提问人：bruno 提问时间：8/11/2023 更新时间：8/11/2023 访问量：22
在 Objective-C 中定义 completionHandler 的类型
Defining the type of a completionHandler in Objective-C
问：
在 for 周期中，我无法设法获得正确的类型。
试图用 typedef 替换它，但没有运气，只有更多的错误。responseCompletion
@interface ImageManager : NSObject
//typedef void(^responseBlock)(UIImage * _Nullable image);
@property (nonatomic, strong) NSDictionary<NSString *,NSMutableArray<void(^)(UIImage * _Nullable image)> *> *loadingResponses;
@end
-(void)fetchImage:(NSString *)urlString and:(void (^_Nonnull)(UIImage * _Nullable image))completionhHandler {
UIImage *image = [self.cache objectForKey:urlString];
if (image != nil) {
completionhHandler(image);
return;
}
if (self.loadingResponses[urlString] != nil) {
[self.loadingResponses[urlString] addObject:completionhHandler];
return;
} else {
[[self.loadingResponses objectForKey:urlString] setArray:[[NSMutableArray alloc] initWithObjects:completionhHandler, nil]];
}
NSURL *url = [[NSURL alloc] initWithString:urlString];
[[self.session dataTaskWithURL:url completionHandler:^(NSData * _Nullable data, NSURLResponse * _Nullable response, NSError * _Nullable error) {
if (error != nil) {
UIImage *image = [[UIImage alloc] initWithData:data];
[self.cache setObject:image forKey:urlString];
completionhHandler(image);
NSArray *array = [self.loadingResponses objectForKey:urlString];
for ((void(^)(UIImage * _Nullable image) *responseCompletion) in array) {
responseCompletion(image);
}
}
}] resume];
}
答：
1赞
HangarRash
8/11/2023
#1
你很好，虽然我会命名它，但不是.typedefResponseBlockresponseBlock
typedef void(^ResponseBlock)(UIImage * _Nullable image);
使用 时，请勿使用指针。ResponseBlock
我还建议更改为 an，以便您可以为其分配值。loadingResponsesNSMutableDictionary
下面是代码的更新版本：
界面：
typedef void(^ResponseBlock)(UIImage * _Nullable image);
@interface ImageManager : NSObject
@property (nonatomic, strong) NSMutableDictionary<NSString *, NSMutableArray<ResponseBlock> *> *loadingResponses;
@end
方法：
- (void)fetchImage:(NSString *)urlString and:(ResponseBlock)completionHandler {
UIImage *image = [self.cache objectForKey:urlString];
if (image != nil) {
completionHandler(image);
return;
}
if (self.loadingResponses[urlString] != nil) {
[self.loadingResponses[urlString] addObject:completionHandler];
return;
} else {
self.loadingResponses[urlString] = [NSMutableArray arrayWithObject:completionHandler];
}
NSURL *url = [[NSURL alloc] initWithString:urlString];
[[self.session dataTaskWithURL:url completionHandler:^(NSData * _Nullable data, NSURLResponse * _Nullable response, NSError * _Nullable error) {
if (error != nil) {
UIImage *image = [[UIImage alloc] initWithData:data];
[self.cache setObject:image forKey:urlString];
completionHandler(image);
NSArray *array = [self.loadingResponses objectForKey:urlString];
for (ResponseBlock responseCompletion in array) {
responseCompletion(image);
}
}
}] resume];
}
我假设您在某处初始化为：loadingResponses
self.loadingResponses = [NSMutableDictionary dictionary];
如果出现错误，还需要调用完成处理程序。也许你的意思是：
[[self.session dataTaskWithURL:url completionHandler:^(NSData * _Nullable data, NSURLResponse * _Nullable response, NSError * _Nullable error) {
UIImage *image = nil;
if (error != nil) {
image = [[UIImage alloc] initWithData:data];
[self.cache setObject:image forKey:urlString];
}
completionhHandler(image);
NSArray<ResponseBlock> *array = self.loadingResponses[urlString];
for (ResponseBlock responseCompletion in array) {
responseCompletion(image);
}
}] resume];
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