Ios 如何从NSURLSessionDataTask和调用块获取返回值?
我有一个方法,该方法返回nsdata值,但我不知道如何从NSURLSessionDataTask块获取返回值。以及如何调用getDownloadFileData方法。任务的代码是:- 来电者:Ios 如何从NSURLSessionDataTask和调用块获取返回值?,ios,objective-c,block,Ios,Objective C,Block,我有一个方法,该方法返回nsdata值,但我不知道如何从NSURLSessionDataTask块获取返回值。以及如何调用getDownloadFileData方法。任务的代码是:- 来电者: NSData *getFileDataResult = [self getDownloadFileData:pathString]; 方法: - (NSData*) getDownloadFileData : (NSString*) filePath { NSURLSessionDataTas
NSData *getFileDataResult = [self getDownloadFileData:pathString];
方法:
- (NSData*) getDownloadFileData : (NSString*) filePath {
NSURLSessionDataTask *downloadFile = [[NSURLSession sharedSession] dataTaskWithURL:[NSURL URLWithString:filePath] completionHandler:^(NSData *fileData, NSURLResponse *response, NSError *error){
// .....
// fileData should return out.
[downloadFile resume];
});
// I want to return the fileData after download completion.
// how to return?
}
有人能帮我吗
非常感谢。首先,你把简历方法放错地方了。应该是这样的:
- (NSData*) getDownloadFileData : (NSString*) filePath {
NSURLSessionDataTask *downloadFile = [[NSURLSession sharedSession] dataTaskWithURL:[NSURL URLWithString:filePath] completionHandler:^(NSData *fileData, NSURLResponse *response, NSError *error){
// .....
// fileData should return out.
});
[downloadFile resume];//NOTICE THE PLACEMENT HERE
// I want to return the fileData after download completion.
// how to return?
}
第二件事是,您可以简单地创建一个NSData
变量,并在completionblock
中为其赋值,而不是将数据
传递回去
或
只需在完成块中这样做
if(fileData){
return fileData;
}
请检查我的答案,我希望这有帮助
- (NSData *)getDownloadFileData:(NSString *)filePath {
__block NSData *responseData = nil;
dispatch_semaphore_t sema = dispatch_semaphore_create(0);
NSURLSessionDataTask *downloadFile = [[NSURLSession sharedSession] dataTaskWithURL:[NSURL URLWithString:filePath] completionHandler:^(NSData * _Nullable data, NSURLResponse * _Nullable response, NSError * _Nullable error) {
responseData = data;
dispatch_semaphore_signal(sema);
}];
[downloadFile resume];
dispatch_semaphore_wait(sema, DISPATCH_TIME_FOREVER);
return responseData;
}
- (void)whereToCall {
// Because to prevent the semaphore blocks main thread
dispatch_queue_t myQueue = dispatch_queue_create("com.abc", 0);
dispatch_async(myQueue, ^{
NSData *data = [self getDownloadFileData:@"urlString"];
});
}
- (void)betterGetDownloadFileData:(NSString *)filePath completion:(void (^)(NSData * __nullable data))completion {
NSURLSessionDataTask *downloadFile = [[NSURLSession sharedSession] dataTaskWithURL:[NSURL URLWithString:filePath] completionHandler:^(NSData * _Nullable data, NSURLResponse * _Nullable response, NSError * _Nullable error) {
if (completion) {
completion(data);
}
}];
[downloadFile resume];
}
我建议您应该按照我的建议设计代码,而不是使用块。您可以使用完成块,请查看