UISlider inside a custom cell

marklo wrote:
The Tag increments every time a new cell is drawn and doesn't correspond to the cell row number

You're on the right track, but probably just need to use a tag number that conveys more information. Since I'm not clear on your overall objective, I'll just summarize a couple ideas in hopes one or both will lead you in a useful direction:

1) When the cells are created (inside the if-cell-is-nil branch of cellForRowAtIndexPath) give both the cell and its slider the same tag number. I.e. you can increment a static int nTag as you're doing now, but give the cell that same number. When the slider calls the action method, it will then be easy to find the cell and thus the index path. The data source can be an array of dictionaries and the keys can be NSIndexPath objects, or (my preference for storing in a plist) a compound array indexed by section no. and row no.;

2) Make helper methods that encode and decode an index path to/from an int. E.g. if there's only one section, encode by just adding the row number to a base number, kSliderTag. For multiple sections encode with something like tag=kSection*section rowkSliderTag. The decode is then something like section=tag/kSection and row=tag%kSection-kSliderTag (But please check my math, I'm typing a little too fast to know if it's right). Use [NSIndexPath indexPathForRow:row inSection:section] to get an index path object. The structure of the data source can be the same as in no. 1. kSection should be a large number, e.g. 0x10000 allows for 64k sections and 64k rows. The slider tag number will be the encoded index path, and should be assigned to the slider outside of the creation branch. When setting the slider tag, you can identify the slider if you know its position in the cell's subview array. E.g., if it was added as the base subview of cell.contentView in the creation branch:

UISlider slider = [[cell.contentView subviews] objectAtIndex:0];

also I don't seem to be able to set the slider in any of the cells except the first one.

Not sure what's going on with that, but I think we can assume you simply didn't have the correct address for the other sliders. Either of nos. 1 or 2 above should allow you to map a slider 1:1 to an index path or a dictionary key, so you shouldn't have any more problems finding the slider address you want. That said, I always recommend lots of logging when the methods you're calling don't seem to do anything. E.g.:

// method for setting each cell's slider in cellForRowAtIndexPath
- (void)setSliderForCell:(UITableViewCell*)cell { 
 // using above no. 1 so slider has same tag as parent cell
 UISlider *slider = (UISlider*)[cell.contentView viewWithTag:cell.tag];
 // sanity check: watch out for nil slider
 NSLog(@"section=%d row=%d slider=%@",
 indexPath.section, indexPath.row, slider);
 // get the slider value from the data source, an array of section
 // dictionaries, each of which includes an array of row dictionaries
 NSDictionary *sectDict = [self.tableData objectAtIndex:indexPath.section]; 
 NSArray *rows = [sectDict valueForKey:kRows];
 NSDictionary *rowDict = [rows objectAtIndex:indexPath.row];
 NSString *sliderValue = [rowDict valueForKey:kSliderValue];
 slider.value = [sliderValue floatValue];
 NSLog(@"slider.value=%2.0f", slider.value);
}

Finding and setting cell subviews comes up a lot, and the best solution tends to depend on the structure of your code. If the above isn't helpful, please describe a little more about what you're trying to do, and maybe someone around here will be able to hit the target a little better.

- Ray

- (IBAction)readSlider:(id)sender {
 CustomCell *cell; // <-- not set to the address of a cell
 UISlider *theSlider=sender;
 int progressAsInt=(int)(theSlider.value);
 int tagValue=theSlider.tag; // <-- this is correct 
 NSLog(@"slider value is =%i",progressAsInt);
 NSLog(@"slider tag is %i",tagValue); // <-- if this prints 0, the tag was never set
 NSLog(@"celltag is", cell.tag); // <-- cell is a random address => crash
}

marklo wrote:
When the above code runs I get the slider value ok, but get a 0 for the slider tag and a BAD_EXEC for the cell tag.

The BAD_EXEC is easy to explain, since the cell variable was never set to the address of a cell. The above code to read and print the slider tag is correct, so it appears that tag wasn't set correctly.

Since your cells are made from a custom class, the reason the slider tags aren't being set could either be in your nib or in the cellForRowAtIndex (cell factory) data source method. For example, if an IBOutlet for the slider isn't connected in the nib, then cell.slider.tag=tag++ will fail in the cell factory because the 'slider' ivar will be nil.

