Develop Reference

xamarin forms DatePicker Cancel/OK event

I found and tried one example of a custom rendered DatePicker, for Android, for Xamarin Forms and does not show which button was clicked in UnFocus. At least not for me. Its from stackoverflow. Xamarin.Forms Android DatePicker/TimePicker button listener
Has the example in this article helped anyone else? I really need to know when the OK button is clicked.

This extends Nick Kovalsky's answer. I also fixed a bug in that answer, that meant the renderer was never used.
Subclass DatePicker, so that you can add a new BindableProperty and a new method. Place this in your cross-platform project.
OKCancelDatePicker.cs:
using Xamarin.Forms;
// Replace with YOUR namespace.
namespace TestBugs
{
/// <summary>
/// NOTE: Requires custom renderer on each platform.
/// </summary>
public class OKCancelDatePicker : DatePicker
{
public static readonly BindableProperty UserCancelledProperty = BindableProperty.Create(nameof(UserCancelled), typeof(bool), typeof(OKCancelDatePicker), false);
/// <summary>
/// Bind to "UserCancelled", to propagate this change elsewhere (e.g. to a VM, or to trigger some logic).
/// </summary>
public bool UserCancelled {
get => (bool)GetValue(UserCancelledProperty);
set => SetValue(UserCancelledProperty, value);
}
/// <summary>
/// Optionally add code here. Though usually you'll detect the change by binding to UserCancelled.
/// </summary>
public void OnPickerClosed()
{
if (UserCancelled) {
// User cancelled.
_ = 0; // Dummy code, to set a breakpoint on. You can remove this.
} else {
// User selected OK.
_ = 0; // Dummy code, to set a breakpoint on. You can remove this.
}
}
}
}
Create a renderer for Android. Place this in your .Android project.
OKCancelDatePickerRenderer.cs:
using Android.App;
using Android.Content;
using Xamarin.Forms;
using Xamarin.Forms.Platform.Android;
// Replace these with YOUR namespaces.
using TestBugs; // Contains OKCancelDatePicker.
using TestBugs.Droid; // Contains OKCancelDatePickerRenderer.
[assembly: ExportRenderer(typeof(OKCancelDatePicker), typeof(OKCancelDatePickerRenderer))]
// Replace this with YOUR Android namespace.
namespace TestBugs.Droid
{
/// <summary>
/// Based on Nick Kovalsky's https://stackoverflow.com/a/60786875/199364.
/// </summary>
public class OKCancelDatePickerRenderer : DatePickerRenderer
{
public OKCancelDatePickerRenderer(Context context) : base(context)
{
}
protected override void OnElementChanged(ElementChangedEventArgs<Xamarin.Forms.DatePicker> e)
{
base.OnElementChanged(e);
//Disposing
if (e.OldElement != null) {
_element = null;
}
//Creating
if (e.NewElement != null) {
_element = e.NewElement as OKCancelDatePicker;
}
}
protected OKCancelDatePicker _element;
protected override DatePickerDialog CreateDatePickerDialog(int year, int month, int day)
{
// This mimics what the original renderer did.
var dialog = new DatePickerDialog(Context, (o, e) =>
{
_element.Date = e.Date;
((IElementController)_element).SetValueFromRenderer(VisualElement.IsFocusedPropertyKey, false);
}, year, month, day);
// These use our custom actions when buttons pressed.
dialog.SetButton((int)DialogButtonType.Positive, Context.Resources.GetString(global::Android.Resource.String.Ok), OnOk);
dialog.SetButton((int)DialogButtonType.Negative, Context.Resources.GetString(global::Android.Resource.String.Cancel), OnCancel);
return dialog;
}
private void OnCancel(object sender, DialogClickEventArgs e)
{
// This is what the original renderer did when Cancel pressed.
_element.Unfocus();
// This is our custom logic.
_element.UserCancelled = true;
_element?.OnPickerClosed();
}
private void OnOk(object sender, DialogClickEventArgs e)
{
// This is what the original renderer did when OK pressed.
_element.Date = ((DatePickerDialog)sender).DatePicker.DateTime;
_element.Unfocus();
// This is our custom logic.
_element.UserCancelled = false;
_element?.OnPickerClosed();
}
}
}
Usage:
<ContentPage xmlns="http://xamarin.com/schemas/2014/forms"
xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
xmlns:local="clr-namespace:TestBugs"
x:Class="TestBugs.DatePickerTestPage">
<ContentPage.Content>
<StackLayout>
<Label Text="Date Picker Test Page" HorizontalOptions="CenterAndExpand" />
<local:OKCancelDatePicker />
</StackLayout>
</ContentPage.Content>
</ContentPage>
IMPORTANT: If your app runs on other platforms you'll need to do similar on each platform. Per platform, try to find an example to modify. Nick's answer has a link to one for iOS.
TBD: I should add here an example of how to bind to that UserCancelled property, so you can connect it to logic in your page.
For now, read about Bindable Properties, and google for examples of binding to a BindableProperty of a control or view.

