public
class
AlphabetIndexer
extends DataSetObserver
implements
SectionIndexer
| java.lang.Object | ||
| ↳ | android.database.DataSetObserver | |
| ↳ | android.widget.AlphabetIndexer | |
A helper class for adapters that implement the SectionIndexer interface. If the items in the adapter are sorted by simple alphabet-based sorting, then this class provides a way to do fast indexing of large lists using binary search. It caches the indices that have been determined through the binary search and also invalidates the cache if changes occur in the cursor.
Your adapter is responsible for updating the cursor by calling
Developers
setCursor(Cursor) if the
cursor changes. getPositionForSection(int) method does the binary search for the starting
index of a given section (alphabet).
Fields | |
|---|---|
protected
CharSequence |
mAlphabet
The string of characters that make up the indexing sections. |
protected
int |
mColumnIndex
The index of the cursor column that this list is sorted on. |
protected
Cursor |
mDataCursor
Cursor that is used by the adapter of the list view. |
Public constructors | |
|---|---|
AlphabetIndexer(Cursor cursor, int sortedColumnIndex, CharSequence alphabet)
Constructs the indexer. |
|
Public methods | |
|---|---|
int
|
getPositionForSection(int sectionIndex)
Performs a binary search or cache lookup to find the first row that matches a given section's starting letter. |
int
|
getSectionForPosition(int position)
Returns the section index for a given position in the list by querying the item and comparing it with all items in the section array. |
Object[]
|
getSections()
Returns the section array constructed from the alphabet provided in the constructor. |
void
|
onChanged()
This method is called when the entire data set has changed,
most likely through a call to |
void
|
onInvalidated()
This method is called when the entire data becomes invalid,
most likely through a call to |
void
|
setCursor(Cursor cursor)
Sets a new cursor as the data set and resets the cache of indices. |
Protected methods | |
|---|---|
int
|
compare(String word, String letter)
Default implementation compares the first character of word with letter. |
Inherited methods | |
|---|---|
 From
class
android.database.DataSetObserver
| |
From
class
java.lang.Object
| |
From
interface
android.widget.SectionIndexer
| |
CharSequence mAlphabet
The string of characters that make up the indexing sections.
int mColumnIndex
The index of the cursor column that this list is sorted on.
Cursor mDataCursor
Cursor that is used by the adapter of the list view.
AlphabetIndexer (Cursor cursor, int sortedColumnIndex, CharSequence alphabet)
Constructs the indexer.
| Parameters | |
|---|---|
cursor |
Cursor:
the cursor containing the data set |
sortedColumnIndex |
int:
the column number in the cursor that is sorted
alphabetically |
alphabet |
CharSequence:
string containing the alphabet, with space as the first character.
For example, use the string " ABCDEFGHIJKLMNOPQRSTUVWXYZ" for English indexing.
The characters must be uppercase and be sorted in ascii/unicode order. Basically
characters in the alphabet will show up as preview letters.
|
int getPositionForSection (int sectionIndex)
Performs a binary search or cache lookup to find the first row that matches a given section's starting letter.
| Parameters | |
|---|---|
sectionIndex |
int:
the section to search for |
| Returns | |
|---|---|
int |
the row index of the first occurrence, or the nearest next letter. For instance, if searching for "T" and no "T" is found, then the first row starting with "U" or any higher letter is returned. If there is no data following "T" at all, then the list size is returned. |
int getSectionForPosition (int position)
Returns the section index for a given position in the list by querying the item and comparing it with all items in the section array.
| Parameters | |
|---|---|
position |
int:
the position within the adapter for which to return the
corresponding section index |
| Returns | |
|---|---|
int |
the index of the corresponding section within the array of section objects, constrained to fall within the array bounds |
Object[] getSections ()
Returns the section array constructed from the alphabet provided in the constructor.
| Returns | |
|---|---|
Object[] |
the section array |
void onChanged ()
This method is called when the entire data set has changed,
most likely through a call to requery() on a Cursor.
void onInvalidated ()
This method is called when the entire data becomes invalid,
most likely through a call to deactivate() or close() on a
Cursor.
void setCursor (Cursor cursor)
Sets a new cursor as the data set and resets the cache of indices.
| Parameters | |
|---|---|
cursor |
Cursor:
the new cursor to use as the data set
|
int compare (String word, String letter)
Default implementation compares the first character of word with letter.
| Parameters | |
|---|---|
word |
String
|
letter |
String
|
| Returns | |
|---|---|
int |
|