Best practices for exposing multiple tables using content providers in Android

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迷失自我 2020-12-04 05:19

I\'m building an app where I have a table for events and a table for venues. I want to be able to grant other applications access to this data. I have a few questions relate

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一向 (楼主)

2020-12-04 05:52

I found best demo and explanation for ContentProvider and I think it has followed Android Standards.

Contract Classes

 /**
   * The Content Authority is a name for the entire content provider, similar to the relationship
   * between a domain name and its website. A convenient string to use for content authority is
   * the package name for the app, since it is guaranteed to be unique on the device.
   */
  public static final String CONTENT_AUTHORITY = "com.androidessence.moviedatabase";

  /**
   * The content authority is used to create the base of all URIs which apps will use to
   * contact this content provider.
   */
  private static final Uri BASE_CONTENT_URI = Uri.parse("content://" + CONTENT_AUTHORITY);

  /**
   * A list of possible paths that will be appended to the base URI for each of the different
   * tables.
   */
  public static final String PATH_MOVIE = "movie";
  public static final String PATH_GENRE = "genre";

and Inner Classes:

 /**
   * Create one class for each table that handles all information regarding the table schema and
   * the URIs related to it.
   */
  public static final class MovieEntry implements BaseColumns {
      // Content URI represents the base location for the table
      public static final Uri CONTENT_URI =
              BASE_CONTENT_URI.buildUpon().appendPath(PATH_MOVIE).build();

      // These are special type prefixes that specify if a URI returns a list or a specific item
      public static final String CONTENT_TYPE =
              "vnd.android.cursor.dir/" + CONTENT_URI  + "/" + PATH_MOVIE;
      public static final String CONTENT_ITEM_TYPE =
              "vnd.android.cursor.item/" + CONTENT_URI + "/" + PATH_MOVIE;

      // Define the table schema
      public static final String TABLE_NAME = "movieTable";
      public static final String COLUMN_NAME = "movieName";
      public static final String COLUMN_RELEASE_DATE = "movieReleaseDate";
      public static final String COLUMN_GENRE = "movieGenre";

      // Define a function to build a URI to find a specific movie by it's identifier
      public static Uri buildMovieUri(long id){
          return ContentUris.withAppendedId(CONTENT_URI, id);
      }
  }

  public static final class GenreEntry implements BaseColumns{
      public static final Uri CONTENT_URI =
              BASE_CONTENT_URI.buildUpon().appendPath(PATH_GENRE).build();

      public static final String CONTENT_TYPE =
              "vnd.android.cursor.dir/" + CONTENT_URI + "/" + PATH_GENRE;
      public static final String CONTENT_ITEM_TYPE =
              "vnd.android.cursor.item/" + CONTENT_URI + "/" + PATH_GENRE;

      public static final String TABLE_NAME = "genreTable";
      public static final String COLUMN_NAME = "genreName";

      public static Uri buildGenreUri(long id){
          return ContentUris.withAppendedId(CONTENT_URI, id);
      }
  }

Now creating Database using SQLiteOpenHelper:

public class MovieDBHelper extends SQLiteOpenHelper{
    /**
     * Defines the database version. This variable must be incremented in order for onUpdate to
     * be called when necessary.
     */
    private static final int DATABASE_VERSION = 1;
    /**
     * The name of the database on the device.
     */
    private static final String DATABASE_NAME = "movieList.db";

    /**
     * Default constructor.
     * @param context The application context using this database.
     */
    public MovieDBHelper(Context context){
        super(context, DATABASE_NAME, null, DATABASE_VERSION);
    }

    /**
     * Called when the database is first created.
     * @param db The database being created, which all SQL statements will be executed on.
     */
    @Override
    public void onCreate(SQLiteDatabase db) {
        addGenreTable(db);
        addMovieTable(db);
    }

    /**
     * Called whenever DATABASE_VERSION is incremented. This is used whenever schema changes need
     * to be made or new tables are added.
     * @param db The database being updated.
     * @param oldVersion The previous version of the database. Used to determine whether or not
     *                   certain updates should be run.
     * @param newVersion The new version of the database.
     */
    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {

