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Xamarin forms Loading Spinner without button action

I want to make a loading spin in Xamarin forms. After the login screen, the webview on the main screen takes about 3 seconds to load, at that time I want to have a loading spin.I tried using the acr.userdialogs package but I could only trigger it with a button.
my goal is to work for 3 seconds from the moment the page is opened (without triggering it with a button or something like that.) how can i do that? thanks.
EDIT : (In the code I shared, I can trigger it with the login button, but my aim is to do it without triggering it with a button on the main page.)
`async void btnLoginClick(System.Object sender, System.EventArgs e)
{
if (Connectivity.NetworkAccess == NetworkAccess.Internet)
{
var userName = tbName.Text;
var password = tbPassword.Text;
var serviceUrl = "API";
var paramList = new List<ServiceParameterObject>();
paramList.Add(new ServiceParameterObject("_userCode", userName));
paramList.Add(new ServiceParameterObject("_userPassword", password));
var apiResult = ApiResult.SendPostRequestFromBody(serviceUrl, paramList);
if (apiResult.Status)
{
var user = JsonConvert.DeserializeObject<User>(apiResult.Message);
//Preferences.Set("userName", tbName.Text);
//Preferences.Set("Password", tbPassword.Text);
Preferences.Set("userId", user.Id.ToString());
var userIdCookie = Preferences.Get("userId", String.Empty);
await Navigation.PushAsync(new HomeScreen()); //!!!!!!!!!!!!!!
UserDialogs.Instance.ShowLoading("Yukleniyor...",MaskType.Black);
await Task.Delay(3000);
UserDialogs.Instance.HideLoading();
}
else
{
await DisplayAlert("Uyarı", "Kullanıcı Adınız veya Şifreniz hatalıdır. Lütfen tekrar deneyiniz.", "Tamam");
}`

public partial class HomeScreen : ContentPage
{
public HomeScreen ()
{
InitializeComponent ();
var userIdCookie = Preferences.Get("userId", String.Empty);
if (Connectivity.NetworkAccess == NetworkAccess.Internet)
{
//_userCode = Encrytpion.EncryptString(_userCode,"1234567812345678");
OneSignal.Default.SetExternalUserId(userIdCookie);
webView.Source = "wvsource";
Device.BeginInvokeOnMainThread(async () =>
{
UserDialogs.Instance.ShowLoading("Yukleniyor...", MaskType.Black);
await Task.Delay(3000);
UserDialogs.Instance.HideLoading();
});
}
else
{
DisplayAlert("Uyarı", "İnternet bağlantınız yok. Lütfen Bağlantınızı kontrol edip tekrar deneyiniz", "Tamam");
}
}
i did it.