Delegate was deprecated in iOS 12.0. Please adopt WKWebView. How do I fix this in Xamarin?

I am trying to create a Custom WebView Renderer for iOS and Android. My main goal is to make the WebView fit it's HTML contents;
After googling, I soon realized that this is only possible by making custom renderers for both iOS and Android.
I am using a solution that requires a delegate. You can view the solution here. However, this solution was posted in 2016 and therefore I get this compile time error message: "'Delegate' was deprecated in iOS 12.0. No longer supported; please adopt 'WKWebView'.
PostWebView.xaml
<WebView xmlns="http://xamarin.com/schemas/2014/forms" xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml" x:Class="Yoors.Views.Templates.PostWebView" x:Name="WebViewer" BackgroundColor="White" Margin="0, 10, 0, 0" VerticalOptions="FillAndExpand" HeightRequest="1000">
<WebView.Source>
<HtmlWebViewSource Html="{Binding Data.Content}" />
</WebView.Source>
</WebView>
CustomWebViewRenderer.cs
public class CustomWebViewRenderer : WebViewRenderer
{
protected override void OnElementChanged(VisualElementChangedEventArgs e)
{
base.OnElementChanged(e);
Delegate = new CustomUIWebViewDelegate(this);
}
}
CustomUIWebViewDelegate.cs
public class CustomUIWebViewDelegate : UIWebViewDelegate
{
CustomWebViewRenderer _webViewRenderer;
public CustomUIWebViewDelegate(CustomWebViewRenderer webViewRenderer = null)
{
_webViewRenderer = _webViewRenderer ?? new CustomWebViewRenderer();
}
public override async void LoadingFinished(UIWebView webView)
{
var wv = _webViewRenderer.Element as PostWebView;
if (wv != null)
{
await System.Threading.Tasks.Task.Delay(100); // wait here till content is rendered
wv.HeightRequest = (double)webView.ScrollView.ContentSize.Height;
}
}
}
How do I adopt WKWebView according to my code?

Its quite easy actually, Create a Custom Webview something like this:
public class MyWebView : WebView
{
public static readonly BindableProperty UrlProperty = BindableProperty.Create(
propertyName: "Url",
returnType: typeof(string),
declaringType: typeof(MyWebView),
defaultValue: default(string));
public string Url
{
get { return (string)GetValue(UrlProperty); }
set { SetValue(UrlProperty, value); }
}
}
Then in your iOS CustomRenderer do something like this:
[assembly: ExportRenderer(typeof(MyWebView), typeof(MyWebViewRenderer))]
namespace WKWebView.iOS
{
public class MyWebViewRenderer : ViewRenderer<MyWebView, WKWebView>
{
WKWebView _wkWebView;
protected override void OnElementChanged(ElementChangedEventArgs<MyWebView> e)
{
base.OnElementChanged(e);
if (Control == null)
{
var config = new WKWebViewConfiguration();
_wkWebView = new WKWebView(Frame, config);
SetNativeControl(_wkWebView);
}
if (e.NewElement != null)
{
Control.LoadRequest(new NSUrlRequest(new NSUrl(Element.Url)));
}
}
}
}

AdMob not displaying the banner ad on my app why?

