The WPF / Silverlight binding framework revolves around the concept of dependency properties, you can make any property the source of a binding, but the target must be a dependency property (DP). It's defined on the FrameworkElement class, which most UI controls, including the WPF Window, inherits from. To me, it is personal preference or usage-specific. From participating in sites like StackOverflow I have noticed that whilst most people understand how to create a user control, which allows them to 'stamp out' the same XAML in multiple places, many struggle with how to make their user controls flexible by exposing properties that configure how it looks or behaves. Asking for help, clarification, or responding to other answers. But from the Sub Window i can not set the datacontext with my data from the Sub Window. The the datacontext of MyUsercontrol is inherited from mainwindow and is MainWindoViewModel. Since the window has a DataContext, which is Find centralized, trusted content and collaborate around the technologies you use most. You will notice the same thing in Code-behind, where it simply inherits UserControl instead of Window. Site design / logo 2023 Stack Exchange Inc; user contributions licensed under CC BY-SA. The bindings in our FieldUserControl have a value for the Path, which specifies the target, but what is the source? I am Technology Director at Scott Logic and am a prolific technical author, blogger and speaker on a range of technologies. We do this by adding a Label property to our FieldUserControl. EVERYTHING YOU WANTED TO KNOW ABOUT DATABINDING IN WPF, SILVERLIGHT AND WP7 (PART TWO). If you do set it to self and you place this control on a Window or another control, it will not inherit the Windows DataContext. A limit involving the quotient of two sums. I'm also very active on GitHub, contributing to a number of different projects. This article, along with any associated source code and files, is licensed under The Code Project Open License (CPOL), General News Suggestion Question Bug Answer Joke Praise Rant Admin. Bindings have both a source and a target; where the binding framework is responsible for handling change notifications from the source and (optionally) the target, keeping the two synchronized. () . More info about Internet Explorer and Microsoft Edge, In the Sub Window is a UserControl Window. However, the code within the FieldUserControl constructor means that it no longer inherits its parent's DataContext (i.e. You set the properties on your control and those properties should be enough to make it "work". This is not such a big problem, we were going to have to change that anyway, a hard-coded binding to the Shoesize property means that we cannot re-use this control to edit other properties of the model object. F#\WPF-"'abc''xyz'" 5; MainWindowsUserControlDataContext 3; ViewModelDependencyProperty 0; MainWindowUserControlWPF DataContext . TestControl.xaml, ATestControlDataContextDataText Instead, you have to move Do new devs get fired if they can't solve a certain bug? When building user interfaces you will often find . Should you have any questions or need assistance from a member of our team, write to us at info@devexpress.com. Has 90% of ice around Antarctica disappeared in less than a decade? This preserves the Inheritance. defining a source for each binding, and once you really start using data bindings, you will definitely appreciate the time and typing saved. Furthermore, the FieldUserControl and its children all have the FieldUserControl as their DataContext, so their bindings work also: If the technique of binding the layout root of the user control to itself is a bit confusing - the following diagram, which shows the visual tree of our simple application, might help: Again, notice that the DataContext of FieldUserControl is inherited from its parent. (WinUI does still have Binding though.) example: The Code-behind for this example only adds one line of interesting code: After the standard InitalizeComponent() call, we assign the "this" reference to Custom controls are rather special, with the logic being de-coupled from the XAML in order to support templating. Instead you should set the DataContext in the first child UI element in your control. However, user controls in many cases ignore the DataContext and instead expose dependency properties that their host needs to bind to the data. It can be set for any FrameworkElement and specifies the design-time DataContext for a control and its children. This means that any bindings we add to FieldUserControl have the ModelObect as their source. What sort of strategies would a medieval military use against a fantasy giant? This is a summary of the above link. Each of them use data binding for all of the information needed - the Title and MaxLength comes from the Code-behind properties, which we have defined in as regular properties on a regular class. WPFUserControlBinding C# UserControlBinding UserControl <Button Content= "OK" Width= "75" Margin= "15 8 15 8" x:Name= "ButtonOk" /> ButtonOk CommandWindowBinding xaml .csDependencyProperty Do roots of these polynomials approach the negative of the Euler-Mascheroni constant? UserControl.DataContext Main View Main View DataContext Window.DataContext Main View UserControl DataContext Main View UserContext DataContext View ** DataContext is inherited property. Using Kolmogorov complexity to measure difficulty of problems? About an argument in Famine, Affluence and Morality. You can set the datacontext to self at the constructor itself. Staging Ground Beta 1 Recap, and Reviewers needed for Beta 2, UserControl as DataTemplate inside