I need to implement a login/logout using MVVMCross, iOS only to start. After the user logs in, I want to close the view and make the "real" first view the root controller. For logout, I want to do the same in reverse. Whenever the LoginViewModel is requested, clear the root and replace it.
This Remove ViewController from stack indicates there is a ClearTop parameter, but it looks like it is gone in v3?
I then found this What is the best way to handle GoBack for the different MvvmCross (v3) platforms and I implemented this Presenter:
public override void Close(IMvxViewModel toClose)
{
if (toClose is LoginViewModel)
{
ClearBackStack();
Show(new MvxViewModelRequest() { ViewModelType = typeof(FirstViewModel)});
return;
}
base.Close(toClose);
}
public override void Show(MvxViewModelRequest request)
{
if (request.ViewModelType == typeof (LoginViewModel))
{
ClearBackStack();
}
base.Show(request);
}
Is this the correct way to handle this? Is there an easier mechanism (pre-v3 like)? Should I be overriding ChangePresentation instead?
Also, is there a mechanism to call ShowViewModel from a View? Do I need to resolve the IMvxViewDispatcher or is there a more straight forward method?
Yes, if you want to do custom presentation techniques then the easiest way is to implement your own view presenter.
For an introduction and some links on this, see How can I implement SplitView in another view in MvvmCross?
You are free to write code directly in your views, including navigation logic using resolved IoC objects. However, mvvmCross tries to encourage you to put this logic in the viewmodels - especially so that the 'logic' is more easily shared between platforms.
Related
I want to prevent the user that he will loose his changes in an EditView when changing the view to another.
I use MVP4G in my project and the project is divided as mvp's structure (one package for the template another one for views ..) is there any solution to detect the EditView in the eventBus. or detect the current View shown to user
Thanks in advance
Thanks to the Navigation Event feature in mvp4g, the presenter will get control before the view changes. At this point the presenter can decide if the navigation will be done or not. This is the correct place in a mvp4g application to save your data.
First zu have to mark all events in the eventbus that will change your view with:
#Event(..., navigationEvent = true)
void goToPage1();
Next your presenters have to implement the NavigationConfirmationInterface and the requires confirm-method:
public class Presenter extends ... implements NavigationConfirmationInterface {
public void confirm(NavigationEventCommand event) {
//pseudo method to verify if the view has changed
if (isViewModified(){
//Window shouldn't be used inside a presenter
//this is just to give a simple example
if (Window.confirm("Are you sure you want to leave?")){
event.fireEvent();
}
} else {
event.fireEvent();
}
}
}
And the last thing to do, is to set the presenter of the current view to the confirmation presenter by calling:
event.fireEvent(false);
This is usually done when the presenter gets control.
You will find the documentation here:
https://github.com/FrankHossfeld/mvp4g/wiki/03.-Defining-EventBus#navigation-event
Thanks to MVP4G's team including El Hoss who gives me a hint to check the MVP4G's blog.. I've solved my problem by following this example
http://mvp4g.blogspot.com/2011/06/navigation-control.html
I'm building an Android and iOS app using Xamarin Forms.
What I'm simply trying to do is set a background drawable on my Android app for my ListView items. The root view of my ListView items are StackLayout's:
var listView = new ListView
{
ItemsSource = items,
ItemTemplate = new DataTemplate(() =>
{
return new ViewCell
{
View = new StackLayout(...)
};
}
};
I know I can access the native element by using a custom renderer:
public class MyEntryRenderer : EntryRenderer
{
protected override void OnElementChanged(ElementChangedEventArgs<Entry> e)
{
base.OnElementChanged(e);
if (e.OldElement == null) {
var nativeEditText = (EditText)Control;
...
}
}
}
But I'm not sure how this would work for a StackLayout (or any other layout for that matter).
I first extended StackLayout:
public class ListViewItem : StackLayout
{
}
And I read somewhere that layouts use the VisualElementRenderer, so I tried the following:
public class ListViewItemRenderer : VisualElementRenderer<StackLayout>
{
protected override void OnElementChanged(ElementChangedEventArgs<StackLayout> e)
{
base.OnElementChanged(e);
// any way to access the native element?
}
}
But VisualElementRenderer does not seem to give me access to the native element.
So is there any way I can access the native elements of Layout elements? Or maybe there is a different way to simply set a background drawable on layouts within my Android app?
