Am new to xamarin.form having a blockage...
This is what I want to do.
I have a button in welcome.xaml in xamarin.form and I want to perform a click event but I want a method from xamarin.driod to be implemented in the click.event.
Those this makes sense to anyone?
You need to write a custom control.
So you could handle the click event in the Android or IOS.
Read here about how to create a custom controls in xamarin.forms
You could also assign a static class that exist in the shared project from your driod project.
I typically prefer using IOC and Interfaces to implement platform specific logic in the Core project, but simple way to do it may just be to set a static Action on your pages code behind.
public partial class WelcomePage
{
public static Action DroidAction { get; set; }
private void Button_OnClicked(object sender, EventArgs e)
{
if (DroidAction == null)
{
Debug.WriteLine("Action was not set");
}
DroidAction?.Invoke();
}
Your Droids OnCreate could be an option of where to do this.
protected override void OnCreate(Bundle bundle)
{
base.OnCreate(bundle);
WelcomePage.DroidAction = new Action(() => Debug.WriteLine("I a platform specific action!"));
}
Related
For the past 2 month I have been searching tirelessly for a way to implement a proper Page.Loaded event when using Xamarin.Forms but I couldn't implement or find a way to do it.
Most people suggest overriding Page.OnAppearing or adding an event handler for Page.Appearing both of which are not the answers or the proper way to achieve the desired effect and don't event behave as a real Page.Loaded event would.
I would like to know the following:
Why doesn't Xamarin.Forms have a built-in Page.Loaded event?
Is there's a work around?
Can I implement it from the native side?
Edit:
What I mean by "proper Page.Loaded" event is:
It must be called ONCE AND ONLY ONCE the page has loaded all of it's controls, laid them out, initialized them and rendered them for the first time.
It must NOT be called when returning from modal pages.
1.Why not load the data/controls in the constructor of the ContentPage? The constructor method is call only once and it is also called before Page.OnAppearing.
Can I implement it from the native side?
Yes, I think you can.
In iOS, override the ViewDidLoad method in custom renderer:
[assembly:ExportRenderer (typeof(ContentPage), typeof(MyPageRenderer))]
namespace App487.iOS
{
public class MyPageRenderer : PageRenderer
{
protected override void OnElementChanged(VisualElementChangedEventArgs e)
{
base.OnElementChanged(e);
}
public override void ViewDidLoad()
{
base.ViewDidLoad();
//call before ViewWillAppear and only called once
}
public override void ViewWillAppear(bool animated)
{
base.ViewWillAppear(animated);
}
}
}
In Android, try to override the OnAttachedToWindow method:
[assembly: ExportRenderer(typeof(ContentPage), typeof(MyPageRenderer))]
namespace App487.Droid
{
public class MyPageRenderer : PageRenderer
{
public MyPageRenderer(Context context) : base(context)
{
}
protected override void OnElementChanged(ElementChangedEventArgs<Page> e)
{
base.OnElementChanged(e);
}
protected override void OnAttachedToWindow()
{
base.OnAttachedToWindow();
}
}
}
Currently Xamarin.Forms doesn't not provide a proper/complete life cycle events to fulfill all specific requirements, but things are improving, the Dev team is currently working on to address this issue, below mentioned issues and recent pull request on the official GitHub Repos (you may follow, get ideas and maybe implement it yourself before they even ship it), they will for sure provide that in the future, although it is not clear when it will be ready.
Specification: Enhancement Add better life cycle events #2210.
Issue: LifeCycle events for controls #556.
Pull request: Life cycle events for controls
GitHub Branch where currently working on.
MAUI repo (Next evolution of Xamarin) Cross-Platform LifeCycle.
Specification Add Loaded/Unloaded to VisualElement.
I want a process to be called each time I navigated to my view to refresh a list.
I am using Xamarin Forms and prism framework.
I made my ViewModel derivate from ContentPage but the following method is never called :
protected override void OnAppearing()
{
//Do things
}
How am I supposed to do to get the event? Is it better to use OnNavigateTo?
Through the document:
There are times in your application where you may want to invoke code
in your ViewModel based on when the Page Appears or Disappears without
Navigation specific consideration. For these times you can utilize the
IPageLifecycleAware interface to properly respond to the Appearing and
Disappearing events from the Page.
public class ViewAViewModel : IPageLifecycleAware
{
public void OnAppearing()
{
Console.WriteLine("We are appearing");
}
public void OnDisappearing()
{
Console.WriteLine("We are disappearing");
}
}
I found a solution to make my code work, I add to do this in my code behind from the page:
protected override void OnAppearing()
{
(BindingContext as IPageLifecycleAware)?.OnAppearing();
}
Still a mystery why I need to add this and it is not in the sample.
at the time of this post, the sample does it differently. It uses Behaviors to achieve expectation
It has a PageLifeCycleAwareBehavior class
private void OnAppearing(object sender, EventArgs e)
{
MvvmHelpers.InvokeViewAndViewModelAction<IPageLifecycleAware>(AssociatedObject, aware => aware.OnAppearing());
}
private void OnDisappearing(object sender, EventArgs e)
{
MvvmHelpers.InvokeViewAndViewModelAction<IPageLifecycleAware>(AssociatedObject, aware => aware.OnDisappearing());
}
You can see the full implementation here
You can also call Initialize is a good alternative
Add ini to your class
public class HelloViewModel : BindableBase, IInitialize
then add the following method
public void Initialize(INavigationParameters parameters)
{
// Do stuff
}
I'm using the Prism Template Pack for Visual Studio for Mac to generate a new project (tried both shared and pcl) then updating to 7.0.0.340-ci. Is registration of the views to view models done by convention?
