TweetFollow Us on Twitter

Takes All Sorts

Volume Number: 18 (2002)
Issue Number: 8
Column Tag: Mac OS X

Takes All Sorts

Make Your TableViews Autosort!

by Andrew C. Stone

One of the coolest pieces of object technology in the Cocoa bag of tricks is the NSTableView, and its daughter, NSOutlineView. The tableView lets you display a list of items with various properties. As in a spreadsheet, it displays rows of information - anything from simple text to graphics or even quicktime movies! Once you learn the fundamentals of the tableView and the outlineView, they'll quickly become some of your favorite user interface objects.

This article will take the NSTableView further, and show you how to add "auto sort" to your tableView, and the objects it represents. It assumes you have read the documentation for NSTableView and its companion class NSTableColumn and perhaps already have an app with an NSTableView of your own. You can try out this sort idea in Apple's Mail. A Mail Box shows a tableView of the list of messages, sender, subject, date, size, etc:


Figure 1. You can play with quick sort feature in Apple's Mail application.

When you click on the title cell of a column, an arrow appears to show direction of the sort, the cell is highlighted, and the messages are sorted on that key. If you click the title cell of that same column again, it toggles the sort to reverse its direction: if it was an ascending sort, now it's a descending sort. Sorting mail by subject is particularly interesting for deleting spam en masse!

When Time Equals Money...

When preparing TimeEqualsMoney 2.0 <http://www.stone.com/TimeEqualsMoney/> this spring, I decided users would love to be able to sort their time and expense entries on any key, in either direction with a simple click. So I reread the documentation Apple provides on the NSTableView class. I highly recommend actually reading the .h files! It's amazing how much stuff is already anticipated for you! There is a delegate method, - (void) tableView:(NSTableView*)tv didClickTableColumn:(NSTableColumn *)tableColumn. So, it seemed, I simply had to implement this method in my NSWindowController subclass, which is architecturally a sound choice for the NSTableView delegate. However, the method was simply not being called when I clicked on the column header cell. It turns out, and I noted this heavily in my code, that if neither column reodering nor column selection is selected in Interface Builder's NSTableView inspector, then the method is not called. Turning on column reordering was a simple fix and a desired feature! You can, of course, also call one of these methods programmatically with a parameter of YES:

- (void)setAllowsColumnReordering:(BOOL)flag;
- (void)setAllowsColumnSelection:(BOOL)flag;

Following on the Model-View-Controller pattern that I have discussed in previous articles on Cocoa architecture, I decided to store the sort column, and its direction in my NSDocument subclass, as well as make it responsible for the sorting of its items. This way, you can undo the sort, automatically mark the document as unsaved as well as save the sort between sessions. The user clicks the tableView column header, the window controller then sets the document's sort key, or direction if the key was already set to that column. Then the document tells itself to sort, which tells its NSMutableArray of entries to sort its contents. Finally, the document tells its window controllers to reload the tableView, which updates the interface to display the new sort order:


Figure 2. This tableView lets you click a column header to sort on that key - up or down.

Model Behavior

The implementation of the actual sort is trivial: just ask the list to sort itself based on asking its elements to sort using a selector: [list sortUsingSelector:@selector(compare:)];

During the list's sorting procedure, it repeatedly calls, in this case, compare: on one list item against another.

I like to just reuse the Kit's compare: which is implemented in NSString, NSDate, NSCell, NSValue, etc:

- (NSComparisonResult)compare:(id)other;

The NSComparisonResult has these three values: NSOrderedAscending = -1, NSOrderedSame = 0, NSOrderedDescending = 1. Since so many objects reply to compare:, you might implement it something like this in your data object, given that the sort key is the same string as the column identifiers, and you have various numbers, dates, strings and even booleans:

// the Data MODEL - the document has a list of these entities:
@interface PieceWork : NSObject <NSCopying>
{
    NSCalendarDate *startTime;
    NSString *description;
    NSTimeInterval timeOnJob;
    float _rate;
    BOOL paid;
    id owner;
...
}
- (NSComparisonResult)compare:(id)other;
- (void)setOwner:(id)ownsMe;
- (NSCalendarDate *)startTime;
- (NSTimeInterval)timeOnJob;
- (NSString *)workDescription;
- (float)hoursOnJob;
- (float)rate;
- (BOOL)paid;
...
@end
@implementation PieceWork
...
- (NSComparisonResult)compare:(id)other {
    BOOL isDescending = [owner sortIsDescending];
    NSString *key = [owner sortColumn];
   // now determine which one is first based on sort direction:
    PieceWork *first = isDescending ? other : self;
    if (first == other) other = self;
    
