ios - 无法识别完成 block 返回类型

Question

我正在制作我的第一个完成 block ，由于某种原因它无法识别返回类型，所以我无法将值传回方法调用。

这是我的标题声明

+(void)downloadVenues:(void (^)(NSArray *myVenues, NSError *error))block;

这是我的实现

+(void)downloadVenues:(void (^)(NSArray *myVenues, NSError *error))block{


//download scenes
PFQuery *query = [PFQuery queryWithClassName:@"Venues"];
[query orderByDescending:@"createdAt"];
[query findObjectsInBackgroundWithBlock:^(NSArray *objects, NSError *error) {
    if (error) {
        NSLog(@"Error: %@ %@", error, [error userInfo]);
    }
    else {
        // We found messages!
        myVenues = objects;


        NSLog(@"Retrieved %lu messages", (unsigned long)[myVenues count]);




    }
}];

在另一个文件中调用它

//download venues
[Venue downloadVenues:^(NSArray *myVenues, NSError *error){
    if (error) {
        NSLog(@"Error: %@ %@", error, [error userInfo]);
    }
    else {

    NSLog(@"myObjects are: %@", myVenues);
    _venues = myVenues;

    [self loadAnnotations];

    }
}];

出于某种原因，它无法在实现中识别 myVenues。为什么以及如何解决这个问题？谢谢

Answer 1

您的实现永远不会调用完成 block 。这是你应该做的:

+(void)downloadVenues:(void (^)(NSArray *myVenues, NSError *error))block{


//download scenes
PFQuery *query = [PFQuery queryWithClassName:@"Venues"];
[query orderByDescending:@"createdAt"];
[query findObjectsInBackgroundWithBlock:^(NSArray *objects, NSError *error) {
    if (error) {
        NSLog(@"Error: %@ %@", error, [error userInfo]);
        block(nil, error);
    }
    else {
        // We found messages!
        block(objects, nil);


        NSLog(@"Retrieved %lu messages", (unsigned long)[myVenues count]);




    }
}];