Question

I have a question regarding iOS (or perhaps more accurately Objective-C) and properties. I have a UIView with a UISegmentedControl, by default it has 3 segments. I have a message which accepts a parameter and based on this parameter I may want to remove one of the segments. In UIView A I do this:

MyViewController *myview = [[[MyViewController alloc] initWithNibName:@"MyViewController" nib:nil] autorelease];
[[self navigationController] pushViewController:myview animate:YES];
[myview showItem:item];

In UIView B this happens in showItem:

-(void) showItem:(Item*)item{
    if (item.removeSegment){
        [segmentControl removeSegmentAtIndex:0 animate:NO];
    }
}

I have noticed that the segment only gets removed when I call showItem after I have pushed it on the navigation controller. When I swap those two line, so I first call showItem and then push the view, the UISegmentedControl still has three segments instead of two.

This just feels wrong, it seems like bad practice that my code will break if someone doesn’t call two messages in the right order. Is there a better way to do this? I’ve been looking at some sort of a property lifecyle that I can use, I am very familiar with this from ActionScript 3, but I have been unable to find anything on the subject.

(as an aside: in AS3 I would make a property, in the setter I don’t manipulate any screen controls but call InvalideProperties. My overriden methode CommitProperties will be called once the entire object and child controls have been created. In CommitProperties I check if my property value has changed and this is where I would remove the segment.)

Answer 1

A common way of doing something like this is to create an Item *item property in MyViewController and set that when myview is created. So, your code becomes:

MyViewController *myview = [[[MyViewController alloc] initWithNibName:@"MyViewController" nib:nil] autorelease];
myview.item = item;
[[self navigationController] pushViewController:myview animate:YES];

MyViewController would then use that property in its viewWillAppear: method to configure its own segment control.