I'm interested in setting some text into a UILabel, and depending on the directionality of the language (e.g., Hebrew - right-to-left [RTL], English - left-to-right [LTR]) set the alignment of the UILabel.
Note that using iOS 6's NSTextAlignmentNatural does not solve the problem, as it chooses alignment according to the current locale, experiments show.
Ended up following the advice given in this SO answer: write a short script that will parse the Unicode data publicly available here, and generate code to identify whether a code-point has a strong R or AL directionality attribute. Then, the string is searched for the first such character. This is exactly what ubidi_getBaseDirection from the ICU package does.
Since the internal representation of NSString is UTF16 (which is a variable-length encoding), it is first converted to UTF32 in order to simplify the scanning code. An alternative approach would be to decode the string on the fly, which requires dealing with BOM and Unicode surrogates. Yet another approach is simply ignoring characters not representable by one unichar. For more details, see Wikipedia's UTF16 article.
@interface NSString (TextDirectionality)
/* Return 1 if the string is strongly LTR, -1 if strongly RTL, or 0 if neutral. */
/* See http://icu-project.org/apiref/icu4c/ubidi_8h.html#aeb1fd15743833278cc11906cd5a48aef */
-(int)getBaseDirection;
@end
@implementation NSString (TextDirectionality)
// Function takes UTF32 character, and not a unichar (=UTF16 character),
// because some Unicode characters need full 32 bits to represent.
BOOL isCodePointStrongRTL(UTF32Char c) {
return ((c == 0x5BE) || (c == 0x5C0) || (c == 0x5C3) || (c == 0x5C6) || (c >= 0x5D0 && c <= 0x5EA) || (c >= 0x5F0 && c <= 0x5F4) || (c == 0x608) || (c == 0x60B) || (c == 0x60D) || (c == 0x61B) || (c >= 0x61E && c <= 0x64A) || (c >= 0x66D && c <= 0x66F) || (c >= 0x671 && c <= 0x6D5) || (c >= 0x6E5 && c <= 0x6E6) || (c >= 0x6EE && c <= 0x6EF) || (c >= 0x6FA && c <= 0x70D) || (c >= 0x70F && c <= 0x710) || (c >= 0x712 && c <= 0x72F) || (c >= 0x74D && c <= 0x7A5) || (c == 0x7B1) || (c >= 0x7C0 && c <= 0x7EA) || (c >= 0x7F4 && c <= 0x7F5) || (c == 0x7FA) || (c >= 0x800 && c <= 0x815) || (c == 0x81A) || (c == 0x824) || (c == 0x828) || (c >= 0x830 && c <= 0x83E) || (c >= 0x840 && c <= 0x858) || (c == 0x85E) || (c == 0x8A0) || (c >= 0x8A2 && c <= 0x8AC) || (c == 0x200F) || (c == 0xFB1D) || (c >= 0xFB1F && c <= 0xFB28) || (c >= 0xFB2A && c <= 0xFB36) || (c >= 0xFB38 && c <= 0xFB3C) || (c == 0xFB3E) || (c >= 0xFB40 && c <= 0xFB41) || (c >= 0xFB43 && c <= 0xFB44) || (c >= 0xFB46 && c <= 0xFBC1) || (c >= 0xFBD3 && c <= 0xFD3D) || (c >= 0xFD50 && c <= 0xFD8F) || (c >= 0xFD92 && c <= 0xFDC7) || (c >= 0xFDF0 && c <= 0xFDFC) || (c >= 0xFE70 && c <= 0xFE74) || (c >= 0xFE76 && c <= 0xFEFC) || (c >= 0x10800 && c <= 0x10805) || (c == 0x10808) || (c >= 0x1080A && c <= 0x10835) || (c >= 0x10837 && c <= 0x10838) || (c == 0x1083C) || (c >= 0x1083F && c <= 0x10855) || (c >= 0x10857 && c <= 0x1085F) || (c >= 0x10900 && c <= 0x1091B) || (c >= 0x10920 && c <= 0x10939) || (c == 0x1093F) || (c >= 0x10980 && c <= 0x109B7) || (c >= 0x109BE && c <= 0x109BF) || (c == 0x10A00) || (c >= 0x10A10 && c <= 0x10A13) || (c >= 0x10A15 && c <= 0x10A17) || (c >= 0x10A19 && c <= 0x10A33) || (c >= 0x10A40 && c <= 0x10A47) || (c >= 0x10A50 && c <= 0x10A58) || (c >= 0x10A60 && c <= 0x10A7F) || (c >= 0x10B00 && c <= 0x10B35) || (c >= 0x10B40 && c <= 0x10B55) || (c >= 0x10B58 && c <= 0x10B72) || (c >= 0x10B78 && c <= 0x10B7F) || (c >= 0x10C00 && c <= 0x10C48) || (c >= 0x1EE00 && c <= 0x1EE03) || (c >= 0x1EE05 && c <= 0x1EE1F) || (c >= 0x1EE21 && c <= 0x1EE22) || (c == 0x1EE24) || (c == 0x1EE27) || (c >= 0x1EE29 && c <= 0x1EE32) || (c >= 0x1EE34 && c <= 0x1EE37) || (c == 0x1EE39) || (c == 0x1EE3B) || (c == 0x1EE42) || (c == 0x1EE47) || (c == 0x1EE49) || (c == 0x1EE4B) || (c >= 0x1EE4D && c <= 0x1EE4F) || (c >= 0x1EE51 && c <= 0x1EE52) || (c == 0x1EE54) || (c == 0x1EE57) || (c == 0x1EE59) || (c == 0x1EE5B) || (c == 0x1EE5D) || (c == 0x1EE5F) || (c >= 0x1EE61 && c <= 0x1EE62) || (c == 0x1EE64) || (c >= 0x1EE67 && c <= 0x1EE6A) || (c >= 0x1EE6C && c <= 0x1EE72) || (c >= 0x1EE74 && c <= 0x1EE77) || (c >= 0x1EE79 && c <= 0x1EE7C) || (c == 0x1EE7E) || (c >= 0x1EE80 && c <= 0x1EE89) || (c >= 0x1EE8B && c <= 0x1EE9B) || (c >= 0x1EEA1 && c <= 0x1EEA3) || (c >= 0x1EEA5 && c <= 0x1EEA9) || (c >= 0x1EEAB && c <= 0x1EEBB));
}
BOOL isCodePointStrongLTR(UTF32Char c) {
return (c >= 0x41 && c <= 0x5A) || (c >= 0x61 && c <= 0x7A) || (c == 0xAA) || (c == 0xB5) || (c == 0xBA) || (c >= 0xC0 && c <= 0xD6) || (c >= 0xD8 && c <= 0xF6) || (c >= 0xF8 && c <= 0x2B8) || (c >= 0x2BB && c <= 0x2C1) || (c >= 0x2D0 && c <= 0x2D1) || (c >= 0x2E0 && c <= 0x2E4) || (c == 0x2EE) || (c >= 0x370 && c <= 0x373) || (c >= 0x376 && c <= 0x377) || (c >= 0x37A && c <= 0x37D) || (c == 0x386) || (c >= 0x388 && c <= 0x38A) || (c == 0x38C) || (c >= 0x38E && c <= 0x3A1) || (c >= 0x3A3 && c <= 0x3F5) || (c >= 0x3F7 && c <= 0x482) || (c >= 0x48A && c <= 0x527) || (c >= 0x531 && c <= 0x556) || (c >= 0x559 && c <= 0x55F) || (c >= 0x561 && c <= 0x587) || (c == 0x589) || (c >= 0x903 && c <= 0x939) || (c == 0x93B) || (c >= 0x93D && c <= 0x940) || (c >= 0x949 && c <= 0x94C) || (c >= 0x94E && c <= 0x950) || (c >= 0x958 && c <= 0x961) || (c >= 0x964 && c <= 0x977) || (c >= 0x979 && c <= 0x97F) || (c >= 0x982 && c <= 0x983) || (c >= 0x985 && c <= 0x98C) || (c >= 0x98F && c <= 0x990) || (c >= 0x993 && c <= 0x9A8) || (c >= 0x9AA && c <= 0x9B0) || (c == 0x9B2) || (c >= 0x9B6 && c <= 0x9B9) || (c >= 0x9BD && c <= 0x9C0) || (c >= 0x9C7 && c <= 0x9C8) || (c >= 0x9CB && c <= 0x9CC) || (c == 0x9CE) || (c == 0x9D7) || (c >= 0x9DC && c <= 0x9DD) || (c >= 0x9DF && c <= 0x9E1) || (c >= 0x9E6 && c <= 0x9F1) || (c >= 0x9F4 && c <= 0x9FA) || (c == 0xA03) || (c >= 0xA05 && c <= 0xA0A) || (c >= 0xA0F && c <= 0xA10) || (c >= 0xA13 && c <= 0xA28) || (c >= 0xA2A && c <= 0xA30) || (c >= 0xA32 && c <= 0xA33) || (c >= 0xA35 && c <= 0xA36) || (c >= 0xA38 && c <= 0xA39) || (c >= 0xA3E && c <= 0xA40) || (c >= 0xA59 && c <= 0xA5C) || (c == 0xA5E) || (c >= 0xA66 && c <= 0xA6F) || (c >= 0xA72 && c <= 0xA74) || (c == 0xA83) || (c >= 0xA85 && c <= 0xA8D) || (c >= 0xA8F && c <= 0xA91) || (c >= 0xA93 && c <= 0xAA8) || (c >= 0xAAA && c <= 0xAB0) || (c >= 0xAB2 && c <= 0xAB3) || (c >= 0xAB5 && c <= 0xAB9) || (c >= 0xABD && c <= 0xAC0) || (c == 0xAC9) || (c >= 0xACB && c <= 0xACC) || (c == 0xAD0) || (c >= 0xAE0 && c <= 0xAE1) || (c >= 0xAE6 && c <= 0xAF0) || (c >= 0xB02 && c <= 0xB03) || (c >= 0xB05 && c <= 0xB0C) || (c >= 0xB0F && c <= 0xB10) || (c >= 0xB13 && c <= 0xB28) || (c >= 0xB2A && c <= 0xB30) || (c >= 0xB32 && c <= 0xB33) || (c >= 0xB35 && c <= 0xB39) || (c >= 0xB3D && c <= 0xB3E) || (c == 0xB40) || (c >= 0xB47 && c <= 0xB48) || (c >= 0xB4B && c <= 0xB4C) || (c == 0xB57) || (c >= 0xB5C && c <= 0xB5D) || (c >= 0xB5F && c <= 0xB61) || (c >= 0xB66 && c <= 0xB77) || (c == 0xB83) || (c >= 0xB85 && c <= 0xB8A) || (c >= 0xB8E && c <= 0xB90) || (c >= 0xB92 && c <= 0xB95) || (c >= 0xB99 && c <= 0xB9A) || (c == 0xB9C) || (c >= 0xB9E && c <= 0xB9F) || (c >= 0xBA3 && c <= 0xBA4) || (c >= 0xBA8 && c <= 0xBAA) || (c >= 0xBAE && c <= 0xBB9) || (c >= 0xBBE && c <= 0xBBF) || (c >= 0xBC1 && c <= 0xBC2) || (c >= 0xBC6 && c <= 0xBC8) || (c >= 0xBCA && c <= 0xBCC) || (c == 0xBD0) || (c == 0xBD7) || (c >= 0xBE6 && c <= 0xBF2) || (c >= 0xC01 && c <= 0xC03) || (c >= 0xC05 && c <= 0xC0C) || (c >= 0xC0E && c <= 0xC10) || (c >= 0xC12 && c <= 0xC28) || (c >= 0xC2A && c <= 0xC33) || (c >= 0xC35 && c <= 0xC39) || (c == 0xC3D) || (c >= 0xC41 && c <= 0xC44) || (c >= 0xC58 && c <= 0xC59) || (c >= 0xC60 && c <= 0xC61) || (c >= 0xC66 && c <= 0xC6F) || (c == 0xC7F) || (c >= 0xC82 && c <= 0xC83) || (c >= 0xC85 && c <= 0xC8C) || (c >= 0xC8E && c <= 0xC90) || (c >= 0xC92 && c <= 0xCA8) || (c >= 0xCAA && c <= 0xCB3) || (c >= 0xCB5 && c <= 0xCB9) || (c >= 0xCBD && c <= 0xCC4) || (c >= 0xCC6 && c <= 0xCC8) || (c >= 0xCCA && c <= 0xCCB) || (c >= 0xCD5 && c <= 0xCD6) || (c == 0xCDE) || (c >= 0xCE0 && c <= 0xCE1) || (c >= 0xCE6 && c <= 0xCEF) || (c >= 0xCF1 && c <= 0xCF2) || (c >= 0xD02 && c <= 0xD03) || (c >= 0xD05 && c <= 0xD0C) || (c >= 0xD0E && c <= 0xD10) || (c >= 0xD12 && c <= 0xD3A) || (c >= 0xD3D && c <= 0xD40) || (c >= 0xD46 && c <= 0xD48) || (c >= 0xD4A && c <= 0xD4C) || (c == 0xD4E) || (c == 0xD57) || (c >= 0xD60 && c <= 0xD61) || (c >= 0xD66 && c <= 0xD75) || (c >= 0xD79 && c <= 0xD7F) || (c >= 0xD82 && c <= 0xD83) || (c >= 0xD85 && c <= 0xD96) || (c >= 0xD9A && c <= 0xDB1) || (c >= 0xDB3 && c <= 0xDBB) || (c == 0xDBD) || (c >= 0xDC0 && c <= 0xDC6) || (c >= 0xDCF && c <= 0xDD1) || (c >= 0xDD8 && c <= 0xDDF) || (c >= 0xDF2 && c <= 0xDF4) || (c >= 0xE01 && c <= 0xE30) || (c >= 0xE32 && c <= 0xE33) || (c >= 0xE40 && c <= 0xE46) || (c >= 0xE4F && c <= 0xE5B) || (c >= 0xE81 && c <= 0xE82) || (c == 0xE84) || (c >= 0xE87 && c <= 0xE88) || (c == 0xE8A) || (c == 0xE8D) || (c >= 0xE94 && c <= 0xE97) || (c >= 0xE99 && c <= 0xE9F) || (c >= 0xEA1 && c <= 0xEA3) || (c == 0xEA5) || (c == 0xEA7) || (c >= 0xEAA && c <= 0xEAB) || (c >= 0xEAD && c <= 0xEB0) || (c >= 0xEB2 && c <= 0xEB3) || (c == 0xEBD) || (c >= 0xEC0 && c <= 0xEC4) || (c == 0xEC6) || (c >= 0xED0 && c <= 0xED9) || (c >= 0xEDC && c <= 0xEDF) || (c >= 0xF00 && c <= 0xF17) || (c >= 0xF1A && c <= 0xF34) || (c == 0xF36) || (c == 0xF38) || (c >= 0xF3E && c <= 0xF47) || (c >= 0xF49 && c <= 0xF6C) || (c == 0xF7F) || (c == 0xF85) || (c >= 0xF88 && c <= 0xF8C) || (c >= 0xFBE && c <= 0xFC5) || (c >= 0xFC7 && c <= 0xFCC) || (c >= 0xFCE && c <= 0xFDA) || (c >= 0x1000 && c <= 0x102C) || (c == 0x1031) || (c == 0x1038) || (c >= 0x103B && c <= 0x103C) || (c >= 0x103F && c <= 0x1057) || (c >= 0x105A && c <= 0x105D) || (c >= 0x1061 && c <= 0x1070) || (c >= 0x1075 && c <= 0x1081) || (c >= 0x1083 && c <= 0x1084) || (c >= 0x1087 && c <= 0x108C) || (c >= 0x108E && c <= 0x109C) || (c >= 0x109E && c <= 0x10C5) || (c == 0x10C7) || (c == 0x10CD) || (c >= 0x10D0 && c <= 0x1248) || (c >= 0x124A && c <= 0x124D) || (c >= 0x1250 && c <= 0x1256) || (c == 0x1258) || (c >= 0x125A && c <= 0x125D) || (c >= 0x1260 && c <= 0x1288) || (c >= 0x128A && c <= 0x128D) || (c >= 0x1290 && c <= 0x12B0) || (c >= 0x12B2 && c <= 0x12B5) || (c >= 0x12B8 && c <= 0x12BE) || (c == 0x12C0) || (c >= 0x12C2 && c <= 0x12C5) || (c >= 0x12C8 && c <= 0x12D6) || (c >= 0x12D8 && c <= 0x1310) || (c >= 0x1312 && c <= 0x1315) || (c >= 0x1318 && c <= 0x135A) || (c >= 0x1360 && c <= 0x137C) || (c >= 0x1380 && c <= 0x138F) || (c >= 0x13A0 && c <= 0x13F4) || (c >= 0x1401 && c <= 0x167F) || (c >= 0x1681 && c <= 0x169A) || (c >= 0x16A0 && c <= 0x16F0) || (c >= 0x1700 && c <= 0x170C) || (c >= 0x170E && c <= 0x1711) || (c >= 0x1720 && c <= 0x1731) || (c >= 0x1735 && c <= 0x1736) || (c >= 0x1740 && c <= 0x1751) || (c >= 0x1760 && c <= 0x176C) || (c >= 0x176E && c <= 0x1770) || (c >= 0x1780 && c <= 0x17B3) || (c == 0x17B6) || (c >= 0x17BE && c <= 0x17C5) || (c >= 0x17C7 && c <= 0x17C8) || (c >= 0x17D4 && c <= 0x17DA) || (c == 0x17DC) || (c >= 0x17E0 && c <= 0x17E9) || (c >= 0x1810 && c <= 0x1819) || (c >= 0x1820 && c <= 0x1877) || (c >= 0x1880 && c <= 0x18A8) || (c == 0x18AA) || (c >= 0x18B0 && c <= 0x18F5) || (c >= 0x1900 && c <= 0x191C) || (c >= 0x1923 && c <= 0x1926) || (c >= 0x1929 && c <= 0x192B) || (c >= 0x1930 && c <= 0x1931) || (c >= 0x1933 && c <= 0x1938) || (c >= 0x1946 && c <= 0x196D) || (c >= 0x1970 && c <= 0x1974) || (c >= 0x1980 && c <= 0x19AB) || (c >= 0x19B0 && c <= 0x19C9) || (c >= 0x19D0 && c <= 0x19DA) || (c >= 0x1A00 && c <= 0x1A16) || (c >= 0x1A19 && c <= 0x1A1B) || (c >= 0x1A1E && c <= 0x1A55) || (c == 0x1A57) || (c == 0x1A61) || (c >= 0x1A63 && c <= 0x1A64) || (c >= 0x1A6D && c <= 0x1A72) || (c >= 0x1A80 && c <= 0x1A89) || (c >= 0x1A90 && c <= 0x1A99) || (c >= 0x1AA0 && c <= 0x1AAD) || (c >= 0x1B04 && c <= 0x1B33) || (c == 0x1B35) || (c == 0x1B3B) || (c >= 0x1B3D && c <= 0x1B41) || (c >= 0x1B43 && c <= 0x1B4B) || (c >= 0x1B50 && c <= 0x1B6A) || (c >= 0x1B74 && c <= 0x1B7C) || (c >= 0x1B82 && c <= 0x1BA1) || (c >= 0x1BA6 && c <= 0x1BA7) || (c == 0x1BAA) || (c >= 0x1BAC && c <= 0x1BE5) || (c == 0x1BE7) || (c >= 0x1BEA && c <= 0x1BEC) || (c == 0x1BEE) || (c >= 0x1BF2 && c <= 0x1BF3) || (c >= 0x1BFC && c <= 0x1C2B) || (c >= 0x1C34 && c <= 0x1C35) || (c >= 0x1C3B && c <= 