How can a checkmark state be saved in core data?

问题

I have a list app where users hit the + button and enter in an item that they want to appear in the list and hit save. The table is saved with core data. The only problem is when the cell is taped I want a checkmark to be displayed. Ive enabled multiple selection with

UITableViewCell *thisCell = [tableView cellForRowAtIndexPath:indexPath]; 
if (thisCell.accessoryType == UITableViewCellAccessoryNone) {
    thisCell.accessoryType = UITableViewCellAccessoryCheckmark;  
} else {
    thisCell.accessoryType = UITableViewCellAccessoryNone;
} 
[tableView deselectRowAtIndexPath:indexPath animated:NO];

I would like the checkmarks to be persisted in the cell after the user exits. I have created an attribute in my entity called "checks" and gave it the type of boolean but I dont know how to make it where if you hit a row then a check appears and is persisted. Any help would be greatly appreciated. Thanks

回答1:

This is how I do it. One notable point: CoreData does not store booleans, so any property labeled "boolean" is actually of type NSNumber. You've got to remember to convert back and forth when dealing with CoreData and boolean values.

- (void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath {
    NSManagedObject *selectedObject = [self.fetchedResultsController objectAtIndexPath:indexPath];


    if ([[selectedObject valueForKey:@"isDone"] boolValue]) {
        [selectedObject setValue:[NSNumber numberWithBool:NO] forKey:@"isDone"];
    } else {
        [selectedObject setValue:[NSNumber numberWithBool:YES] forKey:@"isDone"];
    }
}

I have my UITableViewController set as the the delegate for the NSFetchedResultsController, so the changes I made to the managed objects in the query ^^^ will cause the following two methods to be run.

- (void)controllerDidChangeContent:(NSFetchedResultsController *)controller {
    [self.tableView reloadData];
}

- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath {
    static NSString *defaultCellIdentifier = @"Item";

    UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:defaultCellIdentifier];
    if (cell == nil) {
        cell = [[[UITableViewCell alloc] initWithStyle:UITableViewCellStyleDefault reuseIdentifier:defaultCellIdentifier] autorelease];
    }

    NSManagedObject *item = [[self fetchedResultsController] objectAtIndexPath:indexPath];
    cell.textLabel.text = [item valueForKey:@"name"];

    if ([[item valueForKey:@"checks"] boolValue]) {
        cell.accessoryType = UITableViewCellAccessoryCheckmark;
    } else {
        cell.accessoryType = UITableViewCellAccessoryNone;
    }

    cell.selectionStyle = UITableViewCellSelectionStyleNone;

    return cell;
}

Here's how everything ties together

User clicks on a row
tableView:didSelectRow... method changes the "isDone" property of the appropriate managed object.
the fetched results controller notices that a managed object has changed and calls the controllerDidChangeContent method on its delegate.
My controllerDidChangeContent method just reloads all the data in the table view
When the tableView is reloaded, my tableView:cellForRow... method checks the "isDone" property of the managed item to see if the cell should have a checkmark or not.

And just so you don't get confused, I initially used a generic NSMangagedObject to store row state, which is why the first method I posted says, [selectedObject valueForKey:@"isDone"]. Later I switched to a subclassed managed object named JKItem, which is why the second set of methods is able to use item.isDone without generating a compiler warning.

来源：https://stackoverflow.com/questions/2215465/how-can-a-checkmark-state-be-saved-in-core-data

标签

iphone

core-data

uitableview

persist