就我而言,我需要在应用程序的开头从数据库中加载一些数据。但是我无法加载数据,因此我测试了我的代码出了什么问题,发现在await database
中花费了一些时间,并且代码跳过了此功能并执行其他操作。结果,我在创建UI之后会获取数据,因此无法显示数据。有什么办法解决吗?这是我的代码和结果-
dbhelper.dart
static Database db_instance;
Future<Database> get db async{
if(db_instance == null)
db_instance = await initDB();
return db_instance;
}
initDB() async{
var dbDir = await getDatabasesPath();
var dbPath = join(dbDir, "test.db");
ByteData data = await rootBundle.load(join("assets","test.db"));
List<int> bytes = data.buffer.asUint8List(data.offsetInBytes, data.lengthInBytes);
await File(dbPath).writeAsBytes(bytes);
var db = await openDatabase(dbPath);
return db;
}
getTest() async{
print("Test1");
var db_connection = await db;
print("Test2");
List<Map> list = await db_connection.rawQuery('SELECT * FROM $TABLE_NAME Where id= 1');
print("Test3");
for(int i=0;i<list.length;i++){
print("Test4");
id = list[i]['id'];
name = list[i]['name'];
phone = list[i]['phone'];
}
print("Test5"+name);
}
main.dart
getContactsFromDB()async{
var dbHelper = DBHelper();
dbHelper.getTest();
print("Test6"+phone);
}
@override
void initState() {
getContactsFromDB();
super.initState();
}
结果
I/flutter (13203): Test1
I/flutter (13203): Test6 // skip Test2,3,4,5 and jump to another operation and data not collected
I/flutter (13203): Test2
I/flutter (13203): Test3
I/flutter (13203): Test4
I/flutter (13203): Test5 Zin
只需使用FutureBuilder。像这里的东西:
Widget projectWidget() {
return FutureBuilder(
future: getContactsFromDB(),
builder: (context, snapshot) {
if (snapshot.connectionState == ConnectionState.done) {
return Container();
} else {
return CircularProgressIndicator();
}
}
)
}