Borkware Quickies

Triggering a low-memory warning on the device (Debugging->General)

Fri, 03 Feb 2012 19:34:35 UTC

You can trigger a low-memory warning in the simulator, but sometimes you use one of the myriad of APIs that aren't supported in the simulator, but you still need to track down something ultimately triggered by a low-memory warning.

Put this somewhere convenient to trigger - in a timer, under a button, or something. Obviously, you don't want to ship with it.

[[UIApplication sharedApplication] performSelector: @selector(_performMemoryWarning)];

Using a nib for a tableview cell (UITableView->General)

Sat, 28 Jan 2012 02:01:55 UTC

You can use a nib file for table view cells pretty easily in iOS5.

1) Make a nib with a single object at the top, a UITableViewCell. Lay it out as you wish. I use view tags to get to the objects contained therein.

enum {
    kTermLabelTag = 1,
    kDetailLabelTag = 2
};

2) Register the nib for a cell reuse identifier. I do it in my -viewDidLoad.

static NSString *g_cellReuseIdentifier = @"BWLookupCellReuseIdentifier"; // file global

...

    UINib *nib = [UINib nibWithNibName: @"BWLookupTableViewCell"  bundle: nil];
    [self.resultsView registerNib: nib
         forCellReuseIdentifier: g_cellReuseIdentifier];

3) Dequeue the cell as usual

    UITableViewCell *cell =
        [tableView dequeueReusableCellWithIdentifier: g_cellReuseIdentifier];

    if (!cell) {
        cell = [[UITableViewCell alloc]
                   initWithStyle: UITableViewCellStyleSubtitle
                   reuseIdentifier: g_cellReuseIdentifier];
    }

4) Dig into the cell with the tags, and go nuts

    UILabel *termLabel = (UILabel *)[cell viewWithTag: kTermLabelTag];
    UILabel *detailLabel = (UILabel *)[cell viewWithTag: kDetailLabelTag];

    termLabel.text = termString;
    detailLabel.text = definition;

Converting degrees to radians and back (Graphics->General)

Thu, 29 Dec 2011 23:31:44 UTC

Most programming interfaces that deal with angles talk in radians (2 pi radians in a circle), like CGAffineTransformRotate. I personally think better in degrees (360 degrees in a circle).

Convert degrees to radians by multiplying by 180 / pi.

Convert radians to degrees by multiplying by pi / 180

I have a couple of #defines I stick into a common header for projects that need it;

#define BWDegToRad(d)   ((d) * M_PI / 180.0)
#define BWRadToDeg(r)   ((r) * 180 / M_PI)

Push/pop CGContext state (Graphics->General)

Thu, 29 Dec 2011 02:56:29 UTC

CGContextRef context = ...;

...
CGContextSaveGState (context); {
    [drawable drawWithContext: context
              inRect: bounds
              withMetrics: self.metrics]; // or whatever drawing you're doing
} CGContextRestoreGState (context);

Edit: Gus Meuller of Flying Meat fame has a block-based utility that does this:

void FMCGContextHoldGState (CGContextRef context, void (^block)()) {
    CGContextSaveGState(context); {
        block ();
    } CGContextRestoreGState(context);
}

and if you're wanting to do something similar with NSGraphicsContexts:

void FMNSContextHoldGState (void (^block)()) {
    [NSGraphicsContext saveGraphicsState]; {
        block ();
    } [NSGraphicsContext restoreGraphicsState];
}

Sort case-insensitive (emacs->General)

Mon, 26 Dec 2011 03:42:07 UTC

M-x sort-lines uses a case-sensitive search. When that sucks, you can tell emacs to be case insensitive (globally) by doing M-x set-variable RET sort-fold-case RET t

UITableView section header titles (UITableView->General)

Mon, 26 Dec 2011 01:45:23 UTC

UITableView won't display its groovy section headers (or footers) until you supply them via the datasource:

- (NSString *) tableView: (UITableView *) tableview
 titleForHeaderInSection: (NSInteger) section {
    NSArray *sections = [BWTermStorage sections];
    return [sections objectAtIndex: section];
} // titleForHeaderInSection

You can return a title for a footer.

You can also return a view:

- (UIView *) tableView: (UITableView *) tableView 
    viewForHeaderInSection: (NSInteger) section;

Filter a table view selection (UITableView->General)

Sun, 18 Dec 2011 00:37:17 UTC

You might have some rows in a UITableView you don't want to be selected. Override willSelectRowAtIndexPath, return nil to reject the selection, return the passed-in indexPath to use as-is, or return your choice of selected cells.