ListBox. DataContext, TestControlDataContextMainWindowDataContext, AUserControlDataContextBMainWindowDataContext By clicking Post Your Answer, you agree to our terms of service, privacy policy and cookie policy. Where to find XAML namespace d="http://schemas.microsoft.com/expression/blend/2008" mapping library? I know this has been answered but none of the explanations give an Understanding of DataContext and how it works. ViewModel runs data getting procedures(separate thread), ViewModel calls OnPropertyChanged("") to alert View that something has changed; check everything. you can easily break the chain of inheritance and override the DataContext with a new value. A Simple Pattern for Creating Re-useable UserControls in WPF / Silverlight. Find centralized, trusted content and collaborate around the technologies you use most. I would prefer to do it in a xaml file anyway. You can download the sourcecode for the example: UserControlExample.zip. Here's the full code sample for our window: With that, we can reuse this entire piece of functionality in a single line of code, as illustrated in this example where we have the limited text input control two times. This is one of the most common anti-patterns in WPF. Most people's first reaction is to set the DataContext of the user control to itself (I distinctly recall doing this myself the first time I encountered this problem!). I set my viewmodel datacontext the same way I observed Blend4 to. By setting the UserControl DataContext to itself, this overwrites the DataContext and breaks Inheritance. A server error occurred while processing your request. Now because we've hardcoded our data-context in the control it will instead attempt to lookup ColorToUse property on the ColorWithText object not your ViewModel, which will obviously fail. This is why you can't set the DataContext on the user control. So you need to set the DataContext on the root element. For example, I may have a complex entry form with a lot of Xaml. A part of the .NET Framework that provides a unified programming model for building line-of-business desktop applications on Windows. By clicking Post Your Answer, you agree to our terms of service, privacy policy and cookie policy. Browse other questions tagged, Where developers & technologists share private knowledge with coworkers, Reach developers & technologists worldwide. The binding in the working code is of course correct. Use Ctrl+Left/Right to switch messages, Ctrl+Up/Down to switch threads, Ctrl+Shift+Left/Right to switch pages. When one designs WPF UI elements in Microsoft Visual Studio or Blend, it is very beneficial to see them populated with sample data. What does this means in this context? We already have the Label dependency property, we now add a Value property: This value property is bound to the user control UI as follows: The idea here is that the exposed Value property 'relays' the value of the binding in our MainPage.xaml, which now has a binding which tells us which model object property is being displayed in our user control: If you compile and run this code you will find that it doesn't work! ex) XAML <UserControl x:Name="View"> Value= {Binding DataContext.ViewVar, ElementName=View} This is the code present in the MainWindow () constructor.The above code is setting the DataContext of the MainWindow as instance of the TaskViewModel. We'll start with a very simple example, an application that displays a simple form field which consists of a name and a value: This UI is bound to a simple model object that implements INotifyPropertyChanged (not shown for the sake of brevity): The constructor instantiates the model object and sets it as the DataContext: This produces the expected behaviour, a label and a text field that allows you to edit the Shoesize property: Let's say we want to allow the user to edit the Height property as well. the DataContext, which basically just tells the Window that we want itself to be the data context. To learn more, see our tips on writing great answers. In your code you have an AllCustomers property on your View Model but you are binding to Customers. You can also try It's a fairly common developer practice to use imperative code (in code-behind) to set a page or user control's DataContext to a view model instance. DataContextWPF. The problem is that the DataContext from the Window inherits to the DataContext from the User Control. Yes that's a better solution to use DI for sure. We have closed this ticket because another page addresses its subject: DevExpress engineers feature-complete Presentation Controls, IDE Productivity Tools, Business Application Frameworks, and Reporting Systems for Visual Studio, Delphi, HTML5 or iOS & Android development. The DataContext is inherited down the visual tree, from each control's parent to child. Within XAML Code-Behind ViewModelLocator Our focus is how to bind DataContext so we are not going to focus on styling or data in this article. I know this is an old post but for anyone else coming herYou don't set up a VM for an individual control. How to tell which packages are held back due to phased updates, How to handle a hobby that makes income in US, Theoretically Correct vs Practical Notation. WPF UserControl doesn't inherit parent DataContext, Styling contours by colour and by line thickness in QGIS. . Could not load type 'System.Windows.Controls.Primitives.MultiSelector' from assembly PresentationFramework. Generally though I always seem to struggle on comboboxes and getting the ItemsSource, SelectedValue and SelectedValuePath set up correctly to successfully show data in the combobox.
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