Trying to insert data as a BLOB, getting Argument Error

Question

in my Flutter project I have a class Category witch contains a String, Icon, IconData and two Colors: (I don't want to store the icon, because I can recreate it with my iconData)

class Category {
  Icon icon;
  IconData iconData;
  Color color;
  Color backgroundcolor;
  String name;

[...]

Map<String, dynamic> toMap() {
    return {
      'iconData': iconData,
      'color': color,
      'backgroundcolor': backgroundcolor,
      'name': name
    };
  }

for my project I imported the sqflite database, created a table categories(with "CREATE TABLE categories(name TEXT, iconData BLOB, color BLOB, backgroundcolor BLOB")) and now want to insert a category into my database with the following:

Future<void> insertCategory(Category category) async {
  // get reference to the database
  final Database db = await database;

  // insert new category
  await db.insert('categories', category.toMap(),
      conflictAlgorithm: ConflictAlgorithm.replace);

  print("Category inserted.");
}

But when I try to insert a category I get an Argument Error (Invalid argument: Instance of 'IconData') and I can't figure out what's the problem.

Blob is raw data - array of bytes (most likely). Here I don't see conversion of IconData to array of bytes. So you can extend your toMap to do so. Other solution is to store only codePoint (may be fontFamily) as that is all you need, and cnostruct IconData from codePoint & fontFamily when required. — Chenna Reddy
– Chenna Reddy, Commented Sep 23, 2019 at 14:53

chunhunghan · Accepted Answer · 2019-09-24 00:56:31Z

0

you can save icon data with String type
and you need a mapping from string to your icon either Icons or FontAwesomeIcons or ...

Map<String, IconData> iconMapping = {
  'facebook' : FontAwesomeIcons.facebook,
  'twitter' : FontAwesomeIcons.twitter,
  'home' : FontAwesomeIcons.home,
  'audiotrack' : Icons.audiotrack,
};

@override
Widget build(BuildContext context) {
  return Icon(iconMapping [icon], color: HexColor(color));
}

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answered Sep 24, 2019 at 0:56

chunhunghan

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1 Comment

jonryan Over a year ago

I used a workaround as suggested by Chenna Reddy. I store values of primitive data types and when reading my data from the database I will recreate my objects. In case of the icon I store the codepoint and fontfamily and create a new IconData object based on this information.

jonryan · Accepted Answer · 2019-09-27 08:36:44Z

My workaround is the following:

Create database with

CREATE TABLE categories( iconData INTEGER, backgroundcolor INTEGER, name TEXT PRIMARY KEY)

My toMap() is

Map<String, dynamic> toMap() {
// Color is stored in a 32-bit integer with alpha, red, green, blue -> ARGB
int bc = backgroundcolor.alpha << 8;
bc = bc + backgroundcolor.red << 8;
bc = bc + backgroundcolor.green << 8;
bc = bc + backgroundcolor.blue;
return {
  'iconData': iconData.codePoint,
  'backgroundcolor': bc,
  'name': name
};

An I read my categories with

Future<List<Category>> getCategoriesFromDatabase() async {
  // get reference to database
  final Database db = await database;

  // Query the table for all categories
  final List<Map<String, dynamic>> maps = await db.query('categories');

  print("Categories read.");
  // Convert the List<Map<String, dynamic> into a List<Category>
  return List.generate(maps.length, (i) {
    // Construct backgroundcolor
    Color bc = Color(maps[i]['backgroundcolor']);
    // Construct iconData
    IconData id =
        IconData(maps[i]['iconData'], fontFamily: Icons.ac_unit.fontFamily);
    return Category(
      name: maps[i]['name'],
      iconData: id,
      backgroundcolor: bc,
    );
  });
}

This workaround should work for most data types. For example, I use the same solution to store dates. I save a year, month, day, ... and when reading from the db I construct a dart date.

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