android.content.UriMatcher

文档已经讲得好明白了：http://developer.android.com/reference/android/content/UriMatcher.html

Utility class to aid in matching URIs in content providers.

To use this class, build up a tree of UriMatcher objects. For example:

    private static final int PEOPLE = 1;
    private static final int PEOPLE_ID = 2;
    private static final int PEOPLE_PHONES = 3;
    private static final int PEOPLE_PHONES_ID = 4;
    private static final int PEOPLE_CONTACTMETHODS = 7;
    private static final int PEOPLE_CONTACTMETHODS_ID = 8;

    private static final int DELETED_PEOPLE = 20;

    private static final int PHONES = 9;
    private static final int PHONES_ID = 10;
    private static final int PHONES_FILTER = 14;

    private static final int CONTACTMETHODS = 18;
    private static final int CONTACTMETHODS_ID = 19;

    private static final int CALLS = 11;
    private static final int CALLS_ID = 12;
    private static final int CALLS_FILTER = 15;

    private static final UriMatcher sURIMatcher = new UriMatcher(UriMatcher.NO_MATCH);

    static
    {
        sURIMatcher.addURI("contacts", "people", PEOPLE);
        sURIMatcher.addURI("contacts", "people/#", PEOPLE_ID);
        sURIMatcher.addURI("contacts", "people/#/phones", PEOPLE_PHONES);
        sURIMatcher.addURI("contacts", "people/#/phones/#", PEOPLE_PHONES_ID);
        sURIMatcher.addURI("contacts", "people/#/contact_methods", PEOPLE_CONTACTMETHODS);
        sURIMatcher.addURI("contacts", "people/#/contact_methods/#", PEOPLE_CONTACTMETHODS_ID);
        sURIMatcher.addURI("contacts", "deleted_people", DELETED_PEOPLE);
        sURIMatcher.addURI("contacts", "phones", PHONES);
        sURIMatcher.addURI("contacts", "phones/filter/*", PHONES_FILTER);
        sURIMatcher.addURI("contacts", "phones/#", PHONES_ID);
        sURIMatcher.addURI("contacts", "contact_methods", CONTACTMETHODS);
        sURIMatcher.addURI("contacts", "contact_methods/#", CONTACTMETHODS_ID);
        sURIMatcher.addURI("call_log", "calls", CALLS);
        sURIMatcher.addURI("call_log", "calls/filter/*", CALLS_FILTER);
        sURIMatcher.addURI("call_log", "calls/#", CALLS_ID);
    }

Then when you need to match against a URI, call match(Uri), providing the URL that you have been given. You can use the result to build a query, return a type, insert or delete a row, or whatever you need, without duplicating all of the if-else logic that you would otherwise need. For example:

    public String getType(Uri url)
    {
        int match = sURIMatcher.match(url);
        switch (match)
        {
            case PEOPLE:
                return "vnd.android.cursor.dir/person";
            case PEOPLE_ID:
                return "vnd.android.cursor.item/person";
... snip ...
                return "vnd.android.cursor.dir/snail-mail";
            case PEOPLE_ADDRESS_ID:
                return "vnd.android.cursor.item/snail-mail";
            default:
                return null;
        }
    }

instead of:

    public String getType(Uri url)
    {
        List pathSegments = url.getPathSegments();
        if (pathSegments.size() >= 2) {
            if ("people".equals(pathSegments.get(1))) {
                if (pathSegments.size() == 2) {
                    return "vnd.android.cursor.dir/person";
                } else if (pathSegments.size() == 3) {
                    return "vnd.android.cursor.item/person";
... snip ...
                    return "vnd.android.cursor.dir/snail-mail";
                } else if (pathSegments.size() == 3) {
                    return "vnd.android.cursor.item/snail-mail";
                }
            }
        }
        return null;
    }