one timer per detail view controller

问题:

I have a view controller with a table view property and a detail view controller connected to each cell in the tableview via the navigation bar. In the detail view controller is a countdown timer, with an interval specified when the user creates the task. I am trying to make it so each cell (or task) has a unique detail view controller. I am using core data. This is what I have now:

-(void)tableView:(UITableView *)tableView 
    didSelectRowAtIndexPath:(NSIndexPath *)indexPath{

    if (!self.detailViewController) {
        self.detailViewController = 
            [[DetailViewController alloc] initWithNibName:@"DetailViewController" 
                                                   bundle:nil];
    }
        Tasks *task = [[self fetchedResultsController] objectAtIndexPath:indexPath];
        self.detailViewController.testTask = task;
        [[self navigationController] pushViewController:self.detailViewController 
                                               animated:YES];

}

DetailViewController.m

@interface DetailViewController : UIViewController <UIAlertViewDelegate>
@property (weak, nonatomic) IBOutlet UILabel *timeLeft;
@property (weak, nonatomic) IBOutlet UILabel *timerLabel;
@property (nonatomic, strong) Tasks *testTask;
@end

I feel like this is the correct way to implement the detail view controller because it minimizes the amount of memory that needs to be created, however it doesn't really suit my needs. Currently when a user taps a cell, and taps back, and taps a different cell, only the first cell's properties are loaded. Also, if I were to delete a cell there would be no way to invalidate its timer (i think) with this method. Any suggestions?

---edit--- I guess the question I should be asking is: How should I make it so that each Detail View has a decrementing label (that gets its information from a timer)?

回答1:

The trouble with your code is that you're only creating one instance of DetailViewController, so each cell is pushing to the same one. You have to have some way in didSelectRowAtIndexPath to look at the index path and use that to determine which instance of DetailViewController to go to. One way to do that would be to create a mutable dictionary to hold references to the instances of DetailViewController. You could have the keys be NSNumbers that correspond to the indexPath.row, and the value would be an instance of DetailViewController. So, your code might look something like this:

-(void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath{

    DetailViewController *detailVC;
    if (![self.detailControllersDict.allKeys containsObject:@(indexPath.row)]) {
        detailVC = [[DetailViewController alloc]initWithNibName:@"DetailViewController" bundle:nil];
        [self.detailControllersDict setObject:detailVC forKey:@(indexPath.row)];
    }else{
        detailVC = self.detailControllersDict[@(indexPath.row)];
    }
    Tasks *task = [[self fetchedResultsController] objectAtIndexPath:indexPath];
    detailVC.testTask = task;
    [[self navigationController] pushViewController:detailVC animated:YES];

}

detailControllersDict is property pointing to an NSMutableDictionary.

回答2:

Your best solution is to follow the MVC properly in this scenario. In your case you are storing data for each detailViewController you are creating (such as task and the countdown timer/interval etc).. and in rdelmar's answer he is suggesting that you store all the view controllers in a mutableArray. I disagree with both approaches as yours will have memory problems when you dismiss the view controller (as u've seen for yourself) and in rdelmar's case, you are storing viewControllers (along with the data they reference) in a mutable array.. which is wasteful.

think about it this way.. you want to keep track of the data in one place (that's unaffected with which view is on display right now.. it could be detailVC 1 or 100 or the VC with the tableView or whichever) and at the same time you want to allocate one detailVC at a time that simply displays whatever the data source tells it to display. That way you can scale your app (imagine what would happen if you had hundreds of indexes in your table.. will you store hundreds of view controllers? very expensive and redundant).

so simply create a singelton.. the singelton will have a mutableArray that stores the timers pertaining to each tapped table index and so on.. the singelton will also launch the timers every time a cell has been tapped and keep a reference to it (ie store the NSIndexPath), so that when you jump back and forth between detailVCs and the table.. the timers are still in operation as required by you (b/c they are referenced by the singelton). the DetailVc will simply ask the singelton for what it should display and display it.

hope this helps. Please let me know if you need any further clarification.