如何在Objective C块中更改BOOL局部变量的值？我用过＆＃34; __ block＆＃34;符号，但它不起作用

Question

如何在Objective C块中更改BOOL局部变量的值？我用过＆＃34; __ block＆＃34;符号，但它不起作用

 - (BOOL)loginUserWithEmail:(NSString *)email andPassword:(NSString *)password {


    __block BOOL result = NO;

    SCPredicate *emailPredicate = [SCPredicate whereKey:@"email" isEqualToString:email];
    SCPredicate *passwordPredicate = [SCPredicate whereKey:@"password" isEqualToString:password];
    SCCompoundPredicate *compoundPredicate = [SCCompoundPredicate compoundPredicateWithPredicates:@[emailPredicate, passwordPredicate]];

    [[SHPerson please] giveMeDataObjectsWithPredicate:compoundPredicate parameters:nil completion:^(NSArray *persons, NSError *error) {

        if (persons != nil) {
            result = YES;
        }
    }];
    return result;
}

Answer 1

您的问题是该方法在您的异步giveMeDataObjectsWithPredicate方法有时间完成之前返回NO的结果。试试这个：

- (void)loginUserWithEmail:(NSString *)email andPassword:(NSString *)password withCompletion:(void(^)(BOOL result))completion {    
    SCPredicate *emailPredicate = [SCPredicate whereKey:@"email" isEqualToString:email];
    SCPredicate *passwordPredicate = [SCPredicate whereKey:@"password" isEqualToString:password];
    SCCompoundPredicate *compoundPredicate = [SCCompoundPredicate compoundPredicateWithPredicates:@[emailPredicate, passwordPredicate]];

    [[SHPerson please] giveMeDataObjectsWithPredicate:compoundPredicate parameters:nil completion:^(NSArray *persons, NSError *error) {
        if (completion) {
            if (persons != nil) {
                completion(YES);
            } else {
                completion(NO);
            }
        }
    }];
}

然后您可以将其用于：

[self loginUserWithEmail:email andPassword:password andCompletion:^(BOOL result) {
    // You can now use result here...
}];