I'm very newbie using MvvmCross and I have an issue. I want to implement taking a photo in an Activity, the native way, but I don't know how I can pass data to the ViewModel.
There is a way to do that?
Passing data to a ViewModel is fairly easy. If you are in the Activity and given that it inherits from MvxActivity or the likes you will have the ViewModel property you can access directly from it.
There are also generic versions of these activities, so you don't have to type cast the ViewModel property yourself.
So if you have:
public class MyActivity : MvxActivity<PictureViewModel>
{
}
Then you can access ViewModel:
ViewModel.SomeViewModelProperty = myData;
This myData object could be a byte array with the picture data.
MvvmCross does have a Picture taking plugin already, which uses the built in Android camera to take pictures with. If you add
MvvmCross.Plugins.PictureChooser
To both your Android and Core project, then you can use the IMvxPictureChooserTask directly in the ViewModel without involving anything else:
public class PictureViewModel : MvxViewModel
{
private IMvxPictureChooserTask _pictureTask;
public PictureViewModel(IMvxPictureChooserTask pictureTask)
{
_pictureTask = pictureTask;
}
private byte[] _pictureBytes;
// in some command:
private void DoTakePicture()
{
_pictureTask.TakePicture(500, 500, stream => {
_pictureBytes = ReadStream(stream);
}, () => {});
}
}
Related
I have worked through the .NET MAUI "Create a .NET MAUI App" startup tutorial.
I modified the tutorial a bit to use a sqlite database instead of files for each row in the CollectionView.
When they go to edit a row in the collection view they pass the id of the DTO of the row to a new view:
await Shell.Current.GoToAsync($"{nameof(NotePage)}?{nameof(NotePage.ItemId)}={SelectedNote.ID}");
and the new view loads the ItemID with the following annotation:
[QueryProperty(nameof(ItemId), nameof(ItemId))]
I was then taking that ItemId and doing another call to the database to return the DTO but since I am loading my data from the database I already have my DTO from the CollectionView and I just want to pass the whole thing over to the new view as some sort of query parameter to save resources.
How do I do this?
I saw someone online with a tutorial that showed to pass it like this:
await Shell.Current.GoToAsync(nameof(NotePage), SelectedNote);
But Visual Studio says that my second parameter has to be a bool so I'm guessing that guys tutorial is wrong.
Anyone know if its possible to pass a DTO from a view in this way or something similar?
Thanks,
the docs demonstrate how to do this
Object-based navigation data can be passed with a GoToAsync overload
that specifies an IDictionary<string, object> argument:
Animal animal = e.CurrentSelection.FirstOrDefault() as Animal;
var navigationParameter = new Dictionary<string, object>
{
{ "Bear", animal }
};
await Shell.Current.GoToAsync($"beardetails", navigationParameter);
then the receiving page or VM can do this
[QueryProperty(nameof(Bear), "Bear")]
public partial class BearDetailPage : ContentPage
{
Animal bear;
public Animal Bear
{
get => bear;
set
{
bear = value;
OnPropertyChanged();
}
}
public BearDetailPage()
{
InitializeComponent();
BindingContext = this;
}
}
I am using Xamarin to develop ios and android apps on one platefrom, c# is the language used.
I have a design that mimics the one below. A manager class that handles operations done to a collection, a Model class that groups data, and a View that displays the models it gets from the manager. I am displaying the models in a table, the view below is how I am doing so on iOS.
The view subscribes to any changes done to the collection in the manager and triggers a view update whenever one occurs. The model is responsible for removing itself from the collection if it is no longer used after a certain amount of time, thus I pass a reference to the list when the model is created.
This pattern is working on android devices but doesn't seem to work when ran on iOS. I've traced the problem to the removeDevice in the model class but can't seem to figure out why it isn't working. My guess if a pass by reference / value problem but I am not sure. Is there something obvious I am missing or do I need to use a different pattern for iOS?
New Information
After experimenting more this seems relevant. The iOS table is in a tab view and not the initial tab which means ViewController is not initialized until the tab is clicked. I found that if I didn't click the tab it would remove the Models from the list. Something else interesting is if I removed the CollectionChanged subscription it would as well.
