I need to just show a message (Under certain circumstance) when I'm leaving a screen.
Found that there's a method called OnDisappearing() that is called when the form is being unloaded (Or also being overlaped by a new one).
What I found:
https://forums.xamarin.com/discussion/89563/intercept-page-leaving-event
https://learn.microsoft.com/en-us/dotnet/api/xamarin.forms.page.ondisappearing?view=xamarin-forms
Issue is that if I just copy the code as it is I get an error cause of the override (no suitable method found to override) that won't let me leave the code as is:
*Same happens with OnBackButtonPressed()
Modified it and just left it without the override and it just won't be called by any mean..
protected void OnDisappearing()
{
Exiting();
}
private async void Exiting()
{
System.Threading.Tasks.Task tmpShouldExit = Application.Current.MainPage.DisplayAlert("Hello", "Hi", "OK");
}
Is something I'm missing?
Is there any other method I can use?
Thanks
As Jason made me notice.
I was placing this in the ViewModel and it has to be in the code of the View cause you're overriding a Method of the Page.
Then if you want to access a method of the ViewModel from the view you can create a BindingContext to do so:
using MyProject.PageModels;
using System;
using System.Collections.Generic;
using Xamarin.Forms;
namespace MyProject.Pages
{
public partial class MyViewPage : ContentPage
{
public MyViewPage()
{
InitializeComponent();
NavigationPage.SetBackButtonTitle(this, string.Empty);
}
protected override void OnDisappearing()
{
base.OnDisappearing();
var pageViewModel = (MyViewModel)this.BindingContext;
if(pageViewModel.CertainConditionShowAlert())
{
System.Threading.Tasks.Task tmpShouldExit = Application.Current.MainPage.DisplayAlert("Hi", "Hello", "OK");
}
}
}
}
Related
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 migratting a xamarin forms 3.x app with Prism to forms 4 with shell navigation.
Do I have to create my custom solution to pass complex parameters to the new page or Xamarin has some buildin feature to receive other than string parameters?
Thanks.
As far as I know, and, reading the docs, the only samples regard passing simple data, like string when navigating.
However, I was able to find an Issue (and Pull Request), for passing objects/ Models, for the next version (I assume this is the case you are referring to).
You can track it here.
I've run some tests which seems to be working. I'm relatively new to Xamarin, hence recommend caution and welcome any feedback for any potential issues I may be overlooking.
I wrote an extension to Shell to accept a data object parameter 'navigationData' as follows:-
await Shell.Current.GoToAsync(state, navigationData, animate);
The extension ...
namespace Xamarin.Forms
{
public static class ShellExtensions
{
public static async Task GoToAsync(this Shell shell, ShellNavigationState state, object navigationData, bool animate=false)
{
shell.Navigated += async (sender, e) =>
{
if ((Shell.Current?.CurrentItem?.CurrentItem as IShellSectionController)?.PresentedPage is MyContentPage
p) await p.InitializeAsync(navigationData).ConfigureAwait(false);
};
await shell.GoToAsync(state, animate);
}
}
}
As shown above the extension:-
hooks to the Shell 'Navigated' event,
retrieves the 'current view (page)' as 'MyContentPage' i.e. subclassed ContentPage,
calls an InitializeAsync method on the view passing in the
navigationData parameter
the view then calls an InitializeAsync
method on the binding context (view model) passing the
navigationData parameter onto the viewModel.
In the extension method above, 'MyContentPage' is a custom abstract subclass of ContentPage with an InitializeAsync(navigationData) method that simply calls a similar method on the viewModel (binding context of the view).
Similarily, ViewModels subclass a custom ViewModelBase class that has a virtual InitializeAsync(navigationData). This can be overridden in the viewModel with the desired implementation and handling of the navigation data.
Simplified sample of Views, ViewModels and related base classes shown below
using System.Threading.Tasks;
using MyXamarinApp.ViewModels;
using Xamarin.Forms;
namespace MyXamarinApp.Views
{
public ItemDetailPage : MyContent<ItemDetailViewModel>{}
public ItemPage : MyContentPage<ItemViewModel>{}
public abstract class MyContentPage<T> : MyContentPage where T : ViewModelBase
{
protected T Vm;
protected override ViewModelBase VmBase => Vm as ViewModelBase;
protected MyContentPage()
{
BindingContext = Vm = ViewModelLocator.Resolve<T>();
}
private Comand _showDetailCommand;
public Command ShowDetailCommand
{
get { return _showDetailCommand ??= new Command(async () =>
await Shell.Current.GoToAsync("itemDetail", new NavigationDataObject())); }
}
}
public abstract class MyContentPage : ContentPage
{
protected abstract ViewModelBase VmBase { get; }
public virtual async Task InitializeAsync(object navigationData)
{
await VmBase.InitializeAsync(navigationData);
}
}
}
public class NavigationDataObject
{
'Properties' etc.
