I am using the ViewModel First approach and i have trouble navigating from one ViewModel to another.
For example, i have two folders, View and ViewModels and i have two files in each Page1View.xaml, Page2View.xaml and Page1ViewModel.cs, Page2ViewModel.cs
In my app launch i have this the line below and it works perfectly fine.
DisplayRootViewFor<Page1ViewModel>();
Now on a button click from Page1ViewModel event when i add the line below, i get a null reference exception.
_navigationService.NavitageToViewModel<Page2ViewModel>();
Am i missing something here? To give more information, This is a UWP application and the container that i am using is WinRTContainer and i have registered both the ViewModels.
You are taking a ViewModel-first approach. Note that DisplayRootViewFor doesn't create a Frame control and doesn't set up a NavigationService.
Have a look at:
https://github.com/Caliburn-Micro/Caliburn.Micro/issues/126
Either switch to a View-first approach, or in your root view, setup a NavigationService passing a Frame to it:
container.RegisterNavigationService(rootFrame);
Related
The situation. I have an a custom alert component in a shared components file. I have my different screens in their respective files, and they all import the custom alert. On navigation away from one screen to another, and then I navigate back via reactnavigation's back arrow, the alert is not remounted, and so its invocation throws an error. How should I take care of this?
I figured out a hack; so long it works for now and maintains the development momentum. So, prior to any function call that will eventually invoke the custom imported alert, I call setState, and update a dummy value, e.g. this.setState({sth:'sth'}). This seems to in turn, reload the component's relation to its imported stuff, and just like that the error is no more.
In our application, there is a tabpanel in which we are adding/removing the panel dynamically.
The panels get added at the click of a menu item by the following code in menu handler:
Ext.getCmp('mainTabPanelId').add(getPanel());
Here getPanel() method returns the panel after creating it.
Assuming that the id of main tab panel is mainTabPanelId and that of the child panel is panelId, in this context, could someone guide at the following:
Is it necessary to call doLayout() on mainTabPanel after the add method?
Should the doLayout() be called on the mainTabPanel or on the newly added child panel, that is, Ext.getCmp('mainTabId').doLayout() or Ext.getCmp('panelId').doLayout()?
Will a call to doLayout() take care of all the issues related to rendering, like scrollbars esp.?
The method getPanel() should return an already created panel (using Ext.create) or should it return a config object (having xtype:'panel')? Which one should be preferred for better performance keeping time in mind?
AbstractContainer::add()
<...> If the Container was configured with a size-managing layout manager, the Container will recalculate its internal layout at this time too.
So you don't have to do 1 — 3 because:
AbstractContainer::doLayout()
<...> The framework uses this internally to refresh layouts form most cases.
AbstractContainer::defaults
For defaults to work, the child items must be added using {xtype: ......} NOT using Ext.create("widget.type",{}) © roger.spall
So I'd prefer return configuration object instead of components itself.
I'm new to Silverlight/MVVM. I tried some example of MVVM Light, it looks great.
For my scenario, I want to create a Panorama Page, for each Panorama Item, showing my usercontrol, a item list for a customer.
I've built usercontrol(view), viewmodel and WCF service model and works well in a single Panorama Item(Only use first customer).
Also, I use Locator of MVVM Light shown in MIX10 demo, it enables me to make design time data for Expression Blend.
My viewmodel will receive a parameter of customer ID then exchange data with WCF based on this ID.
And the customer list also comes from WCF. So I can't actually makes viewmodels in Locator's static constructor.
If viewmodels are built in runtime by calling Locator, how to make data binding?
The only way I think about is to make viewmodel object in usercontrol's constructor and make it datacontext.
Is there a better solution?
If you want to keep the same declarative model in the XAML, you can put a CurrentCustomerViewModel property on the locator and then set property to the right viewmodel before you navigate to the page.
Personally though for pages like that I typically put a viewmodel factory method on the locator (so it can cache them, etc) and call it from the OnNavigatedTo method, something like this.
protected override void OnNavigatedTo(System.Windows.Navigation.NavigationEventArgs e)
{
string id = NavigationContext.QueryString["customerID"];
vm = ViewModelLocator.GetCustomerViewModel(id);
DataContext = vm;
base.OnNavigatedTo(e);
}
Then I just use Blend's sample data capabilities for design time data. This way also helps support pinning the page to the start screen since that will be the entry point to the app and I won't necessarily get a good chance to set the "CurrentCustomerVM" property anyway.
I have a functional MVVM patterned SL app with a RadWindow (essentially a ChildWindow), that I would like to remove the code-behind in my view that shows the window using its ShowDialog. Both the main view and the window is bound to the same ViewModel if that helps.
The button has both a ViewModel command using a MVVMLight RelayCommand to handle setting state as well as the event handler in the View.
The ultimate solution/pattern will be reused 20+ times so something better than code-behind would be great.
Thoughts?
private void Button_Click(object sender, System.Windows.RoutedEventArgs e)
{
var window = new RadWindowTest.Controls.ChildWindow1();
window.Closed += new System.EventHandler<Telerik.Windows.Controls.WindowClosedEventArgs>(window_Closed);
window.ShowDialog();
}
In this case I would suggest you implement DialogService. This service you can inject into your view model, for testing you will have to inject an instance that does not depend on the view, thus maintaining testability. You can use the ViewModelLocator to make this service available to your application.
Another approach would be to implement a ViewBase class that implements an interface that allows you to display the dialog. This interface is now used by the ViewModel to display a dialog. Again to test you need to provide a different implementation of the interface. A sample can be found here.
Both ideas revolve around the same concept of factoring out the function that shows the dialog. In order to strictly de-couple the View and the ViewModel you will have to think about how the ViewModel specifies which dialog has to be shoen, and how the dialog resut or dialog model is returned to the calling ViewModel.
Which approach is better is open to your judgement. Personally I prefer the first approach as I do not have to inherit the views from a common base class.
PS: Use a command to get to the point in your ViewModel where you want to show the dialog. Using a dialog service should need no code behind.
I want to navigate from a login screen to the dashboard in my Silverlight OOB app.
I started using Caliburn.Micro but now I'm having doubts seeing as all I can use is the Conductor. Or am I missing something?
Note: I changed constructor to Conductor as originally intended. This is what you get for not proofreading your questions.
There are several ways you could display a login screen, probably the nicest is to initiate it from your ShellViewModel. So, your ShellViewModel would have a dependency on your LoginViewModel, which you could inject as an abstraction (ILoginViewModel), or better still use an abstract factory instead, and inject that into your ShellViewModel constructor.
Either way, once you have an instance of your LoginViewModel in the ShellViewModel, you can display it either as a modal dialog box (in which case use the Caliburn.Micro WindowManager.ShowDialog method - inject this dependency as an IWindowManager abstraction), or display the login view as part of your shell views main content area, in which case your ShellViewModel would be a conductor, and will activate an instance of your LoginViewModel with the ActivateItem method.
Once you have received input from your LoginViewModel, either as a modal dialog or conducted view, you can display your DashboardViewModel as appropriate using the ShellViewModel as a conductor.