BindingGroup.GetValue(Object, String) Method

Definition

Namespace:

System.Windows.Data

Assembly:

PresentationFramework.dll

Returns the proposed value for the specified property and item.

public:
 System::Object ^ GetValue(System::Object ^ item, System::String ^ propertyName);

public object GetValue (object item, string propertyName);

override this.GetValue : obj * string -> obj

Public Function GetValue (item As Object, propertyName As String) As Object

Parameters

item

Object

The object that contains the specified property.

propertyName

String

The property whose proposed value to get.

Returns

Object

The proposed property value.

Exceptions

InvalidOperationException

There is not a binding for the specified item and property.

ValueUnavailableException

The value of the specified property is not available, due to a conversion error or because an earlier validation rule failed.

Examples

The following example is part of an application that prompts the user to enter multiple customers and assign a sales representative to each customer. The application checks that the sales representative and the customer belong to the same region. The example shows the Validate method, which uses the GetValue(Object, String) method to get values that the customer entered.

public class AreasMatch : ValidationRule
{
    public override ValidationResult Validate(object value, System.Globalization.CultureInfo cultureInfo)
    {
        BindingGroup bg = value as BindingGroup;
        Customer cust = bg.Items[0] as Customer;
        
        if (cust == null)
        {
            return new ValidationResult(false, "Customer is not the source object");
        }

        Region region = (Region)bg.GetValue(cust, "Location");
        ServiceRep rep = bg.GetValue(cust, "ServiceRepresentative") as ServiceRep;
        string customerName = bg.GetValue(cust, "Name") as string;

        if (region == rep.Area)
        {
            return ValidationResult.ValidResult;
        }
        else
        {

            StringBuilder sb = new StringBuilder();
            sb.AppendFormat("{0} must be assigned a sales representative that serves the {1} region. \n ", customerName, region);
            return new ValidationResult(false, sb.ToString());
        }
    }
}

Public Class AreasMatch
    Inherits ValidationRule
    Public Overrides Function Validate(ByVal value As Object, ByVal cultureInfo As System.Globalization.CultureInfo) As ValidationResult
        Dim bg As BindingGroup = TryCast(value, BindingGroup)
        Dim cust As Customer = TryCast(bg.Items(0), Customer)

        If cust Is Nothing Then
            Return New ValidationResult(False, "Customer is not the source object")
        End If

        Dim region As Region = CType(bg.GetValue(cust, "Location"), Region)
        Dim rep As ServiceRep = TryCast(bg.GetValue(cust, "ServiceRepresentative"), ServiceRep)
        Dim customerName As String = TryCast(bg.GetValue(cust, "Name"), String)

        If region = rep.Area Then
            Return ValidationResult.ValidResult
        Else

            Dim sb As New StringBuilder()
            sb.AppendFormat("{0} must be assigned a sales representative that serves the {1} region. " & vbLf & " ", customerName, region)
            Return New ValidationResult(False, sb.ToString())
        End If
    End Function
End Class

Remarks

Use this method in the ValidationRule.Validate method to get the value to be committed to the source. The type of the return value depends on the stage at which the ValidationRule occurs. For example, if a TextBox is data bound to a property of type integer and the ValidationRule that calls GetValue(Object, String) has its ValidationStep set to RawProposedValue, the method returns a string. If the ValidationRule has its ValidationStep set to ConvertedProposedValue, the method returns whatever type that is returned by the binding's converter. In this example, GetValue(Object, String) usually returns an integer.