Even though I still don't know how to access the native element of a layout, the VisualElementRenderer has a method for setting the background drawable on Android (which was exactly what I needed). So I ended up with the following:
protected override void OnElementChanged(ElementChangedEventArgs<StackLayout> e)
{
base.OnElementChanged(e);
SetBackgroundDrawable(Resources.GetDrawable(Resource.Drawable.listViewItem));
}
I understand you want to hook into an existing Layout renderer and extending it to access the native element with extra capabilities like background image.
Eventually the support for background-image will be supported just like background-colour is, I imagine, across the Layout controls. It may be worth while waiting for this as I can't see why they wouldn't implement these in a later release.
In the mean time you would need something that would work and is quite easy to implement?
Creating the background drawable via inheriting the renderer from a Layout may not be the simplest of solutions therefore, although does have its advantages as you can then re-use easily with the extra functionality across all Layouts for an application.
In your code for ListViewItemRenderer, however, it is inheriting from a Xamarin.Forms control (you specified StackLayout) and have not specified a native, platform dependent, control to be the base for the layout control that would have to match the Xamarin.Forms platform dependent control used.
Each Renderer is tied to a native element. Layout controls will be no different than other custom native control renderers.
For a custom control, you will write a renderer something like the following (note I haven't specified a layout renderer as I haven't had a need to do this yet and am just going from past experience - but similar rules should apply to implementing a renderer for a layout as opposed to a custom control):-
// System.Windows.Controls.Grid in this case is the root native control for a WindowsPhone renderer of MyControl
public class MyControlRenderer : ViewRenderer<MyControlView, System.Windows.Controls.Grid>
There is a simpler approach, however to achieve what you want to do:-
The simpler approach would be instead of inheriting from the Stack Layout control, it would be better to inherit from Grid as the root of the control.
Then you can add an Image control to the Grid and also a Stack Layout for the same Grid Row and Column.
By doing the above you will be able to achieve a background-image across the entire listview item row.
I'm using the BTProgressHUD Xamarin component in an app that is built using MvvmCross. I'm currently working on the iOS version of the app. My ViewModels make several web service calls and expose an 'IsBusy' property, which the associated views are binding to, in order to show or hide the progress spinner. This is pretty much the way things are set up in the N=34 MvvmCross sample (https://github.com/MvvmCross/NPlus1DaysOfMvvmCross/tree/master/N-34-Progress) as well.
The problem is that in some cases a ViewModel must automatically call a service as soon as it is created. I tried to make the call in the Start() function of the ViewModel, but I noticed that the BTProgressHUD spinner does not show up on top of the view. I suspect that the problem is that BTProgressHUD must be displayed only after a view has been made visible, and probably this is not the case when ViewModel.Start() runs.
Has anyone encountered this before? Is there a simple way to run code in the ViewModel after the view has been made visible?
Thanks.
Is there a simple way to run code in the ViewModel after the view has been made visible?
The N=42 video - http://slodge.blogspot.co.uk/2013/11/n42-is-my-viewmodel-visible-can-i-kill.html - introduces an IVisible interface that you can add to your ViewModel - it's your job to call this from your View - but this is easy to do on each platform. For example,, on iOS it is done using ViewDidAppear/ViewDidDisappear in https://github.com/MvvmCross/NPlus1DaysOfMvvmCross/blob/master/N-42-Lifecycles/Lifecycle.Touch/Views/FirstView.cs
protected IVisible VisibleViewModel
{
get { return base.ViewModel as IVisible; }
}
public override void ViewDidAppear(bool animated)
{
base.ViewDidAppear(animated);
VisibleViewModel.IsVisible(true);
}
public override void ViewDidDisappear(bool animated)
{
base.ViewDidDisappear(animated);
VisibleViewModel.IsVisible(false);
}
We're using MVVMCross within our application and I've come up against something that I'm not sure I've solved in the best way possible.
One of our ViewModels contains 3 other view models - a dashboard and 2 lists. In iOS this is presented using a MvxTabBarViewController which works great. Android and WP present this view in a similar manner. An example of the object model is below:
public class ProjectViewModel : MvxViewModel
{
public DashboardViewModel Dashboard {get;set;}
public FirstListViewModel FirstList {get;set;}
public SecondListViewModel SecondList {get;set;}
}
We're now in the situation where if a certain action happens within the DashboardViewModel we would like to instruct the navigation to change the tab in iOS and the same thing to happen on the other platforms.
