WPF，将数据添加到数据库后如何更新/刷新UI

Question

How can I make it so that whenever I add/update/remove data to database the UI is updated(in wpf). I am using entity framework + local sql. I have the following classes generated by entityframework : When I add the a transaction : I need/can specify a Payee and a TransactionCategory objects. public partial class Transaction { public int TransactionId { get; set; }

    [Column(TypeName = "money")]
    public decimal TransactionAmmount { get; set; }

    public int? TransactionCategoryId { get; set; }

    public int? PayeeId { get; set; }

    [Column(TypeName = "money")]
    public decimal? TotalAmmount { get; set; }

    public int? TransactionType { get; set; }

    [Column(TypeName = "date")]
    public DateTime? TransactionDate { get; set; }


    public virtual Payee Payee { get; set; }

    public virtual TransactionCategory TransactionCategory { get; set; }
}


public partial class Payee
{
    public Payee()
    {
        Bills = new HashSet<Bill>();
        Transactions = new HashSet<Transaction>();
    }

    public int PayeeId { get; set; }

    [Required]
    [StringLength(50)]
    public string PayeeName { get; set; }

    public bool HasAccounts { get; set; }

    [StringLength(50)]
    public string PayeePhone { get; set; }

    [StringLength(50)]
    public string PayeeAddress { get; set; }

    public virtual ICollection<Bill> Bills { get; set; }

    public virtual ICollection<Transaction> Transactions { get; set; }
}

public partial class TransactionCategory
{
    public TransactionCategory()
    {
        Bills = new HashSet<Bill>();
        Transactions = new HashSet<Transaction>();
    }

    [Key]
    public int CategoryId { get; set; }

    [Required]
    [StringLength(50)]
    public string CategoryName { get; set; }

    [Column(TypeName = "money")]
    public decimal CategoryExpenseLimit { get; set; }

    [Column(TypeName = "money")]
    public decimal CategoryExpense { get; set; }

    [Column(TypeName = "money")]
    public decimal CategoryIncome { get; set; }

    [StringLength(50)]
    public string Period { get; set; }

    public virtual ICollection<Bill> Bills { get; set; }

    public virtual ICollection<Transaction> Transactions { get; set; }
}

And in their viewmodels the method I use to add data:

The PayeeViewModel class : and the method to add.

 private void Update()
    {
        using (var context = new Ents())
        {
            if (this.Mode == Mode.Add)
            {
                if (string.IsNullOrEmpty(PayeeName))
                {
                    MessageBox.Show("A Payee Name must be entered");
                }
                else
                {      
                    PayeeModel payee = new PayeeModel() { ThePayee = { PayeeName = PayeeName, PayeeAddress = PayeeAddress, PayeePhone = PayeePhone, HasAccounts = PayeeHasAccount } };

                        context.Payees.Add(payee.ThePayee);
                        context.SaveChanges();

                }
            }
       }
   }

The TransactionCategoryViewModel update method is identical except the fields.

In my TransactionViewModel :

I have a Payees and a Categories list :

The Payees list :

 private ObservableCollection<PayeeModel> payees;
        private PayeeModel selectedPayee;

        public ObservableCollection<PayeeModel> Payees
        {
            get { return payees; }
            set
            {
                payees = value;
                OnPropertyChanged("Payees");
            }
        }

        public PayeeModel SelectedPayee
        {
            get { return selectedPayee; }
            set { selectedPayee = value;
            OnPropertyChanged("SelectedPayee");
            }
        }

The Categories List

private ObservableCollection<CategoryModelModel> categories;
        private CategoryModel selectedCategory;

        public ObservableCollection<CategoryModel> Categories
        {
            get { return payees; }
            set
            {
                payees = value;
                OnPropertyChanged("Categories");
            }
        }

        public CategoryModel SelectedCategory
        {
            get { return selectedCategory; }
            set { selectedCategory = value;
            OnPropertyChanged("SelectedCategory");
            }
        }

and the constructor of the TransactionViewModel

  internal TransactionViewModel(TransactionModel transaction, IEventAggregator eventAggregator)
    {
        this.eventAggregator = eventAggregator;
        TransactionId = transaction.TheTransaction.TransactionId;
        ammount = (double)transaction.TheTransaction.TransactionAmmount;
        PayeeId = transaction.TheTransaction.PayeeId;

         GetCategories();
         GetPayees();
         SelectedPayee = payees.Where(i => i.ThePayee.PayeeId == PayeeId).First();
         SelectedCatgory = categories.Where(i => i.TheCategory.CategoryId == CategoryId).First();


    }

When I add a payee or transactioncategory to the database I'd like it to be reflected in all the views that contain a payee or transactioncategory. For example in the TransactionView(used to add/edit transactions) I have the fields mentioned in the TransactionClass and two combo boxes:one is binded to the Payees list and one to the CategoriesList.

Problem is if I add/remove or update a Payee/TransactionCategory the comboboxes in the TransactionView are not updated accordingly.

The TransactionView comboboxes:

   <Label Content="Payee" Grid.Row="2" Margin="3" />
        <ComboBox Grid.Column="1" Grid.Row="2" Margin="3" Width="100" ItemsSource="{Binding Payees}" SelectedItem="{Binding SelectedPayee}"
                  DisplayMemberPath="ThePayee.PayeeName"/>
        <Label Content="Category" Grid.Row="3" Margin="3" />
        <ComboBox Grid.Column="1" Grid.Row="3" Margin="3" Width="100" ItemsSource="{Binding Categories}" 
                  SelectedItem="{Binding SelectedCategory}"  DisplayMemberPath="TheCategory.CategoryName" />

Answer 1

Answering so it doesn't stay open. I created an ObservableCollection at startup which I added as a resource then declared local instances where I needed them.