>>>I have a textbox which is bound to a field on an entity. I need to run some code whenever the entity's field changes. I've tried calling my code in the textbox's Text_Changed event, but referring to the entity's field at this point in time does not reflect the value entered in the textbox.
>>>
>>>At what point in time would the entity's field get updated with the value entered in the textbox?
>>>
>>>Or is there another way to trap/raise an event when the entity's filed changes?
>>
>>Usually, the UI field is bound to a property that implements INotifyPropertyChanged. You can process your code changes there when the properties value changes. Or trap the PropertyChanged event in the UI and fire off your code there..
>
>Thanks John, but this is really all Greek to me at the moment.
>
>The form I am dealing with has:
>1. a field to enter the deposit amount
>2. A grid to enter the deposit details
>3. A textbox to show the total of the deposit details
>4. Another textbox to show the difference between the Deposit Amount and the total of the deposit details.
>
>I have this defined:
>
>

        private decimal depositTotal;
>        
>        public decimal DepositTotal
>        {
>            get
>            {
>                return this.depositTotal;
>            }
>
>            set
>            {
>                if (value != this.depositTotal)
>                {
>                    this.depositTotal = value;
>                    this.OnPropertyChanged("DepositTotal");
>                }
>            }
>        }
>
>        private decimal balanceOutstanding;
>
>        public decimal BalanceOutstanding
>        {
>            get
>            {
>                return this.balanceOutstanding;
>            }
>
>            set
>            {
>                if (value != this.balanceOutstanding)
>                {
>                    this.balanceOutstanding = value;
>                    this.OnPropertyChanged("BalanceOutstanding");
>                }
>            }
>        }

>
>I have the txtDepositTotal defined like this:
>
>

<TextBox Name="txtDepositTotal" Text="{Binding RelativeSource={RelativeSource FindAncestor, AncestorType={x:Type Window}}, Path=DepositTotal}"/>

>
>and the txtBalanceOutstanding like this:
>
>

<TextBox  Name="txtBalanceOutstanding"Text="{Binding RelativeSource={RelativeSource FindAncestor, AncestorType={x:Type Window}}, Path=BalanceOutstanding}" />

>
>and the DepositAmount:
>
>

<TextBox  Text="{Binding dep_amount, Mode=Default}" 
>                                  Name="txtDep_Amount" 
>                                  VerticalAlignment="Center" />

>
>Can you give me an example showing what I should do?

When you set the value of DepositTotal = _value in the property defined above, that is the point when the on PropertyChyanged fires. You can either add a method call at that time, i.e.,

        public decimal DepositTotal
        {
            get
            {
                return this.depositTotal;
            }

            set
            {
                if (value != this.depositTotal)
                {
                    this.depositTotal = value;
                    this.MyDepositTotalChangedDoSomething();
                    this.OnPropertyChanged("DepositTotal");
                }
            }
        }

or, you can trap the propertychanged event and do it there...

in the constructor add:

     this.OnPropertyChanged += PropertyChangedDoSomethign());

then in the handler:

    private void PropertyChangedDoSomething(object sender, RoutedEventArgs e)
   {
      if(e.Property.Equals("DepositTotal")
      {
         do something here....
      }
   }

if the property definition and the code are in the same windows, then I prefer to just modify the property definition ala the first example. If they are spread across different code behinds, then example 2.

Hope this helps..