The only way I've been able to get the tab to change on iOS is to use this.SelectedIndex = 1; from within the iOS ProjectView.
At the moment also the only way I've managed to trigger this change is to fire an event from the DashboardViewModel and then the ProjectViewModel subscribes to this and fires another event which is subscribed to by the ProjectView to instruct it to change the tab in whatever device specific way it needs to. I can't help but think there is a better way to do this.
I've tried taking a look at a custom ViewPresenter for iOS and calling ShowViewModel FirstListViewModel from within the DashboardViewModel but the presenter doesn't appear to be getting used so we just transition normally. My idea was I could get in the middle, cancel the navigation request and then flip the active tab on the ProjectView.
Any suggestions would be appreciated on how we could do this in a better cross platform way using MVVMCross to handle the change if at all possible.
You should be able to do this in any of several ways:
using a custom presenter with overridden Show as you suggest
using a custom presenter with overridden ChangePresentation - and using a custom hint
using a custom binding or a binding to a property within the ProjectView to drive the transition
using a custom IMvxInteraction property
using a custom event from VM to View
using a messenger to send a message from the ViewModels to the Views.
Ultimately lots of these could work and which of these I might choose would depend on which one worked and which one the team are happy with - shipping the working app is always the ultimate goal.
Given where I am with MvvmCross experience, I'd probably opt today for trying the approach of trying a custom IMvxInteraction property. But this might not be for everyone... it certainly might be overkill for this sample...
However, to do this, I would try:
add a public enum Display { Dash, First, Second } to the Core project
add a ProjectViewModel property:
private MvxInteraction<Display> _display = new MvxInteraction< Display >();
public IMvxInteraction<Display> DisplayChange { get { return _display; } }
whenever this ViewModel wants to fire the change it can fire it using e.g. _display.Raise(Display.First)
the ProjectView could then bind Display to its own property which might be implemented like:
private IDisposable _subscription;
private IMvxInteraction<Display> _displayInteraction;
public IMvxInteraction<Display> ChangeDisplay
{
get { return _displayInteraction; }
set
{
if (_subscription != null)
{
_subscription.Dispose();
_subscription = null;
}
_displayInteraction = value;
if (_displayInteraction != null)
{
_subscription = _displayInteraction.WeakSubscribe(DoDisplayChange);
}
}
}
private void DoDisplayChange(Display which)
{
// change the tab display here
}
the binding would be added in ViewDidLoad like:
set.Bind(this).For(v => v.ChangeDisplay).To(vm => vm.DisplayChange);
I'm creating an IPad application using C#, Mono develop and Monotouch.
I've been using Monotouch.Dialog to create functionality similar to the wifi-settings on an iPhone. I'm using StyledStringElement with an accessory and am now trying to differentiate between tapping the row and tapping the DetailDisclosureButton.
I've been found out that I should override the UITableViewDelegate.AccessoryButtonTapped on the UITableView. I've tried to created a derived class from UITableViewDelegate and hook this into the Monotouch.Dialog. But this is where I got stuck. I didn't manage to replace the existing UITableViewDelegate with my extended version.
So my questions are:
Is this the preferred way of handling this event (to be able to differentiate between a tap on the element and a tap on the DetailDisclosureButton) ?
If not, any pointer on how to accomplish this ?
I have been searching the web for a (similar) example but have not found any yet. Any examples that you know of that could get me started ?
Thanks,
boris
event EventHandler accessoryPushed;
public override void AccessoryButtonTapped (UITableView tableView, NSIndexPath indexPath)
{
if(!accessoryPushed)
{
accessoryPushed(this,EventArgs.Empty);
}
}
You will need to add this to the DailogViewController code that you are using (this will override the tapping action). Instead of a simple function, you may want an event to be triggered, so just handle the event in your main code. That is probably your best bet.
Once you change this line, you will have to implement new functions like AccessorySelected (just mimic the path the code follows when a row is selected except with accessory).
On the other hand, you could try a different navigation method, often disclosure buttons are annoying and you don't want to click on them except to get simple information about the button (like a help feature).
I haven't found any other examples, sorry!