Disable barcode scanner on preview window closing

When I close the preview window of my BarcodeScanner the webcam stay active and I want to prevent that because it's kind of weird to see that the camera is still on and that you can still scan some barcode even if I close the preview.
I can't figure out how to disable the BarcodeScanner when I close the preview window.
Here's my 'BarcodeScanner' code :
private async Task<bool> ClaimScanner()
{
bool res = false;
string selector = BarcodeScanner.GetDeviceSelector();
DeviceInformationCollection deviceCollection = await DeviceInformation.FindAllAsync(selector);
if(scanner == null)
scanner = await BarcodeScanner.FromIdAsync(deviceCollection[0].Id);
if (scanner != null)
{
if(claimedBarcodeScanner == null)
claimedBarcodeScanner = await scanner.ClaimScannerAsync();
if (claimedBarcodeScanner != null)
{
claimedBarcodeScanner.DataReceived += ClaimedBarcodeScanner_DataReceivedAsync;
claimedBarcodeScanner.ReleaseDeviceRequested += ClaimedBarcodeScanner_ReleaseDeviceRequested;
claimedBarcodeScanner.IsDecodeDataEnabled = true;
claimedBarcodeScanner.IsDisabledOnDataReceived = true;
await claimedBarcodeScanner.EnableAsync();
res = true;
Debug.WriteLine("Barcode Scanner claimed");
}
}
antispam = false;
return res;
}
public async void ScanBarcodeAsync()
{
if(claimedBarcodeScanner == null && !antispam)
{
antispam = true;
await ClaimScanner();
}
if(claimedBarcodeScanner != null)
{
await claimedBarcodeScanner.ShowVideoPreviewAsync();
await claimedBarcodeScanner.StartSoftwareTriggerAsync();
claimedBarcodeScanner = null;
}
}
private async void ClaimedBarcodeScanner_DataReceivedAsync(ClaimedBarcodeScanner sender, BarcodeScannerDataReceivedEventArgs args)
{
await Windows.ApplicationModel.Core.CoreApplication.MainView.CoreWindow.Dispatcher.RunAsync(CoreDispatcherPriority.Normal, () =>
{
if (currentDataContext != null && currentDataContext is Scannable)
{
Debug.WriteLine(CryptographicBuffer.ConvertBinaryToString(BinaryStringEncoding.Utf8, args.Report.ScanDataLabel));
Scannable obj = (Scannable)currentDataContext;
obj.NumSerie = CryptographicBuffer.ConvertBinaryToString(BinaryStringEncoding.Utf8, args.Report.ScanDataLabel);
}
}
);
}
void ClaimedBarcodeScanner_ReleaseDeviceRequested(object sender, ClaimedBarcodeScanner e)
{
// always retain the device
e.RetainDevice();
}
EDIT : I used the library indicated by Microsoft provided by Digimarc : https://learn.microsoft.com/en-us/windows/uwp/devices-sensors/pos-camerabarcode

Disable barcode scanner on preview window closing
ClaimedBarcodeScanner has StopSoftwareTriggerAsync method, if you want to disable barcode scanner on preview window closing, you just invoke StopSoftwareTriggerAsync method after HideVideoPreview.
private async void HidePreviewButton_Click(object sender, RoutedEventArgs e)
{
claimedScanner?.HideVideoPreview();
await claimedScanner?.StopSoftwareTriggerAsync();
}

UWP C# Menuflyout Unable To Display Item Properly During 1st Click

I am having an issue with my code to add button from json where the first attempt i click add button, the menuflyout won't have any respond but second click attempt then it will work properly.
Can advise did i do anything wrong? Thanks.
private async void AddButton_Click(object sender, RoutedEventArgs e)
{
List<ClientList> clientLists;
var jsonSerializer = new DataContractJsonSerializer(typeof(List<ClientList>));
var myStream = await ApplicationData.Current.LocalFolder.OpenStreamForReadAsync(CLIENTSLIST);
clientLists = (List<ClientList>)jsonSerializer.ReadObject(myStream);
var menuFlyout = new MenuFlyout();
int isEmpty = myGrid.Children.Count;
if (isEmpty == 0)
{
foreach (var device in clientLists)
{
var menuFlyoutItem = new MenuFlyoutItem() { Name = device.clientname, Text = device.clientname };
menuFlyoutItem.Tag = device.clientaddress;
menuFlyoutItem.Click += AddMenuFlyoutItem_Click;
menuFlyout.Items.Add(menuFlyoutItem);
}
}else
{
foreach (var device in clientLists)
{
bool toAddButton = true;
foreach (Button btn in myGrid.Children.OfType<Button>())
{
if (btn.Content.ToString() == device.clientname)
{
toAddButton = false;
}
}
if (toAddButton)
{
var menuFlyoutItem = new MenuFlyoutItem() { Name = device.clientname, Text = device.clientname };
menuFlyoutItem.Tag = device.clientaddress;
menuFlyoutItem.Click += AddMenuFlyoutItem_Click;
menuFlyout.Items.Add(menuFlyoutItem);
}
}
}
AddButton.Flyout = menuFlyout;
}

