In the StockTraderRI sample code the ViewModel is injected by MEF using a property:
[Export(typeof(IOrdersView))]
[PartCreationPolicy(CreationPolicy.NonShared)]
public partial class OrdersView : UserControl, IOrdersView
{
public OrdersView()
{
InitializeComponent();
}
[Import]
[SuppressMessage("Microsoft.Design", "CA1044:PropertiesShouldNotBeWriteOnly", Justification = "Needs to be a property to be composed by MEF")]
public IOrdersViewModel ViewModel
{
set { this.DataContext = value; }
}
}
What I wonder is: why not use an ImportingConstructor like this to inject the ViewModel:
[Export(typeof(IOrdersView))]
[PartCreationPolicy(CreationPolicy.NonShared)]
public partial class OrdersView : UserControl, IOrdersView
{
[ImportingConstructor]
public OrdersView(IOrdersViewModel ViewModel)
{
InitializeComponent();
this.DataContext = ViewModel;
}
}
Is there a special feature, problem or reason I miss why the StockTraderRI sample does use a Property instead of a paramter to the ctor?
Because types partially defined in XAML don't play well with parametrized constructors. XAML is built on the "create a blank object and fill in the properties afterwards" paradigm.
Related
I am creating UWP app using Template 10. I have created user control like this.
<my:DeviceInfoUserControl OnEndpointTypeChange="{Binding OnEndpointTypeChangeCommand}" Component="{Binding DeviceManagementViewModel,Mode=TwoWay}"></my:DeviceInfoUserControl>
I have Radio Buttons on User Control. I have added User Control on Multiple screens.
This user control has its own ViewModel as well as Some Dependency Properties as follows:
public class DeviceManagementViewModel : ViewModelBase
{
}
public sealed partial class DeviceInfoUserControl : UserControl
{
public bool IsToggled = true;
public DeviceInfoUserControl()
{
this.InitializeComponent();
}
public static readonly DependencyProperty OnEndpointTypeChangeProperty =
DependencyProperty.Register(
"OnEndpointTypeChange",
typeof(ICommand),
typeof(DeviceInfoUserControl), new PropertyMetadata(null));
public ICommand OnEndpointTypeChange
{
get { return (ICommand)GetValue(OnEndpointTypeChangeProperty); }
set { SetValue(OnEndpointTypeChangeProperty, value); }
}
public static readonly DependencyProperty ComponentProperty = DependencyProperty.Register("Component", typeof(DeviceManagementViewModel), typeof(DeviceInfoUserControl), new PropertyMetadata(null));
public DeviceManagementViewModel Component
{
get { return (DeviceManagementViewModel)GetValue(ComponentProperty); }
set { SetValue(ComponentProperty, value); }
}
}
I want to preserve Radio Button Selection across all screens. How should I achieve this?
You have to ensure that the same ViewModel instance is used for all control instance. The XAML way is always create new instance:
<Page.DataContext>
<vm:DetailPageViewModel x:Name="ViewModel" />
</Page.DataContext>
In the Template10's Bootstrapper class with the ResolveForPage method override, you can inject ViewModel's after the page navigation through a custom logic, or through dependency injection LINK
Don't know its better way or not but I have achieved this by making Singletone Viewmodel.
public class DeviceManagementViewModel : ViewModelBase
{
public static readonly DeviceManagementViewModel _instance = new DeviceManagementViewModel ();
private DeviceManagementViewModel ()
{
}
/*Properties and Methods */
}
In Parent Screen ViewModel I have created following property
private DeviceManagementViewModel _deviceManagementViewModel;
public DeviceManagementViewModel DeviceManagementViewModel1
{
get { return _deviceManagementViewModel; }
set { Set(ref _deviceManagementViewModel, value); }
}
I have Instantiated property in Constructor:
public ConfigurationViewModel()
{
DeviceManagementViewModel1 = DeviceManagementViewModel._instance;
}
And on User Control:
<my:DeviceInfoUserControl OnEndpointTypeChange="{Binding OnEndpointTypeChangeCommand}" Component="{Binding DeviceManagementViewModel1,Mode=TwoWay}"></my:DeviceInfoUserControl>
Is there any way to declare dependency property inside viewmodel? I want to declare a dependency property inside viewmodel and change it's value through command.
public class MyViewModel : Prism.Windows.Mvvm.ViewModelBase
{
public bool IsPaneVisible
{
get { return (bool)GetValue(IsPaneVisibleProperty); }
set { SetValue(IsPaneVisibleProperty, value); }
}
public static readonly DependencyProperty IsPaneVisibleProperty =
DependencyProperty.Register("IsPaneVisible", typeof(bool), typeof(MyViewModel), new PropertyMetadata(0));
public ICommand VisibilityChangeCommand { get; set; }
public MyViewModel()
{
VisibilityChangeCommand = new DelegateCommand(OnVisibilityChange);
}
private void OnVisibilityChange()
{
IsPaneVisible = !IsPaneVisible;
}
}
Problem is, I am getting some compilation error in IsPaneVisible' getter/setter : "GetValue does not exist in the current context". Is there any alternative way to do this?