    }

    /**
     * Inserts the genre table into the database.
     * @param db The SQLiteDatabase the table is being inserted into.
     */
    private void addGenreTable(SQLiteDatabase db){
        db.execSQL(
                "CREATE TABLE " + MovieContract.GenreEntry.TABLE_NAME + " (" +
                        MovieContract.GenreEntry._ID + " INTEGER PRIMARY KEY, " +
                        MovieContract.GenreEntry.COLUMN_NAME + " TEXT UNIQUE NOT NULL);"
        );
    }

    /**
     * Inserts the movie table into the database.
     * @param db The SQLiteDatabase the table is being inserted into.
     */
    private void addMovieTable(SQLiteDatabase db){
        db.execSQL(
                "CREATE TABLE " + MovieContract.MovieEntry.TABLE_NAME + " (" +
                        MovieContract.MovieEntry._ID + " INTEGER PRIMARY KEY, " +
                        MovieContract.MovieEntry.COLUMN_NAME + " TEXT NOT NULL, " +
                        MovieContract.MovieEntry.COLUMN_RELEASE_DATE + " TEXT NOT NULL, " +
                        MovieContract.MovieEntry.COLUMN_GENRE + " INTEGER NOT NULL, " +
                        "FOREIGN KEY (" + MovieContract.MovieEntry.COLUMN_GENRE + ") " +
                        "REFERENCES " + MovieContract.GenreEntry.TABLE_NAME + " (" + MovieContract.GenreEntry._ID + "));"
        );
    }
}

Content Provider:

public class MovieProvider extends ContentProvider {
    // Use an int for each URI we will run, this represents the different queries
    private static final int GENRE = 100;
    private static final int GENRE_ID = 101;
    private static final int MOVIE = 200;
    private static final int MOVIE_ID = 201;

    private static final UriMatcher sUriMatcher = buildUriMatcher();
    private MovieDBHelper mOpenHelper;

    @Override
    public boolean onCreate() {
        mOpenHelper = new MovieDBHelper(getContext());
        return true;
    }

    /**
     * Builds a UriMatcher that is used to determine witch database request is being made.
     */
    public static UriMatcher buildUriMatcher(){
        String content = MovieContract.CONTENT_AUTHORITY;

        // All paths to the UriMatcher have a corresponding code to return
        // when a match is found (the ints above).
        UriMatcher matcher = new UriMatcher(UriMatcher.NO_MATCH);
        matcher.addURI(content, MovieContract.PATH_GENRE, GENRE);
        matcher.addURI(content, MovieContract.PATH_GENRE + "/#", GENRE_ID);
        matcher.addURI(content, MovieContract.PATH_MOVIE, MOVIE);
        matcher.addURI(content, MovieContract.PATH_MOVIE + "/#", MOVIE_ID);

        return matcher;
    }

    @Override
    public String getType(Uri uri) {
        switch(sUriMatcher.match(uri)){
            case GENRE:
                return MovieContract.GenreEntry.CONTENT_TYPE;
            case GENRE_ID:
                return MovieContract.GenreEntry.CONTENT_ITEM_TYPE;
            case MOVIE:
                return MovieContract.MovieEntry.CONTENT_TYPE;
            case MOVIE_ID:
                return MovieContract.MovieEntry.CONTENT_ITEM_TYPE;
            default:
                throw new UnsupportedOperationException("Unknown uri: " + uri);
        }
    }

    @Override
    public Cursor query(Uri uri, String[] projection, String selection, String[] selectionArgs, String sortOrder) {
        final SQLiteDatabase db = mOpenHelper.getWritableDatabase();
        Cursor retCursor;
        switch(sUriMatcher.match(uri)){
            case GENRE:
                retCursor = db.query(
                        MovieContract.GenreEntry.TABLE_NAME,
                        projection,
                        selection,
                        selectionArgs,
                        null,
                        null,
                        sortOrder
                );
                break;
            case GENRE_ID:
                long _id = ContentUris.parseId(uri);
                retCursor = db.query(
                        MovieContract.GenreEntry.TABLE_NAME,
                        projection,
                        MovieContract.GenreEntry._ID + " = ?",
                        new String[]{String.valueOf(_id)},
                        null,
                        null,
                        sortOrder
                );
                break;
            case MOVIE:
                retCursor = db.query(
                        MovieContract.MovieEntry.TABLE_NAME,
                        projection,
                        selection,
                        selectionArgs,
                        null,
                        null,
                        sortOrder
                );
                break;
            case MOVIE_ID:
                _id = ContentUris.parseId(uri);
                retCursor = db.query(
                        MovieContract.MovieEntry.TABLE_NAME,
                        projection,
                        MovieContract.MovieEntry._ID + " = ?",
                        new String[]{String.valueOf(_id)},
                        null,
                        null,
                        sortOrder
                );
                break;
            default:
                throw new UnsupportedOperationException("Unknown uri: " + uri);
        }

