Drop Down with sqlite - Flutter

问题

I have database sqlite data and i want to show my data in drop down with changed id of my rows in table because in future i want to create another drop down to change to value of first drop down anyone can help ?

回答1:

Working with SQLite on flutter

To gather the data from a SQLite database you could use the sqflite plugin (independently if is an iOS or Android device). You have to add the dependency to your pubspec.yaml.

dependencies:
  ...
  sqflite: any

When you want to use sqflite you have to import the library.

import 'package:sqflite/sqflite.dart';

Next, you have to open a connection to SQLite, here we create a table in case you didn't have one

Database database = await openDatabase(path, version: 1,
    onCreate: (Database db, int version) async {
  await db.execute(
      'CREATE TABLE Test (id INTEGER PRIMARY KEY, name TEXT, value INTEGER, num REAL)');
});

You can insert or retrieve data using database.rawQuery.

Insert:

int primaryKeyInsertedRow = await database.rawQuery('INSERT INTO Test(name, value, num) VALUES("some name", 1234, 456.789)');

Select:

List<Map> list = await database.rawQuery('SELECT * FROM Test');

Remember to close the database when you are done with it.

await database.close();

Displaying a drop down menu list

For displaying the data you retrieve first you have to create a class that extends StatefulWidget, override the createState() method, and set your own state (in this example, SettingWidgetState)

@override
_SettingsWidgetState createState() => new _SettingsWidgetState();

Second you should define a state for it, defining a class that extends State<NameOfYourWidget>. In that class you should have a list of DropdownMenuItem<String> and a string member of the current selected element.

For the sake of convenience, in this example we are going to use a static list of cities:

List _cities = [
  "Cluj-Napoca",
  "Bucuresti",
  "Timisoara",
  "Brasov",
  "Constanta"
];

Next, we override initState() setting our list of DropDownMenuItem to our list and the currently selected list element. After that we should call super.initState().

Also, we need to override the build() method. The goal is to return a Container that contains a DropDownButton, and that DropDownButton has assigned the list of items (defined in the class), the selected element (also defined in the class) and a event handler for the onChanged: property (here also are inserted additional widgets with the purpose of making it look nice)

@override
Widget build(BuildContext context) {
  return new Container(
    color: Colors.white,
    child: new Center(
        child: new Column(
      crossAxisAlignment: CrossAxisAlignment.center,
      mainAxisAlignment: MainAxisAlignment.center,
      children: <Widget>[
        new Text("Please choose your city: "),
        new Container(
          padding: new EdgeInsets.all(16.0),
        ),
        new DropdownButton(
          value: _currentCity,
          items: _dropDownMenuItems,
          onChanged: changedDropDownItem,
        )
      ],
    )),
  );
}

Lastly we define the method that is going to be called when a new item is selected from the list (changeDropDownItem(string selectedCity) in our example).

  void changedDropDownItem(String selectedCity) {
    setState(() {
      _currentCity = selectedCity;
    });
  }
}

Link where I based my answer for drop down list. You can check out too getting started with sqflite plugin

来源：https://stackoverflow.com/questions/53838685/drop-down-with-sqlite-flutter

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