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Silverlight 3 Quick Tip #9: DataBinding with Validation

Silverlight 3 provides validation mechanism while using Two-Way data binding.

Silverlight 3 also provides default a Validation Exception UI – callout with exception details, which could be customized.

Many input-related controls such as TextBox, CheckBox, etc. have built-in support for validation.

How to use? Simple, like everything with Silverlight: To enable validation, use the ValidatesOnExceptions property.

<TextBox Text="{Binding ID, Mode=TwoWay, ValidatesOnExceptions=True}" />


//Code behind – property definition
public string ID
        {
            get { return id; }
            set
            {
                if (string.IsNullOrEmpty(value))
                    throw new Exception("This field can't be empty!");

                id = value;
            }
        }

Example on ListBox:

<ListBox SelectedItem="{Binding Score,Mode=TwoWay,ValidatesOnExceptions=True}">
                    <sys:String>Best</sys:String>
                    <sys:String>Good</sys:String>
                    <sys:String>Ok</sys:String>
                    <sys:String>Acceptable</sys:String>
                    <sys:String>Bad</sys:String>
</ListBox>

//Code behind  property definition

public string Score
        {
            get { return score; }
            set
            {
                string[] acceptable = new string[] { "Ok", "Best", "Good" };

                if (!acceptable.Contains(value))
                    throw new Exception("The '" + value + "' is unacceptable");
                else if (value == "Ok")
                    throw new Exception("Ok is not the expected answer");

                score = value;
            }
        }

Sample UI:

Enjoy,

Alex