I need to display DisplayAlert from the View Model, however its simply doesn't display. Is there some other way how to display alert from the VM? The permission is true so that works.
private async Task TakePicture()
{
await Permission();
var imageSource = Application.Current.MainPage.DisplayActionSheet(AppResources.AlertNewPhoto, AppResources.AlertNewPhoto, AppResources.AlertGallery);
if (imageSource.Result == AppResources.AlertNewPhoto)
}
You can change your constructor of ViewModel like following code.
public PersonsViewModel(ContentPage page){
page.DisplayAlert("info","test","Ok");
}
In your Layout background code, you can use it following code.
public partial class MainPage : ContentPage
{
PersonsViewModel personsViewModel;
public MainPage()
{
InitializeComponent();
personsViewModel = new PersonsViewModel(this);
this.BindingContext = personsViewModel;
}
If you can use plugin, you can use ACR.UserDialogs. https://github.com/aritchie/userdialogs
I solved this problem using events
public MainPageVewModel()
{
Application.Current.MainPage.Loaded += LoadCards;
}
private async void LoadCards(object sender, EventArgs e)
{
// your code on View Loaded
await Application.Current.MainPage.DisplayAlert("working alert", "alert", "ok");
}
Related
I'm creating an Xamarin.Forms MVVM App (only using Android) which needs certain buttons to be outlined red, whenever their text property holds a specific value. (Purpose: alert the user to press the button and select a value, which will change the Button Text Property and therefore remove the red outline)
To achieve this I've create the following documents:
A custom button CButton that extents the default Button:
public class CButton : Button
{
// this Hides the Default .Text-Property
public string Text
{
get => base.Text;
set
{
base.Text = value;
TextChangedEvent(this, new EventArgs());
}
}
// The Raised Event
protected virtual void TextChangedEvent(object sender, EventArgs e)
{
EventHandler<EventArgs> handler = TextChanged;
handler(sender, e);
}
public event EventHandler<EventArgs> TextChanged;
}
A custom behavior makes use of the raised TextChangedEvent
public class ButtonValBehavior : Behavior<CButton>
{
protected override void OnAttachedTo(CButton bindable)
{
bindable.TextChanged += HandleTextChanged;
base.OnAttachedTo(bindable);
}
void HandleTextChanged(object sender, EventArgs e)
{
string forbidden = "hh:mm|dd.mm.yyyy";
if (forbidden.Contains((sender as CButton).Text.ToLower()))
{
//Do when Button Text = "hh:mm" || "dd.mm.yyyy"
(sender as CButton).BorderColor = Color.Gray;
}
else
{
//Do whenever Button.Text is any other value
(sender as CButton).BorderColor = Color.FromHex("#d10f32");
}
}
protected override void OnDetachingFrom(CButton bindable)
{
bindable.TextChanged -= HandleTextChanged;
base.OnDetachingFrom(bindable);
}
}
The relevant parts of the ViewModel look the following:
public class VM_DIVI : VM_Base
{
public VM_DIVI(O_BasisProtokoll base)
{
Base = base;
}
private O_BasisProtokoll _base = null;
public O_BasisProtokoll Base
{
get => _base;
set
{
_base = value;
OnPropertyChanged();
}
}
Command _datePopCommand;
public Command DatePopCommand
{
get
{
return _datePopCommand ?? (_datePopCommand = new Command(param => ExecuteDatePopCommand(param)));
}
}
void ExecuteDatePopCommand(object param)
{
//launch popup
var p = new PP_DatePicker(param);
PopupNavigation.Instance.PushAsync(p);
}
}
The .xmal looks the following (b is the xmlns of the Namespace):
<b:CButton x:Name="BTN_ED_Datum"
Text="{Binding Base.ED_datum, Mode=TwoWay}"
Grid.Column="1"
Command="{Binding DatePopCommand}"
CommandParameter="{x:Reference BTN_ED_Datum}">
<b:CButton.Behaviors>
<b:ButtonValBehavior/>
</b:CButton.Behaviors>
</b:CButton>
This solution works fine whenever the input is caused by user interaction. However, when a Value is assigned during the initialization of the Page no red outline is created, in fact the TextChangedEvent isn't raised. By using breakpoints I noticed that during initialization the Text Property of CButton is never set, eventhough it actually will be in the view.
Despite fiddling around with my solution I cannot make this work on initialization. I tried to work around this issue by outlining every button by default in their constructor, however this will outline every button red, even when their text value doesn't require them to be.
How can I achieve my initial goal?
Many thanks in advance!
