android:pathPattern for single file

Question

I need to define IntentFilter for single file named myfile.ext. At the moment my manifest looks like:

Answer 1

Android Pattern specifics :

• . matches any character.
• * matches 0 or more occurrences of the character preceding it.
• .* matches 0 or more occurrences of any character.
• \ is used to escape special characters in pattern. \ is also used as an escape character when the string is read from the XML file. Hence to escape special character in a pattern, double-slash \\ has to be used.

Issue: In this pattern ".*\\myfile\\.ext", you are trying to escape character m which is a normal character. Hence it does not make any difference. It is equivalent to ".*myfile\\.ext". The data uri part of intent is file:///mnt/sdcard/tmp/myfile.ext. The pattern is matched against /mnt/sdcard/tmp/myfile.ext, but it fails.

.* tries to match any character until the first occurrence of m, which happens to be the 2nd char i.e. /mnt. Pattern expects the next char to be y, but it gets n and hence the pattern match fails.

Solution: For above path, the pattern /.*/.*/.*/myfile\\.ext works.

For /mnt/sdcard/myfile.ext path, pattern /.*/.*/myfile\\.ext works. If you are not sure the sub-directory level, you will have to add multiple <data> element with different pathPattern values.

<data
    android:scheme="file"
    android:mimeType="*/*"
    android:host="*" />

<data android:pathPattern="/.*/.*/.*/myfile\\.ext" /> <!-- matches file:///mnt/sdcard/tmp/myfile.ext -->

<data android:pathPattern="/.*/.*/myfile\\.ext" /> <!-- matches file:///mnt/sdcard/myfile.ext -->

Here is the PatternMatcher.matchPattern method used for pattern matching:

   static boolean matchPattern(String pattern, String match, int type) {
        if (match == null) return false;
        if (type == PATTERN_LITERAL) {
            return pattern.equals(match);
        } if (type == PATTERN_PREFIX) {
            return match.startsWith(pattern);
        } else if (type != PATTERN_SIMPLE_GLOB) {
            return false;
        }

        final int NP = pattern.length();
        if (NP <= 0) {
            return match.length() <= 0;
        }
        final int NM = match.length();
        int ip = 0, im = 0;
        char nextChar = pattern.charAt(0);
        while ((ip<NP) && (im<NM)) {
            char c = nextChar;
            ip++;
            nextChar = ip < NP ? pattern.charAt(ip) : 0;
            final boolean escaped = (c == '\\');
            if (escaped) {
                c = nextChar;
                ip++;
                nextChar = ip < NP ? pattern.charAt(ip) : 0;
            }
            if (nextChar == '*') {
                if (!escaped && c == '.') {
                    if (ip >= (NP-1)) {
                        // at the end with a pattern match, so
                        // all is good without checking!
                        return true;
                   }
                    ip++;
                    nextChar = pattern.charAt(ip);
                    // Consume everything until the next character in the
                    // pattern is found.
                    if (nextChar == '\\') {
                        ip++;
                        nextChar = ip < NP ? pattern.charAt(ip) : 0;
                    }
                    do {
                        if (match.charAt(im) == nextChar) {
                            break;
                        }
                        im++;
                    } while (im < NM);
                    if (im == NM) {
                        // Whoops, the next character in the pattern didn't
                        // exist in the match.
                        return false;
                    }
                    ip++;
                    nextChar = ip < NP ? pattern.charAt(ip) : 0;
                    im++;
                } else {
                    // Consume only characters matching the one before '*'.
                    do {
                        if (match.charAt(im) != c) {
                            break;
                        }
                        im++;
                    } while (im < NM);
                    ip++;
                    nextChar = ip < NP ? pattern.charAt(ip) : 0;
                }
            } else {
                if (c != '.' && match.charAt(im) != c) return false;
                im++;
            }
        }

        if (ip >= NP && im >= NM) {
            // Reached the end of both strings, all is good!
            return true;
        }

        // One last check: we may have finished the match string, but still
        // have a '.*' at the end of the pattern, which should still count
        // as a match.
        if (ip == NP-2 && pattern.charAt(ip) == '.'
            && pattern.charAt(ip+1) == '*') {
            return true;
        }

        return false;
    }