When I try to run this app it throws this exception: Objective-C exception thrown. Name: NSInternalInconsistencyException Reason: Application windows are expected to have a root view controller at the end of application launch.
Here is the code for the main app.
public partial class App : PrismApplication
{
public App(IPlatformInitializer initializer = null) : base(initializer) { }
protected override void OnInitialized()
{
InitializeComponent();
NavigationService.NavigateAsync("MainPage?title=Hello%20from%20Xamarin.Forms");
}
protected override void RegisterTypes(Prism.Ioc.IContainerRegistry containerRegistry)
{
Prism.Mvvm.ViewModelLocationProvider.Register<MainPage,MainPageViewModel>();
}
//protected override void RegisterTypes()
//{
// Container.RegisterTypeForNavigation<MainPage>();
//}
}
I had to comment out the bottom lines and redo the override due to incompatible signatures.
Where did the Container.RegisterTypeForNavigation go or what is it's replacement?
I also tried it without any code in the RegisterTypes method.
In a debug session exploring the NavigationService properties says MainPage is null.
The RegisterTypes method should look like this.
In prism forms 7.x pages used for navigation must be registered via RegisterForNavigation<>() or RegisterForNavigation().
protected override void RegisterTypes(Prism.Ioc.IContainerRegistry containerRegistry)
{
containerRegistry.RegisterForNavigation<MainPage,MainPageViewModel>();
}
I understand that using AOP tooling could/should interfere with edit and continue for a class that is weaved. But I have a case where simply using MVVMLight and Fody.PropertyChanged in the same project prevents edit and continue anywhere if there is a class inheriting from ObservableObject in the project.
To reproduce, I simply create a WPF 4.6.2 project in VS 2017 Update 3 (happens in all the updates), add nuget references to MVVMLight & Fody.PropertyChanged, and then I can't edit and continue even simple code like this:
private void ButtonBase_OnClick(object sender, RoutedEventArgs e)
{
int i = 0;
i++;
i++;
}
Error is:
CS7038 Failed to emit module 'WithFodyPropertyChangedAndMvvmLight'.
If I remove the PropertyChanged tag from the FodyWeavers.xml file, the problem goes away. If I don't use MVVMLight and instead just:
class Class : INotifyPropertyChanged
{
public int Test { get; set; }
public event PropertyChangedEventHandler PropertyChanged;
}
it works fine. So it looks MVVMLight specific.
Anyone seen this? Thanks!
I'm trying to integrate Autofac into an exsisting ASP.NET web application.
The pages follow the MVP pattern. Each page implements a View and delegate functionality to a Presenter. The View is injected into the Presenter thru the constructor.
I was able to register the Presenter and View and the page loads fine but when a postback happens the user controls on the view are null. It seems that Autofac creates a new instance of the Page to give to the presenter instead of giving it the instance real Page instance. Is there a way to have Page instances registered with Autofac?
Has anyone use Autofac with ASP.NET and MVP?
Thanks!
There is a better way. First, enable the Web integration module. This will enable automatic property injection into the Page instance.
Since your presenter needs the view in its constructor, your page should take a dependency on a presenter factory instead of the presenter itself.
So, first you need the presenter factory, which is a delegate with the necessary parameters:
public delegate IOCTestPresenter IOCTestPresenterFactory(IIOCTestView view);
This delegate must match the parameters (type and name) of the presenter constructor:
public class IOCTestPresenter
{
public IOCTestPresenter(IIOCTestView view)
{
}
}
In your view, add a property receiving the factory delegate, and use the delegate to create the presenter:
public partial class IOCTest
{
public IOCTestPresenterFactory PresenterFactory {get;set;}
protected void Page_Load(object sender, EventArgs e)
{
var presenter = PresenterFactory(this);
}
}
In your container setup you will have to make the following registrations:
builder.Register<IOCTestPresenter>().FactoryScoped();
builder.RegisterGeneratedFactory<IOCTestPresenterFactory>();
I figured out a solution. Basically, you would register the page instance during the Page_PreInit event and then call the container to inject the dependencies. Ex.
public partial class IOCTest : System.Web.UI.Page, IIOCTestView
{
protected void Page_PreInit(object sender, EventArgs e)
{
var containerProviderAccessor = (IContainerProviderAccessor)HttpContext.Current.ApplicationInstance;
var containerProvider = containerProviderAccessor.ContainerProvider;
var builder = new ContainerBuilder();
builder.Register(this).ExternallyOwned().As<IIOCTestView>();
builder.Build(containerProvider.RequestContainer);
containerProvider.RequestContainer.InjectProperties(this);
}
public IOCTestPresenter Presenter { get; set; }
I'm not sure if there is a better way, but this seems to work.