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ICU 77.1: icu::AlphabeticIndex Class Reference

AlphabeticIndex supports the creation of a UI index appropriate for a given language. More...

AlphabeticIndex supports the creation of a UI index appropriate for a given language.

It can support either direct use, or use with a client that doesn't support localized collation. The following is an example of what an index might look like in a UI:

 ... A B C D E F G H I J K L M N O P Q R S T U V W X Y Z  ...

 A
    Addison
    Albertson
    Azensky
 B
    Baker
 ...

The class can generate a list of labels for use as a UI "index", that is, a list of clickable characters (or character sequences) that allow the user to see a segment (bucket) of a larger "target" list. That is, each label corresponds to a bucket in the target list, where everything in the bucket is greater than or equal to the character (according to the locale's collation). Strings can be added to the index; they will be in sorted order in the right bucket.

The class also supports having buckets for strings before the first (underflow), after the last (overflow), and between scripts (inflow). For example, if the index is constructed with labels for Russian and English, Greek characters would fall into an inflow bucket between the other two scripts.

The AlphabeticIndex class is not intended for public subclassing.

Note: If you expect to have a lot of ASCII or Latin characters as well as characters from the user's language, then it is a good idea to call addLabels(Locale::getEnglish(), status).

The following shows an example of building an index directly. The "show..." methods below are just to illustrate usage.

// Create a simple index.  "Item" is assumed to be an application
// defined type that the application's UI and other processing knows about,
//  and that has a name.

UErrorCode status = U_ZERO_ERROR;
AlphabeticIndex index = new AlphabeticIndex(desiredLocale, status);
index->addLabels(additionalLocale, status);
for (Item *item in some source of Items ) {
    index->addRecord(item->name(), item, status);
}
...
// Show index at top. We could skip or gray out empty buckets

while (index->nextBucket(status)) {
    if (showAll || index->getBucketRecordCount() != 0) {
        showLabelAtTop(UI, index->getBucketLabel());
    }
}
 ...
// Show the buckets with their contents, skipping empty buckets

index->resetBucketIterator(status);
while (index->nextBucket(status)) {
   if (index->getBucketRecordCount() != 0) {
       showLabelInList(UI, index->getBucketLabel());
       while (index->nextRecord(status)) {
           showIndexedItem(UI, static_cast<Item *>(index->getRecordData()))

The caller can build different UIs using this class. For example, an index character could be omitted or grayed-out if its bucket is empty. Small buckets could also be combined based on size, such as:

... A-F G-N O-Z ...

Callers can also use the AlphabeticIndex::ImmutableIndex, or the AlphabeticIndex itself, to support sorting on a client that doesn't support AlphabeticIndex functionality.

The ImmutableIndex is both immutable and thread-safe. The corresponding AlphabeticIndex methods are not thread-safe because they "lazily" build the index buckets.

• ImmutableIndex.getBucket(index) provides random access to all buckets and their labels and label types.
• The AlphabeticIndex bucket iterator or ImmutableIndex.getBucket(0..getBucketCount-1) can be used to get a list of the labels, such as "...", "A", "B",..., and send that list to the client.

• When the client has a new name, it sends that name to the server. The server needs to call the following methods, and communicate the bucketIndex and collationKey back to the client.

  int32_t bucketIndex = index.getBucketIndex(name, status);
  const UnicodeString &label = immutableIndex.getBucket(bucketIndex)->getLabel();  // optional
  int32_t skLength = collator.getSortKey(name, sk, skCapacity);
  

• The client would put the name (and associated information) into its bucket for bucketIndex. The sort key sk is a sequence of bytes that can be compared with a binary compare, and produce the right localized result.

Stable:

ICU 4.8

Definition at line 192 of file alphaindex.h.

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