The problem is you are loading the data asynchronously here:
var myStream = await ApplicationData.Current.LocalFolder.OpenStreamForReadAsync(CLIENTSLIST);
When this happens, UI continues executing the Click event, so the button is clicked (and Flyout is null the first time) and Flyout will never display. You should rather load the Flyout before that - either when the page loads or when the data source changes, so that when the user clicks, the flyout is already there. Doing loading in Click is simply too late, if you need an asynchronous operation to finish.
Alternatively you could set the flyout right at the start:
private async void AddButton_Click(object sender, RoutedEventArgs e)
{
var menuFlyout = new MenuFlyout();
AddButton.Flyout = menuFlyout;
List<ClientList> clientLists;
var jsonSerializer = new DataContractJsonSerializer(typeof(List<ClientList>));
var myStream = await ApplicationData.Current.LocalFolder.OpenStreamForReadAsync(CLIENTSLIST);
clientLists = (List<ClientList>)jsonSerializer.ReadObject(myStream);
int isEmpty = myGrid.Children.Count;
if (isEmpty == 0)
{
foreach (var device in clientLists)
{
var menuFlyoutItem = new MenuFlyoutItem() { Name = device.clientname, Text = device.clientname };
menuFlyoutItem.Tag = device.clientaddress;
menuFlyoutItem.Click += AddMenuFlyoutItem_Click;
menuFlyout.Items.Add(menuFlyoutItem);
}
}else
{
foreach (var device in clientLists)
{
bool toAddButton = true;
foreach (Button btn in myGrid.Children.OfType<Button>())
{
if (btn.Content.ToString() == device.clientname)
{
toAddButton = false;
}
}
if (toAddButton)
{
var menuFlyoutItem = new MenuFlyoutItem() { Name = device.clientname, Text = device.clientname };
menuFlyoutItem.Tag = device.clientaddress;
menuFlyoutItem.Click += AddMenuFlyoutItem_Click;
menuFlyout.Items.Add(menuFlyoutItem);
}
}
}
}
This way, the flyout will appear, but will be empty until the asynchronous loading finishes and the items are actually added. Here you are just reading a file, so it should be barely noticeable. Although not as clean as pre-loading the flyout, it should get the job done too.

Set UI element visible in Xamarin C# and then call asynchronous function

Can anybody help me with this code in my Xamarin project. I am trying to set a loading wheel (to signify that an action is happening and to let the user know to wait) when the "Login" button is clicked. For some reason since the function is asynchronous the loading wheel is never set to visible when the API code is run. It just fails to show up when I click login, however, it still does the login function.
// Defined up above in the file
var loginButton = new Button
{
Text = "Login",
};
loginButton.BackgroundColor = Color.Navy;
loginButton.TextColor = Color.White;
loginButton.Clicked += OnLoginButtonClicked;
async void OnLoginButtonClicked(object sender, EventArgs e)
{
loadingWheel.IsVisible = true;
try
{
var restUrl = "*******";
var content = string.Empty;
using (var client = new HttpClient())
{
string body = "{\"UserName\":\"" + usernameEntry.Text + "\", \"Password\":\"" + passwordEntry.Text + "\"}";
var contentType = new StringContent(body, Encoding.UTF8, "application/json");
var result = client.PostAsync(restUrl, contentType).Result;
content = await result.Content.ReadAsStringAsync();
}
if (content.ToLower() != "false")
{
var menuPage = new MenuPage();
NavigationPage = new NavigationPage(new HomePage());
RootPage = new Views.MainPage();
RootPage.Master = menuPage;
RootPage.Detail = NavigationPage;
MainPage = RootPage;
}
else
{
messageLabel.Text = "Username or password incorrect. Please try again.";
passwordEntry.Text = string.Empty;
}
}
catch (Exception ex)
{
messageLabel.Text = "Please check the internet connection for the connectivity.";
}
}
If I comment out the entire try block then the loading wheel does show up. It just does not work with the code in there.
Can anybody help me solve this problem? Thanks.