}
using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Linq.Expressions;
using System.Reflection;
using System.Runtime.CompilerServices;
using System.Threading.Tasks;
namespace MyXamarinApp.ViewModels
{
public ItemViewModel : ViewModelBase{}
public ItemDetailViewModel : ViewModelBase
{
private NavigationDataObject _navData;
public override async Task InitializeAsync(object navigationData)
{
if (navigationData is NavigationDataObject navData)
{
_navData = navData;
}
await base.InitializeAsync(navigationData);
}
}
public abstract class ViewModelBase
{
public virtual Task InitializeAsync(object navigationData)
{
return Task.FromResult(false);
}
}
}
You can always serialize the model to a JSON string and un-serializes it on the other side?
async void Handle_ItemTapped(object sender, ItemTappedEventArgs e)
{
if (e.Item == null)
return;
DailyPnL PnLClicked = (DailyPnL)e.Item;
string jason = await Task.Run(() => JsonConvert.SerializeObject(PnLClicked));
await Shell.Current.GoToAsync($"viewdailypnl?pnlmodel={jason}");
//Deselect Item
((ListView)sender).SelectedItem = null;
}
Then in your code behind:
public string pnlmodel
{
set
{
string derulo = Uri.UnescapeDataString(value);
viewModel.PnL = Task.Run(() => JsonConvert.DeserializeObject<DailyPnL>(derulo)).Result;
}
}
There is a framework called Xamarin.Zero https://github.com/markjackmilian/Xam.Zero
It lets you use shell while giving you convenient ViewModel to ViewModel navigation, IOC.
You can user stored preferences to store complex data like:
private async void OnItemSelected(Item item)
{
if (item == null)
return;
var jsonstr = JsonConvert.SerializeObject(item);
//Clear the shared preferences in case there is any
Preferences.Clear();
//Store your complex json on a shared preference
Preferences.Set("Data", jsonstr);
await Shell.Current.GoToAsync(nameof(DetailsPage));
}
Retrieve it on the details page like:
bool hasKey = Preferences.ContainsKey("Data");
var content = Preferences.Get("Data", string.Empty);
Details details = hasKey ? JsonConvert.DeserializeObject<Model>(content) : null;
I'm trying to program a custom DeploymentPlanExecutor using Microsofts DacFx 3.0 but the OnExecute-Method is never called.
If I use an identical DeploymentPlanModifier instead, OnExecute() is called as expected.
No matter whether I add the Executor, the Modifier, or both, the DAC actually is successfully deployed to the Database.
The Executor seems to be recognized during the Deployment since OnApplyDeploymentConfiguration() is called
Unfortunately I wasn't able to find any examples that use an DeploymentPlanExecutor (only examples with DeploymentPlanModifier) and the documentation of DacFx does not help at all.
My question is, why is OnExecute() in the DeploymentPlanExecutor not called and how can I fix this?
The code for my DeploymentPlanExecutor and DeploymentPlanExecutor:
using System.Collections.Generic;
using Microsoft.SqlServer.Dac.Deployment;
namespace DacTest
{
// The executor that does not work as expected
[ExportDeploymentPlanExecutor(ContributorId, "1.0.0.0")]
public class Executor : DeploymentPlanExecutor
{
public const string ContributorId = "DacTest.Executor";
protected override void OnApplyDeploymentConfiguration(DeploymentContributorContext context, ICollection<DeploymentContributorConfigurationStream> configurationStreams)
{
// Called
}
protected override void OnEstablishDeploymentConfiguration(DeploymentContributorConfigurationSetup setup)
{
// Not called
}
protected override void OnExecute(DeploymentPlanContributorContext context)
{
// Not called!
}
}
// The modifier that does work as expected
[ExportDeploymentPlanModifier(ContributorId, "1.0.0.0")]
public class Modifier : DeploymentPlanModifier
{
public const string ContributorId = "DacTest.Modifier";
protected override void OnApplyDeploymentConfiguration(DeploymentContributorContext context, ICollection<DeploymentContributorConfigurationStream> configurationStreams)
{
// Called
}
protected override void OnEstablishDeploymentConfiguration(DeploymentContributorConfigurationSetup setup)
{
// Not called
}
protected override void OnExecute(DeploymentPlanContributorContext context)
{
// Called!