    if ([key isEqualToString:@"TimeOnJob"]) {
        return [[NSNumber numberWithFloat:[other timeOnJob]] compare: 
        [NSNumber numberWithFloat:[first timeOnJob]]];
    } else if ([key isEqualToString:@"Date"]) {
        return [[other startTime] compare: [first startTime]];
    } else if ([key isEqualToString:@"Description"]) {
// Very handy macro:
#define IS_NULL(s) (!s || [s isEqualToString:@""])
            if (IS_NULL([other workDescription])) return NSOrderedDescending;
            if (IS_NULL([first workDescription])) return NSOrderedAscending;
// people prefer upper and lower case mixed, unlike UNIX:
        return [[other workDescription] caseInsensitiveCompare:[first workDescription]];
    } else if ([key isEqualToString:@"Paid"]) {
        return [[NSNumber numberWithBool:[other paid]] compare:[NSNumber 
        numberWithBool:[first paid]]];
    }
    return 0;
}
@end

Here are the relevant instant variables and methods in the NSDocument subclass:

@interface MyDocument : NSDocument {
    NSMutableArray *_workList;
    NSString *_sortColumn;
    BOOL _sortIsDescending;
.   ...
}
- (void)sort;
- (NSArray *)workList;
- (void)setSortColumn:(NSString *)identifier;
- (NSString *)sortColumn;
- (void)setSortIsDescending:(BOOL)whichWay;
- (BOOL)sortIsDescending;
...
@end
@implementation MyDocument
...
- (void)sort:(NSMutableArray *)list {
    [list makeObjectsPerformSelector:@selector(setOwner:) withObject:self];
    [list sortUsingSelector:@selector(compare:)];  // asks us for how!!
}
- (void) sort {
    if (NOT_NULL(_sortColumn)) {
        [self sort:_workList];
        [[self windowControllers] makeObjectsPerformSelector:@selector(updateTotalsAndReload)];
    }
}
- (void)setSortColumn:(NSString *)identifier {
    if (![identifier isEqualToString:_sortColumn]) {
        [[[self undoManager] prepareWithInvocationTarget:self] setSortColumn:_sortColumn];
    [_sortColumn release];
    _sortColumn = [identifier copyWithZone:[self zone]];
        [[self undoManager] setActionName:NSLocalizedStringFromTable(@"Sort",@"TimeCard",@"title of 
        undo the sort action")];
    }
}
- (NSString *)sortColumn {
    return _sortColumn;
}
- (void)setSortIsDescending:(BOOL)whichWay {
    if (whichWay != _sortIsDescending) {
        [[[self undoManager] prepareWithInvocationTarget:self] setSortIsDescending:_sortIsDescending];
    _sortIsDescending = whichWay;
        [[self undoManager] setActionName:NSLocalizedStringFromTable(@"Sort 
        Direction",@"TimeCard",@"title of undo the sort up or down action")];
    }
}
- (BOOL)sortIsDescending {
    return _sortIsDescending;
}
- (NSArray *)workList { return _workList; }
- (void)setWorkList:(NSMutableArray *)list {
    [[[self undoManager] prepareWithInvocationTarget:self] setWorkList:_workList];
    [_workList release];
    if (NOT_NULL(_sortColumn)) [self sort:list];
    _workList = [list mutableCopyWithZone:[self zone]];
    [_workList makeObjectsPerformSelector:@selector(setOwner:) withObject:self];
    [[self windowControllers] makeObjectsPerformSelector:@selector(updateTotalsAndReload)];
    [[self undoManager] setActionName:NSLocalizedStringFromTable(@"Work Change", @"TimeCard", 
    @"Action name for changing worklist")];
}
// And don't forget to actually archive and read the sort info
// I highly recommended using human readable XML dictionaries:
- (NSMutableDictionary *)workDocumentDictionary {
    NSMutableDictionary *doc = [NSMutableDictionary dictionary];
        unsigned i, c = [_workList count];
        if (NOT_NULL(_sortColumn)) [doc setObject:_sortColumn forKey:SortNameKey];
        if (_sortIsDescending) [doc setObject:@"YES" forKey:SortDescendingKey];
       ...
       return doc;
}
- (BOOL)loadDataRepresentation:(NSData *)data ofType:
                                                      (NSString *)type {
    if ([type isEqualToString:DocumentType]) {
 NSDictionary *doc = [self workDocumentDictionaryFromData:data];
        id obj;
        ...
        obj = [doc objectForKey:SortNameKey];
        if (obj) {
            [self setSortColumn:obj];
        }
      obj = [doc objectForKey:SortDescendingKey];
        if (obj) {
            _sortIsDescending = [@"YES" isEqualToString:obj];
        }
        return YES;
  }
  return NO;
}
@end

Control Freak

Finally, we come to the meat of the matter in our NSWindowController subclass which is our NSTableView's dataSource as well as delegate.