So I tried implementing AdMob to my project but my ad is not showing up and I have no idea why.
I was following a guide online which I can't seem to find at this point but when they did it, it worked just fine, and I followed all the steps, I am starting to consider that it might be Xamarin but I am not sure.
I have a AdMobRenderer.cs that looks like this
using Google.MobileAds;
using UIKit;
using Xamarin.Forms;
using Xamarin.Forms.Platform.iOS;
namespace AdMobTestProject.iOS
{
public class AdMobRenderer : ViewRenderer
{
//hiding the key for this question
private const string adMobId = "ca-app-pub-xxxxxx/xxxxxxx";
private BannerView adView;
private bool viewOnScreen;
protected override void OnElementChanged(ElementChangedEventArgs<View> e)
{
base.OnElementChanged(e);
if (e.NewElement == null)
return;
if (e.OldElement == null)
{
adView = new BannerView(AdSizeCons.SmartBannerPortrait)
{
AdUnitID = adMobId,
RootViewController = UIApplication.SharedApplication.Windows[0].RootViewController
};
adView.AdReceived += (sender, args) =>
{
if (!viewOnScreen)
{
this.AddSubview(adView);
}
viewOnScreen = true;
};
Request request = Request.GetDefaultRequest();
adView.LoadRequest(request);
base.SetNativeControl(adView);
}
}
public AdMobRenderer()
{
}
}
}
And then the XAML aswell
<?xml version="1.0" encoding="utf-8" ?>
<ContentPage xmlns="http://xamarin.com/schemas/2014/forms"
xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
xmlns:local="clr-namespace:AdMobTestProject"
x:Class="AdMobTestProject.MainPage">
<StackLayout>
<!-- Place new controls here -->
<Label Text="Welcome to Xamarin.Forms!"
HorizontalOptions="Center"
VerticalOptions="CenterAndExpand" />
<local:AdMobView WidthRequest="320" HeightRequest="50"></local:AdMobView>
</StackLayout>
</ContentPage>
And ofcourse the MainPage.xaml.cs
namespace AdMobTestProject
{
public partial class MainPage : ContentPage
{
public MainPage()
{
InitializeComponent();
}
}
public class AdMobView : ContentView
{
public AdMobView()
{
}
}
}
Am I missing something? Why is it not displaying anything when I deploy the app to my device? iPhone 7.
I am using Xamarin.Forms

Check the space available for the adview should not be less than 360 pixel wide so check the main layout of the page if there margins remove them.
as a clue check the build output window in visual studio it will show if the ads are loaded or not and show a reason for why ads are not visible if they are loaded.
in your sample remove the WidthRequest.
this is a late reply for future searches.

Try change adMobId to a test ad id.
https://developers.google.com/admob/android/test-ads
(ca-app-pub-3940256099942544/6300978111)
I had the same issue, and if I navigated to another page and went back my ads showed up.

