How do I retrieve UITableView row number of a UISw

问题:

I have tried several approaches posted here, but I cannot get my table full of switches to return an index value for the cell of the changed switch. I am creating the view containing the table programmatically (no xib).

TableSandboxAppDelegate.m I instantiate the view controller in didFinishLaunchingWithOptions: with:

...
TableSandboxViewController *sandboxViewController = [[TableSandboxViewController alloc]
    init];
[[self window] setRootViewController:sandboxViewController];
...

TableViewController.h file reads:

@interface TableSandboxViewController : UITableViewController
{
   NSMutableArray *_questionOrder;
   NSMutableArray *switchStates;
}
@end

TableViewController.m cellForRowAtIndexPath: reads:

UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:@"MainCell"];

UISwitch *theSwitch = nil;

if (cell == nil) {
    cell = [[UITableViewCell alloc] initWithStyle:UITableViewCellStyleDefault
        reuseIdentifier:@"MainCell"];

    theSwitch = [[UISwitch alloc] initWithFrame:CGRectZero];
    theSwitch.tag = 100;
    [theSwitch addTarget:self action:@selector(switchChanged:)   
        forControlEvents:UIControlEventValueChanged];
    [cell.contentView addSubview:theSwitch];

} else {
    theSwitch = [cell.contentView viewWithTag:100];
}

if ([[switchStates objectAtIndex:indexPath.row] isEqualToString:@"ON"]) {
    theSwitch.on = YES;
} else {
    theSwitch.on = NO;
}

return cell;

TableViewController.m -(IBAction)switchChanged:(UISwitch *)sender reads:

UITableViewCell *theParentCell = [[sender superview] superview];
NSIndexPath *indexPathOfSwitch = [self.tableView indexPathForCell:theParentCell];

NSLog(@"Switch changed at index: %d", indexPathOfSwitch.row);

My log result is always "Switch changed at index: 0". I feel like the problem is in that CGPoint line where I've tried combinations of replacements for "sender" ([sender superview], [[sender superview]superview], etc). I don't feel like that line is pointing to the view that displays the table.

What am I doing wrong?

Note added 10/9, 9:15 EDT: my goal is to be able to handle about 100 yes/no questions in the table, so reuse is a key. I want to scroll and have the table the state of each switch, as well as be able to retrieve them when leaving the view.

回答1:

Tags is an okay solution, but a little clumsy because the cells - and therefore their subviews - are continually being reused, changing their rows - and therefore the tags they need.

Instead, I generally keep one of these around:

- (NSIndexPath *)indexPathWithSubview:(UIView *)subview {

    while (![subview isKindOfClass:[UITableViewCell self]] && subview) {
        subview = subview.superview;
    }
    return [self.tableView indexPathForCell:(UITableViewCell *)subview];
}

Then when I get an IBAction:

- (IBAction)someSubviewAction:(id)sender {

    NSIndexPath *indexPath = [self indexPathWithSubview:(UIView *)sender];
    // carry on from here
}

回答2:

You may set switch view tag to row index. Instead of theSwitch.tag = 100;

do

-(UITableViewCell*)tableView:table cellForRowAtIndexPath:indexPth
{
    UISwitch *theSwitch = nil;
    if (cell == nil) {
        ...
        // as per your example
        [cell.contentView addSubview:theSwitch];
    } else {
        theSwitch = subviewWithClass(cell.contentView, [UISwitch class]);
    }

    theSwitch.tag = indexPath.row;
    ...
}

Add this helper function to replace viewWithTag: call

UIView *subviewWithClass(UIView *contentview, Class klass)
{
    for (UIView *view in contentview.subviews)
        if ([view isKindOfClass:klass])
            return view;
    return nil;
}

Then retrieve tag, that is a row index now, in your switchChanged function

-(IBAction)switchChanged:(UISwitch *)sender {
    NSLog(@"Selected Switch - %d", sender.tag);
    ...
 }

回答3:

If you use something block-based (like https://github.com/brightsoftdev/iOS-Block-Based-Bindings/blob/master/UISwitch%2BBindings.m), you don't need to worry about getting the row, because you can reference the indexPath that is passed into tableView:cellForRowAtIndexPath: in your block.

回答4:

Similar to @danh, I've come up with this solution using an extention which I've used multiple times.

@interface UIView (Find)
- (id)findSuperviewOfClass:(Class)class;
- (NSIndexPath *)findIndexPath;
@end

@implementation UIView (Find)
- (id)findSuperviewOfClass:(Class)class
{
    return [self isKindOfClass:class] ? self : [self.superview findSuperviewOfClass:class];
}

- (NSIndexPath *)findIndexPath
{
    UITableView *tableView = [self findSuperviewOfClass:[UITableView class]];
    return [tableView indexPathForCell:[self findSuperviewOfClass:[UITableViewCell class]]];
}
@end

回答5:

for iOS6+ you could maintain a NSMutableArray queuedSwitches

in -tableView:cellForrowAtIndexPath: you would take a switch, if not empty and places it on the custom cell and assign it to a property. If empty you create a new one.

in -tableView:didEndDisplayingCell:forRowAtIndexPath: you would add it to quededSwitches and remove it from it cell.

This will just allocate enough switches for visible cells and reuse them.

the switches are all wired up to one action.

-(void)switchAction:(UISwitch *)switch 
{
    NSIndexPath *indexPath = [self.tableView indexPathForCell:[switch superView]];

    //…
}

回答6:

You could create a subclass of UISwitch and add an indexPath property, then just set the indexPath in cellForRowAtIndexPath:

-(UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
    SwitchCell *returnCell = [tableView dequeueReusableCellWithIdentifier:@"SwitchCell" forIndexPath:indexPath];
    returnCell.switch.indexPath = indexPath;

    return returnCell;
}