情景

顺序执行操作，但只有异步调用方法可供使用。

回调地狱书写不美观，容易出错切难以维护。

方案

以AFNetWorking为例，做一个简单的链式封装。

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typedef void (^NextAction)();

@interface RequestBase : NSObject
@property (nonatomic, copy) NextAction nextAction;
@end

@implementation RequestBase

- (void)startRequest
{
    AFHTTPRequestOperationManager *manager = [AFHTTPRequestOperationManager manager];
    [manager POST:_url parameters:_parameters success:^(AFHTTPRequestOperation *operation, id responseObject) {
        
        // TODO: onSuccess
        
        if(_nextAction != nil)
        {
            _nextAction();
        }
    } failure:^(AFHTTPRequestOperation *operation, NSError *error) {
        // TODO: onFailure
    }];
}

@end

调用范例

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__block NextAction action1, action2, action3;
action1 = ^(){
    RequestBase *request = [[RequestBase alloc] init];
    request.nextAction = action2;
    [request startRequest];
};
action2 = ^(){
    RequestBase *request = [[RequestBase alloc] init];
    request.nextAction = action3;
    [request startRequest];
};
action3 = ^(){
    RequestBase *request = [[RequestBase alloc] init];
    [request startRequest];
};

action1();