I think you can try with BeginInvokeOnMainThread
Device.BeginInvokeOnMainThread (() => {
loadingWheel.IsVisible = true;
});
UPDATE
I have also create this REPO... it works without BeginInvodeOnMainThread
public class MyPage6 : ContentPage
{
ActivityIndicator _ac = new ActivityIndicator { IsVisible = false, IsRunning = false };
public MyPage6()
{
Button b = new Button {Text = "Press for ActivityIndicator" };
b.Clicked += B_Clicked;
Content = new StackLayout
{
Children = {
_ac,
b,
new Label { Text = "Hello ContentPage" }
}
};
}
async void B_Clicked(object sender, EventArgs e)
{
_ac.IsRunning = true;
_ac.IsVisible = true;
await Task.Delay(2000);
_ac.IsRunning = false;
_ac.IsVisible = false;
}
}

UWP problems with multiple views

I am writing an app which should be able to run multiple views to edit different documents each in their own window. I've wrote some code which works, but I'm having some problems with it. The code I wrote is based upon the Multiple Views sample provided by Microsoft (https://github.com/Microsoft/Windows-universal-samples/tree/master/Samples/MultipleViews).
I have mainly two problems. The first one is if I close the main view, that is the first window that was open when the application was launched, then I cannot open any new views/windows by clicking in the app tile or opening an associated file type, until I close all views/windows and relaunch the app. The second one, is that when I try to open a new view/window from MainPage.xaml.cs, the app just crashes.
The code that I use to manage the views in App.xaml.cs is the following:
sealed partial class App : Application
{
//I use this boolean to determine if the application has already been launched once
private bool alreadyLaunched = false;
public ObservableCollection<ViewLifetimeControl> SecondaryViews = new ObservableCollection<ViewLifetimeControl>();
private CoreDispatcher mainDispatcher;
public CoreDispatcher MainDispatcher
{
get
{
return mainDispatcher;
}
}
private int mainViewId;
public int MainViewId
{
get
{
return mainViewId;
}
}
public App()
{
this.InitializeComponent();
this.Suspending += OnSuspending;
}
protected override async void OnLaunched(LaunchActivatedEventArgs e)
{
Frame rootFrame = Window.Current.Content as Frame;
if (rootFrame == null)
{
rootFrame = new Frame();
rootFrame.NavigationFailed += OnNavigationFailed;
if (e.PreviousExecutionState == ApplicationExecutionState.Terminated)
{
//TODO: Load state from previously suspended application
}
// Place the frame in the current Window
Window.Current.Content = rootFrame;
}
if (rootFrame.Content == null)
{
alreadyLaunched = true;
rootFrame.Navigate(typeof(MainPage), e.Arguments);
}
else if(alreadyLaunched)
{
var selectedView = await createMainPageAsync();
if (null != selectedView)
{
selectedView.StartViewInUse();
var viewShown = await ApplicationViewSwitcher.TryShowAsStandaloneAsync(
selectedView.Id,
ViewSizePreference.Default,
ApplicationView.GetForCurrentView().Id,
ViewSizePreference.Default
);
await selectedView.Dispatcher.RunAsync(CoreDispatcherPriority.Normal, () =>
{
var currentPage = (MainPage)((Frame)Window.Current.Content).Content;
Window.Current.Activate();
});
selectedView.StopViewInUse();
}
}
// Ensure the current window is active
Window.Current.Activate();
}
protected override async void OnFileActivated(FileActivatedEventArgs args)
{
base.OnFileActivated(args);
if (alreadyLaunched)
{
//Frame rootFrame = Window.Current.Content as Frame;
//((MainPage)rootFrame.Content).OpenFileActivated(args);
var selectedView = await createMainPageAsync();
if (null != selectedView)
{
selectedView.StartViewInUse();
var viewShown = await ApplicationViewSwitcher.TryShowAsStandaloneAsync(
selectedView.Id,
ViewSizePreference.Default,
ApplicationView.GetForCurrentView().Id,
ViewSizePreference.Default
);
