We have a couple of Fragments that we use as common controls:
MyCommonHeaderA
MyCommonHeaderB
In our common View class we call base.OnCreate(bundle) and once that has returned we fish out the fragment instances and set their ViewModels
var commonHeaderAFragment = (MyCommonHeaderA)this.SupportFragmentManager.FindFragmentById(Resource.Id.header1banner);
if (commonHeaderAFragment != null)
{
commonHeaderAFragment.ViewModel = this.ViewModel;
}
var commonHeaderBFragment = (MyCommonHeaderB)this.SupportFragmentManager.FindFragmentById(Resource.Id.header2banner);
if (commonHeaderBFragment != null)
{
commonHeaderBFragment.ViewModel = this.ViewModel;
}
Until recently this has been working with no problem. Recently we have upgraded Xamarin and MVVMCross.
Now whenever we rotate the device OnCreate is called and the execution path ends up in MvxFragmentExtensions.OnCreate where it tries to lookup a type for the Fragment using FindAssociatedViewModelTypeOrNull. There is no associated ViewModel type for the Fragment. We never needed to, should we have associated a type?
I did try MvxViewForAttribute and concrete typed ViewModel property but neither of those worked as they wanted to create new VM instances.
I have a solution which is that in the base OnCreate, if we have a bundle try and find the Fragments and set their ViewModel property before base.onCreate and when there is no bundle we set the ViewModel property after OnCreate. It is clunky but works. I just wanted to check if we should have been setting up our Fragments differently so that we would not have hit this issue
There is an example available that uses the MvxCachingFragmentActivity: https://github.com/MvvmCross/MvvmCross-AndroidSupport/tree/master/Samples
In there you don't need to worry about those kind of problems anymore.
Related
I have upgraded to the latest version of MvvmCross (6.4.1) from 4.2.3. I and using Xamarin Android not Xamarin forms
In the view which initiates the dialog I do the following
Create dialog fragment derived from MvxDialogFragment
Assign a view model to it
Then call ShowView on the fragment
However when I rotate the device it fails in OnCreate with the message
Your fragment is not generic and it does not have MvxFragmentPresentationAttribute attribute set!
This did not happen in 4.2.3. The reason I create dialog this way is that I want it to use different view models depending on where I need this dialog. For example I want to show a different list of data, but in the same format in the dialog.
It seems this will only work if we apply the MvxFragmentPresentationAttribute which needs the type of view model to be defined at design time rather than run time.
Is there anything I can do to achieve this
Any help will be appreciated
If you somehow need to specify the ViewModel type at runtime, you can instead of decorating the class with the MvxFragmentPresentationAttribute let it implement, IMvxOverridePresentationAttribute and return it there with the appropriate ViewModel to be presented in.
Something like:
public class MyDialog : MvxDialogFragment, IMvxOverridePresentationAttribute
{
public MvxBasePresentationAttribute PresentationAttribute(MvxViewModelRequest request)
{
return new MvxFragmentPresentationAttribute
{
ActivityHostViewModelType = myDynamicType
};
}
}
Where you implement some kind of logic to get the myDynamicType somewhere.
However, you should be able to use MvxDialogFragmentPresentationAttribute instead though and the presenter will attempt to use the topmost Android Activity to present it in if you provide a null ref as the ActivityHostViewModelType.
Currently I am only testing on an Android emulator. I have installed the Theme Nuget packages.
In my App constructor I have:
// Load the desired theme (default to Light)
if (Current.Properties.TryGetValue("Theme", out object theme))
Resources = theme as ResourceDictionary;
else
Resources = new LightThemeResources();
I then have a method in the App class:
public async Task SwitchTheme()
{
// Switch the current theme from List to Dark to Light
if (Resources?.GetType() == typeof(DarkThemeResources))
Resources = new LightThemeResources();
else
Resources = new DarkThemeResources();
// Persist the Theme
Current.Properties.Add("Theme", Resources);
await Current.SavePropertiesAsync();
}
When I call the method the theme switches from light-dark-light etc. But when I restart the App, it always defaults to Light. As if the "await Current.SavePropertiesAsync();" did not work.
Can anyone suggest what the problem may be?
Xamarin Forms Properties is intended for use with C# value types and objects that can be easily serialized - not complex objects like Resources.
From the docs
Values saved in the properties dictionary must be primitive types,
such as integers or strings. Attempting to save reference types, or
collections in particular, can fail silently.
All you really need to do is store a string value - either 'light' or 'dark' and then load the appropriate theme based on that. You don't actually need to store the theme itself.
I have a WPF application that is utilizing the reporting tools included with Visual Studio 2010. I've had some other problems that I've solved by creating a graph of objects that are all marked as serializable, etc., as mentioned on various other web pages.
The ReportViewer control is contained in a WindowsFormsHost. I'm handling the SubreportProcessing event of the ReportViewer.LocalReport object to provide the data for the sub report.
The object graph that I'm reporting on is generated in my viewmodel, and that viewmodel holds a reference to it. The SubreportProcessing handler is in my code behind of my window (may not be the best place - but I simply want to get the ReportViewer working at this point).
Here's the problem: In my event handler, I'm attempting to get a reference to my viewmodel using the following code:
var vm = DataContext as FailedAssemblyReportViewModel;
When the handler is called, this line throws an InvalidOperationException with the message The calling thread cannot access this object because a different thread owns it.