A DependencyProperty is used on a DependencyObject, an example of this is a UserControl. Prism's ViewModelBase is no DependencyObject, mainly because this type is platform specific. To support binding from a viewmodel, we typically use INotifyPropertyChanged.
Prism implements this interface in the BindableBase base class, from which ViewModelBase derives as well. You define your properties like this:
private string _imagePath;
public string ImagePath
{
get { return _imagePath; }
set { SetProperty(ref _imagePath, value); }
}
If you install the Prism Template Pack Visual Studio extension, you can use the propp code snippet.
I read lots of articles, And found that lots of people use INotifyPropertyChanged in ViewModel either Model as well. So, I am confused about INotifyPropertyChanged where to use.
A popular approach is to use a base class which Implements InotifyPropertyChanged interface and then inherit this base class in your View Model.
example:
public class NotifyPropertyBase : INotifyPropertyChanged
{
public event PropertyChangedEventHandler PropertyChanged;
public void OnPropertyChanged(string propertyName)
{
if (PropertyChanged != null)
{
PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
}
}
}
Then inherit the base class in the view model:
class MainViewModel : NotifyPropertyBase
Finally, raise the OnPropertyChanged event in the property setter of your view model passing in the property name string as the parameter:
private string _name;
public string Name
{
get { return _name; }
set
{
_name= value;
OnPropertyChanged("Name");
}
}
Now your UI should update at run time provided the binding is declared correctly in the Xaml.
When I implement the ICommand interface, the following methods are created
#region ICommand Members
public bool CanExecute(object parameter)
{
}
public event EventHandler CanExecuteChanged;
public void Execute(object parameter)
{
}
#endregion
The interesting part is
public void Execute(object parameter)
{
}
Simply because it indicates that it expects 1 parameter. What if I don't need to pass a parameter? In my ViewModel I have the following code
public class DownloadViewModel : BaseViewModel
{
public ICommand BrowseForFile { get; set; }
public string File { get; set; }
public DownloadViewModel()
{
BrowseForFile = new RelayCommand(new Action<object>(OpenDialog));
}
private void OpenDialog(object o)
{
var dialog = new System.Windows.Forms.FolderBrowserDialog();
System.Windows.Forms.DialogResult result = dialog.ShowDialog();
File = dialog.SelectedPath;
}
}
The OpenDialog method does not require the parameter but it appears as if I have to just so I can satisfy the Interface.
Am I doing this right or have I missed the point?
Yes, ICommand always needs an object and RelayCommand too. If you don't need it, you pass null and don't use it in your method, which is ugly.
I would use Prism's DelegateCommand instead. This exists in a non-generic version, which doesn't take parameters:
Command = new DelegateCommand(DoSomething);
CommandWithParameter = new DelegateCommand<int>(DoSOmethingWithInt);
Its in the PRISM assembly, which you have to download and reference.
using Microsoft.Practices.Prism;
PRISM
Alternatively, use the MVVMLight toolkit, which provides a command class which does basically the same thing. There is no point in using MVVM without a MVVM framework anyway. I can recommend PRISM, also for it's basic stuff like the DelegateCommand or the EventAggregator.
The fact that Execute takes a parameter is irrelevant to the method from your ViewModel. The only thing that affects what parameters OpenDialog needs is your implementation of ICommand.
If your implementation is, for example:
public class MyRandomCommand : ICommand
{
private readonly Action _action;
public MyRandomCommand(Action action)
{
_action = action;
}
public void Execute(object parameter)
{
_action();
}
...
}
Then no parameters will be required for your OpenDialog method, as you can create a command as follows:
public ICommand Command { get { return new MyRandomCommand(OpenDialog); } }
You can, however, require any signature you like for the method you are passing to your command.
The most common, off-the-shelf implementations of RelayCommand can take methods with either 0 or 1 parameter and will be called from Execute appropriately.
i am creating custom membership provider using ninject for binding to sql classes.
my class in looks like
public MyMembershipProvider(IUsersRepository userRepository)
{
this.userRepository = userRepository;
}
How can i create from this parameterless constructor?
kernel.Bind<IUsersRepository>().To<UsersRepository>();
kernel.Bind<MembershipProvider>().To<MyMembershipProvider>();
and then:
public class AccountController : Controller
{
private readonly MembershipProvider _membershipProvider;
public AccountController(MembershipProvider membershipProvider)
{
_membershipProvider = membershipProvider;
}
public ActionResult Foo()
{
// TODO: Use the membership provider to do some processing
return View();
}
}