Re: Binding table columns that change at runtime

[BareFeet]

Thanks Brent for your input:

You will probably want to use KVO to observe changes to the array  
holding the list of column names to show.

I'm not sure how to do that. It's probably enough in my case to  
intercept setContent calls to the NSArrayController, changing the  
table columns during that process.

You can subclass NSArrayController.

I ended up doing that. I only had to intercept setContent and add an  
IBOutlet instance variable linked to the NSTableView, so I could set  
up the needed columns based on the newContent:

//  BFArrayController.h

@interface BFArrayController : NSArrayController
{
        IBOutlet NSTableView* myTableView;
}

@property (retain) NSTableView* myTableView;

- (void) setContent: (id) newContent;

@end


//  BFArrayController.m

#import "BFArrayController.h"
#import "BFTableViewCategory.h"

@implementation BFArrayController

@synthesize myTableView;

- (void) setContent: (id) newContent
{
        if ([newContent count] > 0)
        {
                NSArray* columnNameArray = [[newContent objectAtIndex:0] 
allKeys];
                [myTableView createColumns:(NSArray*)columnNameArray 
bindTo:self];
        }
        [super setContent: newContent];
}

@end


And I implemented a new createColumns:bindTo: method as a category for  
NSTableViews:

//  BFTableViewCategory.h

#import <Cocoa/Cocoa.h>

@interface NSTableView (ExtrasByTom)

- (void) createColumns:(NSArray*)columnNameArray bindTo: 
(NSArrayController*) tableArrayController;

@end


//  BFTableViewCategory.m

#import "BFTableViewCategory.h"

@implementation NSTableView (ExtrasByTom)

- (void) createColumns:(NSArray*)columnNameArray bindTo: 
(NSArrayController*) tableArrayController
{
        // Remove old columns:
	NSMutableArray* oldTableColumns = [NSArray arrayWithArray: [self  
tableColumns]];
        for(NSTableColumn* oldTableColumn in oldTableColumns)
                [self removeTableColumn:oldTableColumn];

        // Add new columns:
        for (NSString* columnName in columnNameArray)
        {
		NSTableColumn* newTableColumn = [[[NSTableColumn alloc]  
initWithIdentifier:columnName] autorelease];
                [[newTableColumn headerCell] setStringValue:columnName];
                [self addTableColumn:newTableColumn];
		[newTableColumn bind:@"value" toObject:tableArrayController  
withKeyPath:[NSString stringWithFormat: @"arrangedObjects.%@",  
columnName] options:nil];
        }
}
@end

You could go all-out and add support for a new binding or the custom  
controller could just add itself as an observer of the arranged  
objects property of the relevant array controller (the one managing  
the list of column names). Then implement the KVO observation method  
(-observeValueForKeyPath:ofObject:change:context:), where you will  
do the right thing depending on whether a column was added or removed.


Hmmm, that's interesting. It would be useful to be able to bind the  
array of NSTableColumns used by an NSTableView to some array in the  
model data. Probably a bit beyond me at the moment.

Thanks,
Tom
BareFeet

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