Xamarin Forms Binding Issues using Mvvm Light

Good afternoon everyone. I have just begun to work with Xamarin Forms as I will need it for my job and wanted to learn best practices from the beginning so I went for Mvvm Light. My current problem is that, whatever I do, I really can't make binding work (NOTE: it worked for my first project, a simple page where I had a button which was used to navigate to another page). Now, for my current project, an EventApp I tried everything I could, looking on lots of forums and tried various settings and implementations but couldn't make the binding work again. I will show you some of my current code for a test page I've done just for testing purposes.
App.cs class:
public partial class App : Application
{
private static ViewModelLocator _locator;
public static ViewModelLocator Locator { get { return _locator ?? (_locator = new ViewModelLocator()); } }
public App()
{
InitializeComponent() //Tried both with and without this
registerNavigationService();
}
protected override void OnStart()
{
}
protected override void OnSleep()
{
// Handle when your app sleeps
}
protected override void OnResume()
{
// Handle when your app resumes
}
public void registerNavigationService()
{
NavigationService nav = new NavigationService();
nav.Configure(PageNames.GeneralNotificationPage, typeof(GeneralNotificationPage));
nav.Configure(PageNames.CreateNotificationPage, typeof(CreateNotificationPage));
nav.Configure(PageNames.SelectSongPage,typeof(SelectSongPage));
SimpleIoc.Default.Register<INavigationService>(() => nav);
var firstPage = new NavigationPage(new SelectSongPage());
nav.Initialize(firstPage);
MainPage = firstPage;
}
}
`
App.xaml:
<?xml version="1.0" encoding="utf-8"?>
<Application xmlns="http://xamarin.com/schemas/2014/forms"
xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
x:Class="EventAppMvvm.App"
>
</Application>
-Note: here I tried to set a static resource for my ViewModelLocator the next way:
xlmns:vm="clr-namespace:EventAppMvvm.ViewModel;assembly=EventAppMvvm"
and then in resources
<vm:ViewModelLocator x:Key="Locator"/>
doesn't work, if I try in one of my pages to set the DataContext, it says it hasn't found any bindable property. If I set the BindingContext to that I get an NPE when I run the app as there is no object created. So I ended up using the code behind to do the BindingContext and instantiate the locator in my App.cs file so I won't receive an NPE.
ViewModelLocator:
public class ViewModelLocator
{
/// <summary>
/// Initializes a new instance of the ViewModelLocator class.
/// </summary>
public ViewModelLocator()
{
ServiceLocator.SetLocatorProvider(() => SimpleIoc.Default);
////if (ViewModelBase.IsInDesignModeStatic)
////{
//// // Create design time view services and models
//// SimpleIoc.Default.Register<IDataService, DesignDataService>();
////}
////else
////{
//// // Create run time view services and models
//// SimpleIoc.Default.Register<IDataService, DataService>();
////}
SimpleIoc.Default.Register<CreateNotificationPageViewModel>();
SimpleIoc.Default.Register<SelectSongPageViewModel>();
SimpleIoc.Default.Register<GeneralNotificationPageViewModel>();
}
public CreateNotificationPageViewModel CreateNotificationPageVM
{
get
{
return ServiceLocator.Current.GetInstance<CreateNotificationPageViewModel>();
}
}
public SelectSongPageViewModel SelectSongPageVM
{
get
{
return ServiceLocator.Current.GetInstance<SelectSongPageViewModel>();
}
}
public GeneralNotificationPageViewModel GeneralNotificationPageVM
{
get
{
return ServiceLocator.Current.GetInstance<GeneralNotificationPageViewModel>();
}
}
public static void Cleanup()
{
// TODO Clear the ViewModels
}
}
One of my ViewModels(test one):
public class SelectSongPageViewModel : ViewModelBase
{
RelayCommand _commandTest;
Song _selectedSong;
INavigationService navigation;
string clicked = "3";
string _message = "I ve not been clicked yet";
public SelectSongPageViewModel(INavigationService navigation)
{
this.navigation = navigation;
}
RelayCommand CommandTest
{
get
{
if(_commandTest == null)
{
_commandTest= new RelayCommand(() =>
{
Message = _message;
//navigation.NavigateTo(PageNames.CreateEventPage);
});
}
return _commandTest;
}
}
public string Message
{
get
{
return clicked;
}
set
{
clicked = value;
RaisePropertyChanged("Message");
}
}
}
Actual page of that ViewModel:
Notes: if I try to use DataContext (defined as static resource previously in App.xaml), no matter if I give the correct namespace and assembly, it says that it hasn't found any binding, property there, if I use BindingContext, it works, I don't get any errors at compile time but I can't make the buttons do something as it is like it doesn't recognize my defined commands but for some reason it just binds simple data like my Message property.
<ContentPage xmlns="http://xamarin.com/schemas/2014/forms"
xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
x:Class="EventAppMvvm.Views.SelectSongPage"
xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
mc:Ignorable="d"
>
<ContentPage.Content>
<StackLayout>
<Label Text="{Binding Message}"></Label>
<Button Text="Press me" Command="{Binding CommandTest}"></Button>
</StackLayout>
</ContentPage.Content>
</ContentPage>
And the code behind for this page.
namespace EventAppMvvm.Views
{
public partial class SelectSongPage : ContentPage
{
public SelectSongPage()
{
InitializeComponent();
var vm = App.Locator.SelectSongPageVM;
BindingContext = vm;
}
}
}
Whatever I do, I can't make the commands/Complex binding work again for some reason but still simple property binding works, I'm using VisualStudio for Mac if it matters.