@interface JobWindowController : NSWindowController 
{
    IBOutlet NSTableView *tableView;
    NSImage *descendingSortingImage;
    NSImage *ascendingSortingImage;
    ...
}

We have work to do in our window initialization method that gets called when the Interface has loaded, awakeFromNib. We want to get the images that we shall display when a sort is made. Using class-dump as described in my iPhoto Exporter bundle article <http://www.omnigroup.com/~nygard/Projects/index.html>, you might note that there are hidden, private Apple internal API to access the images to indicate ascending or descending sorts! Since one should absolutely never rely on hidden API to not dissolve into the ether in subsequent system releases, always bracket the use of these methods with a "respondsToSelector:" query, and provide backup images of your own:

- (void)awakeFromNib
{
    // private images:
    if ([[NSTableView class] respondsToSelector:@selector(_defaultTableHeaderSortImage)])
    ascendingSortingImage = [[NSTableView class] _defaultTableHeaderSortImage];
    else ascendingSortingImage = [[NSImage imageNamed:@"ascendingSort"] retain];
    if ([[NSTableView class] respondsToSelector:@selector(_defaultTableHeaderReverseSortImage)])
    descendingSortingImage = [[NSTableView class] _defaultTableHeaderReverseSortImage];
    else descendingSortingImage = [[NSImage imageNamed:@"descendingSort"] retain];
...
}

If you allow users to move and resize columns, then you definitely want to additionaly call these two methods in awakeFromNib - this will reestablish their preferences and give the system a name to save the column order and sizes.

    [tableView setAutosaveTableColumns:YES];
    [tableView setAutosaveName:@"WorkTable"];
    

So, now we're ready to implement the delegate method which gets called when the column title cell is clicked. The one fine point is that we want to make a note of which item was selected before the sort, so we can reselect it after the sort (its row number may have changed after the sort). We ask the tableView if it already has an image in that column, thus indicating that we need to toggle the direction, otherwise, we'll set the new sort key. The actual work of setting up the tableView's header hilighting is done in updateTableHeaderToMatchCurrentSort. This is factored into a separate method so we can also call it when loading a document to restore last saved sort state.

// BIG COCOA NOTE: if column reordering or column selection is not on
// then this doesn't get called!!
- (void) tableView:(NSTableView*)tv didClickTableColumn:(NSTableColumn *)tableColumn {
    NSImage *sortOrderImage = [tv indicatorImageInTableColumn:tableColumn];
    NSString *columnKey = [tableColumn identifier];
    MyDocument *doc = [self document];
    PieceWork *work = [self selectedWork];
    // If the user clicked the column which already has the sort indicator
    // then just flip the sort order.
    
    if (sortOrderImage || columnKey == [doc sortColumn]) {
        [doc setSortIsDescending:![doc sortIsDescending]]; 
    } else {
        [doc setSortColumn:columnKey];
    }
    [self updateTableHeaderToMatchCurrentSort];
    // now do it - doc calls us back when done
    [doc sort];
    // but reselect the one previously selected:
    if (work) [self selectWork:work];
}

This method updates the state of the NSTableColumn by first clearing all cells, and then setting the correct image and hilighting on the column to sort by, if any:

- (void)updateTableHeaderToMatchCurrentSort {
    BOOL isDescending = [[self document] sortIsDescending];
    NSString *key = [[self document] sortColumn];
    NSArray *a = [tableView tableColumns];
    NSTableColumn *column = [tableView tableColumnWithIdentifier:key];
    unsigned i = [a count];
    
    while (i-- > 0) [tableView setIndicatorImage:nil inTableColumn:[a objectAtIndex:i]];
    
    if (NOT_NULL(key)) {
        [tableView setIndicatorImage:(isDescending ? ascendingSortingImage:descendingSortingImage) 
        inTableColumn:column];
        
        [tableView setHighlightedTableColumn:column];
    } else [tableView setHighlightedTableColumn:nil];
}

And our helper functions to make the code neat and compact:

