Lập trình Wrox Professional Xcode 3 cho Mac OS part 38 pdf

You model classes by creating a class model document.. If you are intent on keeping a class model, it should be stored in your project’s folder, added to the project’s source group, and

Class Modeling

WHAT'S IN THIS CHAPTER?

Graphically modeling classes Learning the basics of the Xcode modeling tools Customizing diagrams and fi ltering out extraneous detail

To be an effective object - oriented programmer, you must have a clear mental picture of the classes in your application and their relationships Sometimes this “ picture ” is hard to form, because class relationships can be both complex and abstract The class browser, discussed

in Chapter 9, uses the project ’ s index to list your project ’ s classes Although this helps, it still doesn ’ t present a bird ’ s - eye view of your application ’ s structure Enter class modeling Class modeling performs the same function as the class browser, but in a much more visual and customizable way

You model classes by creating a class model document The document can include any set of classes; this could be your entire application or just a set of functionally related classes Xcode then graphs those classes, as shown in Figure 14 - 1 The class model tracks, and instantly refl ects, any changes made to your source fi les Unlike data modeling, discussed in the next chapter, the class modeler is not an editor You cannot design or alter the declarations in a class model and then transform that model into code In other words, the class modeler is not

a UML design tool

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Class models are really useful when:

You want to maintain a clear picture of a complex set of classes

You ’ re considering refactoring a group of classes

You ’ re trying to assimilate a set of classes written by another developer or team

You want to clearly document a set of classes for other developers

If you ’ re not in any of those circumstances, don ’ t skip to the next chapter just yet There ’ s one more

reason why you should learn to use the class modeler:

The class modeling tools use nearly the same interface as the data modeling tools

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FIGURE 14 - 1

The data modeling tools, described in the next chapter, build on the interface elements you learn in this chapter The data modeling tools are used to create Core Data models — something in which you should

defi nitely be interested At the very least, skim this chapter to learn the basics of creating, browsing,

navigating, editing, and customizing models That knowledge will serve you well in Chapter 15

CREATING A CLASS MODEL

A class model is stored in a class model document The documents themselves are extremely lightweight, containing little more than a list of source fi les Think of a class model document as just another “ view ” into your project

The information about your classes is gleaned from the project’s Code Sense index This exposes two very important prerequisites of class model documents:

Your project must be indexed for class modeling to work.

The project containing your classes must be open.

If Code Sense indexing is turned off, turn it on in the Code Sense panel

of the Xcode Preferences If your project is currently being indexed in the background, class modeling starts working as soon as the index is complete.

Class model documents cannot be used outside the context of a project You cannot open a class model document unless the project that it refers to is also open Although it is possible to create class model documents outside of your project, it is not advisable If you are intent on keeping a class model, it should

be stored in your project’s folder, added to the project’s source group, and only opened when the project is open.

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For small projects, I tend to create a Models source group and store my project ’ s class model documents there For larger projects, like the one shown in Figure 14 - 2,

I organize my classes into functional groups, and then store the class model document in the group that contains the classes it models

FIGURE 14 - 2

Creating a New Class Model Document

You add a class model document to your project much as you would any new source fi le:

1. Choose File ➪ New File

2. Choose the Class Model document template

3. Give the class model document a name

4. Ignore the project targets

5. Select the source fi les and source groups that you want to model

You begin by using the File ➪ New File (or any equivalent) command If you have any questions

about that process, see the “ Creating New Source Files ” section in Chapter 5

Next, select the Class Model document type from the list of fi le templates, as shown in

Figure 14 - 3 You will fi nd the Class Model template under the Mac OS X “ Other ” group Class

model documents are universal, applying equally well to iPhone and other project types Give the

document a name Xcode will want you to select the targets the class model document should

be included in, as it does for any new project fi le; don ’ t check any targets in the list Class model

documents are for reference only; they shouldn ’ t be included in any build targets

FIGURE 14 - 3

After naming your new document, Xcode presents the model ’ s fi le tracking dialog box, shown in

Figure 14 - 4

On the left are all the source groups and fi les defi ned in the project On the right is the list of fi les

or groups that will be tracked by the new model Select the source fi les, or source groups, that you want to model on the left and click the Add button to include them in the model You can do this

all at once or incrementally The Add All button adds every single source fi le and group in your

project This is usually excessive and is not recommended; it ’ s only useful in the case where it ’ s more

succinct to specify the fi les and groups you do not want to track

If you have added too many sources, select them in the list on the right and click the Remove button Remove All removes all of the sources, so you can start over

