Question

我创建了一个表，用于将一些收藏的电影列表保存到SQLite中数据库。将有一个星状菜单，将改变回收站视图项目进入收藏状态。

FavoriteHelper.java

public static final String DATABASE_TABLE = TABLE_FAVORITE;
private static DatabaseHelper databaseHelper;
private static FavoriteHelper INSTANCE;

public static SQLiteDatabase database;

public FavoriteHelper(Context context){
    databaseHelper = new DatabaseHelper(context);
}

public static FavoriteHelper getInstance(Context context){
    if(INSTANCE == null){
        synchronized (SQLiteOpenHelper.class){
            if(INSTANCE == null){
                INSTANCE = new FavoriteHelper(context);
            }
        }
    }
    return INSTANCE;
}

public void open() throws SQLException{
    database = databaseHelper.getWritableDatabase();
}

public void close(){
    databaseHelper.close();

    if(database.isOpen()){
        database.close();
    }
}

public ArrayList<Movie> getAllFavorites(){
    ArrayList<Movie> arrayList = new ArrayList<>();
    Cursor cursor = database.query(DATABASE_TABLE, null,
            null,
            null,
            null,
            null,
            _ID + " ASC",
            null);
    cursor.moveToFirst();
    Movie favorite;
    if(cursor.getCount() > 0){
        do {
            favorite = new Movie();
            favorite.setId(cursor.getInt(cursor.getColumnIndexOrThrow(_ID)));
            favorite.setTitle(cursor.getString(cursor.getColumnIndexOrThrow(TITLE)));
            favorite.setOriginalTitle(cursor.getString(cursor.getColumnIndexOrThrow(ORIGINAL_TITLE)));
            favorite.setRating(cursor.getString(cursor.getColumnIndexOrThrow(RATING)));
            favorite.setReleaseDate(cursor.getString(cursor.getColumnIndexOrThrow(RELEASE_DATE)));
            favorite.setOverview(cursor.getString(cursor.getColumnIndexOrThrow(OVERVIEW)));
            favorite.setPhotoLink(cursor.getString(cursor.getColumnIndexOrThrow(PHOTO_LINK)));

            arrayList.add(favorite);
            cursor.moveToNext();

        } while (!cursor.isAfterLast());
    }
    cursor.close();
    return arrayList;
}

public long insertFavorite(Movie favorite){
    ContentValues args = new ContentValues();
    args.put(TITLE, favorite.getTitle());
    args.put(ORIGINAL_TITLE, favorite.getOriginalTitle());
    args.put(RATING, favorite.getRating());
    args.put(RELEASE_DATE, favorite.getReleaseDate());
    args.put(OVERVIEW, favorite.getOverview());
    args.put(PHOTO_LINK, favorite.getPhotoLink());
    return database.insert(DATABASE_TABLE, null, args);
}

public int deleteFavorite(int id){
    return database.delete(TABLE_FAVORITE, _ID + " = '" + id + "'", null);
}

DetailActivity.java

    @Override
public boolean onCreateOptionsMenu(Menu menu) {
    getMenuInflater().inflate(R.menu.detail_menu, menu);
    menuItem = menu;
    setFavorite();
    return super.onCreateOptionsMenu(menu);
}

@Override
public boolean onOptionsItemSelected(@NonNull MenuItem item) {
    switch(item.getItemId()){
        case R.id.add_to_favorite_button:
            if(isFavorite) removeFavorite(); else saveFavorite();
            isFavorite = !isFavorite;
            setFavorite();
            return true;
    }
    Intent intent = new Intent(getApplicationContext(), MainActivity.class);
    startActivityForResult(intent, 0);
    return true;
}    
private void favoriteState(){
    String results = String.format("SELECT * FROM favorite WHERE _ID=%s",ids);
    if(results != null) isFavorite = true;
}

private void saveFavorite(){
    FavoriteHelper favoriteDbHelper = new FavoriteHelper(this);
    favoriteDbHelper.open();

    Movie fav = new Movie();
    fav.setId(ids);
    fav.setTitle(titleBar);
    fav.setOriginalTitle(nameDetail.getText().toString());
    fav.setRating(rateDetail.getText().toString());
    fav.setReleaseDate(dateDetail.getText().toString());
    fav.setOverview(descDetail.getText().toString());
    fav.setPhotoLink(tvImageView.getText().toString());

    favoriteDbHelper.insertFavorite(fav);
    favoriteDbHelper.close();
}

private void removeFavorite(){
    FavoriteHelper favoriteHelper = new FavoriteHelper(this);
    favoriteHelper.open();
    favoriteHelper.deleteFavorite(ids);
    favoriteHelper.close();
}

private void setFavorite(){
    if(isFavorite){
        menuItem.getItem(0).setIcon(ContextCompat.getDrawable(this, R.drawable.ic_added_to_favorites));
    }else{
        menuItem.getItem(0).setIcon(ContextCompat.getDrawable(this, R.drawable.ic_add_to_favorites));
    }
}

但是每次我单击按钮时，数据都不会保存到表中。如何将数据保存到表中并检查该表中是否存在数据，因此如果我转到有数据存在的DetailActivity，则可以使用favouriteState（）函数更改isFavorite变量。

Answer 1

当您返回insert方法的结果（其rowid或别名）时，可以使用：-

 long id = favoriteDbHelper.insertFavorite(fav);

如果 id 的值大于0，则表示已插入一行，该值将是 rowid 的值，因此是< strong> rowid （如果存在）（通常您的 _ID 将是 rowid 的别名）。
如果该值为-1，则可能是由于约束冲突而未插入行。
根据您的要求，您可能会给 id 更大的范围。

Answer 2

检查表中是否已存在数据：

public boolean isDataAvailable(String title) {
        SQLiteDatabase db = this.getWritableDatabase();

        boolean isAvailable = false;

        try {
            Cursor cursor;
            String sql = "SELECT * FROM " + TABLE_NAME + " WHERE fav_id =" + id; // you can check it by comparing any unique value 
            cursor = db.rawQuery(sql, null);
            isAvailable = cursor.getCount() > 0;
            cursor.close();
        } catch (Exception e) {
            e.printStackTrace();
        }

        return isAvailable;
    }

将插入方法更改为：

public insertFavorite(Movie favorite) {
        ContentValues args = new ContentValues();
        args.put(TITLE, favorite.getTitle());
        args.put(ORIGINAL_TITLE, favorite.getOriginalTitle());
        args.put(RATING, favorite.getRating());
        args.put(RELEASE_DATE, favorite.getReleaseDate());
        args.put(OVERVIEW, favorite.getOverview());
        args.put(PHOTO_LINK, favorite.getPhotoLink());

        if (isDataAvailable(favorite.getTitle())) {
            database.update(DATABASE_TABLE, args, "title = " + favorite.getTitle(), null);
        } else {
            database.insert(DATABASE_TABLE, null, args);
        }

    }

此方法将更新您喜欢的收藏夹（如果存在）或不存在插入ID。

如何将数据保存到SQLite数据库并检查ID是否存在的数据

2 个答案: