This is useful for applying validation error information in bindings at the template level. This is useful for binding one property of an element to another property on the same element. Type: System. RelativeSource The relative location of the binding source to use. The default is nulla null reference Nothing in Visual Basic. The Binding has already been attached to a target element, and cannot be modified.
The ElementName or Source property has already been set. Source , RelativeSource, and ElementName are mutually exclusive in a binding. If you have set one of these attributes, then setting either of the other two in a binding through XAML or through code will cause an exception. This is also true if you are creating the entire binding as a Binding Markup Extension , in which case the RelativeSource Markup Extension is nested within the RelativeSource component of the expression.
Like most templates in Silverlight, you can use a DataGridTemplate column to display nearly anything you want inside a grid — use calendars, stack panels, colored rectangles, etc. Notice the TimeCards column in the above screen shot.
Now look at the following XAML:. Using the DataGridTemplateColumn we can even define a nested data grid to display all the time cards for an employee. For more information about the grid control, I highly recommend the following blog posts. The problem is that validation errors are tricky to catch with the DataGrid. Validation is only a concern for TwoWay data bindings.
When Silverlight moves data from your view back into your model — how do you control the values your model accepts? One example is trying to place an order for —1 books. You want the quantity value of an order to always be positive. In these cases you must your model throw an exception when Silverlight sets the value. How do you know the exception occurred? Silverlight can tell you about both types of validation errors, but you must set two properties on a binding to true. The first property is the ValidatesOnExceptions property.
This property tells Silverlight to catch exceptions that occur when data moves from the view to the model. In order to know about these exceptions you must also set the NotifyOnValidationError property to true. When true, Silverlight will raise a BindingValidationError event. The BindingValidationError event can tell you the source of an error, and also if the error is being added the user just entered bad input or removed the user corrected a bad input.
We can use this information to change elements on the screen, such as making the control that is the source of the failure turn red. Silverlight data binding features are flexible and powerful, and provide you with everything you need to build an effective business application.
Moving data back and forth has never been easier! Articles Blog Videos Archive About. Databinding in Silverlight Saturday, March 28, Scott Allen Subscribe. The purpose of dependency properties is to provide a way to determine the value of a property based on inputs including, but not limited to, user preferences, resources, styles, or data binding.
This would allow the color of the rectangle to be determined at runtime. Dependency Properties are not declared as a standard. If the backing property name has the Property suffix then it is generally the backing property for a Dependency Property.
The instance of the backing property,FillProperty. A dependency property can also get its value through a data-binding operation. Instead of setting the value to a specific color or a Brush, the value can be set through data-binding.
The binding uses an inherited data context and an instance of an object data source referred to as MyShape. The binding syntax and the DataContext will be explored later in this article. Besides basic data binding, styles and templates are a huge beneficiary of using dependency properties. Controls that use styles are indicated through a StaticResource defined in app. The style resources are often set to a Dependency Property to achieve a more elegant appearance.
Dependency Property values are determined using an order of precedence. For example a style resource may set the Background Dependency Property to White for a canvas control. However the Background color can be overridden in the control itself by setting the Background property to Blue. The order of precedence exists in order to ensure that the values are set in a consistent and predictable manner.
The previous example of the Rectangle control shows that the locally-set property value has a higher precedence than a resource. When creating a binding, a Dependency Property of a FrameworkElement must be assigned to the binding. This is the target of the binding operation. The source of the binding can be assigned through the DataContext property of the UI element or any UI element that is a container for the bound UI element. One of the main pieces of functionality offered by the Dependency Property is its ability to be data bound.
In XAML, the data binding works through a specific markup extension syntax. Alternatively, the binding can be established through. NET code. A set of XAML attributes exist in order to support the data binding features. A basic example of the usage of these extensions is shown in the pseudo-code examples below. The element must be a FrameworkElement thus the name someFrameworkElement. The property would be replaced with the name of the property that will be the target of the binding.
For example the element might be a TextBox and the property might be Text. To bind the value of the property to a source the binding markup extensions can be used. The Binding attribute indicates that the value for the Dependency Property will be derived from a data binding operation.
The binding gets its source from the DataContext for the element or the DataContext that is inherited from the closest parent element. As we discussed earlier, we need to allow changes made in the data source to reflect immediately on the target. How is this possible? This is possible by implementing the INotifyPropertyChanged interface. What you need to do is take the namespace System. This has the single method called PropertyChanged.
When setting a property value, you need to call the OnPropertyChanged method if any value changes. Add a reference to System. ObjectModel before using ObservableCollection. I hope you enjoyed my article. Please do not forget to write your comments on this article, which is very important for me.
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