You can add any kind of source fi le that you like, but the class modeler is only interested in class defi nitions For Objective - C and C++, this will typically be the class ’ s header ( .h ) fi le In Java, the .java fi le that defi nes the class should be added The class modeler creates a model using every class defi nition that it fi nds in those fi les Files that contain non - class declarations, libraries, and

so on are ignored There ’ s no harm in adding those fi les to the model, but there ’ s no point either

It also makes no difference how many source fi les defi ne the same class; a class appears in the model only once

Here are the key points to keep in mind when building the tracking list for a class model:

Adding a source group to a model implicitly tracks every source fi le contained in that group

If the contents of the group change, so do the fi les in the model

You can add both a source fi le and the group that contains that source fi le to the model

One reason for doing this would be to avoid having a class disappear from a model if it were moved outside its current source group

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FIGURE 14 - 4

Frameworks can be added A framework is, logically, a source group that contains a number

of header fi les All of the classes defi ned in those headers will be added to the model

Don ’ t fret about what fi les to include, or exclude, at this point The list of sources for the model can be freely edited in the future (as explained in the “ Changing the Tracking ” section)

Be judicious when adding system frameworks, because these typically defi ne scores, if not

hundreds, of classes This can make for an unwieldy model If you want to include classes defi ned in

frameworks, add the specifi c headers you want by digging into the framework group

After assembling your initial list of choices, click the Finish button The class model document is

added to the project and Xcode displays the new model

Figure 14 - 1 showed a typical class model window Like any project document, a class model

pane can appear in the project window or in a separate window The top portion of the pane

contains the class browser and the bottom portion shows the class diagram The horizontal divider

between the two can be resized to show just one or the other As a shortcut, the Design ➪ Hide/

Show Model Browser (Control+Command+B) command quickly collapses or expands the browser

portion of the pane

Creating a Quick Model

The Quick Model command is a fast way of creating an ephemeral model for a select group of

classes, and is an alternative to the more formal procedure for creating class model documents that

was just described Follow these steps to create a quick class model:

1. Select one or more source fi les or groups in an open project You can do this in the project

source group or in the details list

2. Choose Design ➪ Class Model ➪ Quick Model

The Design ➪ Class Model ➪ Quick Model command immediately constructs a class model from

the selected sources The new model window is not associated with a class model document and

nothing is added to your project

Use the Quick Model command to gain quick insight into the class structure of an application

When you are done with the model, simply close it If you made no modifi cations to the model, it

just goes away If you did, Xcode treats it like any unnamed document window and prompts you

to save it As mentioned earlier, class model documents are useless outside the context of the open

project If you don ’ t want to keep the model, discard the changes or just save the fi le as is The

document is a temporary fi le, so just saving the fi le doesn ’ t preserve it — it will still be deleted once

you ’ re fi nished with the diagram

If you later decide you want to save the quick model as a permanent class model document, choose

the File ➪ Save As command, and save the class model document in your project ’ s folder You will

then need to add the new document fi le to your project See Chapter 5 for one of the many ways of

adding a source fi le to your project

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CLASS MODEL BROWSER

The upper pane in the class model is the class model browser, as shown in Figure 14 - 5 On the left is the list of classes being tracked by the model Selecting a class displays the class ’ s members

in the middle list Selecting an item in either list displays additional information about that item in the details pane on the right You can use the dividers between these sections to resize them, within limits

FIGURE 14 - 5

To avoid any confusion, the term “class browser,” or just “browser,” in this chapter refers to the class model browser, not the class browser discussed in Chapter 9

Class modeling can be used to model C++, Java, and Objective - C classes The terminology used in class modeling tends to be neutral:

Properties refer to instance or member variables of a class

Operations refer to class methods, functions, or messages

Protocols refer to either Objective - C protocols or Java interfaces

Categories are Objective - C categories

Packages are Java packages

Not all modeling concepts apply to all languages Categories only appear when modeling Objective - C classes Package names only appear when you ’ re modeling Java classes Multiple - inheritance can only occur with C++ classes

You can customize the browser display a number of different ways In the lower - left corner of both the class and member lists is a pop - up menu that will alter a list ’ s display The choices for the class list, shown on the left in Figure 14 - 6, are Flat List and Inheritance Tree Flat List lists all of the classes alphabetically Inheritance Tree lists the classes in a hierarchical browser

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