}
}
}
The code calling the deployment (has to be in a different assembly):
using (DacPackage dacpac = DacPackage.Load(#"C:\Temp\dac.dacpac"))
{
DacDeployOptions dacDeployOptions = new DacDeployOptions();
dacDeployOptions.AdditionalDeploymentContributors = Executor.ContributorId; // + ";" + Modifier.ContributorId;
DacServices dacServices = new DacServices(connectionString);
dacServices.Deploy(dacpac, databaseName, true, dacDeployOptions);
}
The problem was, that you have to explicitly tell DacFx to use Executors. Modifiers are enabled by default though.
dacDeployOptions.RunDeploymentPlanExecutors = true;
I'm trying build out our logging framework using EntLib Logging and use attribute to indicate which class/method should be logged. So I think Interception would be a good choice. I'm a super noob to Ninject and Interception and I's following the tutorial at Innovatian Software on how to use interception via attributes. But when I run the app, BeforeInvoke and AfterInvoke was never called. Help Please, Thank You!
using System;
using System.Diagnostics;
using System.Collections.Generic;
using Castle.Core;
using Ninject;
using Ninject.Extensions.Interception;
using Ninject.Extensions.Interception.Attributes;
using Ninject.Extensions.Interception.Request;
class Program
{
static void Main(string[] args)
{
var kernel = new StandardKernel();
kernel.Bind<ObjectWithMethodInterceptor>().ToSelf();
var test= kernel.Get<ObjectWithMethodInterceptor>();
test.Foo();
test.Bar();
Console.ReadLine();
}
}
public class TraceLogAttribute : InterceptAttribute
{
public override IInterceptor CreateInterceptor(IProxyRequest request)
{
return request.Context.Kernel.Get<TimingInterceptor>();
}
}
public class TimingInterceptor : SimpleInterceptor
{
readonly Stopwatch _stopwatch = new Stopwatch();
protected override void BeforeInvoke(IInvocation invocation)
{
Console.WriteLine("Before Invoke");
_stopwatch.Start();
}
protected override void AfterInvoke(IInvocation invocation)
{
Console.WriteLine("After Invoke");
_stopwatch.Stop();
string message = string.Format("Execution of {0} took {1}.",
invocation.Request.Method,
_stopwatch.Elapsed);
Console.WriteLine(message);
_stopwatch.Reset();
}
}
public class ObjectWithMethodInterceptor
{
[TraceLog] // intercepted
public virtual void Foo()
{
Console.WriteLine("Foo - User Code");
}
// not intercepted
public virtual void Bar()
{
Console.WriteLine("Bar - User Code");
}
}
I figured it out, I missed the part where I've to disable auto module loading and manually load the DynamicProxy2Module to the kernel. Here's the change to the code:
//var kernel = new StandardKernel(); //Automatic Module Loading doesn't work
var kernel = new StandardKernel(new NinjectSettings() { LoadExtensions = false }, new DynamicProxy2Module());
Hope this help someone else.
In my Asp.Net project I wanna use Property Auto-wiring, e.g. for my ILogger. Basically I placed it as Property into class where I need to use it. Like below.
public class UserControlBase : UserControl
{
public ILogger CLogger { get; set; }
....
}
public partial class IPTracking : UserControlBase
{
protected void Page_Load(object sender, EventArgs e)
{
if (!IsPostBack)
{
string ip = HttpContext.Current.Request.ServerVariables["REMOTE_ADDR"];
//it works
ILogger logger = ObjectFactory.GetInstance<ILogger>();
logger.LogInfo(string.Format("Client IP: {0}", ip));
//it does not work
CLogger.LogInfo(string.Format("Client IP: {0}", ip));
}
}
}
However when calling in inherited control, logger is null. I checked the container and it'a definitely set as above implementation shows. Below is setting which is called from Global.asax.
public static void SetupForIoC()
{
Debug.WriteLine("SetupForIoC");
ObjectFactory.Initialize(x =>
{
x.FillAllPropertiesOfType<ILogger>().Use<EntLibLogger>();
});
Debug.WriteLine(ObjectFactory.WhatDoIHave());
}
Thanks for any advice, tip? X.
Update:
- I didnt mentioned before, but its Asp.Net webforms 3.5.
- I can't see what I am missing. I guess it could be because the injection gets involved later in process and didnt get set in requested class.
Link to desc. of usage: http://structuremap.github.com/structuremap/ConstructorAndSetterInjection.htm#section7
Give something like this a shot.
FillAllPropertiesOfType<ILogger>().AlwaysUnique().Use(s => s.ParentType == null ? new Log4NetLogger(s.BuildStack.Current.ConcreteType) : new Log4NetLogger((s.ParentType)));
Check out another StackOverflow answer I have which discusses using StructureMap to auto wire loggers.
Where do you actually set the CLogger property on the user control? Also, if you wanted to use one logger within the page, you could have the User cotnrol do:
public ILogger CLogger
{
get
{
if (this.Page is PageBase)
return ((PageBase)this.Page).Logger;
else
return null;
}
}