navigation to a new page removes backstack

I have a strange recurring problem. Sometimes it goes away, other times it comes back. I can't pinpoint at all the issue, all my breakpoints seem to be hit in expected order.
When I navigate to a new page, my backstack keeps getting deleted, so pressing back just backgrounds the app. Obviously this is a problem.
I think it may be a result of my more complex page and viewmodel structures. I created a new class for all the NavigationHelper stuff for Pages enforcing that all my Pages subclass from the new class. I enforce that all my Pages attach themselves to a base PageViewModel class to resolve the communication between the two (I had a better way but Xaml doesn't play well), and I navigate using a NavigationService, where I call CurrentFrame, which is a static method for return Windows.Current.Content as Frame.
Here are what I think are relevant code. Any ideas? Thanks a bunch in advance. I have no clue what's going on :/
I navigate forward using the Navigate method in NavigationService (not the other two lolol), but my back button doesn't go back properly.
public abstract class BaseViewModelPage : Page
{
protected readonly NavigationHelper NavigationHelper;
protected BaseViewModelPage()
{
NavigationHelper = new NavigationHelper(this);
NavigationHelper.LoadState += navigationHelper_LoadState;
NavigationHelper.SaveState += navigationHelper_SaveState;
this.NavigationCacheMode = NavigationCacheMode.Required;
}
protected BasePageViewModel CurrentPageViewModel
{
get { return DataContext as BasePageViewModel; }
}
#region Navigation Registration
protected override void OnNavigatedTo(NavigationEventArgs e)
{
NavigationHelper.OnNavigatedTo(e);
}
protected override void OnNavigatedFrom(NavigationEventArgs e)
{
NavigationHelper.OnNavigatedFrom(e);
}
protected virtual void LoadState(LoadStateEventArgs e)
{
if (CurrentPageViewModel != null)
{
CurrentPageViewModel.LoadState(e);
}
}
protected virtual void SaveState(SaveStateEventArgs e)
{
if (CurrentPageViewModel != null)
{
CurrentPageViewModel.SaveState(e);
}
}
private void navigationHelper_LoadState(object sender, LoadStateEventArgs e)
{
LoadState(e);
}
private void navigationHelper_SaveState(object sender, SaveStateEventArgs e)
{
SaveState(e);
}
#endregion
}
public abstract class BasePageViewModel : ViewModelBase
{
private bool _isLoading = false;
public bool IsLoading
{
get
{
return _isLoading;
}
set
{
if (_isLoading == value)
{
return;
}
_isLoading = value;
RaisePropertyChanged();
}
}
public virtual void LoadState(LoadStateEventArgs e)
{
}
public virtual void SaveState(SaveStateEventArgs e)
{
}
}
public class NavigationService : INavigationService
{
public static readonly Dictionary<Type, Type> PageDictionary;
static NavigationService()
{
PageDictionary = new Dictionary<Type, Type>();
PageDictionary.Add(typeof(LogInPageViewModel), typeof(LogInPage));
PageDictionary.Add(typeof(RegisterUserPageViewModel), typeof(RegisterUserPage));
}
public bool Navigate(Type pageViewModelType, Object parameter = null)
{
if (PageDictionary.ContainsKey(pageViewModelType))
{
if (parameter != null)
{
return App.CurrentFrame.Navigate(PageDictionary[pageViewModelType], parameter);
}
else
{
return App.CurrentFrame.Navigate(PageDictionary[pageViewModelType]);
}
}
return false;
}
public bool GoBack()
{
if (CanGoBack())
{
App.CurrentFrame.GoBack();
}
return false;
}
public bool CanGoBack()
{
return App.CurrentFrame.CanGoBack;
}
public bool NavigateAndRemoveSelf(Type pageViewModelType, object parameter = null)
{
if (Navigate(pageViewModelType, parameter))
{
if (App.CurrentFrame.CanGoBack)
{
App.CurrentFrame.BackStack.RemoveAt(App.CurrentFrame.BackStackDepth - 1);
return true;
}
}
return false;
}
public bool NavigateAndRemoveAll(Type pageViewModelType, object parameter = null)
{
if (Navigate(pageViewModelType, parameter))
{
while (App.CurrentFrame.CanGoBack)
{
App.CurrentFrame.BackStack.RemoveAt(App.CurrentFrame.BackStackDepth - 1);
}
return true;
}
return false;
}
}
Update [solved]:
The error is caused by using a Universal App Class Library.
I wanted to separate the NavigationHelper.cs class (generated by default in WP8 apps) into a library. so that I could unit test the VM directly (I could not reference the WP8 app with the Unit Test project). Thus, I placed the NavigationHelper.cs class, plus all my relevant code above, in a new Universal App Class Library.
The NavigationHelper class relies on two things, a WINDOWS_PHONE_APP macro in the BUILD, which affects this specific part in the NavigationHelper class, the HardwareButton BackPressed listener.
#if WINDOWS_PHONE_APP
Windows.Phone.UI.Input.HardwareButtons.BackPressed += HardwareButtons_BackPressed;
#else
and a second reliance on the Windows.Phone assembly. The assembly exists in a WP8 app, but not for a Universal App Class Library. This means that even if I add the WINDOWS_PHONE_APP macro to the library, the app will not compile. You cannot use the NavigationHelper generated by Windows Phone 8/8.1 projects inside a Universal App Class Library. I will try to raise this issue. Thanks!