await selectedView.Dispatcher.RunAsync(CoreDispatcherPriority.Normal, () =>
{
var currentPage = (MainPage)((Frame)Window.Current.Content).Content;
Window.Current.Activate();
currentPage.OpenFileActivated(args);
});
selectedView.StopViewInUse();
}
}
else
{
Frame rootFrame = new Frame();
rootFrame.Navigate(typeof(MainPage), args);
Window.Current.Content = rootFrame;
Window.Current.Activate();
alreadyLaunched = true;
}
}
partial void Construct();
partial void OverrideOnLaunched(LaunchActivatedEventArgs args, ref bool handled);
partial void InitializeRootFrame(Frame frame);
partial void OverrideOnLaunched(LaunchActivatedEventArgs args, ref bool handled)
{
// Check if a secondary view is supposed to be shown
ViewLifetimeControl ViewLifetimeControl;
handled = TryFindViewLifetimeControlForViewId(args.CurrentlyShownApplicationViewId, out ViewLifetimeControl);
if (handled)
{
var task = ViewLifetimeControl.Dispatcher.RunAsync(CoreDispatcherPriority.Normal, () =>
{
Window.Current.Activate();
});
}
}
partial void InitializeRootFrame(Frame frame)
{
mainDispatcher = Window.Current.Dispatcher;
mainViewId = ApplicationView.GetForCurrentView().Id;
}
bool TryFindViewLifetimeControlForViewId(int viewId, out ViewLifetimeControl foundData)
{
foreach (var ViewLifetimeControl in SecondaryViews)
{
if (ViewLifetimeControl.Id == viewId)
{
foundData = ViewLifetimeControl;
return true;
}
}
foundData = null;
return false;
}
private async Task<ViewLifetimeControl> createMainPageAsync()
{
ViewLifetimeControl viewControl = null;
await CoreApplication.CreateNewView().Dispatcher.RunAsync(CoreDispatcherPriority.Normal, () =>
{
// This object is used to keep track of the views and important
// details about the contents of those views across threads
// In your app, you would probably want to track information
// like the open document or page inside that window
viewControl = ViewLifetimeControl.CreateForCurrentView();
viewControl.Title = DateTime.Now.ToString();
// Increment the ref count because we just created the view and we have a reference to it
viewControl.StartViewInUse();
var frame = new Frame();
frame.Navigate(typeof(MainPage), viewControl);
Window.Current.Content = frame;
// This is a change from 8.1: In order for the view to be displayed later it needs to be activated.
Window.Current.Activate();
//ApplicationView.GetForCurrentView().Title = viewControl.Title;
});
((App)App.Current).SecondaryViews.Add(viewControl);
return viewControl;
}
void OnNavigationFailed(object sender, NavigationFailedEventArgs e)
{
throw new Exception("Failed to load Page " + e.SourcePageType.FullName);
}
private void OnSuspending(object sender, SuspendingEventArgs e)
{
var deferral = e.SuspendingOperation.GetDeferral();
//TODO: Save application state and stop any background activity
deferral.Complete();
}
//I call this function from MainPage.xaml.cs to try to open a new window
public async void LoadNewView()
{
var selectedView = await createMainPageAsync();
if (null != selectedView)
{
selectedView.StartViewInUse();
var viewShown = await ApplicationViewSwitcher.TryShowAsStandaloneAsync(
selectedView.Id,
ViewSizePreference.Default,
ApplicationView.GetForCurrentView().Id,
ViewSizePreference.Default
);
await selectedView.Dispatcher.RunAsync(CoreDispatcherPriority.Normal, () =>
{
var currentPage = (MainPage)((Frame)Window.Current.Content).Content;
Window.Current.Activate();
currentPage.LoadNewFile();
});
selectedView.StopViewInUse();
}
}
}
The code I use to try to launch a new view/window from MainPage.xaml.cs:
((App)App.Current).LoadNewView();
I've been reading the Microsoft documentation to try and understand what is the issue, but I still don't understand how exactly do Multiple Views work, like if the App class instantiated every time I open a new view/window.
I'd really appreciate the help.

