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does anyone have an example of how to use NSComboBoxCell in an NSTableView column? A sample project would be preferred but sample code would be much appreciated too.

Thanks for your help.

It took me a little while and some experimentation to understand how it works. I could not find a working sample code at the time so I will post one below. You need understand the following in order to use NSComboBoxCell and NSTableView:

In other words, there are two controls (table view and combo box cell), each with a specific role. The table view displays the value and records the user selection (the last bit is somewhat counter-intuitive but it makes sense given how the table view works). The combo box cell displays the list of choices but it does not record the selection.

Here’s the promised code sample. You will need to create a project (sorry, can’t upload a project right now) and do some of the work in interface builder yourself:

/* for this example to work, the class must be set as:

@implementation ComboBoxDS

/* create, randomly initialize and release the data structure for the data source we’ll store the data in an array, each line is a dictionary with 3 entries:

-(id)init { self = [super init]; if(self) records = [[NSMutableArray arrayWithCapacity:25] retain]; return self; }

-(void)dealloc { [records release]; [super dealloc]; }

-(void)awakeFromNib { srand([[NSDate date] timeIntervalSince1970]); int l = rand()/(int)(((unsigned)RAND_MAX + 1) / 25); int i, j; for(i = 0;i < l;i++) { int r = rand()/(int)(((unsigned)RAND_MAX + 1) / 15) + 1; NSMutableArray *list = [NSMutableArray arrayWithCapacity:r]; for(j = 0;j < r;j++) [list addObject:[NSString stringWithFormat:@”data %d from line %d”,j,i]]; NSMutableDictionary *dic = [NSMutableDictionary dictionaryWithCapacity:3]; [dic setObject:[NSNumber numberWithInt:i] forKey:@”pos”]; [dic setObject:list forKey:@”combov”]; [dic setObject:[list objectAtIndex:0] forKey:@”combo”]; [records addObject:dic]; } }

/* data source for the NSComboBoxCell it reads the data from the representedObject the cell is responsible to display and manage the list of options (we set representedObject in tableView:willDisplayCell:forTableColumn:row:) this is optional, the alternative is to enter a list of values in interface builder */

-(id)comboBoxCell:(NSComboBoxCell*)cell objectValueForItemAtIndex:(int)index { NSArray *values = [cell representedObject]; if(values == nil) return @””; else return [values objectAtIndex:index]; }

-(int)numberOfItemsInComboBoxCell:(NSComboBoxCell*)cell { NSArray *values = [cell representedObject]; if(values == nil) return 0; else return [values count]; }

-(int)comboBoxCell:(NSComboBoxCell)cell indexOfItemWithStringValue:(NSString)st { NSArray *values = [cell representedObject]; if(values == nil) return NSNotFound; else return [values indexOfObject:st]; }

/* data source for the NSTableView the table is responsible to display and record the user selection (as opposed to the list of choices) this is required */

-(int)numberOfRowsInTableView:(NSTableView*)tableView { return [records count]; }

-(id)tableView:(NSTableView)tableView objectValueForTableColumn:(NSTableColumn)tableColumn row:(int)index { return records objectAtIndex:index] objectForKey:[tableColumn identifier; }

-(void)tableView:(NSTableView)tableView setObjectValue:(id)value forTableColumn:(NSTableColumn)tableColumn row:(int)index { if(nil == value) value = @””; if(tableColumn identifier] isEqual:@”combo”]) [[records objectAtIndex:index] setObject:value forKey:@”combo”]; }

/* delegate for the [[NSTableView since there’s only one combo box for all the lines, we need to populate it with the proper values for the line as set its selection, etc. this is optional, the alternative is to set a list of values in interface builder */

-(void)tableView:(NSTableView)tableView willDisplayCell:(id)cell forTableColumn:(NSTableColumn)tableColumn row:(int)index { if(tableColumn identifier] isEqual:@”combo”] && [cell isKindOfClass:[[[NSComboBoxCell class]]) { NSDictionary *dic = [records objectAtIndex:index]; [cell setRepresentedObject:[dic objectForKey:@”combov”]]; [cell reloadData]; [cell selectItemAtIndex:[self comboBoxCell:cell indexOfItemWithStringValue:[dic objectForKey:@”combo”]]]; [cell setObjectValue:[dic objectForKey:@”combo”]]; } }


Note that the combo box data source and the table delegate are not required if the list of values is identical for every line. The indirection is only required if you need to set the list of values programmatically. The table data source is always required.

For simplicity, I have only one class that implements the two data sources and the delegate. For more complex applications, you may want to spread the code over multiple classes.

Let me know if it helps.


Question: Do you have to call selectItemAtIndex from within willDisplayCell? I ask, because willDisplayCell gets called very often, once for every cell. I’d rather only call selectItemAtIndex when the cell is being clicked upon, if possible.

That’s my understanding.

Obviously it gets called once for every cell because you’re in charge of displaying the cell. You’d need a mechanism to recognize whether the call is to display a list or to display just the value in order to optimize. I don’t think Cocoa passes a flag or something you could use to test in which case you are but I’d love to be proven wrong. Please post if you find how to optimize.


If the comboboxcell in question will have only one instance, the fast way is to just record the current row and combo box in willDisplayCell. Then in the combobox delegate functions for numberOfItems and objectValueForItemAtIndex refer to the externally saved row when you decide what to return. That way you only reload the combobox choices when the box is about to display its contents.