0x1C49) || (c >= 0x1C4D && c <= 0x1C7F) || (c >= 0x1CC0 && c <= 0x1CC7) || (c == 0x1CD3) || (c == 0x1CE1) || (c >= 0x1CE9 && c <= 0x1CEC) || (c >= 0x1CEE && c <= 0x1CF3) || (c >= 0x1CF5 && c <= 0x1CF6) || (c >= 0x1D00 && c <= 0x1DBF) || (c >= 0x1E00 && c <= 0x1F15) || (c >= 0x1F18 && c <= 0x1F1D) || (c >= 0x1F20 && c <= 0x1F45) || (c >= 0x1F48 && c <= 0x1F4D) || (c >= 0x1F50 && c <= 0x1F57) || (c == 0x1F59) || (c == 0x1F5B) || (c == 0x1F5D) || (c >= 0x1F5F && c <= 0x1F7D) || (c >= 0x1F80 && c <= 0x1FB4) || (c >= 0x1FB6 && c <= 0x1FBC) || (c == 0x1FBE) || (c >= 0x1FC2 && c <= 0x1FC4) || (c >= 0x1FC6 && c <= 0x1FCC) || (c >= 0x1FD0 && c <= 0x1FD3) || (c >= 0x1FD6 && c <= 0x1FDB) || (c >= 0x1FE0 && c <= 0x1FEC) || (c >= 0x1FF2 && c <= 0x1FF4) || (c >= 0x1FF6 && c <= 0x1FFC) || (c == 0x200E) || (c == 0x2071) || (c == 0x207F) || (c >= 0x2090 && c <= 0x209C) || (c == 0x2102) || (c == 0x2107) || (c >= 0x210A && c <= 0x2113) || (c == 0x2115) || (c >= 0x2119 && c <= 0x211D) || (c == 0x2124) || (c == 0x2126) || (c == 0x2128) || (c >= 0x212A && c <= 0x212D) || (c >= 0x212F && c <= 0x2139) || (c >= 0x213C && c <= 0x213F) || (c >= 0x2145 && c <= 0x2149) || (c >= 0x214E && c <= 0x214F) || (c >= 0x2160 && c <= 0x2188) || (c >= 0x2336 && c <= 0x237A) || (c == 0x2395) || (c >= 0x249C && c <= 0x24E9) || (c == 0x26AC) || (c >= 0x2800 && c <= 0x28FF) || (c >= 0x2C00 && c <= 0x2C2E) || (c >= 0x2C30 && c <= 0x2C5E) || (c >= 0x2C60 && c <= 0x2CE4) || (c >= 0x2CEB && c <= 0x2CEE) || (c >= 0x2CF2 && c <= 0x2CF3) || (c >= 0x2D00 && c <= 0x2D25) || (c == 0x2D27) || (c == 0x2D2D) || (c >= 0x2D30 && c <= 0x2D67) || (c >= 0x2D6F && c <= 0x2D70) || (c >= 0x2D80 && c <= 0x2D96) || (c >= 0x2DA0 && c <= 0x2DA6) || (c >= 0x2DA8 && c <= 0x2DAE) || (c >= 0x2DB0 && c <= 0x2DB6) || (c >= 0x2DB8 && c <= 0x2DBE) || (c >= 0x2DC0 && c <= 0x2DC6) || (c >= 0x2DC8 && c <= 0x2DCE) || (c >= 0x2DD0 && c <= 0x2DD6) || (c >= 0x2DD8 && c <= 0x2DDE) || (c >= 0x3005 && c <= 0x3007) || (c >= 0x3021 && c <= 0x3029) || (c >= 0x302E && c <= 0x302F) || (c >= 0x3031 && c <= 0x3035) || (c >= 0x3038 && c <= 0x303C) || (c >= 0x3041 && c <= 0x3096) || (c >= 0x309D && c <= 0x309F) || (c >= 0x30A1 && c <= 0x30FA) || (c >= 0x30FC && c <= 0x30FF) || (c >= 0x3105 && c <= 0x312D) || (c >= 0x3131 && c <= 0x318E) || (c >= 0x3190 && c <= 0x31BA) || (c >= 0x31F0 && c <= 0x321C) || (c >= 0x3220 && c <= 0x324F) || (c >= 0x3260 && c <= 0x327B) || (c >= 0x327F && c <= 0x32B0) || (c >= 0x32C0 && c <= 0x32CB) || (c >= 0x32D0 && c <= 0x32FE) || (c >= 0x3300 && c <= 0x3376) || (c >= 0x337B && c <= 0x33DD) || (c >= 0x33E0 && c <= 0x33FE) || (c == 0x3400) || (c == 0x4DB5) || (c == 0x4E00) || (c == 0x9FCC) || (c >= 0xA000 && c <= 0xA48C) || (c >= 0xA4D0 && c <= 0xA60C) || (c >= 0xA610 && c <= 0xA62B) || (c >= 0xA640 && c <= 0xA66E) || (c >= 0xA680 && c <= 0xA697) || (c >= 0xA6A0 && c <= 0xA6EF) || (c >= 0xA6F2 && c <= 0xA6F7) || (c >= 0xA722 && c <= 0xA787) || (c >= 0xA789 && c <= 0xA78E) || (c >= 0xA790 && c <= 0xA793) || (c >= 0xA7A0 && c <= 0xA7AA) || (c >= 0xA7F8 && c <= 0xA801) || (c >= 0xA803 && c <= 