如果我的搜索谓词返回 nil，则尝试弹出 UIAlert
如果用户进行搜索并且谓词返回 nil，我会尝试弹出一条警告，提示“未找到记录”。
我尝试过这个，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];
}
I'm trying to pop an alert that says "No records found" if the user does a search and the predicate returns nil.
I tried this, but the alert never gets called. I just get an empty tableview.
- (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];
}
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评论（2）
谓词没有
-count。谓词 是一个计算结果为true或false 的表达式。就是这样。您可以向
NSFetchedResultsController询问其-fetchedObjects（返回一个数组），然后向该数组询问其-count，但您可以仅在调用-performFetch:后执行此操作。A predicate does not have a
-count. A predicate is an expression that evaluates totrueorfalse. That's it.You can ask the
NSFetchedResultsControllerfor its-fetchedObjects(which returns an array), and then ask that array for its-count, but you can only do this after you invoke-performFetch:.哈哈！知道了...
Ha ha! Got it...