BidiFormatter

Added in 1.1.0

public final class BidiFormatter

Utility class for formatting text for display in a potentially opposite-directionality context without garbling. The directionality of the context is set at formatter creation and the directionality of the text can be either estimated or passed in when known. Provides the following functionality:

1. Bidi Wrapping When text in one language is mixed into a document in another, opposite-directionality language, e.g. when an English business name is embedded in a Hebrew web page, both the inserted string and the text surrounding it may be displayed incorrectly unless the inserted string is explicitly separated from the surrounding text in a "wrapper" that:

- Declares its directionality so that the string is displayed correctly. This can be done in Unicode bidi formatting codes by unicodeWrap and similar methods.

- Isolates the string's directionality, so it does not unduly affect the surrounding content. Currently, this can only be done using invisible Unicode characters of the same direction as the context (LRM or RLM) in addition to the directionality declaration above, thus "resetting" the directionality to that of the context. The "reset" may need to be done at both ends of the string. Without "reset" after the string, the string will "stick" to a number or logically separate opposite-direction text that happens to follow it in-line (even if separated by neutral content like spaces and punctuation). Without "reset" before the string, the same can happen there, but only with more opposite-direction text, not a number. One approach is to "reset" the direction only after each string, on the theory that if the preceding opposite- direction text is itself bidi-wrapped, the "reset" after it will prevent the sticking. (Doing the "reset" only before each string definitely does not work because we do not want to require bidi-wrapping numbers, and a bidi-wrapped opposite-direction string could be followed by a number.) Still, the safest policy is to do the "reset" on both ends of each string, since RTL message translations often contain untranslated Latin-script brand names and technical terms, and one of these can be followed by a bidi-wrapped inserted value. On the other hand, when one has such a message, it is best to do the "reset" manually in the message translation itself, since the message's opposite-direction text could be followed by an inserted number, which we would not bidi-wrap anyway. Thus, "reset" only after the string is the current default. In an alternative to "reset", recent additions to the HTML, CSS, and Unicode standards allow the isolation to be part of the directionality declaration. This form of isolation is better than "reset" because it takes less space, does not require knowing the context directionality, has a gentler effect than "reset", and protects both ends of the string. However, we do not yet allow using it because required platforms do not yet support it.

Providing these wrapping services is the basic purpose of the bidi formatter.

2. Directionality estimation How does one know whether a string about to be inserted into surrounding text has the same directionality? Well, in many cases, one knows that this must be the case when writing the code doing the insertion, e.g. when a localized message is inserted into a localized page. In such cases there is no need to involve the bidi formatter at all. In some other cases, it need not be the same as the context, but is either constant (e.g. urls are always LTR) or otherwise known. In the remaining cases, e.g. when the string is user-entered or comes from a database, the language of the string (and thus its directionality) is not known a priori, and must be estimated at run-time. The bidi formatter can do this automatically using the default first-strong estimation algorithm. It can also be configured to use a custom directionality estimation object.

Summary

Nested types
public final class BidiFormatter.Builder

A class for building a BidiFormatter with non-default options.

Public methods
static BidiFormatter

Factory for creating an instance of BidiFormatter for the default locale directionality.
static BidiFormatter

Factory for creating an instance of BidiFormatter given the context locale.
static BidiFormatter
getInstance(boolean rtlContext)

Factory for creating an instance of BidiFormatter given the context directionality.
boolean
boolean

Operates like isRtl, but takes a CharSequence instead of a string.
boolean

Estimates the directionality of a string using the default text direction heuristic.
boolean
CharSequence

Operates like unicodeWrap, but uses the formatter's default direction estimation algorithm and assumes isolate is true.
String

Operates like unicodeWrap, but uses the formatter's default direction estimation algorithm and assumes isolate is true.
CharSequence

Operates like unicodeWrap, but assumes isolate is true.
CharSequence
unicodeWrap(CharSequence str, boolean isolate)

Operates like unicodeWrap, but uses the formatter's default direction estimation algorithm.
String

Operates like unicodeWrap, but assumes isolate is true.
String
unicodeWrap(String str, boolean isolate)

Operates like unicodeWrap, but uses the formatter's default direction estimation algorithm.
CharSequence
unicodeWrap(
    CharSequence str,
    TextDirectionHeuristicCompat heuristic,
    boolean isolate
)

Operates like unicodeWrap, but takes a CharSequence instead of a string
String
unicodeWrap(
    String str,
    TextDirectionHeuristicCompat heuristic,
    boolean isolate
)

Formats a string of given directionality for use in plain-text output of the context directionality, so an opposite-directionality string is neither garbled nor garbles its surroundings.

Public methods

getInstance

Added in 1.1.0
public static BidiFormatter getInstance()

Factory for creating an instance of BidiFormatter for the default locale directionality.

getInstance

Added in 1.1.0
public static BidiFormatter getInstance(Locale locale)

Factory for creating an instance of BidiFormatter given the context locale.

Parameters
Locale locale

The context locale.

getInstance

Added in 1.1.0
public static BidiFormatter getInstance(boolean rtlContext)

Factory for creating an instance of BidiFormatter given the context directionality.

