How to implement an accordion view for an iPhone SDK app?

Question

Has anyone seen an implementation of an \"accordion\" (maybe called \"animated outline\") view for the iPhone? I found an example project for Cocoa, but before trying a port

Answer 1

Here's the CollapsingTableViewDelegate class that I'm currently working with to do this. This only works with static table content.

You supply the CollapsingTableCellDelegate implementation to this class, which must know how to compute the collapsed and expanded sizes of each row, and how to create a UIView for each row. The view stays the same whether collapsed or expanded, so that the top sliver of each row's view serves as that row's clickable header.

You then make this class the datasource and delegate for your UITableView.

Header file CollapsingTableViewDelegate.h:

#import 

@protocol CollapsingTableCellDelegate

@required
- (CGFloat)collapsingCellHeightForRow:(int)row expanded:(BOOL)expanded;
- (UIView *)collapsingCellViewForRow:(int)row;

@optional
- (BOOL)collapsingCellAllowCollapse:(int)row;

@end

struct cell;

@interface CollapsingTableViewDelegate : NSObject  {
    id cellDelegate;
    int numCells;
    int currentSelection;
    struct cell *cells;
}

@property (nonatomic, retain, readonly) id cellDelegate;
@property (nonatomic, assign, readonly) int numCells;
@property (nonatomic, assign) int currentSelection;
@property (nonatomic, assign, readonly) struct cell *cells;

- (CollapsingTableViewDelegate *)initWithCellDelegate:(id)delegate numCells:(int)numCells;
- (void)tableView:(UITableView *)tableView touchRow:(int)newSelection;

@end

and source file CollapsingTableViewDelegate.m:

#import "CollapsingTableViewDelegate.h"

@implementation CollapsingTableViewDelegate

struct cell {
    u_char expanded;
    u_char collapsable;
};

@synthesize cellDelegate;
@synthesize currentSelection;
@synthesize cells;
@synthesize numCells;

#pragma mark -
#pragma mark Setup and Teardown

- (CollapsingTableViewDelegate *)initWithCellDelegate:(id)delegate numCells:(int)num {
    if ([super init] == nil)
        return nil;
    if ((cells = calloc(num, sizeof(*cells))) == NULL) {
        [self autorelease];
        return nil;
    }
    cellDelegate = [delegate retain];
    numCells = num;
    for (int row = 0; row < self.numCells; row++) {
        struct cell *const cell = &self.cells[row];

        cell->collapsable = ![self.cellDelegate respondsToSelector:@selector(collapsingCellAllowCollapse:)]
          || [self.cellDelegate collapsingCellAllowCollapse:row];
        cell->expanded = !cell->collapsable;
    }
    currentSelection = -1;
    return self;
}

- (void)dealloc {
    [cellDelegate release];
    free(cells);
    [super dealloc];
}

- (void)tableView:(UITableView *)tableView reloadRow:(int)row fade:(BOOL)fade {
    [tableView reloadRowsAtIndexPaths:[NSArray arrayWithObject:[NSIndexPath indexPathForRow:row inSection:0]]
                     withRowAnimation:fade ? UITableViewRowAnimationFade : UITableViewRowAnimationNone];
}

- (void)tableView:(UITableView *)tableView touchRow:(int)newSelection {

    // Sanity check
    if (newSelection < -1 || newSelection >= self.numCells) {
        NSLog(@"CollapsingTableViewDelegate: invalid row %d not in the range [-1..%d)", newSelection, self.numCells);
        return;
    }

    // Gather info
    int oldSelection = self.currentSelection;
    BOOL sameCellSelected = newSelection == oldSelection;
    struct cell *const oldCell = oldSelection != -1 ? &self.cells[oldSelection] : NULL;
    struct cell *const newCell = newSelection != -1 ? &self.cells[newSelection] : NULL;

    // Mark old cell as collapsed and new cell as expanded
    if (newCell != NULL)
        newCell->expanded = TRUE;
    if (oldCell != NULL)
        oldCell->expanded = FALSE;
    self.currentSelection = sameCellSelected ? -1 : newSelection;

    // Update table view
    if (oldSelection >= newSelection) {
        if (oldSelection != -1)
            [self tableView:tableView reloadRow:oldSelection fade:sameCellSelected];
        if (newSelection != -1 && !sameCellSelected)
            [self tableView:tableView reloadRow:newSelection fade:TRUE];
    } else {
        if (newSelection != -1 && !sameCellSelected)
            [self tableView:tableView reloadRow:newSelection fade:TRUE];
        if (oldSelection != -1)
            [self tableView:tableView reloadRow:oldSelection fade:sameCellSelected];
    }

    // If expanding a cell, scroll it into view
    if (newSelection != -1 && !sameCellSelected) {
        [tableView scrollToRowAtIndexPath:[NSIndexPath indexPathForRow:newSelection inSection:0]
                         atScrollPosition:UITableViewScrollPositionTop
                                 animated:TRUE];
    }
}

#pragma mark -
#pragma mark Table view data source

- (NSInteger)numberOfSectionsInTableView:(UITableView *)tableView {
    return 1;
}

- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section {
    return self.numCells;
}

- (CGFloat)tableView:(UITableView *)tableView heightForRowAtIndexPath:(NSIndexPath *)indexPath {
    int row = [indexPath row];
    struct cell *const cell = &self.cells[row];
    return [self.cellDelegate collapsingCellHeightForRow:row expanded:cell->expanded];
}

- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath {
    int row = [indexPath row];
    UIView *cellView = [self.cellDelegate collapsingCellViewForRow:row];
    [cellView removeFromSuperview];
    UITableViewCell *tvcell = [[[UITableViewCell alloc] initWithStyle:UITableViewCellStyleDefault reuseIdentifier:nil] autorelease];
    [tvcell.contentView addSubview:cellView];
    tvcell.clipsToBounds = TRUE;
    tvcell.selectionStyle = UITableViewCellSelectionStyleNone;
    return tvcell;
}

#pragma mark -
#pragma mark Table view delegate

- (NSIndexPath *)tableView:(UITableView *)tableView willSelectRowAtIndexPath:(NSIndexPath *)indexPath {
    int row = [indexPath row];
    struct cell *const cell = &self.cells[row];
    return cell->collapsable ? indexPath : nil;
}

- (void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)newSelection {
    [tableView deselectRowAtIndexPath:newSelection animated:TRUE];
    [self tableView:tableView touchRow:[newSelection row]];
}

@end

Not perfection, but seems to basically work for me.