Validating data in wpf northlondondating com
Main Take note of how I set the Data Context of the Window to a new instance of Main Window View Model; this causes the instance of Main Window View Model to flow to the Data Context properties of all of the window’s child elements (unless explicitly set otherwise) such as our Text Box and Check Box controls.That way, when we use our statements for the Text Box and Check Box controls used in this example we know that we are binding directly to our Main Window View Model instance.
In our Required If Attribute we provide the means to perform validation on property “A” only if the value of property “B” equals values “C”, “D” or “F”.
As I mentioned in a previous post, you can specify validation by creating a Validation class (or classes).
You do this by deriving a new class from the Validation Rule class and overriding the Validate method.
The idea behind this is to be able to do something like this: Looking at the [Required If(...)] attribute, simply put it means: “`Last Name´ is required if the property `Is Last Name Required´ equals true. Okay, let’s have a look at our view-model and the XAML for the window we will be binding to the view-model: Main Window View Note that in the constructor I am setting `Use Explicit Validation´ to true, and also that I am raising the `On Property Changed´ event each time a property is set.
When validation fails, the error message to display is `Last name is required.´”. Raising the Property Changed event is very important to ensure that binding works and for the framework to know when a property has changed.In this post, I’m going to show you how to use the IData Error Info interface along with INotify Property Changed and the MVVM pattern to perform cross-field validation (e.g. Now, I want to point out that I wrote the Validation View Model to work with two different methods of validation: “Implicit” and “Explicit” – implicit meaning that the validation is executed automatically on a control’s default validation check which occurs on binding, and explicit meaning that you need to explicitly call the Validate() method on the view-model to trigger validation.field A should only be validated if field B is true) using nothing but attributes (and of course a little bit of helper code, which I’ll give you). Before you get started, you need to add a reference to the System. To change the mode, you can set the property `Use Explicit Validation´ in your view-model constructor (or change it at any time elsewhere).Since we’re using some Text Box controls it might be worth mentioning that Text Box.