Path property to specify the value to use for your binding. If you're binding to XML data, you use the Binding. XPath property to specify the value. In some cases, it may be applicable to use the Path property even when your data is XML. For example, if you want to access the Name property of a returned XmlNode as a result of an XPath query , you should use the Path property in addition to the XPath property.
For more information, see the Path and XPath properties. Although we have emphasized that the Path to the value to use is one of the four necessary components of a binding, in the scenarios that you want to bind to an entire object, the value to use would be the same as the binding source object. In those cases, it's applicable to not specify a Path.
Consider the following example. When the path isn't specified, the default is to bind to the entire object. In other words, in this example, the path has been left out because we are binding the ItemsSource property to the entire object. See the Binding to collections section for an in-depth discussion. Other than binding to a collection, this scenario is also useful when you want to bind to an entire object instead of just a single property of an object.
For example, if your source object is of type String , you may simply want to bind to the string itself. Another common scenario is when you want to bind an element to an object with several properties. You may need to apply custom logic so that the data is meaningful to your bound target property. The custom logic may be in the form of a custom converter if default type conversion doesn't exist.
See Data conversion for information about converters. Before getting into other features and usages of data binding, it's useful to introduce the BindingExpression class. As you have seen in previous sections, the Binding class is the high-level class for the declaration of a binding; it provides many properties that allow you to specify the characteristics of a binding.
A related class, BindingExpression , is the underlying object that maintains the connection between the source and the target.
A binding contains all the information that can be shared across several binding expressions. A BindingExpression is an instance expression that cannot be shared and contains all the instance information of the Binding.
Consider the following example, where myDataObject is an instance of the MyData class, myBinding is the source Binding object, and MyData is a defined class that contains a string property named ColorName.
You can use the same myBinding object to create other bindings. For example, you can use the myBinding object to bind the text content of a check box to ColorName. In that scenario, there will be two instances of BindingExpression sharing the myBinding object. The following articles demonstrate some of the usages of the BindingExpression class:.
In the Create a binding section, the button is red because its Background property is bound to a string property with the value "Red". This string value works because a type converter is present on the Brush type to convert the string value to a Brush. Adding this information to the figure in the Create a binding section looks like this. However, what if instead of having a property of type string your binding source object has a Color property of type Color? In that case, in order for the binding to work you would need to first turn the Color property value into something that the Background property accepts.
You would need to create a custom converter by implementing the IValueConverter interface, as in the following example. See IValueConverter for more information. To reiterate, default conversions may be available because of type converters that are present in the type being bound to. This behavior will depend on which type converters are available in the target. If in doubt, create your own converter. Your data should be displayed differently, depending on culture.
The data being used isn't necessarily intended to change the text value of a property, but is instead intended to change some other value, such as the source for an image, or the color or style of the display text. Converters can be used in this instance by converting the binding of a property that might not seem to be appropriate, such as binding a text field to the Background property of a table cell.
More than one control or multiple properties of controls are bound to the same data. In this case, the primary binding might just display the text, whereas other bindings handle specific display issues but still use the same binding as source information. A target property has a collection of bindings, which is termed MultiBinding. For example, color may be computed from red, blue, and green values, which can be values from the same or different binding source objects.
See MultiBinding for examples and information. A binding source object can be treated either as a single object whose properties contain data or as a data collection of polymorphic objects that are often grouped together such as the result of a query to a database. So far we've only discussed binding to single objects. However, binding to a data collection is a common scenario. For example, a common scenario is to use an ItemsControl such as a ListBox , ListView , or TreeView to display a data collection, such as in the app shown in the What is data binding section.
Fortunately, our basic diagram still applies. If you're binding an ItemsControl to a collection, the diagram looks like this. As shown in this diagram, to bind an ItemsControl to a collection object, ItemsControl. ItemsSource property is the property to use. You can think of ItemsSource as the content of the ItemsControl.
You can enumerate over any collection that implements the IEnumerable interface. However, to set up dynamic bindings so that insertions or deletions in the collection update the UI automatically, the collection must implement the INotifyCollectionChanged interface. This interface exposes an event that should be raised whenever the underlying collection changes.
