Having defined Validation Rule as above if user input is invalid, Text Box will have a red border.Like everything in WPF it is possible to customize it by setting a custom Control Template.Correspondingly, an underlying data value in the view model is automatically updated when the user modifies the bound value in the view.Provided that the view model has a property called “Name”, you bind it to a Text Box’s Text property in XAML the following way: Besides the path that specifies the name of the property to bind to, the binding must also have a source object.In this example I am implementing an generic validation rule that takes a regular expression as validation rule. If the expression matches the data is treated as valid. If you don’t specify a source explicitly by setting the Source property of the binding, it will inherit the Data Context from its parent element to use as its source.In a MVVM WPF application, the view model acts as the window’s Data Context: This means that that all controls inside the window will inherit its Data Context unless some parent element of a control overrides this by setting its own Data Context property.
I believe a good code must be simple and easy to understand. In that style we defining how our validation will look like.
The Mode property of the , which is the default for the Text property of the Text Box control, the text you type into the Text Box does not update the source property until the control loses focus which happens when you click away from it. the setter for the bound property of the Data Context to get called, as the user is typing into the Text Box you set the Update Source Trigger property to enumeration.
Setting the property to this value means that the value of the source property only gets updated when you explicitly call the Binding Expression. You will typically never use this approach in an MVVM application though.
Is there any way I can disable this validation errors on controls till user tries to submit the form? Error Content, you can add , Binds Directly To Source="True" and it will always show the first error and won't "lie to you" about errors that have already been corrected.
Except that the error will not necessarily be correct if there's more than one error. Alternatively, you could replace your Validation Tool Tip Template with the following: Thanks for your nice tutorial.