Learn more. Asked 7 years ago. Active 7 years ago. Viewed 1k times. I have a Forecast class. Dry: return ""; case GeneralForecast. Rainy: return "88FF"; case GeneralForecast. Snowy: return "FF22"; case GeneralForecast. Add a comment. Active Oldest Votes. But when you assign color in C somehow, you may not set the color as string. Instead you should use something like SolidColorBrush instances. To convert data during binding, you must create a class that implements the IValueConverter interface, which includes the Convert and ConvertBack methods.
The following example shows the implementation of a date converter that converts the date value passed in so that it only shows the year, the month, and the day. When implementing the IValueConverter interface, it is a good practice to decorate the implementation with a ValueConversionAttribute attribute to indicate to development tools the data types involved in the conversion, as in the following example:.
In the following example, src maps to the namespace in which DateConverter is defined. Finally, you can use the converter in your binding using the following syntax. In the following example, the text content of the TextBlock is bound to StartDate , which is a property of an external data source. 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. The view over the collection allows you to impose an order, or change the default order, based on comparison criteria that you supply. Because it's a client-based view of the data, a common scenario is that the user might want to sort columns of tabular data per the value that the column corresponds to. Using views, this user-driven sort can be applied, again without making any changes to the underlying collection or even having to requery for the collection content.
For an example, see Sort a GridView column when a header is clicked. The following example shows the sorting logic of the "Sort by category and date" CheckBox of the app UI in the What is data binding section.
Views can also apply a filter to a collection, so that the view shows only a certain subset of the full collection. You might filter on a condition in the data. If you're using one of the CollectionView classes directly instead of CollectionViewSource , you would use the Filter property to specify a callback.
For an example, see Filter Data in a View. Except for the internal class that views an IEnumerable collection, all collection views support grouping , which allows the user to partition the collection in the collection view into logical groups.
The groups can be explicit, where the user supplies a list of groups, or implicit, where the groups are generated dynamically depending on the data. The following example shows the logic of the "Group by category" CheckBox. Views also support the notion of a current item. You can navigate through the objects in a collection view.
As you navigate, you're moving an item pointer that allows you to retrieve the object that exists at that particular location in the collection. For an example, see Navigate through the objects in a data CollectionView. Because WPF binds to a collection only by using a view either a view you specify, or the collection's default view , all bindings to collections have a current item pointer. In the following example, the data context is a collection view.
The first line binds to the collection. The second line binds to the current item in the collection. The third line binds to the Description property of the current item in the collection.
The slash and property syntax can also be stacked to traverse a hierarchy of collections. The following example binds to the current item of a collection named Offices , which is a property of the current item of the source collection.
The current item pointer can be affected by any sorting or filtering that is applied to the collection. Sorting preserves the current item pointer on the last item selected, but the collection view is now restructured around it. Perhaps the selected item was at the beginning of the list before, but now the selected item might be somewhere in the middle.
Filtering preserves the selected item if that selection remains in view after the filtering. Otherwise, the current item pointer is set to the first item of the filtered collection view. The notion of a current item is useful not only for navigation of items in a collection, but also for the master-detail binding scenario.
Consider the app UI in the What is data binding section again. In that app, the selection within the ListBox determines the content shown in the ContentControl. To put it in another way, when a ListBox item is selected, the ContentControl shows the details of the selected item. You can implement the master-detail scenario simply by having two or more controls bound to the same view. The following example from the Data binding demo shows the markup of the ListBox and the ContentControl you see on the app UI in the What is data binding section.
Notice that both of the controls are bound to the same source, the listingDataView static resource see the definition of this resource in the How to create a view section. This binding works because when a singleton object the ContentControl in this case is bound to a collection view, it automatically binds to the CurrentItem of the view. The CollectionViewSource objects automatically synchronize currency and selection. If your list control isn't bound to a CollectionViewSource object as in this example, then you would need to set its IsSynchronizedWithCurrentItem property to true for this to work.
