Question

I have a simple master-detail application and I’m using the detail view to configure data to insert into the master list.

I have a custom class called “Calculation,” which is the object I need to insert into each row.

I can pass the object from the detail view to the master view just fine, it just won’t insert a new row.

In the detail view I Initiate my object, populate it with data and send it to the “insertNewObject” method in the MasterViewController using a custom segue:

- (IBAction)prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender {

    NSNumberFormatter * f = [[NSNumberFormatter alloc] init];
    [f setNumberStyle:NSNumberFormatterDecimalStyle];
    NSString *s = @"1";
    NSNumber *n = [f numberFromString:s];

    Calculation *calc = [[Calculation alloc] initWithValue:@"$1661.70" descr:@"1 Ounce 24k Gold" textInput:@"1" percentDisplay:@"0%" purityIndex:n metalIndex:n weightUnitIndex:n sliderValue:n];

    [segue.destinationViewController insertNewObject:calc];
}

And in the MasterViewController, here is my insert code:

    -(void)insertNewObject:(NSObject *)newCalculation {

        if (!_objects) {
            _objects = [[NSMutableArray alloc] init];
        }
        [_objects insertObject:newCalculation atIndex:0];
        NSIndexPath *indexPath = [NSIndexPath indexPathForRow:0 inSection:0];

        [self.tableView insertRowsAtIndexPaths:[NSArray arrayWithObject:indexPath] withRowAnimation:UITableViewRowAnimationAutomatic];

    }

- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
    UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:@"Cell"];

    NSObject *object = [_objects objectAtIndex:indexPath.row];
    cell.textLabel.text = [object valueForKey:@"value"];
    cell.detailTextLabel.text = [object valueForKey:@"descr"];
    cell.textLabel.shadowColor = [UIColor blackColor];
    cell.textLabel.shadowOffset = CGSizeMake(0, -1);
    return cell;
}

I can print the object all day with NSLog in the MVC, but not matter how many times I add an object from the detail view controller, the array count is always 1, and no cell ever gets added to the tableview.

The same exact code works fine if I instantiate the object in MVC, and insert it.

Answer 1

A segue is really the wrong mechanism for sending data from detail to master. (It works great the other direction!) You’d be better off defining a delegate protocol that has -(void)insertNewObject:(NSObject *)newCalculation; as a required method, making your master implement that protocol, and passing it as a delegate to your detail controller.

Then the detail controller just calls [delegate insertNewObject:calc];.