Update [solved]:
The error is caused by using a Universal App Class Library.
I wanted to separate the NavigationHelper.cs class (generated by default in WP8 apps) into a library. so that I could unit test the VM directly (I could not reference the WP8 app with the Unit Test project). Thus, I placed the NavigationHelper.cs class, plus all my relevant code above, in a new Universal App Class Library.
The NavigationHelper class relies on two things, a WINDOWS_PHONE_APP macro in the BUILD, which affects this specific part in the NavigationHelper class, the HardwareButton BackPressed listener.
#if WINDOWS_PHONE_APP
Windows.Phone.UI.Input.HardwareButtons.BackPressed += HardwareButtons_BackPressed;
#else
...
#endif
Because the MACRO wasn't defined, the back button wouldn't actually go back.
A second problem was the missing Windows.Phone assembly. The assembly exists in a WP8 app, but not for a Universal App Class Library. This means that even if I add a WINDOWS_PHONE_APP macro to the library, the app will not compile. You cannot use the NavigationHelper generated by Windows Phone 8/8.1 projects inside a Universal App Class Library. I will try to raise this issue. Thanks!

You can leave your NavigationHelper in your shared project, just add this to your MainPage in the Windows Phone project..
static MainPage()
{
HardwareButtons.BackPressed += (sender, args) =>
{
var frame = Window.Current.Content as Frame;
if (frame != null && frame.CanGoBack)
{
frame.GoBack();
args.Handled = true;
}
};
}
This solved my BackButton issues.