I am trying to make a wizard in wpf using the wpf toolkit extended wizard control.
I need to prevent the user from proceeding to the next page unless certain conditions are met.
This answer to another question suggested binding the CanSelectNextPage property to a boolean property in the code behind the current page.
I am having trouble implementing INotifyPropertyChanged. In the answer linked above, his MainWindow class extends INotifyPropertyChanged. How is that possible? Wouldn't the MainWindow class have to extend the Window class?
Also, what assembly is INotifyPropertyChanged located in? MSDN says it is in System.ObjectModel.dll which I don't seem to have...
His MainWindow class implements INotifyPropertyChanged, which is found in System.ComponentModel.
This MSDN article should explain how to use it: https://msdn.microsoft.com/en-us/library/vstudio/system.componentmodel.inotifypropertychanged(v=vs.100).aspx
INotifyPropertyChanged will notify clients, such as your UI, when a given property changes. You could bind the visibility of your 'next' button to a boolean property of your class, and set the boolean property to true once all of your other properties are set.
EDIT: I should add that in order to bind a boolean value to the visibility of a button, you'll need to use an IValueConverter.
First off, INotifyPropertyChanged is an interface, not a class. So while a class can inherit from a single class only (here the Window class), it can implement multiple interfaces.
The interface itself is located in the System.dll assembly in the System.ComponentModel namespace.
Related
I'm programming a bunch of WPF usercontrols (not CommonControls!) using an Interface for the common properties like the alignments or the Content (depending on the control; TextBox returns the Text, and Label the Content per example).
Now i get to controls like the Checkbox, which have the not so common property IsChecked.
Do i have to implement this property by the Interface or is it allowed to program it in the usercontrol itself?
I hope you're talking about binding a property to a view model or directly mentioning the property value in the xaml itself.
It actually depends upon your requirement. We normally bind a property value to a view model or code behind when that property needs to be checked by certain conditions and then to be set. If you're sure of the property's value, you can set it in xaml itself.
For example if you want to set a textbox's IsEnabled property, and you're sure that the text box is always editable. Then set it as true in xaml itself. But if you're text box need to be enabled during an event is handled, bind it to a property in view model and set it to true during the event trigger.
Okay, i have to guess it was a dumb question.
But after eight hours you don't know anymore, if you're Hillary or Donald.
The answer is: An Interface can inherit from another and implement all members from the "parent" interface.
I develop WPF MVVM application that uses class which inherits from TriggerAction<UIElement> base class.
public class DropTrigger : TriggerAction<UIElement> {...}
This class handle drop files event and should pass the list of files to the ViewModel bounded class.
In this case, should the DropTrigger class be in View or ViewModel?
If it should be in the view (like I think), how can I execute methods in the MVVM bounded class from DropTrigger class?
Thank you !
I cannot give you a definitive answer without seeing more of your code. The most likely case is you would have an ICommand dependency property on your DropTrigger that you bind to a ViewModel property, then you pass the files in the CommandParameter.
The Trigger is, like the behavior, neither View nor ViewModel. Create a separate project folder containing these classes.
I have a custom Control with dependency property attached by its parent and i need to implement some hook that will be triggered on all attached property changes. In WPF it was rather easy but i have no idea how this can be achieved in WinRT environment.
For example, i have Control with attached property X and its parent is GraphArea. So attached property for Control is GraphArea.X.
Please give me some clues, thanks :)
Found the way to do this though not exactly as i wanted to. Instead of hooking to X change inside every Control i've hooked to attached property changed callback of the parent.
Additionaly, i've implemented new interface for all children that must receive notification when this property changes. And as i've implemented interface methods as explicit interface implementations they are not be visible from derived classes (which is good as this operation must be internal).
Another solution is to make code-behind binding between dependency property and attached property and define OnChanged callback for DP. But in WinRT this approach only works for internal Attached Properties (not the custom created).
I have an MvxListView that binds to a property on the ViewModel which is a List<MyClass>.
