如何使用 UISearchDisplayController/UISearchBar 过滤 NSFetchedResultsController (CoreData) [英] How to filter NSFetchedResultsController (CoreData) with UISearchDisplayController/UISearchBar
问题描述
我正在尝试在基于 CoreData 的 iPhone 应用程序中实现搜索代码.我不知道如何继续.该应用程序已经有一个带有谓词的 NSFetchedResultsController 来检索主 TableView 的数据.在更改太多代码之前，我想确保自己走在正确的道路上.我很困惑，因为很多示例都是基于数组而不是 CoreData.
I'm trying to implement search code in my CoreData-based iPhone app. I'm not sure how to proceed. The app already has an NSFetchedResultsController with a predicate to retrieve the data for the primary TableView. I want to make sure I'm on the right path before I change too much code. I'm confused because so many of the examples are array-based instead of CoreData.
这里有一些问题:
我是否需要第二个 NSFetchedResultsController 来仅检索匹配的项目，还是可以使用与主 TableView 相同的一个?
Do I need to have a second NSFetchedResultsController that retrieves only the matching items or can I use the same one as the primary TableView?
如果我使用同一个，是不是像清除FRC缓存然后在handleSearchForTerm:searchString方法中改变谓词一样简单?谓词是否必须包含初始谓词以及搜索词，或者它是否记得它首先使用谓词来检索数据?
If I use the same one, is it as simple as clearing the FRC cache and then changing the predicate in the handleSearchForTerm:searchString method? Does the predicate have to contain the initial predicate as well as the search terms or does it remember that it used a predicate to retrieve data in the first place?
我怎样才能回到原来的结果?我是否只是将搜索谓词设置为 nil?这不会杀死最初用于检索 FRC 结果的原始谓词吗?
How do I get back to the original results? Do I just set the search predicate to nil? Won't that kill the original predicate that was used to retrieve the FRC results in the first place?
如果有人有使用 FRC 搜索的代码示例，我将不胜感激！
If anyone has any examples of code using search with the FRC, I would greatly appreciate it!
推荐答案
我实际上只是在我的一个项目中实现了这个(你的问题和另一个错误的答案暗示了该怎么做).我尝试了 Sergio 的回答，但在设备上实际运行时遇到了异常问题.
I actually just implemented this on one of my projects (your question and the other wrong answer hinted at what to do). I tried Sergio's answer but had exception issues when actually running on a device.
是的，您创建了两个获取结果控制器:一个用于正常显示，另一个用于 UISearchBar 的表格视图.
Yes you create two fetch results controllers: one for the normal display and another one for the UISearchBar's table view.
如果您只使用一个 FRC (NSFetchedResultsController)，那么原始 UITableView(不是搜索时处于活动状态的搜索表视图)可能会在您搜索时调用回调，并尝试错误地使用 FRC 的过滤版本，而您将看到因部分或部分中的行数不正确而引发的异常.
If you only use one FRC (NSFetchedResultsController) then the original UITableView (not the search table view that is active while searching) will possibly have callbacks called while you are searching and try to incorrectly use the filtered version of your FRC and you will see exceptions thrown about incorrect number of sections or rows in sections.
这是我所做的:我有两个 FRC 作为属性 fetchedResultsController 和 searchFetchedResultsController.除非有搜索，否则不应使用 searchFetchedResultsController(当搜索被取消时，您可以在下面看到此对象已被释放).所有 UITableView 方法都必须弄清楚它将查询哪个表视图以及从哪个适用的 FRC 中提取信息.FRC 委托方法还必须确定要更新哪个 tableView.
Here is what I did: I have two FRCs available as properties fetchedResultsController and searchFetchedResultsController. The searchFetchedResultsController should not be used unless there is a search (when the search is canceled you can see below that this object is released). All UITableView methods must figure out what table view it will query and which applicable FRC to pull the information from. The FRC delegate methods must also figure out which tableView to update.
令人惊讶的是，其中有多少是样板代码.
It is surprising how much of this is boilerplate code.