0xA805) || (c >= 0xA807 && c <= 0xA80A) || (c >= 0xA80C && c <= 0xA824) || (c == 0xA827) || (c >= 0xA830 && c <= 0xA837) || (c >= 0xA840 && c <= 0xA873) || (c >= 0xA880 && c <= 0xA8C3) || (c >= 0xA8CE && c <= 0xA8D9) || (c >= 0xA8F2 && c <= 0xA8FB) || (c >= 0xA900 && c <= 0xA925) || (c >= 0xA92E && c <= 0xA946) || (c >= 0xA952 && c <= 0xA953) || (c >= 0xA95F && c <= 0xA97C) || (c >= 0xA983 && c <= 0xA9B2) || (c >= 0xA9B4 && c <= 0xA9B5) || (c >= 0xA9BA && c <= 0xA9BB) || (c >= 0xA9BD && c <= 0xA9CD) || (c >= 0xA9CF && c <= 0xA9D9) || (c >= 0xA9DE && c <= 0xA9DF) || (c >= 0xAA00 && c <= 0xAA28) || (c >= 0xAA2F && c <= 0xAA30) || (c >= 0xAA33 && c <= 0xAA34) || (c >= 0xAA40 && c <= 0xAA42) || (c >= 0xAA44 && c <= 0xAA4B) || (c == 0xAA4D) || (c >= 0xAA50 && c <= 0xAA59) || (c >= 0xAA5C && c <= 0xAA7B) || (c >= 0xAA80 && c <= 0xAAAF) || (c == 0xAAB1) || (c >= 0xAAB5 && c <= 0xAAB6) || (c >= 0xAAB9 && c <= 0xAABD) || (c == 0xAAC0) || (c == 0xAAC2) || (c >= 0xAADB && c <= 0xAAEB) || (c >= 0xAAEE && c <= 0xAAF5) || (c >= 0xAB01 && c <= 0xAB06) || (c >= 0xAB09 && c <= 0xAB0E) || (c >= 0xAB11 && c <= 0xAB16) || (c >= 0xAB20 && c <= 0xAB26) || (c >= 0xAB28 && c <= 0xAB2E) || (c >= 0xABC0 && c <= 0xABE4) || (c >= 0xABE6 && c <= 0xABE7) || (c >= 0xABE9 && c <= 0xABEC) || (c >= 0xABF0 && c <= 0xABF9) || (c == 0xAC00) || (c == 0xD7A3) || (c >= 0xD7B0 && c <= 0xD7C6) || (c >= 0xD7CB && c <= 0xD7FB) || (c == 0xD800) || (c >= 0xDB7F && c <= 0xDB80) || (c >= 0xDBFF && c <= 0xDC00) || (c >= 0xDFFF && c <= 0xE000) || (c >= 0xF8FF && c <= 0xFA6D) || (c >= 0xFA70 && c <= 0xFAD9) || (c >= 0xFB00 && c <= 0xFB06) || (c >= 0xFB13 && c <= 0xFB17) || (c >= 0xFF21 && c <= 0xFF3A) || (c >= 0xFF41 && c <= 0xFF5A) || (c >= 0xFF66 && c <= 0xFFBE) || (c >= 0xFFC2 && c <= 0xFFC7) || (c >= 0xFFCA && c <= 0xFFCF) || (c >= 0xFFD2 && c <= 0xFFD7) || (c >= 0xFFDA && c <= 0xFFDC) || (c >= 0x10000 && c <= 0x1000B) || (c >= 0x1000D && c <= 0x10026) || (c >= 0x10028 && c <= 0x1003A) || (c >= 0x1003C && c <= 0x1003D) || (c >= 0x1003F && c <= 0x1004D) || (c >= 0x10050 && c <= 0x1005D) || (c >= 0x10080 && c <= 0x100FA) || (c == 0x10100) || (c == 0x10102) || (c >= 0x10107 && c <= 0x10133) || (c >= 0x10137 && c <= 0x1013F) || (c >= 0x101D0 && c <= 0x101FC) || (c >= 0x10280 && c <= 0x1029C) || (c >= 0x102A0 && c <= 0x102D0) || (c >= 0x10300 && c <= 0x1031E) || (c >= 0x10320 && c <= 0x10323) || (c >= 0x10330 && c <= 0x1034A) || (c >= 0x10380 && c <= 0x1039D) || (c >= 0x1039F && c <= 0x103C3) || (c >= 0x103C8 && c <= 0x103D5) || (c >= 0x10400 && c <= 0x1049D) || (c >= 0x104A0 && c <= 0x104A9) || (c == 0x11000) || (c >= 0x11002 && c <= 0x11037) || (c >= 0x11047 && c <= 0x1104D) || (c >= 0x11066 && c <= 0x1106F) || (c >= 0x11082 && c <= 0x110B2) || (c >= 0x110B7 && c <= 0x110B8) || (c >= 0x110BB && c <= 0x110C1) || (c >= 0x110D0 && c <= 0x110E8) || (c >= 0x110F0 && c <= 0x110F9) || (c >= 0x11103 && c <= 0x11126) || (c == 0x1112C) || (c >= 0x11136 && c <= 0x11143) || (c >= 0x11182 && c <= 0x111B5) || (c >= 0x111BF && c <= 0x111C8) || (c >= 0x111D0 && c <= 0x111D9) || (c >= 0x11680 && c <= 0x116AA) || (c == 0x116AC) || (c >= 0x116AE && c <= 0x116AF) || (c == 0x116B6) || (c >= 0x116C0 && c <= 0x116C9) || (c >= 0x12000 && c <= 0x1236E) || (c >= 0x12400 && c <= 0x12462) || (c >= 0x12470 && c <= 0x12473) || (c >= 0x13000 && c <= 0x1342E) || (c >= 0x16800 && c <= 0x16A38) || (c >= 0x16F00 && c <= 0x16F44) || (c >= 0x16F50 && c <= 0x16F7E) || (c >= 0x16F93 && c <= 0x16F9F) || (c >= 0x1B000 && c <= 0x1B001) || (c >= 0x1D000 && c <= 0x1D0F5) || (c >= 0x1D100 && c <= 0x1D126) || (c >= 0x1D129 && c <= 0x1D166) || (c >= 0x1D16A && c <= 0x1D172) || (c >= 0x1D183 && c <= 0x1D184) || (c >= 0x1D18C && c <= 0x1D1A9) || (c >= 0x1D1AE && c <= 0x1D1DD) || (c >= 0x1D360 && c <= 0x1D371) || (c >= 0x1D400 && c <= 0x1D454) || (c >= 0x1D456 && c <= 0x1D49C) || (c >= 0x1D49E && c <= 0x1D49F) || (c == 0x1D4A2) || (c >= 0x1D4A5 && c <= 0x1D4A6) || (c >= 0x1D4A9 && c <= 0x1D4AC) || (c >= 0x1D4AE && c <= 0x1D4B9) || (c == 0x1D4BB) || (c >= 0x1D4BD && c <= 0x1D4C3) || (c >= 0x1D4C5 && c <= 0x1D505) || (c >= 0x1D507 && c <= 0x1D50A) || (c >= 0x1D50D && c <= 0x1D514) || (c >= 0x1D516 && c <= 0x1D51C) || (c >= 0x1D51E && c <= 0x1D539) || (c >= 0x1D53B && c <= 0x1D53E) || (c >= 0x1D540 && c <= 0x1D544) || (c == 0x1D546) || (c >= 0x1D54A && c <= 0x1D550) || (c >= 0x1D552 && c <= 0x1D6A5) || (c >= 0x1D6A8 && c <= 0x1D6DA) || (c >= 0x1D6DC && c <= 0x1D714) || (c >= 0x1D716 && c <= 0x1D74E) || (c >= 0x1D750 && c <= 0x1D788) || (c >= 0x1D78A && c <= 0x1D7C2) || (c >= 0x1D7C4 && c <= 0x1D7CB) || (c >= 0x1F110 && c <= 0x1F12E) || (c >= 0x1F130 && c <= 0x1F169) || (c >= 0x1F170 && c <= 0x1F19A) || (c >= 0x1F1E6 && c <= 0x1F202) || (c >= 0x1F210 && c <= 0x1F23A) || (c >= 0x1F240 && c <= 0x1F248) || (c >= 0x1F250 && c <= 0x1F251) || (c == 0x20000) || (c == 0x2A6D6) || (c == 0x2A700) || (c == 0x2B734) || (c == 0x2B740) || (c == 0x2B81D) || (c >= 0x2F800 && c <= 0x2FA1D) || (c == 0xF0000) || (c == 0xFFFFD) || (c == 0x100000) || (c == 0x10FFFD);
}
-(int)getBaseDirection {
// Decode string into UTF32.
NSData *utf32data = [self dataUsingEncoding:NSUTF32StringEncoding];
// NSUTF32StringEncoding has the platform's byte-order, which should
// be the same as UTF32Char's.
UTF32Char *utf32chars = (UTF32Char *)[utf32data bytes];
for (NSUInteger i = 0; i < self.length; i++) {
// UTF32 is a fixed-length encoding, so utf32chars[i] will
// always give us the i'th character.
if (isCodePointStrongRTL(utf32chars[i]))
return -1;
if (isCodePointStrongLTR(utf32chars[i]))
return 1;
}
return 0;
}
@end
isCodePointStrong{RTL,LTR}Create a script hex_numbers_to_dec_ranges_py,
import sys
from itertools import groupby, count
numberlist = []
for line in sys.stdin:
numberlist.append(int(line, 16));
def as_range(iterable): # not sure how to do this part elegantly
l = list(iterable)
if len(l) > 1:
return '(c >= 0x{0:X} && c <= 0x{1:X})'.format(l[0], l[-1])
else:
return '(c == 0x{0:X})'.format(l[0])
print ' || '.join(as_range(g) for _, g in groupby(numberlist, lambda n, c=count(): n-next(c)))
(code shamelessly stolen from this excellent answer at StackExhange's Code Review).