To fully support transferring data values from source objects to targets, each object in your collection that supports bindable properties must also implement the INotifyPropertyChanged interface. If you have an advanced scenario and want to implement your own collection, consider using IList , which provides a non-generic collection of objects that can be individually accessed by the index, and thus provides the best performance.
Once your ItemsControl is bound to a data collection, you may want to sort, filter, or group the data. To do that, you use collection views, which are classes that implement the ICollectionView interface.
A collection view is a layer on top of a binding source collection that allows you to navigate and display the source collection based on sort, filter, and group queries, without having to change the underlying source collection itself.
A collection view also maintains a pointer to the current item in the collection. If the source collection implements the INotifyCollectionChanged interface, the changes raised by the CollectionChanged event are propagated to the views.
Because views do not change the underlying source collections, each source collection can have multiple views associated with it.
For example, you may have a collection of Task objects. With the use of views, you can display that same data in different ways. For example, on the left side of your page you may want to show tasks sorted by priority, and on the right side, grouped by area. One way to create and use a view is to instantiate the view object directly and then use it as the binding source.
For example, consider the Data binding demo app shown in the What is data binding section. The app is implemented such that the ListBox binds to a view over the data collection instead of the data collection directly. The following example is extracted from the Data binding demo app.
The resource listingDataView then serves as the binding source for elements in the app, such as the ListBox. To create another view for the same collection, you can create another CollectionViewSource instance and give it a different x:Key name. The following table shows what view data types are created as the default collection view or by CollectionViewSource based on the source collection type. Specifying a collection view as a binding source is one way to create and use a collection view.
WPF also creates a default collection view for every collection used as a binding source. If you bind directly to a collection, WPF binds to its default view. This default view is shared by all bindings to the same collection, so a change made to a default view by one bound control or code such as sorting or a change to the current item pointer, discussed later is reflected in all other bindings to the same collection. To get the default view, you use the GetDefaultView method.
For an example, see Get the default view of a data collection. To improve performance, collection views for ADO. NET DataTable or DataView objects delegate sorting and filtering to the DataView , which causes sorting and filtering to be shared across all collection views of the data source. To enable each collection view to sort and filter independently, initialize each collection view with its own DataView object.
As mentioned before, views can apply a sort order to a collection. As it exists in the underlying collection, your data may or may not have a relevant, inherent order.
Connect and share knowledge within a single location that is structured and easy to search. For each index, I want to look up its record in a database table. But a breakpoint in the converter is telling me that the value being read in by the ItemTemplate binding is of the window itself — i. Pardon a bit of candidness, but this seems DUMB.
The entire point of the ItemTemplate is to render each element within the ItemsSource , so I guess I figured that the DataContext of the ItemTemplate would be the individual element being rendered.
So, that said, how do I tell the ItemTemplate that it should worry about the individual elements represented by the ItemsSource and not use the entire window's DataContext? You need to use a data template for the ItemTemplate. This is then applied to each item in the list. The issue her is about data context scope. When you bind any property on the ListBox, it will use the data context of the ListBox - hence why that data context is being passed to the converter. If you set a data template inside the ItemTemplate, it will apply that template to each item in the list.
I guess based on the simple code you've provided you would need to have the converter inside the data template:. Great web site. Commented on 9.
November Worst discussion No Hemanath It is not like that It is really worth reading WPF rocks It is a worthy read, but I need a few results now. I downloaded the sample and all it has it a bunch of checkboxes and textbox, i don't see any datatemplaing in the working Wow, I worked for a very long time on how to put together a dynamic property editor, and you make it look so easy. The key was Grid. Well done and thanks! Commented on 3. Hi, I tried you method, all the text content are not rendered the TextBlock showing nothing, even I place a button and bind Name for the content, still nothing.
I am sure there is data, and before using data template, it's showing. The easiest and the most obvious way to achieve this is to bind the Visibility property of the elements so that one is shown while the other is collapsed or hidden. However, this approach comes at a cost. Changing the value of Visibility property tends to get the job done but it has some noticeable drawbacks:.
The last point is something that tends to get overlooked and may lead to problems.
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