头文件的相关位:
@interface BlahViewController : UITableViewController <UISearchBarDelegate, NSFetchedResultsControllerDelegate, UISearchDisplayDelegate>
{
// other class ivars
// required ivars for this example
NSFetchedResultsController *fetchedResultsController_;
NSFetchedResultsController *searchFetchedResultsController_;
NSManagedObjectContext *managedObjectContext_;
// The saved state of the search UI if a memory warning removed the view.
NSString *savedSearchTerm_;
NSInteger savedScopeButtonIndex_;
BOOL searchWasActive_;
}
@property (nonatomic, retain) NSManagedObjectContext *managedObjectContext;
@property (nonatomic, retain, readonly) NSFetchedResultsController *fetchedResultsController;
@property (nonatomic, copy) NSString *savedSearchTerm;
@property (nonatomic) NSInteger savedScopeButtonIndex;
@property (nonatomic) BOOL searchWasActive;
实现文件的相关部分:
@interface BlahViewController ()
@property (nonatomic, retain) NSFetchedResultsController *fetchedResultsController;
@property (nonatomic, retain) NSFetchedResultsController *searchFetchedResultsController;
@property (nonatomic, retain) UISearchDisplayController *mySearchDisplayController;
@end
在使用所有 UITableViewDelegate/DataSource 方法时，我创建了一个有用的方法来检索正确的 FRC:
I created a helpful method to retrieve the correct FRC when working with all of the UITableViewDelegate/DataSource methods:
- (NSFetchedResultsController *)fetchedResultsControllerForTableView:(UITableView *)tableView
{
return tableView == self.tableView ? self.fetchedResultsController : self.searchFetchedResultsController;
}
- (void)fetchedResultsController:(NSFetchedResultsController *)fetchedResultsController configureCell:(UITableViewCell *)theCell atIndexPath:(NSIndexPath *)theIndexPath
{
// your cell guts here
}
- (UITableViewCell *)tableView:(UITableView *)theTableView cellForRowAtIndexPath:(NSIndexPath *)theIndexPath
{
CallTableCell *cell = (CallTableCell *)[theTableView dequeueReusableCellWithIdentifier:@"CallTableCell"];
if (cell == nil)
{
cell = [[[CallTableCell alloc] initWithStyle:UITableViewCellStyleDefault reuseIdentifier:@"CallTableCell"] autorelease];
}
[self fetchedResultsController:[self fetchedResultsControllerForTableView:theTableView] configureCell:cell atIndexPath:theIndexPath];
return cell;
}
- (NSInteger)numberOfSectionsInTableView:(UITableView *)tableView
{
NSInteger count = [[[self fetchedResultsControllerForTableView:tableView] sections] count];
return count;
}
- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section
{
NSInteger numberOfRows = 0;
NSFetchedResultsController *fetchController = [self fetchedResultsControllerForTableView:tableView];
NSArray *sections = fetchController.sections;
if(sections.count > 0)
{
id <NSFetchedResultsSectionInfo> sectionInfo = [sections objectAtIndex:section];
numberOfRows = [sectionInfo numberOfObjects];
}
return numberOfRows;
}
搜索栏的委托方法:
#pragma mark -
#pragma mark Content Filtering
- (void)filterContentForSearchText:(NSString*)searchText scope:(NSInteger)scope
{
// update the filter, in this case just blow away the FRC and let lazy evaluation create another with the relevant search info
self.searchFetchedResultsController.delegate = nil;
self.searchFetchedResultsController = nil;
// if you care about the scope save off the index to be used by the serchFetchedResultsController
//self.savedScopeButtonIndex = scope;
}
#pragma mark -
#pragma mark Search Bar
- (void)searchDisplayController:(UISearchDisplayController *)controller willUnloadSearchResultsTableView:(UITableView *)tableView;
{
// search is done so get rid of the search FRC and reclaim memory
self.searchFetchedResultsController.delegate = nil;
self.searchFetchedResultsController = nil;
}
- (BOOL)searchDisplayController:(UISearchDisplayController *)controller shouldReloadTableForSearchString:(NSString *)searchString
{
[self filterContentForSearchText:searchString
scope:[self.searchDisplayController.searchBar selectedScopeButtonIndex]];
// Return YES to cause the search result table view to be reloaded.
