Lập trình Wrox Professional Xcode 3 cho Mac OS part 17 pdf

Using and customizing syntax coloring Folding code blocks Accepting code completion suggestions Inserting text macros In Chapter 6, you learned a lot of editing features specifi cally de

Syntax - Aware Editing

WHAT'S IN THIS CHAPTER?

Using and customizing syntax coloring Folding code blocks

Accepting code completion suggestions Inserting text macros

In Chapter 6, you learned a lot of editing features specifi cally designed to make writing source code easier, but most of these features are just textual aides that know little or nothing about your code and symbols

Xcode ’ s syntax - aware features pick up where the basic text editing aides leave off — with

some overlap between them Syntax - aware editing means that the editor analyzes your source

code and uses that knowledge to highlight your code ’ s structure and symbols, offer suggestions, and make intelligent changes

You ’ ve already encountered a few syntax - aware features The Balance command, which fi nds

a matching brace or bracket, understands the block structure, string format, comment syntax, and other details of your programming language

This chapter describes the various syntax - aware editing features and tools available in Xcode Xcode can know a lot about your code ’ s structure, and its vocabulary is quite broad;

it understands languages from ADA to XML The code analysis is performed continuously and in the background It won ’ t get in the way of your development, and it ’ s almost always

up - to - date

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128 ❘ CHAPTER 7 SYNTAX-AWARE EDITING

CODE SENSE

Code Sense is the technology that analyzes your code continuously while you write it It assembles

and maintains a database, called the Code Sense index , of the classes, variables, methods,

functions, structures, types, data models, and constants defi ned in your application It also tracks

class inheritance and fi le references Many of the syntax - aware features described in this chapter

rely on Code Sense

Code sense updates its index incrementally, analyzing only the function or method that you ’ re

editing and the source fi les that have been saved recently Updates are typically quite fast — on the

order of a few seconds This means that Code Sense recognizes local variables in the method you ’ re

editing almost instantly, and changes to classes, methods, functions, and types as soon as you save

the fi le

If a symbol doesn ’ t appear to be in the Code Sense index (that is, you can ’ t jump to its defi nition, or it doesn ’ t appear in the auto - completion list), save all of your source fi les to disk (File ➪ Save All, Option + Command + S) If the symbol still fails

to appear within a reasonable amount of time, compile your code and check for syntax errors Code Sense may not be able to index source fi les that won ’ t compile

Enabling Code Sense

You enable Code Sense globally for all projects in the Code Sense panel of the Xcode preferences, as

shown in Figure 7 - 1

FIGURE 7 - 1

The Enable for All Projects option turns all Code Sense – dependent features on or off This includes some syntax coloring, code completion, jump to defi nition, the Included Files and Class Hierarchy navigation menus, the Symbols smart group, and the Class Browser The only real motivation for disabling Code Sense is to avoid the CPU, memory, and disk space required to maintain it, but these seem like small prices to pay for the enormous benefi ts that Code Sense provides I would recommend disabling it only if absolutely necessary

Code Sense works by interacting intimately with the compiler This also requires that all the source items are members of a “ native ” target Native targets are targets that Xcode knows how to build (see Chapter 16), and by extension it knows what compilers will be used to compile each source fi le

External (non - native) targets defer the actual build process to some external program, such as Make

or Ant Items in external targets cannot use Code Sense

TIP TO REMEMBER

If you would like to use Code Sense in a project that requires the use of an external target, you still can Simply create an additional native target that includes all of the source fi les and libraries you want Code Sense to see Code Sense indexes all

of the native source fi les referred to in a project You never have to build that target; it just has to be defi ned

Because Code Sense works silently in the background,

it ’ s sometimes hard to tell whether a symbol isn ’ t in the Code Sense index or whether Code Sense just hasn ’ t reindexed it yet The Window ➪ Activity window tells when Code Sense is working and how far along it is If Code Sense isn ’ t working, and a symbol isn ’ t in the index, either there ’ s a syntax error preventing Code Sense from indexing your source fi les

or the index needs to be rebuilt

Reindexing a Project

If you suspect that the Code Sense index has gotten out of synchronization with your project, open the Info widow for the project (Project ➪ Edit Project Settings) At the bottom of the project ’ s Info window, shown in Figure 7 - 2, is a Rebuild Code Sense Index button Clicking it fl ushes the index for that project and queues Code Sense to index the entire project For large projects, this could take some time

The Code Sense index is stored in your account ’ s

~/Library/Caches folder If the Code Sense index

is ever deleted or is not in synchronization, Xcode automatically rebuilds it

130 ❘ CHAPTER 7 SYNTAX-AWARE EDITING

SYNTAX COLORING

The most visible and passive of the syntax - aware editing features is syntax coloring It uses a basic

knowledge of a language ’ s syntax to colorize the text of source code so that keywords, comments,

literals, symbols, and other language elements are displayed in distinctive colors, fonts, or styles

The intent is to make it easier to read the code by highlighting the functionality of elements in the

source

Customizing Syntax Coloring

You control the colors that syntax coloring uses, or whether syntax coloring is done at all, in the

Fonts & Colors tab of the Xcode Preferences, shown in Figure 7 - 3

FIGURE 7-3

Each entry in the table controls the color, and possibly the font, used to display a category of editor

element The entire collection is collectively referred to as a theme Xcode provides several themes

that you can choose from, and you can create your own The major categories are described in the

following table

You can control syntax - aware coloring globally with the Use Syntax - Based Formatting and Color

