SQLite 多参数插入注意事项 insert multiple parameters

1.) Do not reuse a parameter

2.)  VALUES(@str, @new) ParameterName="@str." ParameterName="@new."
As the error indicates, you are using the parameters @str and @new and adding two different parameters. Read the error message, it is there for a reason and told you exactly what is wrong!

3.) Here is how I would write it (in this context).

using (SQLiteConnection cnn = new SQLiteConnection("Data Source=C://EEk.db"))
using (SQLiteCommand cmd = Database.CreateCommand())
{
    cmd.CommandText = "INSERT INTO test (Field1,fname) VALUES(@str, @new)";
    cmd.Parameters.AddWithValue("@str", textBox1.Text);
    cmd.Parameters.AddWithValue("@new", textBox2.Text);

    cnn.Open();
    cmd.ExecuteNonQuery();
    cnn.Close();
}

While you can use DbConnection and DbCommand and make a factory pattern sort of implementation (which I doubt is going here...) I suggest you do not. Use the SqliteConnection, SqliteCommand, etc. The provider specific objects generally have features that make coding easier. In this case, the AddWithValue method.