        // Set the notification URI for the cursor to the one passed into the function. This
        // causes the cursor to register a content observer to watch for changes that happen to
        // this URI and any of it's descendants. By descendants, we mean any URI that begins
        // with this path.
        retCursor.setNotificationUri(getContext().getContentResolver(), uri);
        return retCursor;
    }

    @Override
    public Uri insert(Uri uri, ContentValues values) {
        final SQLiteDatabase db = mOpenHelper.getWritableDatabase();
        long _id;
        Uri returnUri;

        switch(sUriMatcher.match(uri)){
            case GENRE:
                _id = db.insert(MovieContract.GenreEntry.TABLE_NAME, null, values);
                if(_id > 0){
                    returnUri =  MovieContract.GenreEntry.buildGenreUri(_id);
                } else{
                    throw new UnsupportedOperationException("Unable to insert rows into: " + uri);
                }
                break;
            case MOVIE:
                _id = db.insert(MovieContract.MovieEntry.TABLE_NAME, null, values);
                if(_id > 0){
                    returnUri = MovieContract.MovieEntry.buildMovieUri(_id);
                } else{
                    throw new UnsupportedOperationException("Unable to insert rows into: " + uri);
                }
                break;
            default:
                throw new UnsupportedOperationException("Unknown uri: " + uri);
        }

        // Use this on the URI passed into the function to notify any observers that the uri has
        // changed.
        getContext().getContentResolver().notifyChange(uri, null);
        return returnUri;
    }

    @Override
    public int delete(Uri uri, String selection, String[] selectionArgs) {
        final SQLiteDatabase db = mOpenHelper.getWritableDatabase();
        int rows; // Number of rows effected

        switch(sUriMatcher.match(uri)){
            case GENRE:
                rows = db.delete(MovieContract.GenreEntry.TABLE_NAME, selection, selectionArgs);
                break;
            case MOVIE:
                rows = db.delete(MovieContract.MovieEntry.TABLE_NAME, selection, selectionArgs);
                break;
            default:
                throw new UnsupportedOperationException("Unknown uri: " + uri);
        }

        // Because null could delete all rows:
        if(selection == null || rows != 0){
            getContext().getContentResolver().notifyChange(uri, null);
        }

        return rows;
    }

    @Override
    public int update(Uri uri, ContentValues values, String selection, String[] selectionArgs) {
        final SQLiteDatabase db = mOpenHelper.getWritableDatabase();
        int rows;

        switch(sUriMatcher.match(uri)){
            case GENRE:
                rows = db.update(MovieContract.GenreEntry.TABLE_NAME, values, selection, selectionArgs);
                break;
            case MOVIE:
                rows = db.update(MovieContract.MovieEntry.TABLE_NAME, values, selection, selectionArgs);
                break;
            default:
                throw new UnsupportedOperationException("Unknown uri: " + uri);
        }

        if(rows != 0){
            getContext().getContentResolver().notifyChange(uri, null);
        }

        return rows;
    }
}

I hope it will helps you.

Demo on GitHub: https://github.com/androidessence/MovieDatabase

Full Article : https://guides.codepath.com/android/creating-content-providers

References:

http://code.tutsplus.com/tutorials/android-sdk_content-providers--mobile-5549
http://www.grokkingandroid.com/android-tutorial-writing-your-own-content-provider/
http://developer.android.com/guide/topics/providers/content-providers.html
https://thenewcircle.com/s/post/1375/android_content_provider_tutorial
http://www.grokkingandroid.com/android-tutorial-content-provider-basics/
http://androidessence.com/

Note : I copied code just because if link of demo or article may be remove in future.

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