会调用下一个下载

AFImageRequestOperation为了不异步

3 个答案: