Core data 如果搜索谓词返回nil，尝试弹出UIAlert

我试图弹出一个警告，如果用户进行搜索，谓词返回nil，则提示“未找到记录”

我试过了，但警报从未被调用。我只是得到一个空的桌面视图

- (void)searchBarSearchButtonClicked:(UISearchBar *)searchBar {

    if (self.sBar.text != nil){

        NSPredicate *template = [NSPredicate predicateWithFormat:@"name contains[cd] $SEARCH OR optionOne contains[cd] $SEARCH OR optionTwo contains[cd] $SEARCH"];
        NSDictionary *replace = [NSDictionary dictionaryWithObject:self.sBar.text forKey:@"SEARCH"];
        NSPredicate *predicate = [template predicateWithSubstitutionVariables:replace];

        [fetchedResultsController.fetchRequest setPredicate:predicate];

    }

    [[fetchedResultsController fetchedObjects] count];

    if (fetchedResultsController.fetchedObjects != nil) {

        //do nothing

    } else {

        //display alert
            UIAlertView *alert = [[UIAlertView alloc] initWithTitle:nil message:@"No records match." 
                                                           delegate:self cancelButtonTitle:@"OK" otherButtonTitles:nil];
            [alert show];
            [alert release];

    }

    NSError *error = nil;
    if (![[self fetchedResultsController] performFetch:&error]) {

        // Handle error
        NSLog(@"Unresolved error %@, %@", error, [error userInfo]);
        abort();  // Fail
    }           

    [self.myTable reloadData];

    [sBar resignFirstResponder];  

}

---

谓词没有

-count

。谓词。就这样

您可以向

NSFetchedResultsController

请求其

-fetchedObject

（返回一个数组），然后向该数组请求其

-count

，但您只能在调用

-performFetch:

哈哈！明白了

- (void)searchBarSearchButtonClicked:(UISearchBar *)searchBar {

    if (self.sBar.text != nil) {

        NSPredicate *template = [NSPredicate predicateWithFormat:@"name contains[cd] $SEARCH OR optionOne contains[cd] $SEARCH OR optionTwo contains[cd] $SEARCH"];
        NSDictionary *replace = [NSDictionary dictionaryWithObject:self.sBar.text forKey:@"SEARCH"];
        NSPredicate *predicate = [template predicateWithSubstitutionVariables:replace];

        [fetchedResultsController.fetchRequest setPredicate:predicate];

    }

    NSError *error = nil;
    if (![[self fetchedResultsController] performFetch:&error]) {

        // Handle error
        NSLog(@"Unresolved error %@, %@", error, [error userInfo]);
        exit(-1);  // Fail
    } 

    if ([[fetchedResultsController fetchedObjects] count] != 0)  {

        [self.myTable reloadData];
        [sBar resignFirstResponder];  

    }
    else {

        //display alert
            UIAlertView *alert = [[UIAlertView alloc] initWithTitle:nil message:@"No records match." 
                                                           delegate:self cancelButtonTitle:@"OK" otherButtonTitles:nil];
            [alert show];
            [alert release];

    }   
}

---

…添加了FetchedObject计数，但仍然没有任何结果。@RyeMAC3您是否先执行了

performFetch:

？