BindingGroup.TryGetValue Method

Updated: July 2008

Attempts to get the proposed value for the specified property and item.

Namespace:  System.Windows.Data
Assembly:  PresentationFramework (in PresentationFramework.dll)

public bool TryGetValue(
	Object item,
	string propertyName,
	out Object value
)
You cannot use methods in XAML.

Parameters

item
Type: System.Object

The object that contains the specified property.

propertyName
Type: System.String

The property whose proposed value to get.

value
Type: System.Object%

When this method returns, contains an object that represents the proposed property value. This parameter is passed uninitialized.

Return Value

Type: System.Boolean
true if value is the proposed value for the specified property; otherwise, false.

TryGetValue returns false if there is not a binding for the specified item and property or if the value of the specified property is not available, due to a conversion error or because an earlier validation rule failed.

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

The following example creates a custom ValidationRule named ValidateDateAndPrice. In the Validate method, the example uses the TryGetValue method and the Items property to get the values the user entered into the form. Then the example checks that if an item is over 100 dollars, it will be available for at least seven days. For the entire example, see Validate the Data of an Object Sample.

public class ValidateDateAndPrice : ValidationRule
{
    // Ensure that an item over $100 is available for at least 7 days. 
    public override ValidationResult Validate(object value, CultureInfo cultureInfo)
    {
        BindingGroup bg = value as BindingGroup;

        // Get the source object.
        PurchaseItem item = bg.Items[0] as PurchaseItem;

        object doubleValue;
        object dateTimeValue;

        // Get the proposed values for Price and OfferExpires. 
        bool priceResult = bg.TryGetValue(item, "Price", out doubleValue);
        bool dateResult = bg.TryGetValue(item, "OfferExpires", out dateTimeValue);

        if (!priceResult || !dateResult)
        {
            return new ValidationResult(false, "Properties not found");
        }

        double price = (double)doubleValue;
        DateTime offerExpires = (DateTime)dateTimeValue;

        // Check that an item over $100 is available for at least 7 days. 
        if (price > 100)
        {
            if (offerExpires < DateTime.Today + new TimeSpan(7, 0, 0, 0))
            {
                return new ValidationResult(false, "Items over $100 must be available for at least 7 days.");
            }
        }

        return ValidationResult.ValidResult;

    }
}

Windows 7, Windows Vista, Windows XP SP2, Windows Server 2008 R2, Windows Server 2008, Windows Server 2003

The .NET Framework and .NET Compact Framework do not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.

.NET Framework

Supported in: 3.5 SP1, 3.0 SP2

Date

History

Reason

July 2008

Added topic for new class.

SP1 feature change.

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