I have created a service interface:
public interface IMessageDialogService
{
void ShowDialog(object context,string title,string message,string buttonTitle);
}
I have implemented that interface on both Android and iOS. The context is only used on Android where an Android Context is needed to display a message dialog. I pass this interface into my ViewModel to be injected by IoC. My problem is in my platform independent ViewModel which calls a WebService and then handles the return value. It checks the return value for an error condition and needs to display a message dialog. iOS does not need any context to display a UIAlertView, but on Android how do I get a hold of an Android context to pass in as the first argument?
Is there an easier way to display a simple informational dialog from a ViewModel?
After inspecting the source for the WebBrowserTask, it looks like I can always grab the current Activity by:
var activity = Mvx.Resolve<IMvxAndroidCurrentTopActivity> ().Activity;
so I don't have to pass it down, but have my implementation of IMessageDialogService on Android grab it and use it to display the message dialog.
Related
I have a command that shows a view model:
private void DoShowImportCommand()
{
this.ShowViewModel<GeometryImportViewModel>();
}
but I only want to execute it if that view model isn't already shown. Is there a way to
detect if that view model is already on screen and if so don't execute the command?
MvvmCross doesn't track this by default - what is currently shown depends on the UI and can be interpreted in different ways in different situations (popups, tabs, pivots, dialogs, back stacks, etc)
If you want to track this in your own application, you could do it using UI project components (e.g. custom presenters) or you could do it using a shared code component - e.g. you could add "alive" tracking to the Views/ViewModels (see the N=42 video on http://mvvmcross.blogspot.com) and could then use some service to track which viewmodels are shown.
In my Windows Phone App there's a simple hierarchical model consisting of a class containing a collection of other domain objects.
In my xaml i have declared an ItemsContainer control that renders the items in the above mentioned collection as simple rectangles.
Now, at the VM level i have a structure that resembles my model with a parent VM having a collection of children VMs. Each child-VM encapsulates its own model.
Whenever the user taps the view bound to a child-VM a method of the parent-model object should be invoked taking the relevant child-model as parameter. This will in turn change some internal state that will be reflected (possibly) on all the child-views (not just the tapped one).
SO... given that i'm using the MVVM Light framework my current implementation is as follows:
Child-VM exposes a command
The command Execute method will use the messenger to notify the parent-VM of the tap event. The message (GenericMessage class) content will be the domain object encapsulated by the VM
The parent-VM executes the method of the parent-model using the message content as parameter
If the operation succeeds the parent-VM sends a new message to inform child-VMs of this fact. Once again the message content is the model object used as parameter in the method that was just invoked
Child-VMs raise a couple of PropertyChanged events that, finally, will update the bound views
It works but i fill it's a bit cumbersome. The thing that bugs me the most is the fact that when a child-view is tapped the associated VM will broadcast its encapsulated model object. Do you feel that there would be a better way of implementing such a system?
Thanks in advance for your precious help
Could you not just put the command on the parent viewmodel and pass the child viewmodel as the command parameter?
The parent view model can then just call methods on the child viewmodels to update them. I'm not sure I see the need for all these messages?
I have an Android app which uses a SupportActionBar that contains a bunch of tabs. These tabs each have a fragment that in turn are connected to a ViewModel in my core project. This works great and when i start the app they are all initialized right away and setup correctly.
What i would like to do is to call on a method on one of these ViewModels from my main activity that contains all the tabs and fragments.
I read in another post that in WP you could cast the DataContext to the ViewModel but that might not work in Android. I haven't been able to do this, maybe because my DataContext is not the currently displayed ViewModel but the MainViewModel connected to my main activity. Or maybe it's not supposed to be done that way, i'm not sure.
I'm trying to do this:
var test = (MessagesViewModel)this.DataContext;
test.GetViewDataFromApi();
To update the data in the view when i press the tab. I can't use the Init function for this for example since the ViewModel isn't recreated everytime i show the view.
Are you trying to update some data in the tab's fragment when tab is selected?
If that's the case, one way to do it is to
1) handle the tab selection event to get the current tab(maybe using TabListener),
2) get the fragment (MvxFagment) in the selected tab
3) get the (IMvxViewModel) view-model from the fragment
4) call the method you need to update data on the view-model
I assume you are using a MvxFragment (https://github.com/MvvmCross/MvvmCross/blob/v3.1/Cirrious/Cirrious.MvvmCross.Droid.Fragging/Fragments/MvxFragment.cs?source=cc) so you can access the view-model from the MvxFragment's ViewModel property.
