更新fetchedResultsController以获取UISearchBar设置的谓词

Question

重构为香草 UIViewController

而不是具有UITableView活性和非活性之间切换UISearchController,我重构到香草UIViewController与UISearchBar在顶部和一个UITableView直接在其下面.

我正在尝试做的是切换fetchedResultsController具有由searchBar中的文本设置的谓词和捕获所有内容的谓词.

我找到了这个答案,它描述了Objective-C中类似问题的解决方案,并作为我重构Swift项目的基础:

如何使用UISearchDisplayController/UISearchBar过滤NSFetchedResultsController(CoreData) /sf/answers/665902401/

我的问题:如何更新我的fetchedResultsController searchBar文本？

该tableView填入正确的,但我无法弄清楚如何更新fetchedResultsController我的searchPredicate这是我已经试过.

下面是我怎样,我宣布我NSPredicate和NSFetchedResultsController在类的顶部:

var searchPredicate = NSPredicate()

// Create fetchedResultsController to store search results
lazy var fetchedResultsController: NSFetchedResultsController = {
    let fetchRequest = NSFetchRequest(entityName: "Song")
    let sortDescriptor = NSSortDescriptor(key: "songDescription", ascending: true);
    // ** THESE TWO LINES CAUSE A CRASH, BUT NO COMPILER ERRORS **
    // let predicate = self.searchPredicate
    // fetchRequest.predicate = predicate
    fetchRequest.sortDescriptors = [sortDescriptor]
    fetchRequest.fetchBatchSize = 20

    let frc = NSFetchedResultsController (fetchRequest: fetchRequest, managedObjectContext: self.managedObjectContext, sectionNameKeyPath: "songDescription", cacheName: nil)

    frc.delegate = self

    return frc
}()

这是我的UISearchBarDelegate方法:

// MARK: - UISearchBarDelegate methods
// called when text changes (including clear)
internal func searchBar(searchBar: UISearchBar, textDidChange searchText: String) {
    print("searchText = \(searchBar.text)")
    searchPredicate = NSPredicate(format: "(songDescription contains [cd] %@) || (songStar contains[cd] %@)", searchBar.text!, searchBar.text!)
    // TODO: figure out how to update fetchedResultsController w/ predicate
}

// called when cancel button pressed
internal func searchBarCancelButtonClicked(searchBar: UISearchBar) {
    searchBar.resignFirstResponder()
    searchBar.text = ""
    // TODO: flip back to normal fetchResultsController
}

这是我的NSFetchedResultsControllerDelegate方法

internal func controllerWillChangeContent(controller: NSFetchedResultsController) {
    print("controllerWillChangeContent")
    tableView.beginUpdates()
}

internal func controllerDidChangeContent(controller: NSFetchedResultsController) {
    print("controllerDidChangeContent")
    tableView.reloadData()
    tableView.endUpdates()
}

internal func controller(controller: NSFetchedResultsController, didChangeObject anObject: AnyObject, atIndexPath indexPath: NSIndexPath?, forChangeType type: NSFetchedResultsChangeType, newIndexPath: NSIndexPath?) {
    switch type {
    case .Insert:
        tableView.insertRowsAtIndexPaths([newIndexPath!], withRowAnimation: .Automatic)
    case .Delete:
        tableView.deleteRowsAtIndexPaths([indexPath!], withRowAnimation: .Automatic)
    case .Update:
        tableView.reloadRowsAtIndexPaths([indexPath!], withRowAnimation: .Automatic)
    case .Move:
        tableView.deleteRowsAtIndexPaths([indexPath!], withRowAnimation: .Automatic)
        tableView.insertRowsAtIndexPaths([indexPath!], withRowAnimation: .Automatic)
    }
}

谢谢你的阅读.我欢迎你的建议.

Answer 1

这不是那么快 - 伪代码......它肯定不会用任何swift编译器编译.

您的FRC没有使用缓存,因此没有要删除的缓存,我们只需将谓词分配给现有的FRC获取请求即可.

您可能不希望对搜索栏中的每个字符更改执行全新的提取,或者您可能只想对第一个字符执行搜索,并将子集用于后续字符.

// called when text changes (including clear)
internal func searchBar(searchBar: UISearchBar, textDidChange searchText: String) {
    var predicate:NSPredicate = nil
    if searchBar.text.length != 0 {
        predicate = NSPredicate(format: "(songDescription contains [cd] %@) || (songStar contains[cd] %@)", searchBar.text!, searchBar.text!)
    }
    fetchedResultsController.fetchRequest.predicate = predicate
    fetchedResultsController.performFetch()
    tableView.reloadData()
}

// called when cancel button pressed
internal func searchBarCancelButtonClicked(searchBar: UISearchBar) {
    searchBar.resignFirstResponder()
    searchBar.text = ""
    fetchedResultsController.fetchRequest.predicate = nil
    fetchedResultsController.performFetch()
    tableView.reloadData()
}