public partial class ViewController: UIViewController
{
private List<Model> itemList;
private BlueTooth ble;
private UITableView deviceTable;
public ViewController (IntPtr handle) : base (handle)
{
ble = BlueTooth.Instance;
}
public override void ViewDidLoad ()
{
manager = ble.getManager();
itemList = manager.modelList.ToList();
manager.modelList.CollectionChanged += UpdateView;
deviceTable = new UITableView
{
Source = new DeviceTableSource(itemList)
};
View.AddSubview(deviceTable);
}
void UpdateView(object sender, EventArgs e)
{
itemList = ble.getManager().ModelList.ToList();
deviceTable.Source = new DeviceTableSource(itemList);
deviceTable.ReloadData();
}
}
Manager Class
class Manager{
public ObservableCollection<Model> modelList {get; set;}
public Manager(){
modelList= new ObervableCollection<Model>();
}
public addModel(){
Create a Model object with reference to ModelList
Add Model to ModelList
}
public updateModel(){
update Model in List
}
}
Model Class
class Model{
private ObservableCollection<Model> list;
private Timer removeTimer;
Model(modelList){
removeTimer += onTimedEvent
}
OnTimedEvent(){
removeDevice();
}
removeDevice(){
modelList.remove(this);
}
}
I have a WPF application which is written with an implementation of MVVM. There's no extra framework for the MVVM pattern.
My entities from EF db first are wrapped in their own viewmodels and I have a modelcontroller to load them into their viewmodels from a 'window' viewmodel.
Example of an entity viewmodel:
public class PurchaseOrderViewModel : ViewModels.ViewModelBase
{
private someType _prop;
public someType Prop
{
get
{
return _prop;
}
set
{
_prop = value;
OnPropertyChanged();
}
}
// ...
// Other Properties
// ...
public PurchaseOrderViewModel() {
// default constructor for LINQ
}
public PurchaseOrderViewModel(purchaseorder entity)
{
// load values from entity in properties
}
}
Example of a window viewmodel:
public class MainViewModel: ViewModels.ViewModelBase
{
private IModelController modelController = new ModelController();
private List<PurchaseOrderViewModel> _poList;
public List<PurchaseOrderViewModel> POList
{
get
{
return _poList;
}
set
{
_poList = value;
OnPropertyChanged();
}
}
// ...
// Other Properties
// ...
public MainViewModel()
{
POList = modelController.GetPurchaseOrders();
}
}
Example of ModelController:
public class ModelController : IModelController
{
public List<PurchaseOrderViewModel> GetPurchaseOrders()
{
using (var model = new DBContext())
{
return model.purchaseorders
.Select(new PurchaseOrderViewModel { /* assign properties */ })
.ToList();
}
}
}
Where am I supposed to save this wrapped viewmodel (PurchaseOrderViewModel) once the user is done editing it? As I see it, there are 2 options:
Create a save function in each viewmodel that points back to the modelController, but this feels like an inappropriate approach.
Create a save function in the modelcontroller and pass the viewmodel as an argument
It's most likely that I'm missing something in the MVVM pattern, but please point me in the right direction. Thank you!
EDIT: I excluded the view (MainView) from the info provided, but this view binds directly to the properties exposed by MainViewModel.
First up, I problably wouldn't name it ModelController as that's slightly confusing makes people think you are speaking MVC. Instead, if you call it xxxxService (e.g. PurchaseOrdersService) it makes more sense and it no longer feels "inappropriate" because having a VM delegate the actual work is what many users of IoC do. Plus it keeps your VM clean.
NOTE: By "service" I don't necessarily mean that your VM will be calling a WCF service directly (nor should you). Service is just a means to achieve something in an abstract and encapsulated way on behalf of clients. Examples include:
saving information to a DB
getting the current log mechanism
They can even be facades whereby they create a WCF client proxy and call a remote service on your behalf without you having to know the details.
So a typical flow is:
Command >> View code behind >> VM >> Service
The reason I include the view's code behind is that typically this is where you:
Catch exceptions
The starting point of async/await for asynchonous calls to your VM and service
Now when you pass context fromt the VM back to the service, there is no rule on what exactly you pass however I see no reason to pass VM to the service because that contains information the service doesn't care about.
Just pass the M which your VM should have bound to in the first place and continued to update via binding.
Does anyone know how to view an existing IMvxViewModel?
In my app, I have already created a bunch of ViewModels (PhotoViewModel) inside of another view model. They exist as a property on the parent ViewModel (AlbumViewModel). It would be very nice to just show a particular instance of a PhotoViewModel instead of creating a new instance of that view model when I want to view it.
public class AlbumViewModel : MvxViewModel {
public ObservableCollection<PhotoViewModel> Photos
{
get { return GetValue(() => Photos); }
set { SetValue(value, () => Photos); }
}
}
public class PhotoViewModel : MvxViewModel { }
I was wondering if there was a way, other then creating my own IMvxViewModelLocator, to accomplish this task. I think having a protected method on the MvxNavigationObject called View could be really helpful both for new developers using the framework as well as performance. We'd be able to skip all of the reflection done currently to instantiate a view model.
The default ShowViewModel mechanism in MvvmCross uses page-based navigation - this navigation has to use Uris on WindowsPhone and Intents on Android.
Because of this, MvvmCross does not allow navigation by 'rich' objects - simple serialisable POCOs are Ok, but complicated 'rich' objects are not supported.
This is further essential because of 'tombstoning' - if your app/page/activity is later rehydrated then you cannot be sure of what historic View or ViewModel objects are actually in your history "back" stack.
If you want to navigate by rich object then the best way is to store those rich objects in a lookup service and to then navigate by some key/index into the lookup. However, I would personally call those lookedup objects Models rather than ViewModels (but the boundary does sometimes become blurred!)
Although based on MvvmCross v1 code, this question still gives quite a good background to this - What is the best way to pass objects to "navigated to" viewmodel in MVVMCross?
Some more up-to-date explanations include:
How to pass data across screens using mvvmcross
Custom types in Navigation parameters in v3
https://github.com/slodge/MvvmCross/wiki/ViewModel--to-ViewModel-navigation (under construction)
One final thing....
... the MvvmCross manifesto insists that MvvmCross is very open to customisation ...
Because of this you can override MvvmCross navigation and view model location if you want to. To do this, creating your own IMvxViewModelLocator would probably be a good way to start.
After some testing, below is a proposed solution. I'm not 100% in love with it, but it does work and provide the type developer experience I was looking for. So lets dig in.
To start, all of my ViewModels (VM) inherit from a base VM, AVM. This abstract base class supports looking up of an object as a public static method. It's a little gross, but it works well if you're willing to sip on the Kool-Aid. Below is the portion of the class that's relevant to this problem:
public abstract class AVM : MvxViewModel {
private static readonly Dictionary<Guid, WeakReference> ViewModelCache = new Dictionary<Guid, WeakReference>();
private static readonly string BUNDLE_PARAM_ID = #"AVM_ID";
private Guid AVM_ID = Guid.NewGuid();
private Type MyType;
protected AVM()
{
MyType = this.GetType();
ViewModelCache.Add(AVM_ID, new WeakReference(this));
}
public static bool TryLoadFromBundle(IMvxBundle bundle, out IMvxViewModel viewModel)
{
if (null != bundle && bundle.Data.ContainsKey(BUNDLE_PARAM_ID))
{
var id = Guid.Parse(bundle.Data[BUNDLE_PARAM_ID]);
viewModel = TryLoadFromCache(id);
return true;
}
viewModel = null;
return false;
}
private static IMvxViewModel TryLoadFromCache(Guid Id)
{
if (ViewModelCache.ContainsKey(Id))
{
try
{
var reference = ViewModelCache[Id];
if (reference.IsAlive)
return (IMvxViewModel)reference.Target;
}
catch (Exception exp) { Mvx.Trace(exp.Message); }
}
return null;
}
protected void View()
{
var param = new Dictionary<string, string>();
param.Add(BUNDLE_PARAM_ID, AVM_ID.ToString());
ShowViewModel(MyType, param);
}
In order to get this all wired up, you have to create a custom view model locator. Here's the custom locator:
public class AVMLocator : MvxDefaultViewModelLocator
{
public override bool TryLoad(Type viewModelType, IMvxBundle parameterValues, IMvxBundle savedState, out IMvxViewModel viewModel)
{
if (AVM.TryLoadFromBundle(parameterValues, out viewModel))
return true;
return base.TryLoad(viewModelType, parameterValues, savedState, out viewModel);
}
}
Lastly you have to wire up. To do so, go into your App.cs and override CreateDefaultViewModelLocator like so:
protected override IMvxViewModelLocator CreateDefaultViewModelLocator()
{
return new AVMLocator();
}
You're all set. Now in any of your derived ViewModels that are already alive and well, you can do the following:
myDerivedVM.View();
There's still some more I need to do (like making sure the WeakReferences do their job and I don't have memory leaks and some additional error handling), but at the very least it's the experience I was going for. The last thing I did was add the following command to the AVM base class:
public MvxCommand ViewCommand
{
get { return new MvxCommand(View); }
}
Now you can bind that command to any UI object and when invoked, it'll launch that view with that very instance of the VM.
Stuart, thanks for your help in steering me in the right direction. I'd be interested in hearing your feedback on the solution I provided. Thanks for all of your work with MVVMCross. It really is a very beautiful bit of code.
Cheers.
For the past couple of weeks I've been working on developing a cross platform app (IOS/Android/WP7) using the MVVMCross framework. Today I ran into a problem I don't really know how to solve, so hopefully you can push me in the right direction.