Indexed Symbols options Turning the fi rst option off disables all syntax coloring With syntax

coloring enabled, the second option determines whether only basic language elements are colorized,

or whether project symbols in the Code Sense index are also colorized

In addition to the syntax coloring, this preference pane also establishes the font and color scheme used in all editing panes This includes the background color of the pane and the color used to highlight selected text The list is broadly organized into three groups of entries:

The Background, Selection, Insertion Point, and Plain Text categories apply globally to all text editor panes

The categories Comments through Attributes affect recognized language elements when the Use Syntax - Based Formatting option is enabled

The remaining categories change the color of recognized symbols when the Color Indexed Symbols option is enabled

Text that isn ’ t colorized — either because it ’ s not one of the recognized categories or you ’ ve turned off the Use Syntax - Based Formatting or Color Index Symbols options — is displayed using the Plain Text color and font

Background The background color for all editor panes Make sure that it

contrasts well with the colors chosen for text selections, the insertion point, and text Any element that ’ s the same color as the background will be invisible

Selection, Insertion Point The colors used to indicate the current text selection and

insertion point

Plain Text The color, font, and size for all text that ’ s not colorized using

one of the other categories

Comments Comments in the source code For C, Java, and similar

languages this means text enclosed by / and * / character sequences, and the text following a // For property lists and shell scripts, comments are lines that begin with # AppleScript denotes comments between pairs of ( and * ) and after - - Documentation Comments Java ’ s JavaDoc and Darwin ’ s HeaderDoc tools scan source

code fi les and generate documentation for a program or library

Both rely on specially formatted comments that begin with /

or / ! and contain annotations and keywords

Documentation Comments Keywords

JavaDoc and HeaderDoc comments can also include any number of keywords that identify the diff erent parts of the comment For instance, the @param keyword is used to document a single parameter of a function call

Strings String literals contained between pairs of double quotes Xcode

interprets escape characters; it won ’ t be confused by strings such as “ North Carolina (the \ “ Tar Heel\ ” State) “

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132 ❘CHAPTER 7 SYNTAX-AWARE EDITING

Characters Character literals contained between single quotes

Numbers Numeric constants Xcode recognizes decimal, octal, and

hexadecimal numbers that begin with 0x It does not recognize numeric Unicode constants

Keywords The standard keywords for the language Obviously, this

will vary wildly from one language to the next For C - like languages, words such as for , if , else , and then are keywords The word register is a keyword in a C ++ source

fi le, but not in a Java fi le For shell scripts, the keywords are the bash built - in commands

Preprocessor Statements Preprocessor directives used by C - based languages, such

as #include or #define Xcode understands multi - line preprocessor statements

Font & Color themes provided by Xcode are not editable To create a customized theme, begin by

clicking the Duplicate button to make a copy of any existing theme To delete a custom theme, select

it as the current theme and click the Delete button If you attempt to edit a built - in theme, Xcode

alerts you and gives you the opportunity to duplicate it

To customize an element, select the category (or categories) in the list and apply any of the text

styling commands found in the Edit ➪ Format menu As a shortcut, double - clicking a font name

opens the Font palette, and double - clicking a color opens the Color - picker palette Font styles (bold,

italic, underline, strikethrough) are generally ignored, unless the font family has variants for specifi c

styles like bold or italic You can only set the color of the background, selection, insertion point,

and index symbol types; these categories don ’ t use a font, or will use the font of the Plain Text

category

Changing Syntax Coloring for a Single File

Syntax coloring is naturally dependent on Xcode knowing in what language your source fi le is

written By default, Xcode uses the fi le ’ s type (see the “ Source Item Attributes ” section in Chapter 5)

to determine this The vast majority of time this is correct If, for any reason, Xcode guesses wrong,

you can manually specify that it use a different language when interpreting the fi le by selecting the

correct language (or None) from the View ➪ Syntax Coloring menu, as shown in Figure 7 - 4

(continued)

FIGURE 7 - 4

When Default is selected, the language Xcode has chosen is displayed as a dash in the menu of available languages

For fi les that belong to a project, this setting is stored in the project document and is persistent

Otherwise, the selection is lost when the editor pane is closed

134 ❘ CHAPTER 7 SYNTAX-AWARE EDITING

CODE FOLDING

Code folding highlights blocks of structured text and allows them to be collapsed — or

“ folded ” — so that you can concentrate on the higher - level structure of your code Code folding

is supported in all C - like languages (C + + , Objective - C, Java) and XML, as shown in Figure 7 - 5

To see and use code folding, you must have the Show Code Folding Ribbon option turned on

in the Text Editing pane of the Xcode Preferences

FIGURE 7-5

The code folding ribbon appears between the gutter and the text The depth of the blocks in your

text is graphed using gradations of grey; the darker the ribbon, the deeper the text in that line is

nested Hovering your cursor over the ribbon presents collapse controls for the block of text that

begins on that line

Code Focus

Code focus highlights a block of text in the editor, making it easier to see what the block

encompasses, as shown in the bottom window in Figure 7 - 5 Code focus appears when you hover

your cursor over the code folding ribbon Uncheck the Code Focus option in the preferences to

disable this behavior

If you fi nd code focus really useful, even temporarily, and are tired of moving your cursor over the

code folding ribbon, you can have code focus follow your current text selection by choosing View

➪ Code Folding ➪ Focus Follows Selection (Control + Option + Command + F) Now, the code focus

animation will continuously highlight the block containing the current selection or insertion point

Invoke the command a second time to toggle the feature off again