- (NSArray *)workList {
   return [[self document] workList];
}
- (void)updateTotalsAndReload {
// other ui:
//    [self updateTotals];
    [tableView reloadData];
}
- (PieceWork *)selectedWork {
   NSArray *workList = [self workList];
   int row = [tableView selectedRow];
   if (row > -1 && row < [workList count]) return [workList objectAtIndex:row];
   return nil;
}
- (void)selectWork:(PieceWork *)work {
    NSArray *a = [self workList];
    unsigned i = [a indexOfObject:work];
    if (i != NSNotFound) [self selectRow:i];
}

Devil in the Details

So, now we got sorting working, what sort of problems might we run into? Let's say a user edits the field of an entry in the sorted column. Upon finishing editing, they may have changed the relative order of that entry, requiring a new sort, and a reloading of the tableView again! We can check if we have the sorted column when the data gets set in - tableView:setObjectValue:forTableColumn:row:

- (void)tableView:(NSTableView *)tv setObjectValue:(id)object 
forTableColumn:(NSTableColumn *)tc row:(int)row;
{
        NSArray *workList = [self workList];
        NSString *ident = [tc identifier];
        if (tv == tableView) {
            PieceWork *work = [workList objectAtIndex:row];
            if ([ident isEqual:@"Description"]) {
                [work setWorkDescription:object];
                [self sortIfSortedOn:ident work:work];
           } else if ....
}

Isn't the devil in the details? Because the tableView will want to "select next" after setObjectValue: is called, the wrong row might be selected if the sort changed the currently selected item's row. By calling this method, we'll first end editing on the tableView so any inadvertent select next is foiled. Note the delay of 0.0 seconds which means to schedule the call of the method after the current event loop finishes:

- (void)afterSort:(PieceWork *)work {
    [[self window] makeFirstResponder:[self window]];
    [self selectWork:work];
}
- (void)sortIfSortedOn:(NSString *)ident work:(PieceWork *)work {
    if ([[[self document] sortColumn] isEqualToString:ident])  {
        int oldPosition
        [[self window] makeFirstResponder:[self window]];
        [[self document] sort];
        [self performSelector:@selector(afterSort:) withObject:work afterDelay:0.0];
    } else [self updateTotalsAndReload];
}

Conclusion

Sorting is something users expect tableViews to do now - and with a little effort, all of your tableViews can sort themselves!


Andrew Stone, andrew@stone.com, is Chief Chef at Stone Design, http://www.stone.com, has this to say about Cocoa and Stone Studio with all due respect to Gary Snyder's Turtle Island, "It's objects all the way down" .

 

Community Search:
MacTech Search:

Software Updates via MacUpdate

How to deal with wind in Angry Birds Act...
Angry Birds Action! is a physics-based puzzler in which you're tasked with dragging and launching birds around an obstacle-littered field to achieve a set objective. It's simple enough at first, but when wind gets introduced things can get pretty... | Read more »
How to get three stars in every level of...
Angry Birds Action! is, essentially, a pinball-style take on the pull-and-fling action of the original games. When you first boot it up, you'll likely be wondering exactly what it is you have to do to get a good score. Well, never fear as 148Apps... | Read more »
The beginner's guide to Warbits
Warbits is a turn-based strategy that's clearly inspired by Nintendo's Advance Wars series. Since turn-based strategy games can be kind of tricky to dive into, see below for a few tips to help you in the beginning. Positioning is crucial [Read... | Read more »
How to upgrade your character in Spellsp...
So you’ve mastered the basics of Spellspire. By which I mean you’ve realised it’s all about spelling things in a spire. What next? Well you’re going to need to figure out how to toughen up your character. It’s all well and good being able to spell... | Read more »
5 slither.io mash-ups we'd love to...
If there's one thing that slither.io has proved, it's that the addictive gameplay of Agar.io can be transplanted onto basically anything and it will still be good fun. It wouldn't be surprising if we saw other developers jumping on the bandwagon,... | Read more »
How to navigate the terrain in Sky Charm...
Sky Charms is a whimsical match-'em up adventure that uses creative level design to really ramp up the difficulty. [Read more] | Read more »
Victorious Knight (Games)
Victorious Knight 1.3 Device: iOS Universal Category: Games Price: $1.99, Version: 1.3 (iTunes) Description: New challenges awaits you! Experience fresh RPG experience with a unique combat mechanic, packed with high quality 3D... | Read more »
Agent Gumball - Roguelike Spy Game (Gam...
Agent Gumball - Roguelike Spy Game 1.0 Device: iOS Universal Category: Games Price: $2.99, Version: 1.0 (iTunes) Description: Someone’s been spying on Gumball. What the what?! Two can play at that game! GO UNDERCOVERSneak past enemy... | Read more »
Runaway Toad (Games)
Runaway Toad 1.0 Device: iOS Universal Category: Games Price: $2.99, Version: 1.0 (iTunes) Description: It ain’t easy bein’ green! Tap, hold, and swipe to help Toad hop to safety in this gorgeous new action game from the creators of... | Read more »
PsyCard (Games)
PsyCard 1.0 Device: iOS Universal Category: Games Price: $1.99, Version: 1.0 (iTunes) Description: From the makers och Card City Nights, Progress To 100 and Ittle Dew PSYCARD is a minesweeper-like game set in a cozy cyberpunk... | Read more »

