Best way to apply a theme to an iPhone app

Question

Hi I am trying to write some iPhone app with a theme switcher, where users can select a theme to change the background color, alpha, images, and some push buttons\' look and fee

Answer 1

Here's how I implemented the ability to change themes in FemCal. I've included some of the details in the form of code snippets.

1. Create a singleton ThemeMgr class that stores colors, images etc. Fetch the singleton when needed.

   @interface ThemeMgr : NSObject 
   {
   // selected color and image
   NSString * selectedColor;
   NSString * selectedPicture;
   // dictionaries for color and image
   NSDictionary * colorData;
   NSDictionary * imageData;
   NSDictionary * backgroundData;
   // names
   NSArray * colors;
   NSArray * images;
   // themes
   UIColor * tintColor;
   UIImageView * panelTheme;
   UIColor * tableBackground;
   }

2. Use notifications to broadcast theme changes. I used @"ThemeChange" as the notification.

   - (void)fireTimer:(NSTimer *)timer
   {
   NSNotification * themeChange = [NSNotification notificationWithName:@"ThemeChange" object:nil];
   [[NSNotificationQueue defaultQueue] enqueueNotification:themeChange postingStyle:NSPostWhenIdle];
   }

   Obviously, you'll have some UI to select a desired theme. In this case, the user chooses a theme and fireTimer is fired after 0.5 seconds. This gives a nice delay for other UI to update before I force the UI to redraw itself.

3. Listen for notifications anywhere you need to act on a theme change.

   // listen for change notification
   [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(updateAppearance:) name:@"ThemeChange" object:nil];

   I only have a few views, so I've written the code in each controller I use, but you can use the power of objective-C to mix code in to handle this in a better way.

4. Implement the code to actually redraw your view based on the theme.

   - (void)updateAppearance:(NSNotification *)notification
   {
   // background for grouped table view
   ThemeMgr * themeMgr = [ThemeMgr defaultMgr];
   // change color and reload
   [self.tableView setBackgroundColor:[themeMgr tableBackground]];
   [self.tableView reloadData];
   self.navigationController.navigationBar.tintColor = [themeMgr tintColor];
   }
   

Don't forget to resign any notifications when necessary, and you'll have to write code in viewDidLoad or similar to apply any themes before the view is displayed.