AFNetworking 2：取消批量请求

Posted 2023-02-24

【中文标题】AFNetworking 2：取消批量请求

【英文标题】：AFNetworking 2: canceling batch requests

【发布时间】：2013-12-23 18:16:34

【问题描述】：

我正在使用 AFNetworking2 代码来批处理请求。我从示例代码中复制并粘贴，并将上传操作更改为下载。我需要取消控制器消失的下载操作。我正在尝试实现取消：

    [[self.imagesQueue.operations 
filteredArrayUsingPredicate:[NSPredicate predicateWithBlock:^BOOL(id evaluatedObject, NSDictionary *bindings) 
 return [evaluatedObject isKindOfClass:[AFHTTPRequestOperation class]]; ]] makeObjectsPerformSelector:@selector(cancel)];

批量请求（下载图片）：

-(void) startDownloadImages 

    NSMutableArray *mutableOperations = [NSMutableArray array];
    //self.downloadOperations = [NSMutableArray array];
    for (NSString *str in _project.frames) 

        NSURLRequest *request =
        [[AFHTTPRequestSerializer serializer] requestWithMethod:@"GET"
                                                      URLString:str
                                                     parameters:nil];

        AFHTTPRequestOperation *operation = [[AFHTTPRequestOperation alloc] initWithRequest:request];
        [operation setCompletionBlockWithSuccess:^(AFHTTPRequestOperation *operation, id responseObject) 

         NSLog(@"OK %@", str);


         failure:^(AFHTTPRequestOperation *operation, NSError *error) 
            NSLog(@"FAILS %@", str);
        ];

        [mutableOperations addObject:operation];
    

    NSArray *operations =
    [AFURLConnectionOperation batchOfRequestOperations:mutableOperations
                                         progressBlock:^(NSUInteger numberOfFinishedOperations, NSUInteger totalNumberOfOperations) 
        NSLog(@"%lu of %lu complete", (unsigned long)numberOfFinishedOperations, (unsigned long)totalNumberOfOperations);
     completionBlock:^(NSArray *operations) 
        NSLog(@"All operations in batch complete");

    ];

    self.imagesQueue = [[NSOperationQueue alloc] init];
    self.imagesQueue.name = @"com.imagesqueue";
    self.imagesQueue.maxConcurrentOperationCount = 1;

    [self.imagesQueue addOperations:operations waitUntilFinished:NO];
    //[[NSOperationQueue mainQueue] addOperations:operations waitUntilFinished:NO];

一系列启动和取消导致 EXC_BREAKPOINT（代码=EXC_ARM_BREAKPOINT，子代码=0xdefe）：

libdispatch.dylib`dispatch_group_leave:
    0x37e1e7d8:  dmb    ishst
    0x37e1e7dc:  ldrex  r1, [r0, #40]
    0x37e1e7e0:  adds   r1, #1
    0x37e1e7e2:  strex  r2, r1, [r0, #40]
    0x37e1e7e6:  cmp    r2, #0
    0x37e1e7e8:  bne    0x37e1e7dc                ; dispatch_group_leave + 4
    0x37e1e7ea:  cmp.w  r1, #4294967295
    0x37e1e7ee:  ble    0x37e1e7fe                ; dispatch_group_leave + 38
    0x37e1e7f0:  mvn    r2, #2147483648
    0x37e1e7f4:  cmp    r1, r2
    0x37e1e7f6:  it     eq
    0x37e1e7f8:  beq.w  0x37e21df8                ; _dispatch_group_wake
    0x37e1e7fc:  bx     lr
    0x37e1e7fe:  trap   
    0x37e1e800:  nop    
    0x37e1e802:  nop 

有什么建议吗？

【问题讨论】：

AFNetworking 正在以巨大的速度变化。您的问题可能更适合 github 问题列表。

【参考方案1】：

尝试将 str 声明为块变量（您在块中访问它）：

__block NSString *str;

for (str in _project.frames) 

您也可以在执行取消选择器之前尝试检查操作是否已完成。

在 view will dissappear 方法中，您可以调用图像队列上的 cancelAllOperations 来取消所有剩余的操作。