Here's some sample code which tags the slider of each custom cell object and uses the tag to update an array of slider values:

// CustomCell.h
#import <UIKit/UIKit.h>
@interface CustomCell : UITableViewCell {
 IBOutlet UILabel *nameLabel;
 IBOutlet UISlider *slider;
}
@property (nonatomic, retain) UILabel *nameLabel;
@property (nonatomic, retain) UISlider *slider;
@end
// The nib for each cell consists of the custom cell, a label subview, and a slider subview, each of
// which is connected to the outlets defined above. In addition, the Value Changed event of the
// slider is connected to the myAction connector of File's Owner. Since File's Owner is set to 'self'
// in the CellsViewController implementation, the Value Changed event of each slider instance will
// fire the myAction method of the controller object
// CustomCell.m
#import "CustomCell.h"
@implementation CustomCell
@synthesize nameLabel;
@synthesize slider;
- (void)dealloc {
 [nameLabel release];
 [slider release];
 [super dealloc];
}
@end
// CellsViewController.h
#import <UIKit/UIKit.h>
#define kTableViewRowCount 30
#define kTableViewRowHeight 66 
@interface CellsViewController : UIViewController
 <UITableViewDataSource, UITableViewDelegate> {
 UITableView *theTableView;
 NSMutableArray *sliderValues;
}
@property (nonatomic, retain)IBOutlet UITableView *theTableView;
@property (nonatomic, retain)NSMutableArray *sliderValues;
- (IBAction)myAction:(id)sender;
@end
// CellsViewController.m
#import "CellsViewController.h"
#import "CustomCell.h"
@implementation CellsViewController
@synthesize theTableView;
@synthesize sliderValues;
- (IBAction)myAction:(id)sender {
 // NSLog(@"myAction: sender=%@", sender);
 UISlider *theSlider = sender;
 CustomCell *cell;
 NSUInteger row = -1;
 for (cell in [theTableView visibleCells]) {
 // NSLog(@" cell=%@", cell);
 if (cell.slider.tag == theSlider.tag) {
 row = [[theTableView indexPathForCell:cell] row];
 break;
 }
 }
 if (row >=0 && row < kTableViewRowCount)
 [self.sliderValues replaceObjectAtIndex:row
 withObject:[NSNumber numberWithFloat:cell.slider.value]];
 NSLog(@"myAction row=%d slider.tag=%d slider.value=%2.2f",
 row, cell.slider.tag, cell.slider.value);
}
- (void)viewDidLoad {
 [super viewDidLoad];
 // initialize the slider data
 self.sliderValues = [NSMutableArray arrayWithCapacity:kTableViewRowCount];
 for (int iRow = 0; iRow < kTableViewRowCount; iRow++)
 [self.sliderValues addObject:[NSNumber numberWithFloat:0.0]];
}
- (void)dealloc {
 [theTableView release];
 [sliderValues release];
 [super dealloc];
}
#pragma mark -
#pragma mark Table Data Source Methods
- (NSInteger)numberOfSectionsInTableView:(UITableView *)tableView {
 return 1;
}
- (NSInteger)tableView:(UITableView*)tableView
 numberOfRowsInSection:(NSInteger)section {
 return [sliderValues count];
}
- (UITableViewCell)tableView:(UITableView)tableView
 cellForRowAtIndexPath:(NSIndexPath*)indexPath {
 
 static NSString *CustomCellIdentifier = @"CustomCellIdentifier";
 static NSUInteger nTag = 100;
 
 CustomCell *cell = (CustomCell*)[tableView
 dequeueReusableCellWithIdentifier:CustomCellIdentifier];
 if (cell == nil) {
 NSArray *nib = [[NSBundle mainBundle] loadNibNamed:@"CustomCell"
 owner:self options:nil];
 cell = [nib objectAtIndex:0];
 if (nTag <= 100)
 NSLog(@"nib=%@", nib);
 cell.slider.tag = nTag++;
 NSLog(@"new cell: identifier=%@ slider.tag=%d",
 [cell reuseIdentifier], cell.slider.tag);
 }
 int row = indexPath.row;
 cell.nameLabel.text = [NSString stringWithFormat:@"Row %d", row];
 cell.slider.value = [[self.sliderValues objectAtIndex:row] floatValue];
 NSLog(@"cellForRowAtIndexPath: row=%d slider.tag=%d slider.value=%2.2f",
 row, cell.slider.tag, cell.slider.value);
 return cell;
}
#pragma mark -
#pragma mark Table Delegate Methods
- (CGFloat)tableView:(UITableView*)tableView
 heightForRowAtIndexPath:(NSIndexPath*)indexPath {
 return kTableViewRowHeight;
}
- (void)tableView:(UITableView*)tableView didSelectRowAtIndexPath:(NSIndexPath*)indexPath {
 NSLog(@"didSelectRowAtIndexPath: row=%d", [indexPath row]);
 CustomCell *cell = (CustomCell*)[tableView cellForRowAtIndexPath:indexPath];
 UISlider *slider = cell.slider;
 NSLog(@"Selected row=%d slider.tag=%d slider.value=%2.2f",
 indexPath.row, slider.tag, slider.value);
}
@end

The example is based on the "Cells" project in Chapter 8 of +Beginning iPhone 3 Development: Exploring the iPhone SDK+ by Dave Mark and Jeff LaMarche. I can't recommend a better first book for iPhone developers. The projects in Chapter 8 will explain almost everything you need to successfully use table views in your apps.

Hope that helps!
- Ray