退出视图控制器后不要调用回调块

Question

当我构建我的应用程序时，我创建了一个名为 NetEngine 的 Class 来管理所有网络请求。但是我发现在退出使用 NetEngine 的视图控制器后，我仍然调用成功或失败块。

viewcontroller:

    [[NetEngine engine] GET:httpUrl success:^(id responseObject) {
         //some code here
         //It's still called after I quit viewctroller
    } failure:^(NSError *error) {
         //some code here
         //It's still called after I quit viewctroller
    }];

网络引擎：

typedef void(^SuccessBlock) (id responseObject);
typedef void(^FailureBlock) (NSError *error);

@interface NetEngine ()

@property (nonatomic, strong) AFHTTPSessionManager *httpManager;

@end

@implementation NetEngine

+ (NetEngine *)engine {
    static NetEngine *_sharedEngengine = nil;
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        _sharedEngengine = [[self alloc] init];
    });

    return _sharedEngengine;
}

- (id)init {
    if (self = [super init]) {
        _httpManager = [[AFHTTPSessionManager alloc] initWithBaseURL:[NSURL URLWithString:BZTVBaseServerPath]];
        [_httpManager.requestSerializer setValue:@"application/json" forHTTPHeaderField:@"accept"];
        _httpManager.requestSerializer.cachePolicy = NSURLRequestReloadIgnoringLocalCacheData;
        _httpManager.operationQueue.maxConcurrentOperationCount = 4;
        [_httpManager.requestSerializer setTimeoutInterval:10.0];
    }
    return self;
}

- (void)GET:(NSString *)URLString success:(SuccessBlock)successBlock failure:(FailureBlock)failureBlock {
    // some thing about cache

    [_httpManager GET:encodeUrl parameters:nil success:^(NSURLSessionDataTask * _Nonnull task, id  _Nonnull responseObject) {
        [[self defaultCache] setObject:responseObject forKey:cacheKey];
        if (successBlock) {
            successBlock(responseObject);
        }
    } failure:^(NSURLSessionDataTask * _Nullable task, NSError * _Nonnull error) {
        if (isCache) {            
            if (successBlock) {
                successBlock([[self defaultCache] objectForKey:cacheKey]);
            }
        }
        if (failureBlock) {
            failureBlock(error);
        }
    }];
}

Answer 1

如果您想在退出视图控制器时取消网络调用，请执行以下操作：

创建一个cancelBOOL变量

添加 viewWillDisappear 方法：

-(void) viewWillDisappear:(BOOL)animated {
    [super viewWillDisappear:animated];

    cancel = YES;
}

检查回调方法中的 cancel 是否为 YES :

   [[NetEngine engine] GET:httpUrl success:^(id responseObject) {
         //some code here
         //It's still called after I quit viewctroller
         if (!cancel) {
            //do what you have to do
         }
    } failure:^(NSError *error) {
         //some code here
         //It's still called after I quit viewctroller
         if (!cancel) {
            //do what you have to do
         }
    }];

Answer 2

来自文档："Blocks are a language-level feature added to C, Objective-C and C++, which allow you to create distinct segments of code that can be passed around to methods or functions as if they were values"。因此，块本身是一个对象，这意味着它的生命周期不依赖于创建它的对象。

如果您不想 NetEngine 使用您提供给它的代码，您需要一种在 "quit" 视图控制器时将信息传递给它的方法。

基本上：

[[NetEngine engine] GET:httpUrl success:^(id responseObject) {
    // if the view controller still wants me to do this {
       //some code here
    // }
} failure:^(NSError *error) {
    // if the view controller still wants me to do this {
       //some code here
    // }
}];

退出视图控制器后不要调用回调块

Don't call callback block after exiting view controller

networking

block

objective-c

ios

afnetworking