MyClass is a plain old object that has a boolean property named Completed that I've bound to the Checked property of a CheckedTextView in my list view item template.
When I click on the list view item, it invokes a command which calls a DoSomething(MyClass item) method. In the DoSomething method, I set the Completed property to its new value. However, because MyClass is not a ViewModel with RaisePropertyChanged properties, the checked property doesn't get updated in the user interface.
How would I accomplish data binding on this basic POCO to get the user interface to update when the Completed property changes?
How would I accomplish data binding on this basic POCO to get the user interface to update when the Completed property changes?
Xaml/C# style Data-Binding relies on INotifyPropertyChanged - without this the UI has no way to know that it needs to update.
So to get data-binding to work, your MyClass objects can't just be a POCO - it needs to implement INotifyPropertyChanged somehow - e.g. by inheriting from MvxNotifyPropertyChanged or by implementing INotifyPropertyChanged directly (e.g. see http://msdn.microsoft.com/en-us/library/vstudio/ms229614%28v=vs.100%29.aspx)
Aside: MvvmCross does also make other binding patterns possible beyond INotifyPropertyChanged - e.g. see INotifyChanged in FieldBinding in https://github.com/MvvmCross/MvvmCross/wiki/Databinding#rio - but this still requires something more than just POCOs for dynamically updating bindings.
I have an ObservableCollection that's binded to a WPF ListView, and all the values appear correct. But how can I get a notification when something that has a 2-way binding changes?
Should I use INotifyPropertyChanged just like in Winforms? Or are there better practices to do these?
I saw some people suggesting using dependency properties online, but not sure if that's what should do.
If the class I want to add a property is a DependencyObject, I generally add a DependencyProperty. If the class is a POCO (plain old clr objects), then I implement INotifyPropertyChanged.
In generall, all my business objects are POCOs and therefore I use INotifyPropertyChanged. In the WPF world, I mostly use DependencyObjects (view models, custom controls, UserControls...) and therefore they are DependencyProperties. An exception are ViewModels representing items (to be used as items in an items source). In this case I think DependencyProperties are not very practical (Because Equals() and GetHashCode() of DependencyObjects are sealed and DependencyObject is thread-dependent).
If your class already is a DependencyObject, using DependencyProperties may give you some nice advantages: You don't have to back every value, a powerfull inheritance system, default-values, property changed callbacks per property, value coercion ... (I like DependencyProperties probably more than other people them like :)
Conclusion:
Based on the title of your question: How to get notified when something changes in a WPF window?, my way would be to add a DependencyProperty and not a clr-property because the Window is a DependencyObject. By the way, Visual Studio has a nice Snippet to create DependencyProperties.
There are really two scenarios:
1) Notifying the UI when a piece of data changes-either in the ViewModel or a Model that is bound to some UI elements (usually due to a data binding). In this scenario you'd use INotifyPropertyChanged.
Example: you have a Person object that binds it's Name to a TextBox. Person needs to implement INotifyPropertyChanged and the appropriate code needs to be attached to the Name Property's setter.
2) Creating custom UI elements where you'd want data to be bound. In this case, you'd use custom dependency properties.
Example: you have a custom UI element that spins when a certain condition is met. So you create an IsSpinning dependency property that you can bind to your ViewModel's IsLoading property. The custom control then uses the IsSpinning property to modify its behavior.
I hope that was clear...
You are right. You can use INotifyPropertyChanged or you can implement dependency properties. Personally I prefer INotifyPropertyChanged, it's more light and easyer to implement than dependency property.
I've generally used INotifyPropertyChanged for my data objects.
DependencyProperties can only be implemented on framework elements I believe.
Edit: I take that back... DependencyProperties can only be implemented on DependencyObjects (A FrameworkElement is an example of that as it derives from UIElement which derives from Visual which derives from DependencyObject).
If you have a UserControl, you may wish to implement a Dependency Property so you can Bind that Property (in XAML) to some other property. You could not do this scenario with INotifyPropertyChanged.