Question

Mailcore有一个很酷的method下载附件并接受一个块作为参数来返回下载进度：

- (CTCoreAttachment *)fetchFullAttachmentWithProgress:(CTProgressBlock)block;

其中CTProgressBlock定义为

typedef void (^CTProgressBlock)(size_t curr, size_t max);

通常我会这样使用它：

//AttachmentDownloader.m
int fileNum = x; // explained later
CTCoreAttachment* fullAttachment = 
    [attachment fetchFullAttachmentWithProgress:^(size_t curr, size_t max) {
    NSLog(@"::: this is curr: %zu", curr);
    NSLog(@"::: this is max: %zu\n\n", max);
}];

问题是我的主UI类FileBucket.m调用了最后一个方法，而这个类依次为许多不同的UI元素提取许多附件。我希望这个回调方法向FileBucket.m报告这个进程所属的附件。所以换句话说，我想要的是：

// FileBucket.m
[AttachmentDownloader runMultiple:attachmentTree 
                     withProgress:^(size_t curr, size_t max, int fileNum) {
    NSLog(@"::: this is curr: %zu", curr);
    NSLog(@"::: this is max: %zu\n\n", max);
    NSLog(@"::: this progress belongs to element %d", fileNum);
}];

我知道这很难解释/说明..还有一件事：AttachmentDownloader.m知道这个进展的附件是什么......但它只是想把它传递给FileBucket.m 每次调用回调块。

Answer 1

我并不特别知道这个类，但通常任何块都“捕获”变量在街区内使用。所以这应该“正常”：

int fileNum = x;
CTCoreAttachment* fullAttachment = 
    [attachment fetchFullAttachmentWithProgress:^(size_t curr, size_t max) {
    // ..
    NSLog(@"::: this progress belongs to element %d", fileNum);
}];

该块在创建块时捕获变量的值。

（如果使用fileNum修饰符声明__block，情况会略有不同，但这可能与你的问题无关。）

Answer 2

我想出来的方法是将其分为两个步骤：

通过委托
将委托转换为基于块的方法。

由于这个问题很难通过英语解释，我认为最好通过示例代码解释：）

委派解决方案：

// AttachmentDownloader.m
+(void)runMultiple:(NSDictionary *)attachmentTree 
      withDelegate:(id<AttachmentDownloaderDelegate>)delegate  {
    ..

    CTCoreAttachment* fullAttachment = 
       [attachment fetchFullAttachmentWithProgress:^(size_t curr, size_t max) {
            NSLog(@"::: this is curr: %zu", curr);
            NSLog(@"::: this is max: %zu\n\n", max);
            NSLog(@"::: this is attachment uid %@", [message uid]);
            [delegate deliverProgressWithInfo:@{@"uid":[message uid],
                                                @"curr":[NSNumber numberWithInt:curr],
                                                @"max":[NSNumber numberWithInt:max]}];
     }];


// FileBucket.m
[AttachmentDownloader runMultiple:attachmentTree withProgress:^(size_t curr, size_t max) {
    NSLog(@"::: this is curr: %zu", curr);
    NSLog(@"::: this is max: %zu\n\n", max);
} withDelegate:self];

// delegate method
-(void)deliverProgressWithInfo:(NSDictionary *)dict {
    NSLog(@"filebucket: this is info being updated %@", dict);
}

阻止解决方案：

// AttachmentDownloader.m
+(void)runMultiple:(NSDictionary *)attachmentTree 
      withProgress:(void(^)(NSDictionary *))block {
    ..

    CTCoreAttachment* fullAttachment = 
        [attachment fetchFullAttachmentWithProgress:^(size_t curr, size_t max) {
        NSLog(@"::: this is curr: %zu", curr);
        NSLog(@"::: this is max: %zu\n\n", max);
        NSLog(@"::: this is attachment uid %@", [message uid]);
        block(@{@"uid":  [message uid],
                @"curr": [NSNumber numberWithInt:curr],
                @"max":  [NSNumber numberWithInt:max]});
    }];


// FileBucket.m
-(void)downloadSelectedAttachments {
    NSDictionary* attachmentTree = [self getAttachmentTree];
    [AttachmentDownloader runMultiple:attachmentTree withProgress:^(NSDictionary * dict) {
        NSLog(@"filebucket: this is info being updated %@", dict);
    }];
}

如何为块添加额外的参数

2 个答案: