如何从任何视图控制器全局访问sql db

public class MedicineTransation{
[PrimaryKey, AutoIncrement]
public int   Id { get; set; }
public string name {get;set;}
public int age {get;set;}
public string grade {get;set;}
}               
// StudentViewController
//Add student Record to student database.  
btn_AddRecord.TouchUpInside += ((object sender, EventArgs e) => { 
    string folder = Environment.GetFolderPath (Environment.SpecialFolder.Personal);
    var db = new SQLiteConnection (System.IO.Path.Combine (folder, "student.db"));
    db.CreateTable<MedicineTransation>();
    var student = new Student { 
    name = studentName;
    age = studentage;
    grade = studentGrade;
    };
  db.Insert (student);
)};
//DetailedViewController
//Delete student Record to student database.  
   btn_DeleteRecord.TouchUpInside += ((object sender, EventArgs e) => { 
//  db.Insert (student); Insert Record into database.
//  db.Delete (student); Delete Record from database.
}

想从另一个视图控制器访问相同的数据库