Run from a terminal:
curl http://www.unicode.org/Public/UNIDATA/UnicodeData.txt > /tmp/UnicodeData.txt
cat /tmp/UnicodeData.txt | awk -F';' '$5 == "R" || $5 == "AL"' | cut -d';' -f1 | python hex_numbers_to_dec_ranges.py > rtl.m
cat /tmp/UnicodeData.txt | awk -F';' '$5 == "L"' | cut -d';' -f1 | python hex_numbers_to_dec_ranges.py > ltr.m
rm /tmp/UnicodeData.txt
EDIT: As @masmor correctly noted, the for loop in getBaseDirection scans characters, and not bytes. Therefore, it should terminate after "character" number of iterations, and not "bytes" number of iterations. In other words, self.length times and not utf32data.length times. The code is now corrected.
unichar represents a UTF-16 character, while the data I parsed describes Unicode code points (whose range requires 32 bits per code point). So my code might get the wrong result for strings with Unicode surrogates (characters which require more than unichar to represent). The code should be modified to take surrogates into account; I might get to it during the weekend. –
Hectometer I think the scan loop in -getBaseDirection should be for self.length times instead of utf32data.length in the accepted answer.
utf32data.length is the size in bytes while sizeof(UTF32Char) == 4, which would result in an overrun.
In action, the current code sporadically returns false positives for identical input, depending on what it overruns onto (maybe it'll segfault on a sufficiently bad day). Everything else seems to be working perfectly with the fix.
In HTML5 this can be done by applying dir="auto" to the element. It's implemented in WebKit, though I'm not completely sure that it's available in iOS.
dir="auto" is very simple, and you can probably implement it yourself - just search for the first character that has strong directionality, and apply its directionality to the whole thing.
If you can't find anything in iOS, you can try to take some smarter ideas from the way StatusNet implemented it: http://status.net/sites/default/files/issues/1346_jquery.directionDetector.js
There is a solution that is based on the language detection of the string.
Method returns NSTextAlignmentNatural if direction can not be identified.
@implementation NSString (StringAlignmentDetection)
- (NSTextAlignment)naturalTextAligment
{
NSArray *tagschemes = [NSArray arrayWithObjects:NSLinguisticTagSchemeLanguage, nil];
NSLinguisticTagger *tagger = [[NSLinguisticTagger alloc] initWithTagSchemes:tagschemes options:0];
[tagger setString:self];
NSString *language = [tagger tagAtIndex:0 scheme:NSLinguisticTagSchemeLanguage tokenRange:NULL sentenceRange:NULL];
NSTextAlignment alignment = NSTextAlignmentNatural;
if(!language)
{
return alignment;
}
NSLocaleLanguageDirection direction = [NSLocale characterDirectionForLanguage: language];
switch (direction)
{
case NSLocaleLanguageDirectionLeftToRight:
alignment = NSTextAlignmentLeft;
break;
case NSLocaleLanguageDirectionRightToLeft:
alignment = NSTextAlignmentRight;
break;
default:
alignment = NSTextAlignmentNatural;
break;
}
return alignment;
}
@end
The ICU Project offers methods for what you are trying to achieve and on Xcode 11 it is possible to link the ICU library into an iOS application or iOS framework target. To do so, open your target and on the "General" tab under "Frameworks and Libraries" add libicucore.tbd.
It might happen that Xcode chooses the macOS variant of the library if you do that in which case you'll see something like this in your project file.
ABCDEFGHIJKLMNOPQRSTUVWX /* libicucore.tbd */ = {isa = PBXFileReference; lastKnownFileType = "sourcecode.text-based-dylib-definition"; name = libicucore.tbd; path = Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.15.sdk/usr/lib/libicucore.tbd; sourceTree = DEVELOPER_DIR; };
To force the iOS variant, simply edit the project file with a text editor to make the line look something like this
ABCDEFGHIJKLMNOPQRSTUVWX /* libicucore.tbd */ = {isa = PBXFileReference; lastKnownFileType = "sourcecode.text-based-dylib-definition"; name = libicucore.tbd; path = usr/lib/libicucore.tbd; sourceTree = SDKROOT; };
Unfortunately, the version of the library that ships with iOS is a bit older and doesn't include ubidi_getBaseDirection. There is, however, a method u_charDirection that you can use to rebuilt ubidi_getBaseDirection. Simply walk the characters in the string and return the direction of the first character with strong directionality. Below is an example of how to do this in Swift (Objective-C port should be straightforward).
enum Direction {
case leftToRight
case rightToLeft
case neutral
}
func ubidi_getBaseDirection(of string: String) -> Direction {
guard let data = string.data(using: .utf32) else {
return .leftToRight
}
let chars = data.withUnsafeBytes { $0.bindMemory(to: UChar32.self) }
for c in chars {
let direction = u_charDirection(c)
if direction == U_RIGHT_TO_LEFT || direction == U_RIGHT_TO_LEFT_ARABIC {
return .rightToLeft
} else if direction == U_LEFT_TO_RIGHT {
return .leftToRight
}
}
return .neutral
}
Note that since libicucore is a pure C library, you'll need to add it to your bridging header / umbrella header if you're working in Swift. I've found the following to be enough.
#include "unicode/utypes.h"
You can use NLLanguageRecognizer available since since iOS 12:
import NaturalLanguage
extension String {
var isRightToLeft: Bool {
guard let language = NLLanguageRecognizer.dominantLanguage(for: self) else {
return false
}
switch language {
case .arabic, .hebrew, .persian, .urdu:
return true
default:
return false
}
}
}
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return ... (c >= 0x10800 && c <= 0x10805).... This is becauseunicharisunsigned shortwhich has a maximum value of 0xFFFF and these constants are larger than that. Where do these constants come from? Maybe I should create a new question? – Wits