I´m developing an App that will be available for Windows Phone 8 and the Windows Store. To reduce redundancy I´m using a Portable Class Library (PCL) and on top of that I'm trying to apply the MVVM pattern with the help of the MVVM Light PCL Toolkit. The ViewModels are placed in the PCL and are bound directly in the XAML of the Apps pages.
When the data is received without an error, everything works fine. But I don´t know how to get the exceptions/error message back to the App when errors do happen.
Inside the Windows Store App errors will show as a MessageDialog while the Wp8 App will use the MessageBox class. Obviously the PCL isn´t aware of any of these classes. What I´m not getting is how to know if a ViewModel ran into an error, and how to get the message inside the App. Is this even possible when the ViewModels are bound inside the XAML?
The code in the ViewModel (inside the PCL) looks like this:
DataService.Authenticate((token, error) =>
{
if (error != null)
{
// This is, obviously, not going to work.
MessageBox.Show(error.Message);
return;
}
Token = token;
});
So I have to save the error somehow and let the App itself know the error has occurred, and then call the matching way of showing the error to the user.
Currently I´m thinking of something like defining an Error-property inside the BaseViewModel and fill it when errors in the ViewModel occur. Then, in the CodeBehind of the pages, make them aware of the current ViewModel and bind a PropertyChanged-event to this Error-property. But I was not able to implement it yet, so I don't know if this is even the right way to go.
Do I have to step down from the idea to bind the ViewModels inside the XAML, and do I instead have to initialize them inside the pages Codebehind?
Your instinct is correct, but there are more than a few ways of going about this.
First and foremost, you can use Mvvm's Messaging library, which will allow your ViewModel to send messages directly to your View. Your View can then handle it in any way it wishes, including but not limited to using a MessageDialog.
Secondly, you can also create a Function or Action (likely the former) in your ViewModelLocator for ShowMessageDialog. This Function will likely take a string and return a Task. Then, after you initialize your ViewModelLocator initially, you can inject your ShowMessageDialog code. Your ViewModels can then use whatever platform's MessageDialogs that they please.
Ex:
Note: This code uses the BCL Async libraries that are accessible in Nuget. They work in the PCL just fine.
ViewModelLocator:
public static Func<string, Task> ShowMessageDialog { get; set; }
App.xaml.cs:
ViewModelLocator.ShowMessageDialog = (message) =>
{
// For Windows Phone
return TaskFactory.StartNew(() => MessageBox.Show(message));
// For Windows 8
MessageDialog md = new MessageDialog(message);
return md.ShowAsync().AsTask();
};
ViewModel:
await ViewModelLocator.ShowMessageDialog("This is my message.");
Secondary Note: The md.ShowAsync().AsTask(); must be run on the UI Thread. This means that you will have to invoke it via the dispatcher in the case that you are running it in a task asynchronously. This is possible using a similar method of injecting the use of the app's CoreDispatcher via the RunAsync method.
This means that you can, on any platform (Windows 8 and Windows Phone shown above), inject whatever Message Dialog system you want and use it in your PCL.
I would say that it is much easier to do the first method I suggested, as that is what it is there for, but the Function method version is definitely helpful at times.
I implemented the exception filter like here: http://www.asp.net/web-api/overview/web-api-routing-and-actions/exception-handling
And registered it globally, like microsoft or stackoverflow-users ( How to add global ASP.Net Web Api Filters? ) explained.
public static void RegisterWebApiFilters(System.Web.Http.Filters.GlobalFilterCollection filters)
{
//other filters
filters.Add(new MyExceptionFilter());
}
But if I throw an exception, my method is not called.
My exception-handling method is called only if I add the attribute [MyExceptionFilter] to the controller-method, but I hoped I can avoid that for all methods by registering the filter globally.
I tried to set a order for the filters, but this had no effect.
Edit: I have noticed, that in the new Wep Api RC the method is called "RegisterGlobalFilters" and this seems to be the MVC filter collection.
If I call
GlobalConfiguration.Configuration.Filters.Add(new MyExceptionFilter());
it works. This is the collection for the Web Api.
Looks like I have to build my own "FilterConfig" class for the web api...
Like I mentioned in my question: There are different filter collections. One for MVC and one for the web api.
If you want to add the filter to the web api, add this line of code to the global.asax
GlobalConfiguration.Configuration.Filters.Add(new MyExceptionFilter());