return YES;
}
- (BOOL)searchDisplayController:(UISearchDisplayController *)controller shouldReloadTableForSearchScope:(NSInteger)searchOption
{
[self filterContentForSearchText:[self.searchDisplayController.searchBar text]
scope:[self.searchDisplayController.searchBar selectedScopeButtonIndex]];
// Return YES to cause the search result table view to be reloaded.
return YES;
}
确保在从 FRC 委托方法获取更新时使用正确的表视图:
make sure that you use the correct table view when getting updates from the FRC delegate methods:
- (void)controllerWillChangeContent:(NSFetchedResultsController *)controller
{
UITableView *tableView = controller == self.fetchedResultsController ? self.tableView : self.searchDisplayController.searchResultsTableView;
[tableView beginUpdates];
}
- (void)controller:(NSFetchedResultsController *)controller
didChangeSection:(id <NSFetchedResultsSectionInfo>)sectionInfo
atIndex:(NSUInteger)sectionIndex
forChangeType:(NSFetchedResultsChangeType)type
{
UITableView *tableView = controller == self.fetchedResultsController ? self.tableView : self.searchDisplayController.searchResultsTableView;
switch(type)
{
case NSFetchedResultsChangeInsert:
[tableView insertSections:[NSIndexSet indexSetWithIndex:sectionIndex] withRowAnimation:UITableViewRowAnimationFade];
break;
case NSFetchedResultsChangeDelete:
[tableView deleteSections:[NSIndexSet indexSetWithIndex:sectionIndex] withRowAnimation:UITableViewRowAnimationFade];
break;
}
}
- (void)controller:(NSFetchedResultsController *)controller
didChangeObject:(id)anObject
atIndexPath:(NSIndexPath *)theIndexPath
forChangeType:(NSFetchedResultsChangeType)type
newIndexPath:(NSIndexPath *)newIndexPath
{
UITableView *tableView = controller == self.fetchedResultsController ? self.tableView : self.searchDisplayController.searchResultsTableView;
switch(type)
{
case NSFetchedResultsChangeInsert:
[tableView insertRowsAtIndexPaths:[NSArray arrayWithObject:newIndexPath] withRowAnimation:UITableViewRowAnimationFade];
break;
case NSFetchedResultsChangeDelete:
[tableView deleteRowsAtIndexPaths:[NSArray arrayWithObject:theIndexPath] withRowAnimation:UITableViewRowAnimationFade];
break;
case NSFetchedResultsChangeUpdate:
[self fetchedResultsController:controller configureCell:[tableView cellForRowAtIndexPath:theIndexPath] atIndexPath:theIndexPath];
break;
case NSFetchedResultsChangeMove:
[tableView deleteRowsAtIndexPaths:[NSArray arrayWithObject:theIndexPath] withRowAnimation:UITableViewRowAnimationFade];
[tableView insertRowsAtIndexPaths:[NSArray arrayWithObject:newIndexPath]withRowAnimation:UITableViewRowAnimationFade];
break;
}
}
- (void)controllerDidChangeContent:(NSFetchedResultsController *)controller
{
UITableView *tableView = controller == self.fetchedResultsController ? self.tableView : self.searchDisplayController.searchResultsTableView;
[tableView endUpdates];
}
其他视图信息:
- (void)loadView
{
[super loadView];
UISearchBar *searchBar = [[[UISearchBar alloc] initWithFrame:CGRectMake(0, 0, self.tableView.frame.size.width, 44.0)] autorelease];
searchBar.autoresizingMask = (UIViewAutoresizingFlexibleWidth);
searchBar.autocorrectionType = UITextAutocorrectionTypeNo;
self.tableView.tableHeaderView = searchBar;
self.mySearchDisplayController = [[[UISearchDisplayController alloc] initWithSearchBar:searchBar contentsController:self] autorelease];
self.mySearchDisplayController.delegate = self;
self.mySearchDisplayController.searchResultsDataSource = self;
self.mySearchDisplayController.searchResultsDelegate = self;
}
- (void)didReceiveMemoryWarning
{
self.searchWasActive = [self.searchDisplayController isActive];
self.savedSearchTerm = [self.searchDisplayController.searchBar text];
self.savedScopeButtonIndex = [self.searchDisplayController.searchBar selectedScopeButtonIndex];
fetchedResultsController_.delegate = nil;
[fetchedResultsController_ release];
fetchedResultsController_ = nil;
searchFetchedResultsController_.delegate = nil;
[searchFetchedResultsController_ release];
searchFetchedResultsController_ = nil;
[super didReceiveMemoryWarning];
}
- (void)viewDidDisappear:(BOOL)animated
{
// save the state of the search UI so that it can be restored if the view is re-created
self.searchWasActive = [self.searchDisplayController isActive];
self.savedSearchTerm = [self.searchDisplayController.searchBar text];
self.savedScopeButtonIndex = [self.searchDisplayController.searchBar selectedScopeButtonIndex];
}
- (void)viewDidLoad
{
// restore search settings if they were saved in didReceiveMemoryWarning.
