I am building a WPF 4.0 Application using MVVM. The Model is generated using Entity Framework 4.0. I am using Data binding on the WPF to bind the user input to model properties.
What is the easiest way to validate user input ? I prefer an approach where I can set the validation rules on the Model rather than on the WPF itself. How can this be done? Any samples are appreciated.
The easiest way i found is taken from this book, pages 624-625.
The ViewModel should implement IDataErrorInfo
private string _newItem;
public string NewItem
{
get { return _newItem; }
set
{
if (Equals(_newItem, value)) return;
_newItem = value;
SendPropertyChanged("NewItem");
}
}
public string this[string propertyName]
{
get
{
if (propertyName == "NewItem")
{
var valid = NewItem.All(Char.IsLetterOrDigit);
if (!valid)
return "NewItem can only contain letters and numbers.";
}
return null;
}
}
And the view the long version:
<TextBox>
<TextBox.Text>
<Binding UpdateSourceTrigger="PropertyChanged" Path="NewItem">
<Binding.ValidationRules>
<DataErrorValidationRule></DataErrorValidationRule>
</Binding.ValidationRules>
</Binding>
</TextBox.Text>
</TextBox>
Or the short version:
<TextBox Text="{Binding NewItem,UpdateSourceTrigger=PropertyChanged,ValidatesOnDataErrors=True}"/>
It should create a nice red border around your textbox when rule fails, and you can play around with the error message the way you want, for example bind the error message to a textbox tool tip (MSDN):
<Window.Resources>
<Style x:Key="TextBoxInError" TargetType="TextBox">
<Style.Triggers>
<Trigger Property="Validation.HasError" Value="true">
<Setter Property="ToolTip"
Value="{Binding RelativeSource={x:Static RelativeSource.Self},
Path=(Validation.Errors)[0].ErrorContent}"/>
</Trigger>
</Style.Triggers>
</Style>
</Window.Resources>
And then just add this to the textbox:
Style="{StaticResource TextBoxInError}"
Cheers!
The BookLibrary sample application of the WPF Application Framework (WAF) project shows a MVVM application. It uses the Entity Framework and defines the validation rules on the Model (Entity) classes.
