Undefined Value

Newcomers to iPhone development are sometimes surprised at how ugly the standard button controls are. They quickly learn that they need a graphics person to create a nice-looking button image in Photoshop and then attach that to the buttons. However, in this tutorial, I'll show how to create nice shiny buttons in code, without any image files, by using a CAGradientLayer.

As an exercise in using the Core Animation API, I've implemented a little iPhone app that reproduces the behavior of the iPhone home screen's icon reorganization interface. (You know, dragging the wiggly icons around.) You can download my sample code to see how it works. Some descriptions of the highlights follow below.

When you create a table-view-based iPhone app, by default you get tables with plain white rows. But all the cool kids are making apps with 3D-ish gradient backgrounds. You want to make those kinds of apps too, right? This article explains how.

While working on an iPhone application, I decided I wanted to change the colors of the background and section headers of a UITableView with the UITableViewStyleGrouped style. It took a lot more work than I expected, so I'm sharing what I learned with anyone else who needs to do this.

For an iPhone app that I'm working on, I want to be able to save the screen image to the Photos album. My first attempt at this was complicated: I created a color space, a bitmap context, a CGImage, and finally a UIImage, copying and pasting most of the code from the Quartz 2D Programming Guide. Unfortunately, it didn't work; I kept getting BAD_ACCESS signals when I called UIImageWriteToSavedPhotosAlbum(), even though it looked to me like everything was correct.

After Googling for a bit for known issues with UIImageWriteToSavedPhotosAlbum, I ran across a far easier solution to the problem. Here are the methods I ended up with:

// Create an image for the view and save it to the Photos library
- (void)savePhotoOfView:(UIView *)view
{
    UIGraphicsBeginImageContext(view.bounds.size);
    [view drawRect:view.bounds];
    UIImage *image = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();

    UIImageWriteToSavedPhotosAlbum(image,
                                   self,
                                   @selector(savedPhotoImage:didFinishSavingWithError:contextInfo:),
                                   NULL);
}

// Called by UIImageWriteToSavedPhotosAlbum() when it completes
- (void)   savedPhotoImage:(UIImage *)image
  didFinishSavingWithError:(NSError *)error
               contextInfo:(void *)contextInfo
{    
    NSString *message = @"This image has been saved to your Photos album";
    if (error) {
        message = [error localizedDescription];
    }
    UIAlertView *alert = [[UIAlertView alloc] initWithTitle:nil
                                                    message:message
                                                   delegate:nil
                                          cancelButtonTitle:@"OK"
                                          otherButtonTitles:nil];
    [alert show];
    [alert release];
}

These just call the view's drawRect method to create an image, save the image to the Photos library, and then pop up an alert box to let the user know what happened.