if (self.savedSearchTerm)
{
[self.searchDisplayController setActive:self.searchWasActive];
[self.searchDisplayController.searchBar setSelectedScopeButtonIndex:self.savedScopeButtonIndex];
[self.searchDisplayController.searchBar setText:savedSearchTerm];
self.savedSearchTerm = nil;
}
}
FRC 创建代码:
- (NSFetchedResultsController *)newFetchedResultsControllerWithSearch:(NSString *)searchString
{
NSArray *sortDescriptors = // your sort descriptors here
NSPredicate *filterPredicate = // your predicate here
/*
Set up the fetched results controller.
*/
// Create the fetch request for the entity.
NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];
// Edit the entity name as appropriate.
NSEntityDescription *callEntity = [MTCall entityInManagedObjectContext:self.managedObjectContext];
[fetchRequest setEntity:callEntity];
NSMutableArray *predicateArray = [NSMutableArray array];
if(searchString.length)
{
// your search predicate(s) are added to this array
[predicateArray addObject:[NSPredicate predicateWithFormat:@"name CONTAINS[cd] %@", searchString]];
// finally add the filter predicate for this view
if(filterPredicate)
{
filterPredicate = [NSCompoundPredicate andPredicateWithSubpredicates:[NSArray arrayWithObjects:filterPredicate, [NSCompoundPredicate orPredicateWithSubpredicates:predicateArray], nil]];
}
else
{
filterPredicate = [NSCompoundPredicate orPredicateWithSubpredicates:predicateArray];
}
}
[fetchRequest setPredicate:filterPredicate];
// Set the batch size to a suitable number.
[fetchRequest setFetchBatchSize:20];
[fetchRequest setSortDescriptors:sortDescriptors];
// Edit the section name key path and cache name if appropriate.
// nil for section name key path means "no sections".
NSFetchedResultsController *aFetchedResultsController = [[NSFetchedResultsController alloc] initWithFetchRequest:fetchRequest
managedObjectContext:self.managedObjectContext
sectionNameKeyPath:nil
cacheName:nil];
aFetchedResultsController.delegate = self;
[fetchRequest release];
NSError *error = nil;
if (![aFetchedResultsController performFetch:&error])
{
/*
Replace this implementation with code to handle the error appropriately.
abort() causes the application to generate a crash log and terminate. You should not use this function in a shipping application, although it may be useful during development. If it is not possible to recover from the error, display an alert panel that instructs the user to quit the application by pressing the Home button.
*/
NSLog(@"Unresolved error %@, %@", error, [error userInfo]);
abort();
}
return aFetchedResultsController;
}
- (NSFetchedResultsController *)fetchedResultsController
{
if (fetchedResultsController_ != nil)
{
return fetchedResultsController_;
}
fetchedResultsController_ = [self newFetchedResultsControllerWithSearch:nil];
return [[fetchedResultsController_ retain] autorelease];
}
- (NSFetchedResultsController *)searchFetchedResultsController
{
if (searchFetchedResultsController_ != nil)
{
return searchFetchedResultsController_;
}
searchFetchedResultsController_ = [self newFetchedResultsControllerWithSearch:self.searchDisplayController.searchBar.text];
return [[searchFetchedResultsController_ retain] autorelease];
}
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