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Creating Models

Xcode allows you to create models in two ways, as quick models and as project class model files (model files you create with the New File Assistant). At first glance it may appear that the two sorts of class model are somehow different. It is important to realize that they are functionally the same but created in different ways and usually with a different immediate purpose in mind.

When you create a model, you add the source or the header files (or both), or containers (such as groups, targets, or projects, but not smartgroups, build phases, find results, and so on) that you want to contribute to the model. A model is dynamic, though. It is continuously updated in response to changes in your source code and the organization of your project. For this reason, you might add both a file and a group containing that file to a model, so that if the file is moved out of group it remains in the model (this strategy may be particularly useful early in a project’s lifetime when groups are likely to change).

Note that since class model files depend on the project index, they can’t survive outside the project. Note also that when you add a class to a model, its immediate superclass is implicitly added to the model (even if it’s not in the project).

In this section:

Creating a Quick Model
Creating a Class Model File

Creating a Quick Model

To create a Quick Model, select in the Groups & Files list the files and containers that you want to contribute to the model. Then choose Design > Class Model > Quick Model . Xcode displays the class browser and diagram.

A quick model is untitled and ephemeral. It does not appear in the project file browser, and if unchanged, it is closed without warning. If you make changes, however, you are prompted to save when the project is closed. You can also save the model at any point using Save or Save As if you decide you want to keep the model.

Creating a Class Model File

To create a class model file, choose File > New File and select Class Model from the Design group. You then name the file, and click Next. From the subsequent panel, shown in Figure 11-1, you select the files and containers that you want to contribute to the model.

When you click Finish, Xcode creates the model file, adds it to the project, and displays the class browser and diagram.

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