[英]Xamarin forms: System.InvalidCastException: 'Specified cast is not valid.'
[英]Why does select from sqlite db shows error 'Specified cast is not valid.' in Xamarin Forms?
從 SQLite 數據庫獲取單個值,但出現錯誤 System.InvalidCastException: 'Specified cast is not valid.' 我只需要選擇結果的第一個值,嘗試了 First() 和 ElementAtOrDefault(0) 但同樣的事情發生了。
嘗試分配給變量 IDPromoMainPage 時捕獲錯誤,而不是之前。
基本上這就是我調用值的方式:
private void GetPromoLocal()
{
try
{
var databasePath = System.IO.Path.Combine(Environment.GetFolderPath(Environment.SpecialFolder.Personal), "LocalDB.db3");
var db = new SQLiteConnection(databasePath);
IEnumerable<T_Promo> resultado = SELECT_WHERE(db);
if (resultado.Count() > 0)
{
IDPromoMainPage = Convert.ToInt32(resultado.First()); // ElementAtOrDefault(0));
}
}
catch (Exception)
{
throw;
}
}
public static IEnumerable<T_Promo> SELECT_WHERE(SQLiteConnection db)
{
return db.Query<T_Promo>("SELECT IDPromo FROM T_Promo");
}
這里也發生了同樣的錯誤,正好在“PisterosLista = resultado.Cast().ToList();”行
List<Pisteros> PisterosLista = new List<Pisteros>();
public void GetPisterosLocal()
{
try
{
var databasePath = System.IO.Path.Combine(Environment.GetFolderPath(Environment.SpecialFolder.Personal), "LocalDB.db3");
var db = new SQLiteConnection(databasePath);
IEnumerable<T_Pisteros> resultado = SELECT_WHERE_Pist(db);
if (resultado.Count() > 0)
{
PisterosLista = resultado.Cast<Pisteros>().ToList();
//Console.WriteLine("content :: " + content);
Console.WriteLine("Data :: " + PisterosLista);
}
}
catch (Exception)
{
throw;
}
}
public static IEnumerable<T_Pisteros> SELECT_WHERE_Pist(SQLiteConnection db)
{
return db.Query<T_Pisteros>("SELECT * FROM T_Pisteros");
}
如果列IDPromo
是一個整數,那么就這樣做
IEnumerable<int> resultado = SELECT_WHERE(db);
public static IEnumerable<int> SELECT_WHERE(SQLiteConnection db)
{
return db.Query<int>("SELECT IDPromo FROM T_Promo");
}
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