Custom classes & casting inside conditional statements in Objective-C - objective-c

Question

I ran into this issue twice now, and am curious to know if there is a correct way of getting the following example to work. I know there are other ways /workarounds for doing the same thing but I am wondering why the compiler doesn't recognise my casting and if I am missing something obvious here.
Suppose I have two table views with different style header views that I need to provide. SectionHeaderViewA is a UIView subclass with a custom property textLabelA, SectionHeaderViewB is also a UIView subclass with a custom property textLabelB.
In the method:
- (UIView*)tableView:(UITableView *)tableView viewForHeaderInSection:(NSInteger)section
{
id headerView;
if (tableView.tag == TAG_A)
{
headerView = (SectionHeaderViewA*)[[SectionHeaderViewA alloc] init];
headerView.textLabelA = ... // I am unable to access the custom property here even after casting (SectionHeaderViewA*) above.
} else if (tableView.tag == TAG_B) {
headerView = (SectionHeaderViewB*)[[SectionHeaderViewB alloc] init];
headerView.textLabelB = ... // Same as above, even after casting the custom property is not recognised
}
return headerView;
}
Even after casting (SectionHeaderViewA*) and (SectionHeaderViewB*) to my headerView ivar, I am still unable to access their respective custom properties. It's like the compiler is still seeing headerView as an unknown / id type but why?

Answer 1

The cast is not in the correct place. Cast headerView before sending the appropriate textLabel A or B message.
id headerView;
if (tableView.tag == TAG_A)
{
headerView = [[SectionHeaderViewA alloc] init];
((SectionHeaderViewA*)headerView).textLabelA = ... // I am unable to access the custom property here even after casting (SectionHeaderViewA*) above.
} else if (tableView.tag == TAG_B) {
headerView = [[SectionHeaderViewB alloc] init];
((SectionHeaderViewB*)headerView).textLabelB = ... // Same as above, even after casting the custom property is not recognized
}
return headerView;
Once you move the cast, you will be able to send the correct message.

Answer 2

the type of headerView is "id", which means it doesn't know about your extra properties etc (the cast doesn't change the type of "headerView").
you could do something like:
if (tableView.tag == TAG_A)
{
SectionHeaderViewA* headerView = [[SectionHeaderViewA alloc] init];
headerView.textLabelA = ...
return headerView;
} else if (tableView.tag == TAG_B) {
SectionHeaderViewB* headerView = [[SectionHeaderViewB alloc] init];
headerView.textLabelB = ...
return headerView;
}
return nil;

Answer 3

Your cast is not doing anything as you are casting into id.
Whilst #sean's answer works and it does the single exit it is pretty ugly having all the curly brackets I would probably go for
id headerView = nil; // Initialize to nil... you may not go into either side of your if
if (TAG_A == tableView.tag) {
SectionHeaderViewA *sectionHeaderViewA = [[SectionHeaderViewA alloc] init];
sectionHeaderViewA.textLabelA = ...
headerView = sectionHeaderViewA;
} else if (TAG_B == tableView.tag) {
SectionHeaderViewB *sectionHeaderViewB = [[SectionHeaderViewB alloc] init];
sectionHeaderViewB.textLabelB = ...
headerView = sectionHeaderViewB;
}
return headerView;
Or another possibility (potentially over engineering the problem) is make both sectionHeaderViewA and sectionHeaderViewB conform to a protocol and then you can make it a little tidier still.
SectionHeaderInterface.h
#protocol SectionHeaderInterface <NSObject>
#property (strong, nonatomic) UILabel *textLabel;
#end
SectionHeaderView(A|B).h
#import "SectionHeaderInterface.h"
#interface SectionHeaderView(A|B) : UIView <SectionHeaderInterface>
// ... rest of interface
#end
SectionHeaderView(A|B).m
#implementation SectionHeaderView(A|B)
#synthesize textLabel = _textLabel;
// ... rest of your class
#end
YourController.m
id<SectionHeaderInterface> headerView = nil; // Initialize to nil... you may not go into either side of your if
if (TAG_A == tableView.tag) {
headerView = [[SectionHeaderViewA alloc] init];
} else if (TAG_B == tableView.tag) {
headerView = [[SectionHeaderViewB alloc] init];
}
headerView.textLabel.text = ...
return headerView;