Price Scanner via MacPrices.net

Price drops on clearance 2015 13-inch MacBook...
B&H Photo has dropped prices on clearance 2015 13″ MacBook Airs by up to $250. Shipping is free, and B&H charges NY sales tax only: - 13″ 1.6GHz/4GB/128GB MacBook Air (MJVE2LL/A): $799, $200... Read more
Mac minis on sale for up to $100 off MSRP
B&H Photo has Mac minis on sale for up to $100 off MSRP including free shipping plus NY sales tax only: - 1.4GHz Mac mini: $449 $50 off MSRP - 2.6GHz Mac mini: $649 $50 off MSRP - 2.8GHz Mac mini... Read more
13-inch Retina MacBook Pros on sale for up to...
B&H Photo has 13″ Retina MacBook Pros on sale for $130-$200 off MSRP. Shipping is free, and B&H charges NY tax only: - 13″ 2.7GHz/128GB Retina MacBook Pro: $1169 $130 off MSRP - 13″ 2.7GHz/... Read more
Apple price trackers, updated continuously
Scan our Apple Price Trackers for the latest information on sales, bundles, and availability on systems from Apple’s authorized internet/catalog resellers. We update the trackers continuously: - 15″... Read more
SanDisk Half-Terabyte SSD Optimized for Every...
SanDisk Corporation has announced the SanDisk Z410 SSD, a cost-competitive, half-terabyte solid state drive (SSD) that enables manufacturers to design for a broad range of desktop PCs and laptops.... Read more
Churchill Downs Racetrack Selects VenueNext t...
Churchill Downs Racetrack has announced an agreement with VenueNext to implement its technology platform for the start of Churchill Downs 2016 Spring Meet, which includes the 142nd running of the... Read more
Record 700 Million Pounds of CE Recycled in 2...
The Consumer Technology Association (CTA) reports that a record-setting 700 million pounds of consumer electronics (CE) have been recycled under the eCycling Leadership Initiative (ELI). According to... Read more
Price drops on clearance 12-inch Retina MacBo...
B&H Photo has dropped prices on leftover 2015 12″ Retina MacBooks with models now available starting at $999. Shipping is free, and B&H charges NY tax only: - 12″ 1.1GHz Gray Retina MacBook... Read more
15-inch Retina MacBook Pros available for $20...
B&H Photo has 15″ Retina MacBook Pros on sale for up to $210 off MSRP. Shipping is free, and B&H charges NY tax only: - 15″ 2.2GHz Retina MacBook Pro: $1799 $200 off MSRP - 15″ 2.5GHz Retina... Read more
Target offers Apple Watch Sport for $50 off M...
Target has Apple Watch Sports on sale for $50 off MSRP for a limited time. Choose free shipping or free local store pickup (if available). Sale prices for online orders only, in-store prices may vary... Read more

Jobs Board

*Apple* Retail - Multiple Positions - Apple,...
Job Description: Sales Specialist - Retail Customer Service and Sales Transform Apple Store visitors into loyal Apple customers. When customers enter the store, Read more
Restaurant Manager (Neighborhood Captain) - A...
…in every aspect of daily operation. WHY YOU'LL LIKE IT: You'll be the Big Apple . You'll solve problems. You'll get to show your ability to handle the stress and Read more
Restaurant Manager (Neighborhood Captain) - A...
…in every aspect of daily operation. WHY YOU'LL LIKE IT: You'll be the Big Apple . You'll solve problems. You'll get to show your ability to handle the stress and Read more
Simply Mac *Apple* Specialist- Service Repa...
Simply Mac is the largest premier retailer of Apple products in the nation. In order to support our growing customer base, we are currently looking for a driven Read more
*Apple* Retail - Multiple Positions - Apple,...
Sales Specialist - Retail Customer Service and Sales Transform Apple Store visitors into loyal Apple customers. When customers enter the store, you're also the Read more
All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.