Parameters
boolean rtlContext

Whether the context directionality is RTL.

getStereoReset

Added in 1.1.0
public boolean getStereoReset()
Returns
boolean

Whether directionality "reset" should also be done before a string being bidi-wrapped, not just after it.

isRtl

Added in 1.1.0
public boolean isRtl(CharSequence str)

Operates like isRtl, but takes a CharSequence instead of a string.

Parameters
CharSequence str

CharSequence whose directionality is to be estimated.
Returns
boolean

true if str's estimated overall directionality is RTL. Otherwise returns false.

isRtl

Added in 1.1.0
public boolean isRtl(String str)

Estimates the directionality of a string using the default text direction heuristic.

Parameters
String str

String whose directionality is to be estimated.
Returns
boolean

true if str's estimated overall directionality is RTL. Otherwise returns false.

isRtlContext

Added in 1.1.0
public boolean isRtlContext()
Returns
boolean

Whether the context directionality is RTL

unicodeWrap

Added in 1.1.0
public CharSequence unicodeWrap(CharSequence str)

Operates like unicodeWrap, but uses the formatter's default direction estimation algorithm and assumes isolate is true.

Parameters
CharSequence str

The input CharSequence.
Returns
CharSequence

Input CharSequence after applying the above processing.

unicodeWrap

Added in 1.1.0
public String unicodeWrap(String str)

Operates like unicodeWrap, but uses the formatter's default direction estimation algorithm and assumes isolate is true.

Parameters
String str

The input string.
Returns
String

Input string after applying the above processing.

unicodeWrap

Added in 1.1.0
public CharSequence unicodeWrap(CharSequence str, TextDirectionHeuristicCompat heuristic)

Operates like unicodeWrap, but assumes isolate is true.

Parameters
CharSequence str

The input CharSequence.
TextDirectionHeuristicCompat heuristic

The algorithm to be used to estimate the CharSequence's overall direction. See androidx.core.text.TextDirectionHeuristicsCompat for pre-defined heuristics.
Returns
CharSequence

Input CharSequence after applying the above processing.

unicodeWrap

Added in 1.1.0
public CharSequence unicodeWrap(CharSequence str, boolean isolate)

Operates like unicodeWrap, but uses the formatter's default direction estimation algorithm.

Parameters
CharSequence str

The input CharSequence.
boolean isolate

Whether to directionally isolate the CharSequence to prevent it from garbling the content around it
Returns
CharSequence

Input CharSequence after applying the above processing.

unicodeWrap

Added in 1.1.0
public String unicodeWrap(String str, TextDirectionHeuristicCompat heuristic)

Operates like unicodeWrap, but assumes isolate is true.

Parameters
String str

The input string.
TextDirectionHeuristicCompat heuristic

The algorithm to be used to estimate the string's overall direction.
Returns
String

Input string after applying the above processing.

unicodeWrap

Added in 1.1.0
public String unicodeWrap(String str, boolean isolate)

Operates like unicodeWrap, but uses the formatter's default direction estimation algorithm.

Parameters
String str

The input string.
boolean isolate

Whether to directionally isolate the string to prevent it from garbling the content around it
Returns
String

Input string after applying the above processing.

unicodeWrap

Added in 1.1.0
public CharSequence unicodeWrap(
    CharSequence str,
    TextDirectionHeuristicCompat heuristic,
    boolean isolate
)

Operates like unicodeWrap, but takes a CharSequence instead of a string

Parameters
CharSequence str

The input CharSequence.
TextDirectionHeuristicCompat heuristic

The algorithm to be used to estimate the CharSequence's overall direction. See androidx.core.text.TextDirectionHeuristicsCompat for pre-defined heuristics.
boolean isolate

Whether to directionally isolate the CharSequence to prevent it from garbling the content around it
Returns
CharSequence

Input CharSequence after applying the above processing. null if str is null.

unicodeWrap

Added in 1.1.0
public String unicodeWrap(
    String str,
    TextDirectionHeuristicCompat heuristic,
    boolean isolate
)

Formats a string of given directionality for use in plain-text output of the context directionality, so an opposite-directionality string is neither garbled nor garbles its surroundings. This makes use of Unicode bidi formatting characters.

The algorithm: In case the given directionality doesn't match the context directionality, wraps the string with Unicode bidi formatting characters: RLE+str+PDF for RTL text, or LRE+str+PDF for LTR text.

If isolate, directionally isolates the string so that it does not garble its surroundings. Currently, this is done by "resetting" the directionality after the string by appending a trailing Unicode bidi mark matching the context directionality (LRM or RLM) when either the overall directionality or the exit directionality of the string is opposite to that of the context. Unless the formatter was built using stereoReset with a false argument, also prepends a Unicode bidi mark matching the context directionality when either the overall directionality or the entry directionality of the string is opposite to that of the context. Note that as opposed to the overall directionality, the entry and exit directionalities are determined from the string itself.

Does *not* do HTML-escaping.

Parameters
String str

The input string.
TextDirectionHeuristicCompat heuristic

The algorithm to be used to estimate the string's overall direction.
boolean isolate

Whether to directionally isolate the string to prevent it from garbling the content around it
Returns
String

Input string after applying the above processing. null if str is null.