iphone Programming : Adding Missing Features (part 2) - Adding a Launch Image

2. Adding a Launch Image

One of the ways in which the iPhone and the iPod touch cheat is by providing launch images. A launch image is immediately displayed on the screen when the application is started before the UI is displayed. Your application displays the launch image file while loading, which means there are no more blank screens while the application loads.

Let’s add one of these to the City Guide application. Build and deploy the City Guide application onto your iPhone or iPod touch. While your device is still connected and your application is still running, open the Organizer window by going to Window→Organizer in the Xcode menu bar. You will see a glowing green dot next to your device. Select your device, and in the Screenshots tab click the Capture button. Xcode will take a screen capture from your application, as shown in Figure 5.

Click the Save As Default Image button and select your project from the menu. When you return to the project in Xcode, you’ll notice a Default.png image file appear in the Resources group in your project. If you rebuild the City Guide application at this point and redeploy it, the application will apparently now load instantly.

Although many developers have chosen to use the launch image as a splash screen, that’s not how Apple intended this image to be used. Instead, it is intended to improve the user experience. Its presence adds to the user’s perception that your application is quick to load and immediately ready for use when it does load.

Because this is a mobile platform, users will switch between applications frequently. Even more than on the Web, where users’ attention spans are notoriously short, on the iPhone and iPod touch, users will become frustrated with applications that take a long time to launch (or shut down). You need to work to keep the launch time of your application to a minimum, and use the launch image to make a subtle transition into your application.

The launch image measures 320×480 pixels, and generally should be identical to the first screen of your application. However, since this is an image, the content is static, so you should not include any interface elements that may change from launch to launch. Therefore, avoid displaying elements that might look different between the launch image and your first screen. For instance, the Default.png image file we generated for our City Guide application includes a list of cities, but what happens if the user adds more cities? The list will change. We can’t update the list of cities in the launch image, so it’s probably best to remove them, leaving only the table view as shown in Figure 6. (This also has the benefit of hinting to the user that she can’t interact with the app just yet.)

To do this, right-click on the Default.png image file in Xcode and select Reveal in Finder. This will open the Finder and highlight the image in your project folder. You can now open this image in your preferred image editor and make any changes you want. Remember, you need to save it back as a single-layer PNG file without transparency; otherwise, your application will have problems loading the file at launch.