For other examples, see Bind to a collection and display information based on selection. NET Framework and Use the master-detail pattern with hierarchical data. You may have noticed that the above example uses a template.
In fact, the data would not be displayed the way we wish without the use of templates the one explicitly used by the ContentControl and the one implicitly used by the ListBox. We now turn to data templating in the next section. Without the use of data templates, our app UI in the What is data binding section would look like the following. As shown in the example in the previous section, both the ListBox control and the ContentControl are bound to the entire collection object or more specifically, the view over the collection object of AuctionItem s.
Without specific instructions of how to display the data collection, the ListBox displays the string representation of each object in the underlying collection, and the ContentControl displays the string representation of the object it's bound to.
To solve that problem, the app defines DataTemplates. As shown in the example in the previous section, the ContentControl explicitly uses the detailsProductListingTemplate data template. The ListBox control implicitly uses the following data template when displaying the AuctionItem objects in the collection. With the use of those two DataTemplates, the resulting UI is the one shown in the What is data binding section. As you can see from that screenshot, in addition to letting you place data in your controls, DataTemplates allow you to define compelling visuals for your data.
For more information about data templates, see the Data templating overview. Most app that take user input need to have validation logic to ensure that the user has entered the expected information. The validation checks can be based on type, range, format, or other app-specific requirements.
This section discusses how data validation works in WPF. ValidationRules property. A ValidationRule object checks whether the value of a property is valid. WPF has two types of built-in ValidationRule objects:.
A ExceptionValidationRule checks for exceptions thrown during the update of the binding source property. In the previous example, StartPrice is of type integer. When the user enters a value that cannot be converted to an integer, an exception is thrown, causing the binding to be marked as invalid. For more information about using this validation rule, see DataErrorValidationRule. You can also create your own validation rule by deriving from the ValidationRule class and implementing the Validate method.
Because the UpdateSourceTrigger value is PropertyChanged , the binding engine updates the source value on every keystroke, which means it also checks every rule in the ValidationRules collection on every keystroke. We discuss this further in the Validation Process section. If the user enters an invalid value, you may want to provide some feedback about the error on the app UI.
One way to provide such feedback is to set the Validation. ErrorTemplate attached property to a custom ControlTemplate. The following example shows the definition of validationTemplate.
The AdornedElementPlaceholder element specifies where the control being adorned should be placed. In addition, you may also use a ToolTip to display the error message. The following example shows the definition of textStyleTextBox.
The attached property Validation. HasError is true when one or more of the bindings on the properties of the bound element are in error.
If your Binding has associated validation rules but you do not specify an ErrorTemplate on the bound control, a default ErrorTemplate will be used to notify users when there's a validation error. The default ErrorTemplate is a control template that defines a red border in the adorner layer. For an example of how to provide logic to validate all controls in a dialog box, see the Custom Dialog Boxes section in the Dialog boxes overview. Validation usually occurs when the value of a target is transferred to the binding source property.
To reiterate, what causes a source update depends on the value of the UpdateSourceTrigger property, as described in the What triggers source updates section. The following items describe the validation process. If a validation error or other type of error occurs at any time during this process, the process is halted:. The binding engine checks if there are any custom ValidationRule objects defined whose ValidationStep is set to RawProposedValue for that Binding , in which case it calls the Validate method on each ValidationRule until one of them runs into an error or until all of them pass.
If the converter succeeds, the binding engine checks if there are any custom ValidationRule objects defined whose ValidationStep is set to ConvertedProposedValue for that Binding , in which case it calls the Validate method on each ValidationRule that has ValidationStep set to ConvertedProposedValue until one of them runs into an error or until all of them pass.
The binding engine checks if there are any custom ValidationRule objects defined whose ValidationStep is set to UpdatedValue for that Binding , in which case it calls the Validate method on each ValidationRule that has ValidationStep set to UpdatedValue until one of them runs into an error or until all of them pass.
0コメント