ContentProvider

public void startManagingCursor (Cursor c)的作用

我们将获得的Cursor对象交与Activity 来管理，这样Cursor对象的生命周期便能与当前的Activity自动同步，省去了自己管理Cursor。

 

public class NotesProvider extends ContentProvider {

 public static final String AUTHORITY = "com.example.android.honeypad.notesprovider";

 private static final String NOTE_MIME_TYPE = "vnd.android.cursor.item/vnd.honeypad.note";
 public static final Uri CONTENT_URI = Uri.parse("content://" + AUTHORITY
   + "/notes");

 // The underlying database
 private SQLiteDatabase notesDB;

 // Create the constants used to differentiate between the different URI
 // requests.
 private static final int ALL_NOTES = 1;
 private static final int NOTE_ID = 2;

 private static final UriMatcher uriMatcher;

 // Allocate the UriMatcher object, where a URI ending in 'notes' will
 // correspond to a request for all notes, and 'notes' with a trailing
 // '/[rowID]' will represent a single note row.
 static {
  uriMatcher = new UriMatcher(UriMatcher.NO_MATCH);
  uriMatcher.addURI(AUTHORITY, "notes", ALL_NOTES);
  uriMatcher.addURI(AUTHORITY, "notes/#", NOTE_ID);
 }

 @Override
 public boolean onCreate() {
  NotesDatabaseHelper helper = new NotesDatabaseHelper(getContext());
  notesDB = helper.getWritableDatabase();
  return notesDB != null;
 }

 @Override
 public Cursor query(Uri uri, String[] projection, String selection,
   String[] selectionArgs, String sort) {
  SQLiteQueryBuilder qb = new SQLiteQueryBuilder();
  qb.setTables(DATABASE_TABLE);

  // If this is a row query, limit the result set to the passed in row.
  switch (uriMatcher.match(uri)) {
  case NOTE_ID:
   qb.appendWhere(KEY_ID + "=" + uri.getPathSegments().get(1));
   break;
  default:
   break;
  }

  // Apply the query to the underlying database.
  Cursor c = qb.query(notesDB, projection, selection, selectionArgs,
    null, null, sort);

  // Register the contexts ContentResolver to be notified if
  // the cursor result set changes.
  c.setNotificationUri(getContext().getContentResolver(), uri);

  // Return a cursor to the query result.
  return c;
 }

 @Override
 public Uri insert(Uri uri, ContentValues initialValues) {
  // Insert the new row, will return the row number if
  // successful.
  long rowID = notesDB.insert(DATABASE_TABLE, "note", initialValues);

  // Return a URI to the newly inserted row on success.
  if (rowID > 0) {
   Uri newUri = ContentUris.withAppendedId(CONTENT_URI, rowID);
   getContext().getContentResolver().notifyChange(newUri, null);
   return newUri;
  }
  throw new SQLException("Failed to insert row into " + uri);
 }

 @Override
 public int delete(Uri uri, String where, String[] whereArgs) {
  int count;

  switch (uriMatcher.match(uri)) {
  case ALL_NOTES:
   count = notesDB.delete(DATABASE_TABLE, where, whereArgs);
   break;

  case NOTE_ID:
   String segment = uri.getPathSegments().get(1);
   StringBuilder whereClause = new StringBuilder(KEY_ID).append("=")
     .append(segment);
   if (!TextUtils.isEmpty(where)) {
    whereClause.append(" AND (").append(where).append(")");
   }

   count = notesDB.delete(DATABASE_TABLE, whereClause.toString(),
     whereArgs);
   break;

  default:
   throw new IllegalArgumentException("Unsupported URI: " + uri);
  }

  getContext().getContentResolver().notifyChange(uri, null);
  return count;
 }

 @Override
 public int update(Uri uri, ContentValues values, String where,
   String[] whereArgs) {
  int count;
  switch (uriMatcher.match(uri)) {
  case ALL_NOTES:
   count = notesDB.update(DATABASE_TABLE, values, where, whereArgs);
   break;

  case NOTE_ID:
   String segment = uri.getPathSegments().get(1);
   StringBuilder whereClause = new StringBuilder(KEY_ID).append("=")
     .append(segment);
   if (!TextUtils.isEmpty(where)) {
    whereClause.append(" AND (").append(where).append(")");
   }
   count = notesDB.update(DATABASE_TABLE, values,
     whereClause.toString(), whereArgs);
   break;

  default:
   throw new IllegalArgumentException("Unknown URI " + uri);
  }

  getContext().getContentResolver().notifyChange(uri, null);
  return count;
 }

 @Override
 public String getType(Uri uri) {
  switch (uriMatcher.match(uri)) {
  case ALL_NOTES:
   return "vnd.android.cursor.dir/vnd.honeypad.notes";
  case NOTE_ID:
   return NOTE_MIME_TYPE;
  default:
   throw new IllegalArgumentException("Unsupported URI: " + uri);
  }
 }

 // column names
 public static final String KEY_ID = "_id";
 public static final String KEY_TITLE = "title";
 public static final String KEY_BODY = "body";
 
 // column indexes
 public static final int ID_COLUMN = 0;
 public static final int TITLE_COLUMN = 1;
 public static final int BODY_COLUMN = 2;
 
 private static final String TAG = "NotesDbAdapter";

 private static final String DATABASE_NAME = "honeypad.db";
 private static final String DATABASE_TABLE = "notes";
 private static final int DATABASE_VERSION = 1;

 /**
  * Database creation sql statement
  */
 private static final String DATABASE_CREATE = String.format("create table %s (%s integer primary key autoincrement, %s text not null, %s text not null);",
   DATABASE_TABLE, KEY_ID, KEY_TITLE, KEY_BODY);

 private static class NotesDatabaseHelper extends SQLiteOpenHelper {

  NotesDatabaseHelper(Context context) {
   super(context, DATABASE_NAME, null, DATABASE_VERSION);
  }

  @Override
  public void onCreate(SQLiteDatabase db) {

   db.execSQL(DATABASE_CREATE);
  }

  @Override
  public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
   Log.w(TAG, "Upgrading database from version " + oldVersion + " to "
     + newVersion + ", which will destroy all old data");
   db.execSQL("DROP TABLE IF EXISTS notes");
   onCreate(db);
  }
 }

 }