I didn't realize the handler might be called on a different thread. How can I resolve this?
I attempted some searches, but all I've come up with is in regards to updating the UI from another thread using the Dispatcher, but that won't work in this case...
I solved this problem using something I believe is a hack, by adding the following function:
public object GetDataContext() {
return DataContext;
}
And then replacing the line of code from my question with:
object dc = Dispatcher.Invoke(new Func<object>(GetDataContext), null);
var vm = dc as FailedAssemblyReportViewModel;
However, this seems like a hack, and I might be circumventing some sort of safety check the CLR is doing. Please let me know if this is an incorrect way to accomplish this.
That's a nasty problem you have there.
Why don't you use in the view a content presenter which you bind to a windows form host?
And in the view model you would have a property of type of type WindowsFormsHost. Also,in the view model's constructor you could set the windows form's host Child property with the report viewer.
After that is smooth sailing, you could use your report viewer anywhere in your code. Something like this:
View:
<ContentPresenter Content="{Binding Path=FormHost}"/>
ViewModel:
private ReportViewer report = new ReportViewer();
private WindowsFormsHost host = new WindowsFormsHost();
public WindowsFormsHost FormHost
{
get {return this.host;}
set
{
if(this.host!=value)
{
this.host = value;
OnPropertyChanged("FormHost");
}
}
}
public ViewModel() //constructor
{
this.host.Child = this.report;
}
After that happy coding. Hope it helps.
How do I unload a view from a Prism Region?
I am writing a WPF Prism app with a Ribbon control in the Shell. The Ribbon's Home tab contains a region, RibbonHomeTabRegion, into which one of my modules (call it ModuleA) loads a RibbonGroup. That works fine.
When the user navigates away from ModuleA, the RibbonGroup needs to be unloaded from the RibbonHomeTabRegion. I am not replacing the RibbonGroup with another view--the region should be empty.
EDIT: I have rewritten this part of the question:
When I try to remove the view, I get an error message that "The region does not contain the specified view." So, I wrote the following code to delete whatever view is in the region:
// Get the regions views
var regionManager = ServiceLocator.Current.GetInstance<IRegionManager>();
var ribbonHomeTabRegion = regionManager.Regions["RibbonHomeTabRegion"];
var views = ribbonHomeTabRegion.Views;
// Unload the views
foreach (var view in views)
{
ribbonHomeTabRegion.Remove(view);
}
I am still getting the same error, which tells me there is something pretty basic that I am doing incorrectly.
Can anyone point me in the right direction? Thanks for your help.
I found my answer, although I can't say I fully understand it. I had used IRegionManager.RequestNavigate() to inject the RibbonGroup into the Ribbon's Home tab, like this:
// Load RibbonGroup into Navigator pane
var noteListNavigator = new Uri("NoteListRibbonGroup", UriKind.Relative);
regionManager.RequestNavigate("RibbonHomeTabRegion", noteListNavigator);
I changed the code to inject the view by Registering it with the region, like this:
// Load Ribbon Group into Home tab
regionManager.RegisterViewWithRegion("RibbonHomeTabRegion", typeof(NoteListRibbonGroup));
Now I can remove the RibbonGroup using this code:
if(ribbonHomeTabRegion.Views.Contains(this))
{
ribbonHomeTabRegion.Remove(this);
}
So, how you inject the view apparently matters. If you want to be able to remove the view, inject by registration with the Region Manager
StockTraderRI Example Project by Microsoft contains the following example of removing views from region in ViewModel.
private void RemoveOrdersView()
{
IRegion region = this._regionManager.Regions[RegionNames.ActionRegion];
object ordersView = region.GetView("OrdersView");
if (ordersView != null)
{
region.Remove(ordersView);
}
}
Is it possible you have a RegionAdapter that is wrapping the view inside another view before adding it? The ribbonHomeTabRegion should have a property with the collection of views - is there anything inside it?
I have a tabbed application where I want the user to be able to search for a person and then, in a new view, show the person's details. The user should be able to have multiple person detail views open for different people.
I was a little unsure if I am following the correct procedure for creating my new view. Using Unity (which I am not) it seems you would call Container.Resolve(view) however I am doing the following, the satisfyImports was necessary in order for my imports in the view / viewmodel to be created.
PersonDetailView view = new PersonDetailView();
_container.SatisfyImportsOnce(view);
_regionManager.Regions["MainRegion"].Add(view, this.SelectedPerson.Name);
_regionManager.RequestNavigate("MainRegion", new Uri("PersonDetailView", UriKind.Relative));
In the code for my PersonDetailView I have the following property to set the data context.
[Import]
public PersonDetailsViewModel ViewModel
{
set
{
this.DataContext = value;
}
}
This seems to work but the trouble I am having is that when I create a second person view, the new view is getting the same instance of the datacontext as the view that is already created.
Is this because I am creating my views incorrectly or is there a way that I tell MEF to create a new oject when it fulfills the imports for my new view?
When you export a part, by default it used a CreationPolicy of Shared. This essentially makes the exported instance a singleton in the container. With your export, add another attribute:
[Export, PartCreationPolicy(CreationPolicy.NonShared)]
public class Foo { }
This will ensure a new instance is created each time you call to compose the consumer instance.