Actually the proper way to still be able to open up new windows after the main one is closed is to use one of the overloads provided by TryShowAsStandaloneAsync.
protected override async void OnLaunched(LaunchActivatedEventArgs e)
{
// Create the newWindowId and stuff...
await ApplicationViewSwitcher.TryShowAsStandaloneAsync(newWindowId,
ViewSizePreference.Default,
e.CurrentlyShownApplicationViewId,
ViewSizePreference.Default);
Basically, you need to specify the third parameter anchorViewId which is
the ID of the calling (anchor) window.
In this case, you just need to pass in e.CurrentlyShownApplicationViewId.

I've found the solution to my problems, and I've actually decided not to use the ViewLifeTime control that comes with the sample.
The problem is that when the Main view is closed you have to use the Dispatcher.RunAsync() method from one of the other views that are still open to run it that thread
Here's the code that I've changed in my App.xaml.cs for anyone that is interested:
public bool isMainViewClosed = false;
public ObservableCollection<CoreApplicationView> secondaryViews = new ObservableCollection<CoreApplicationView>();
//...
protected override async void OnLaunched(LaunchActivatedEventArgs e)
{
Frame rootFrame = Window.Current.Content as Frame;
if (rootFrame == null)
{
rootFrame = new Frame();
rootFrame.NavigationFailed += OnNavigationFailed;
if (e.PreviousExecutionState == ApplicationExecutionState.Terminated)
{
//TODO: Load state from previously suspended application
}
Window.Current.Content = rootFrame;
}
if (rootFrame.Content == null)
{
alreadyLaunched = true;
rootFrame.Navigate(typeof(MainPage), e.Arguments);
}
else if(alreadyLaunched)
{
//If the main view is closed, use the thread of one of the views that are still open
if(isMainViewClosed)
{
int newViewId = 0;
await secondaryViews[0].Dispatcher.RunAsync(CoreDispatcherPriority.Normal, () =>
{
var currentPage = (MainPage)((Frame)Window.Current.Content).Content;
Window.Current.Activate();
currentPage.NewWindow();
newViewId = ApplicationView.GetForCurrentView().Id;
});
bool viewShown = await ApplicationViewSwitcher.TryShowAsStandaloneAsync(newViewId);
}
else
{
CoreApplicationView newView = CoreApplication.CreateNewView();
int newViewId = 0;
await newView.Dispatcher.RunAsync(CoreDispatcherPriority.Normal, () =>
{
Frame frame = new Frame();
frame.Navigate(typeof(MainPage), null);
Window.Current.Content = frame;
var currentPage = (MainPage)((Frame)Window.Current.Content).Content;
Window.Current.Activate();
secondaryViews.Add(CoreApplication.GetCurrentView());
newViewId = ApplicationView.GetForCurrentView().Id;
});
bool viewShown = await ApplicationViewSwitcher.TryShowAsStandaloneAsync(newViewId);
}
}
Window.Current.Activate();
}

Optionally you can use multiple instances for your application. You can synchronize settings changes as I have described here.

don't View(your)Lifetime away ... cheers,
int idCreate = 0; List<int> idSaved = new List<int>();
protected override async void OnLaunched(LaunchActivatedEventArgs e)
{
Frame rootFrame = Window.Current.Content as Frame;
if (rootFrame == null)
{
rootFrame = new Frame();
rootFrame.NavigationFailed += OnNavigationFailed;
Window.Current.Content = rootFrame;
}
if (rootFrame.Content == null)
{
rootFrame.Navigate(typeof(MainPage), e.Arguments);
idSaved.Add(ApplicationView.GetForCurrentView().Id);
}
else
{
var create = CoreApplication.CreateNewView();
await create.Dispatcher.RunAsync(CoreDispatcherPriority.Normal, () =>
{
var frame = new Frame();
frame.Navigate(typeof(MainPage), e.Arguments);
Window.Current.Content = frame;
Window.Current.Activate();
idCreate = ApplicationView.GetForCurrentView().Id;
});
for(int i = idSaved.Count - 1; i >= 0; i--)
if (await ApplicationViewSwitcher.TryShowAsStandaloneAsync(
idCreate, ViewSizePreference.UseMinimum,
idSaved[i], ViewSizePreference.UseMinimum)
) break;
idSaved.Add(idCreate);
}
Window.Current.Activate();
}