4: An Introduction to the Code in Objective-C

Create Code 39 Full ASCII in Objective-C 4: An Introduction to the Code

29. Finally, enter so that you can run the code. When your program launches, you will see your picture (or mine) overlaid by a semitransparent button. Follow the directions push the button and check out the result. Figure 4 19 shows the iPhone Simulator, while Figures 4 20 and 4 21 demonstrate the iPad Simulator. Congratulations! You have integrated user/programmer interaction with some cool graphics. You ve also been able to get through this with fewer instructions from me. Well Done!

Figure 4 19. Click the button, and it works!

Figure 4 21. Here is the iPad Simulator in full (2x) view mode before the button gets pressed. The 1x button at the lower-right will change the view to the one in Figure 4 20.

In this new section of the chapter, we will be examining several concepts that have been mentioned but that are probably still shrouded in some degree of mystery. This is an opportunity to read along without definitive understanding. I hereby give you permission to partially get it. Of course, if you happen to attain full comprehension of the subject matter in all its details, let me be the first to commend you. Meanwhile, see if holding on more loosely doesn t, in fact, give you a firmer grasp on the big picture.

These items are basically all the same thing, but different people refer to them in different ways. At a recent conference in Denver, 360iDev for iPhone Developers, it was interesting to hear how so many presenters referred to .xib files as nibs or zibs. Most programmers prefer to say nib files. No matter how we refer to them, it s important for us to understand what s going on with these files. What are they Do we need them Do you need to know how they work Do you recall, from step 16, how we opened Interface Builder That s right it happened automatically when you clicked on a nib file. Once it opened, you saw that the file contained all the code associated with our buttons and images, and that, in fact, this information is stored there. That way, when you run the app, all the objects and all the links associated with the objects are integrated properly, and they can then magically come together and give the user the experience that you envisioned. It turns out that nib files, when examined at the level of Cocoa or Objective-C, contain all the information necessary to activate the UI files, transforming these into a graphical iPhone or iPad work of art. It s also possible to join separate nib files together to create more complex interactions, and you ll see this in the next chapter. All the information that resides in these files is put there so that it can create an instance of the buttons, the labels, the pictures, and so forth that you ve entered. This collection of commands is plonked down and saved into your nib files to become the UI. The code and the commands taken together become real, and they are sensed by the user seen or heard, or even felt. We sometimes use the term instantiate in a similar fashion. For example, when you first save a new project, the computer instantiates makes real and shows you the evidence for a project entity by virtue of assigning it a body of subfiles, as it were. In helloWorld_004, you saw how the project was instantly given arms and legs two AppDelegate files and two ViewController files. We say we ve created an instance of something when we ve told the computer how and when to grab some memory and set it aside for some particular process or collection of processes such that, when the parameters are all met, the user has an experience of this data (i.e., whatever was assigned in memory). Sometimes we refer to these collections or files of descriptions and commands as classes, methods, or objects. In this code-digging session, these terms might seem to run together and appear as