- (NSIndexPath *) tableView: (UITableView *) tableView
   willSelectRowAtIndexPath: (NSIndexPath *) indexPath {
    // don't select the top row sort control.
    if (indexPath.row == 0) return nil;
    else return indexPath;
} // willSelectRowAtIndexPath

Prevent editing / deleting of table rows (UITableView->General)

Sat, 17 Dec 2011 23:58:18 UTC

To prevent a row from being deleted in a UITableView (say a header with sorting controls), override -canEditRowAtIndexPath:

- (BOOL) tableView: (UITableView *) tableView
    canEditRowAtIndexPath: (NSIndexPath *) indexPath {
    if (indexPath.row == 0) return NO;
    else return YES;
} // canEditRowAtIndexPath

Clipping to a CGPath (Graphics->General)

Sat, 26 Nov 2011 00:27:40 UTC

    CGPathRef border = ... get a path from somewhere;


    CGContextRef context = UIGraphicsGetCurrentContext ();

    CGContextSaveGState (context); {
        CGContextAddPath (context, border);
        CGContextClip (context);

        // draw draw draw

    } CGContextRestoreGState (context);

Using Changes.app for hg's diffing (Mercurial->General)

Wed, 23 Nov 2011 20:40:00 UTC

Add this to your ~/.hgrc

[extensions]
extdiff =

[extdiff]
cmd.chdiff = /Local/Apps/Changes.app/Contents/Resources/chdiff
opts.chdiff = --wait

Your Changes.app path is probably different, so be sure to change it. Or add the chdiff's directory to your shell path.

Now you can
% hg chdiff
And get pretty diffing.

Register a notification with a block (Notifications->Blocks)

Mon, 21 Nov 2011 20:04:40 UTC

        [center addObserverForName: kGRZoneSystem_ZoneSystemChangedNotification

                object: nil
                queue: [NSOperationQueue mainQueue]
                usingBlock: ^(NSNotification *notification) {
                [self adaptToZoneChange];
            }];

Moving archived apps from one machine to another (Xcode->General)

Sat, 05 Nov 2011 17:46:37 UTC

To move your archived apps from one machine to another (say you're upgrading to some shinier hardware or doing a nuke-and-pave install), you can find your old archived apps at:

~/Library/Developer/Xcode/Archives

Control + trackpad zoom in Lion (Random->Random)

Fri, 23 Sep 2011 13:52:10 UTC

It took awhile to find where to enable the "zoom into the screen with control+scrollwheel":

System Preferences > Universal Access > Seeing > Zoom in window > Options > Use scroll wheel with modifier keys to zoom

Unicode characters in C strings (General->General)

Mon, 19 Sep 2011 17:11:29 UTC

C strings (and Objective-C @"Strings") are ascii by default, so to include unicode characters, you need to escape-U them:

printf ("\u3232_\u3232\u2122\n");

Determining current localization you're running in. (Random->General)

Thu, 15 Sep 2011 01:16:50 UTC

You can use this to find which of the user's preferred localizations/locales that is also supported by your app. (translation, what localization you're currently running in)

NSString *languageused = [[[NSBundle mainBundle] preferredLocalizations] objectAtIndex: 0];

(thanks to Glenn Fawcett for this one!)

Finding the path corresponding to an open file descriptor (Unix->General)

Wed, 14 Sep 2011 21:30:57 UTC

With fcntl, all things are possible.

char pathbuf[PATH_MAX];

if (fcntl(fd, F_GETPATH, pathbuf) >= 0) {
    printf ("wow: %s\n", pathbuf);
} else {
    printf ("oops %s\n", strerror(errno));
}

Finding this feature was a surprise, having lived under the assumption that you can't map from a file descriptor to a path in the file system. Obviously things like sockets and pipes will return an error, but it actually seems to work.

Setting iPhone status bar to black (General->General)

Mon, 12 Sep 2011 16:11:00 UTC

In the app's info.plist, set UIStatusBarStyle to UIStatusBarStyleOpaqueBlack

Turn off the Lion window animation (General->General)

Mon, 12 Sep 2011 00:52:18 UTC

defaults write NSGlobalDomain NSAutomaticWindowAnimationsEnabled -bool NO

Adding a decimal point to the numeric keyboard (UITextField->General)

Mon, 05 Sep 2011 14:42:58 UTC

Apple added a decimal pad keyboard type. As of Xcode 4.1, not exported in the UI, so you have to set it in code:

textField.keyboardType = UIKeyboardTypeDecimalPad;

Dismissing the on-screen keyboard (UITextField->General)

Mon, 05 Sep 2011 14:41:25 UTC

If you know the text field that is being edited, you can tell it to resign first responder:

[textField resignFirstResponder];

Otherwise, you can tell the enclosing view to end editing, and it'll figure out who is editing and tell them to resign:

[self.view endEditing: YES];