我正在尝试编写返回 NSArray 的方法。我的 NSMutableArray (friendUsers) 添加了正确的对象，但在 dispatch_async 之外，数组是空的。
我尝试在主队列中添加用户(如图所示)，但数组为空。有任何想法吗 ？感谢您的帮助。
- (NSArray *)checkUsersInGroup {
NSMutableArray *friendUsers = [[NSMutableArray alloc] init];
dispatch_queue_t checkUSers = dispatch_queue_create("CheckUsers", NULL);
dispatch_async(checkUSers, ^{
NSArray *totalUsers = [VVDataRead lecturaDades];
NSArray *usersToSearch = [_grup objectForKey:@"groupFriends"];
for (NSString *tempUserId in usersToSearch){
for (NSDictionary *user in totalUsers){
NSString *id = [user objectForKey:@"id"];
if ([tempUserId isEqualToString:id])
dispatch_async(dispatch_get_main_queue(), ^{
[friendUsers addObject:user];
});
}
}
});
NSLog(@"people:%@",friendUsers);
return [friendUsers copy];
}
最佳答案
你可以使用积木，在这种情况下它可以让你的生活更轻松。
- (void)checkUsersInGroupWithCompleteBlock:(void(^)(NSMutableArray * resultArray))completeBlock {
NSMutableArray *friendUsers = [[NSMutableArray alloc] init];
dispatch_queue_t checkUSers = dispatch_queue_create("CheckUsers", NULL);
dispatch_async(checkUSers, ^{
NSArray *totalUsers = [VVDataRead lecturaDades];
NSArray *usersToSearch = [_grup objectForKey:@"groupFriends"];
for (NSString *tempUserId in usersToSearch){
for (NSDictionary *user in totalUsers){
NSString *id = [user objectForKey:@"id"];
if ([tempUserId isEqualToString:id])
dispatch_async(dispatch_get_main_queue(), ^{
[friendUsers addObject:user];
});
}
}
// call the complete block with the result when you finished
if (completeBlock) completeBlock(friendUsers);
});
}
...下面是调用方法的方法:
- (void)anyMethod {
// ... do whetever you want here before
[self checkUsersInGroupWithCompleteBlock:^(NSMutableArray *resultArray) {
NSLog(@"%@", resultArray);
}];
// ... or after
}
已编辑:
注意:这是另一种可能的解决方案，但在您的情况下，它只是暂停主线程(这绝对不好)，因此您使用此解决方案除了痛苦之外不会有任何收获在主线程上，但如果您在两个后台线程上，此解决方案可以提供一个很好的线程间同步示例。
- (NSArray *)checkUsersInGroup {
NSMutableArray *friendUsers = [[NSMutableArray alloc] init];
// our semaphore is here
dispatch_semaphore_t _semaphore = dispatch_semaphore_create(0);
dispatch_queue_t checkUSers = dispatch_queue_create("CheckUsers", NULL);
dispatch_async(checkUSers, ^{
NSArray *totalUsers = [VVDataRead lecturaDades];
NSArray *usersToSearch = [_grup objectForKey:@"groupFriends"];
for (NSString *tempUserId in usersToSearch){
for (NSDictionary *user in totalUsers){
NSString *id = [user objectForKey:@"id"];
if ([tempUserId isEqualToString:id])
dispatch_async(dispatch_get_main_queue(), ^{
[friendUsers addObject:user];
});
}
}
// the process finished
dispatch_semaphore_signal(_semaphore);
});
// ... we are wainitng for the semaphore's signal
dispatch_semaphore_wait(_semaphore, DISPATCH_TIME_FOREVER);
dispatch_release(_semaphore);
NSLog(@"people:%@",friendUsers);
return [friendUsers copy];
}
关于ios - dispatch_queue 和返回数据，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/14276704/