The value obtained from the database is not applied to the variable - flutter

Question

I have a function to get a value from a sqlite database. How do I set this value to a variable?
Get value from DB
getPref(Setting setting) async {
var dbClient = await db;
try {
dbClient.query('settings',
where: 'name = ?',
whereArgs: [setting.name],
columns: ['value']).then((data) {
List<Map<String, dynamic>> s = data;
List<String> list = [];
for (var x in s) {
x.forEach((k, v) => list.add(v));
}
print("NAME: ${setting.name} VALUE: ${list[0]}");
return list[0];
});
} on Exception catch (ex) {
print(ex.toString());
}
}
Result:
NAME: mainPage VALUE: all
But when I put this value it doesn't apply, it throws null.
String page = "";
getPage() {
DBHelper database = DBHelper();
database.getPref(Setting(name: 'mainPage')).then((val) {
setState(() {
print("VAL " + val.toString());
page = val;
});
});
}
Unhandled Exception: type 'Null' is not a subtype of type 'String'

Answer 1

Try replacing:
getPref(Setting setting) async {
var dbClient = await db;
try {
dbClient.query('settings',
where: 'name = ?',
whereArgs: [setting.name],
columns: ['value']).then((data) {
List<Map<String, dynamic>> s = data;
List<String> list = [];
for (var x in s) {
x.forEach((k, v) => list.add(v));
}
print("NAME: ${setting.name} VALUE: ${list[0]}");
return list[0];
});
}
with:
getPref(Setting setting) async {
var dbClient = await db;
try {
var data = await dbClient.query('settings',
where: 'name = ?',
whereArgs: [setting.name],
columns: ['value']);
List<Map<String, dynamic>> s = data;
List<String> list = [];
for (var x in s) {
x.forEach((k, v) => list.add(v));
}
print("NAME: ${setting.name} VALUE: ${list[0]}");
return list[0];
}
What's wrong?
When querying your db you are not waiting to complete the query before returning the list[0]. In other words, you are returning your list[] before getting the data from the database as .then doesn't block the execution onwards and prematurely executes return list[0] which you don't want.