UITableView issue when using separate delegate/dataSource
- by Adam Alexander
General Description:
To start with what works, I have a UITableView which has been placed onto an Xcode-generated view using Interface Builder. The view's File Owner is set to an Xcode-generated subclass of UIViewController. To this subclass I have added working implementations of numberOfSectionsInTableView: tableView:numberOfRowsInSection: and tableView:cellForRowAtIndexPath: and the Table View's dataSource and delegate are connected to this class via the File Owner in Interface Builder.
The above configuration works with no problems. The issue occurs when I want to move this Table View's dataSource and delegate implementations out to a separate class, most likely because there are other controls on the View besides the Table View and I'd like to move the Table View-related code out to its own class. To accomplish this, I try the following:
Create a new subclass of UITableViewController in Xcode
Move the known-good implementations of numberOfSectionsInTableView: tableView:numberOfRowsInSection: and tableView:cellForRowAtIndexPath: to the new subclass
Drag a Table View Controller to the top level of the existing XIB in InterfaceBuilder, delete the View/TableView that are automatically created for this Table View Controller, then set the Table View Controller's class to match the new subclass
Remove the previously-working Table View's existing dataSource and delegate connections and connect them to the new Table View Controller
When complete, I do not have a working Table View. I end up with one of three outcomes which can seemingly happen at random:
When the Table View loads, I get a runtime error indicating I am sending tableView:cellForRowAtIndexPath: to an object which does not recognize it
When the Table View loads, the project breaks into the debugger without error
There is no error, but the Table View does not appear
With some debugging and having created a basic project just to reproduce this issue, I am usually seeing the 3rd option above (no error but no visible table view). I added some NSLog calls and found that although numberOfSectionsInTableView and numberOfRowsInSection are both getting called, cellForRowAtIndexPath is not. I am convinced I'm missing something really simple and was hoping the answer may be obvious to someone with more experience than I have. If this doesn't turn out to be an easy answer I would be happy to update with some code or a sample project. Thanks for your time!
Complete steps to reproduce:
Create a new iPhone OS, View-Based Application in Xcode and call it TableTest
Open TableTestViewController.xib in Interface Builder and drag a Table View onto the provided view surface.
Connect the Table View's dataSource and delegate outlets to File's Owner, which should already represent the TableTestViewController class. Save your changes
Back in Xcode, add the following code to TableTestViewController.m:
- (NSInteger)numberOfSectionsInTableView:(UITableView *)tableView {
NSLog(@"Returning num sections");
return 1;
}
- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section {
NSLog(@"Returning num rows");
return 1;
}
- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath {
NSLog(@"Trying to return cell");
static NSString *CellIdentifier = @"Cell";
UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:CellIdentifier];
if (cell == nil) {
cell = [[[UITableViewCell alloc] initWithFrame:CGRectZero reuseIdentifier:CellIdentifier] autorelease];
}
cell.text = @"Hello";
NSLog(@"Returning cell");
return cell;
}
Build and Go, and you should see the word Hello appear in the TableView
Now to attempt to move this TableView's logic out to a separate class, first create a new file in Xcode, choosing UITableViewController subclass and calling the class TableTestTableViewController
Remove the above code snippet from TableTestViewController.m and place it into TableTestTableViewController.m, replacing the default implementation of these three methods with ours.
Back in Interface Builder within the same TableTestViewController.xib file, drag a Table View Controller into the main IB window and delete the new Table View object that automatically came with it
Set the class for this new Table View Controller to TableTestTableViewController
Remove the dataSource and delegate bindings from the existing, previously-working Table View and reconnect the same two bindings to the new Table Test Table View Controller we created.
Save changes, Build and Go, and if you're getting the results I'm getting, note the Table View no longer functions properly
Solution:
With some more troubleshooting and some assistance from the iPhone Developer Forums at https://devforums.apple.com/message/5453, I've documented a solution! The main UIViewController subclass of the project needs an outlet pointing to the UITableViewController instance. To accomplish this, simply add the following to the primary view's header (TableTestViewController.h):
#import "TableTestTableViewController.h"
and
IBOutlet TableTestTableViewController *myTableViewController;
Then, in Interface Builder, connect the new outlet from File's Owner to Table Test Table View Controller in the main IB window. No changes are necessary in the UI part of the XIB. Simply having this outlet in place, even though no user code directly uses it, resolves the problem completely. Thanks to those who've helped and credit goes to BaldEagle on the iPhone Developer Forums for finding the solution.
