Assigning the outlet for a UITableViewCell using UINib

Question

I looked at the TableViewUpdates/TVAnimationGestures from Apple's WWDC 2010 code and am having trouble duplicating a UITableViewCell subclass. This is what I've done:

I created a new UITableViewCell subclass with some simple properties:

@interface TargetDetailTableViewCell : UITableViewCell

@property (nonatomic, retain) IBOutlet UILabel *DescriptionLabel;
@property (nonatomic, retain) IBOutlet UILabel *ValueLabel;
@property (nonatomic, retain) IBOutlet UIImageView *DotImageView;

In the .m, I just release memory. In IB, I change my class to TargetDetailTableViewCell for the UITableViewCell I just dragged into IB. I connect the outlets from the TargetDetailTableViewCell to the appropriate labels and image view.

In the class I want to use this:

@class TargetDetailTableViewCell;

//some properties
@property (nonatomic, assign) IBOutlet TargetDetailTableViewCell *TargetCell;

In the .m:

- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath {    
    static NSString *TargetCellIdentifier = @"TargetDetailTableViewCellIdentifier";
    TargetDetailTableViewCell *cell = (TargetDetailTableViewCell *)[tableView dequeueReusableCellWithIdentifier:TargetCellIdentifier];

    if (cell == nil) {
        UINib *nib = [UINib nibWithNibName:@"TargetDetailTableViewCell" bundle:nil];
        [nib instantiateWithOwner:self options:nil];
        cell = self.TargetCell;
        self.TargetCell = nil;
    }
// set some labels
return cell;
}

When I run it, I get the error: Terminating app due to uncaught exception 'NSInternalInconsistencyException', reason: 'UITableView dataSource must return a cell from tableView:cellForRowAtIndexPath:'

The only think I can see that is different between Apple's example and mine is that when I ctlr-click on the subclass of UITableViewCell in their IB, they have a File's Owner property set. I have no idea how they connected that outlet as it is declared as a property in the class they use the cell, but there is no physical IB connection they make. Can someone explain that to me or what I am doing wrong?

Also, if anyone can explain this, that would be great:

        UINib *nib = [UINib nibWithNibName:@"TargetDetailTableViewCell" bundle:nil];
        [nib instantiateWithOwner:self options:nil];
        cell = self.TargetCell;
        self.TargetCell = nil;

It seems like you create the nib and the owner of the nib that gets instantiated from memory is the class you are in or self (my viewcontroller). Then the last two lines confuse me. It's like you tell your cell to point to the newly created object, then you set the newly created object to nil. Which in my head I think, the cell now points to nil as well. Thanks.

score 2 · Accepted Answer · answered Feb 02 '12 at 02:08

2

You need to have an owner in your custom table view cell nib and that owner needs to be your TableViewDataSource class (i.e. the table view controller which implements the cellForRowAtIndexPath method and has the TargetCell outlet to the table cell).

You also need to connect this TargetCell outlet from the file owner (the TableViewController) to your custom table view.

The reason for this is that when you load the nib, with your table view controller as the owner, it will then set the outlet that you have (the TargetCell property) to point to the table view cell defined in your nib.

You then copy this reference to the cell method variable, configure it and return it. You assign the property to nil after copying it because you only needed it as a bootstrap to get a reference to the object in the nib for use in the cellForRowAtIndexPath method.

answered Feb 02 '12 at 02:08

gamozzii

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Quick follow up question. so `cell = self.TargetCell` copies the object, doesn't just point to the reference which would make it nil by the next line? If I wanted to reuse this custom UITableViewCell, do I add another File's Owner object to my nib and just do the same thing? Thanks again. – Crystal Feb 02 '12 at 03:04
self.TargetCell is a reference to an instance of the UITableViewCell object. You copy this reference to the local 'cell' variable, thus the object is retained till the end of the method due to this 2nd reference. You then return the cell at the end of the method and the table view now has a reference to it and thus it is retained by the table view. When you are setting self.TargetCell = nil you are just clearing that particular reference to the object (i.e. you are NOT doing [self.TargetCell release]) which would also release the underlying object. It is just the reference you are clearing. – gamozzii Feb 02 '12 at 03:15
To reuse the same custom table cell and nib in a different table view controller, you might need to define a generic 'MyCellOwner' object that has an outlet to this table cell type and set this as the owner in the table cell nib instead of the table view controller. Then in the cellForRowAtIndex code alloc/init a 'MyCellOwner' and use this to load the nib (i.e. as the owner field in the call) which will create a reference to the table cell in that instance of the MyCellOwner object. Then copy across from that reference instead. (There might be a simpler way I could be overcomplicating it.) – gamozzii Feb 02 '12 at 03:22

Assigning the outlet for a UITableViewCell using UINib

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