In the IOS I have the following construction for navigating to another page (the code below is located in a ViewModel):
KeyValuePair<string,string> kvpAct1 = new KeyValuePair<string, string>("short", ".countertest5");
public IMvxCommand BeckhoffActuator1
{
get
{
return new MvxRelayCommand<Type>((type) => this.RequestNavigate<Beckhoff.BeckhoffActuatorViewModel>(kvpAct1));
}
}
When this IMvxCommand is fired (button pressed) the next View is loaded, in this case the BeckhoffActuatorViewModel. In the code of the BeckhoffActuatorView I use the keyvaluepair from above:
public class BeckhoffActuatorView : MvxTouchDialogViewController<BeckhoffActuatorViewModel>
{
ICollection<string> icol;
public BeckhoffActuatorView(MvxShowViewModelRequest request) : base(request, UITableViewStyle.Grouped, null, true)
{
icol = request.ParameterValues.Values;
}
public override void ViewDidLoad()
{
//Code
}
}
This construction is working fine in IOS, but I would like to use the same construction in my android App.
The code in the ViewModel hasn't changed since that's the whole idea of MVVM. But the code of the BackhoffActuatorView is different for Android:
public class BeckhoffActuatorView : MvxBindingActivityView<BeckhoffSensorViewModel>
{
public ICollection<string> icol;
public BeckhoffActuatorView()
{
Debug.WriteLine("Standard");
}
public BeckhoffActuatorView(MvxShowViewModelRequest request)
{
Debug.WriteLine("Custom");
icol = request.ParameterValues.Values;
}
protected override void OnViewModelSet()
{
SetContentView(Resource.Layout.BeckhoffActuatorView);
}
}
The code above isn't working, the MvxBindingActivityView doesn't seem to implement something similar to the ViewController I use in IOS. The code only come in the standard constructor, and when I leave that one out completely it won't compile/run.
Does anyone know know I can access the keyvaluepair I send with the RequestNavigate? Thank you!
MVVMCross is very convention based - and it works on the idea of passing messages between ViewModels wherever possible.
If you navigate to a ViewModel using:
KeyValuePair<string,string> kvpAct1 = new KeyValuePair<string, string>("short", ".countertest5");
public IMvxCommand BeckhoffActuator1
{
get
{
return new MvxRelayCommand<Type>((type) => this.RequestNavigate<Beckhoff.BeckhoffActuatorViewModel>(kvpAct1));
}
}
then you should be able to pick that up in the BeckhoffActuatorViewModel using the constructor:
public class BeckhoffActuatorViewModel : MvxViewModel
{
public BeckhoffActuatorViewModel(string short)
{
ShortValue = short;
}
private string _shortValue;
public string ShortValue
{
get
{
return _shortValue;
}
set
{
_shortValue = value;
FirePropertyChanged("ShortValue");
}
}
}
And your views can then access ViewModel.ShortValue (for iOS this can be done after base.ViewDidLoad(), for Android after OnCreate() and for WP7 after OnNavigatedTo)
For an example of this, take a look at the TwitterSearch example:
https://github.com/slodge/MvvmCrossTwitterSearch
This has a HomeViewModel which calls navigate using:
private void DoSearch()
{
RequestNavigate<TwitterViewModel>(new { searchTerm = SearchText });
}
and a TwitterViewModel which receives the searchTerm using the constructor:
public TwitterViewModel(string searchTerm)
{
StartSearch(searchTerm);
}
Please note that only strings are allowed in this message passing at present - but you can always serialise your own objects using JSON.Net - or you can extend the framework - it's open source.
Please note that only strings, ints, doubles and bools are allowed in this constructor parameter passing at present - this is due to serialisation requirements for Xaml Urls and for Android Intents. If you want to experiment with navigation using your own custom serialised objects, then please see http://slodge.blogspot.co.uk/2013/01/navigating-between-viewmodels-by-more.html.
Also, note that if you want to use the anonymous object navigation (RequestNavigate<TwitterViewModel>(new { searchTerm = SearchText });) then you will need to make sure that an InternalsVisibleTo attribute is set - see https://github.com/slodge/MvvmCrossTwitterSearch/blob/master/TwitterSearch.Core/Properties/AssemblyInfo.cs:
[assembly: InternalsVisibleTo("Cirrious.MvvmCross")]
Further... not for the faint-hearted... and this isn't "good mvvm code"... but if you really want/need to access the MvxShowViewModelRequest data inside an Android activity, then you can extract it from the incoming Intent - there's an Extras string containing the request (see the deserialisation in CreateViewModelFromIntent in https://github.com/slodge/MvvmCross/blob/master/Cirrious/Cirrious.MvvmCross/Android/Views/MvxAndroidViewsContainer.cs)