It's been a while but if I recall correctly what I ended up doing was:
Changing the new Text-Property of my custom Button to CText and
Making sure that I have Mode=TwoWay activated for any Element, that doesn't have it enabled by default. (Look up Binding modes on msdn for more)
making CText a bindable property of CButton
My custom button now looks the following:
using System;
using System.Collections.Generic;
using System.Text;
using Xamarin.Forms;
namespace EORG_Anton.Model
{
public class CButton : Button
{
public static readonly BindableProperty CTextProperty =
BindableProperty.Create(nameof(CText),
typeof(string),
typeof(CButton),
default(string),
BindingMode.TwoWay,
propertyChanged: OnTextChanged);
private static void OnTextChanged(BindableObject bindable, object oldValue, object newValue)
{
var control = (CButton)bindable;
var value = (string)newValue;
control.CText = value;
}
public string CText
{
get => base.Text;
set
{
base.Text = value;
TextChangedEvent(this, new EventArgs());
}
}
protected virtual void TextChangedEvent(object sender, EventArgs e)
{
EventHandler<EventArgs> handler = TextChanged;
handler(sender, e);
}
public event EventHandler<EventArgs> TextChanged;
}
}
I have a Label on MainPage.xaml. I can edit Label Text from MainPage.xaml.cs.
There is a foregroung service running as well. There is function in this service to check a value from SQLite DB for every 10 secs. When value changes, Label text should be updated. I tried binding but it is a bit confusing. I manage updating by using like this: (foreground service timer changes App.SomeValue)
protected override void OnAppearing()
{
lblSyncID.Text = App.SomeValue;
}
But I need to see changes without OnAppearing or any other navigation change.
EDIT:
With #Jason's suggestion I used Messaging Center (and also binding) and it works now:
MainPage.xaml:
<Label Text="{Binding AppWaitingRecordValue}" ...
MainPage.xaml.cs:
public partial class MainPage : ContentPage
{
private string appWaitingRecordValue;
public string AppWaitingRecordValue
{
get { return appWaitingRecordValue; }
set
{
appWaitingRecordValue = value;
OnPropertyChanged(nameof(AppWaitingRecordValue));
}
}
public MainPage()
{
InitializeComponent();
BindingContext = this;
AppWaitingRecordValue = "0";
MessagingCenter.Subscribe<App>((App)Application.Current, "AppRecord", (sender) =>
{
AppWaitingRecordValue = App.recordWaiting.ToString();
});
}
.
.
TimestampService.cs (from Project.Android):
// get i from DB
App.recordWaiting = i;
Xamarin.Forms.MessagingCenter.Send<App>((App)Xamarin.Forms.Application.Current, "AppRecord");
Hi StackOverflow Team,
I am trying to run a background process in my App. This background process should update just Background image on one of the pages in the App every 15 seconds. So far, I tried to create a timer in the App OnStart() method and update the backgroundimage of the page in the BeginInvokeOnMainThread() method but with no success. Can anyone help me with this?
My Code -
{
private static Stopwatch stopWatch = new Stopwatch();
private const int defaultTimespan = 20;
private readonly HomePage homePage;
public App()
{
InitializeComponent();
try
{
MainPage = new MainPage();
homePage = new HomePage();
}
catch(Exception ex)
{
string str = ex.Message;
}
}
protected override void OnStart()
{
if (!stopWatch.IsRunning)
{
stopWatch.Start();
}
Device.StartTimer(new TimeSpan(0, 0, 10), () =>
{
// Logic for logging out if the device is inactive for a period of time.
if (stopWatch.IsRunning && stopWatch.Elapsed.Seconds >= defaultTimespan)
{
//prepare to perform your data pull here as we have hit the 1 minute mark
// Perform your long running operations here.
Device.BeginInvokeOnMainThread(() =>
{
// If you need to do anything with your UI, you need to wrap it in this.
// homePage.BackgroundImageSource = "goldengate.jpg";
homePage.ChangeBackgroundImage();
});
stopWatch.Restart();
}
// Always return true as to keep our device timer running.
return true;
});
}
protected override void OnSleep()
{
//stopWatch.Reset();
}
protected override void OnResume()
{
//stopWatch.Start();
}
//void ChangeHomePageImage()
//{
// Navigation.PushAsync(new HomePage(appBackground));
// Navigation.RemovePage(this);
//}
}
MainPage -
<MasterDetailPage xmlns="http://xamarin.com/schemas/2014/forms"
xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
xmlns:d="http://xamarin.com/schemas/2014/forms/design"
xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
mc:Ignorable="d"
xmlns:local="clr-namespace:Excercise.Views"
x:Class="Excercise.MainPage" IsPresented="False">
<MasterDetailPage.Master>
<local:MenuPage x:Name="menuPage"></local:MenuPage>
</MasterDetailPage.Master>
<MasterDetailPage.Detail>
<NavigationPage>
<x:Arguments>
<local:HomePage x:Name="homePage"></local:HomePage>
</x:Arguments>
</NavigationPage>
</MasterDetailPage.Detail>
</MasterDetailPage>
HomePage -
public partial class HomePage : ContentPage
{
private SQLiteAsyncConnection _connection;
public HomePage()
{
InitializeComponent();
// BindingContext = new HomePageViewModel();
_connection = DependencyService.Get<ISQLiteDb>().GetConnection();
loadData("");
}
public HomePage(string BackgroundimgPath)
{
InitializeComponent();
// BindingContext = new HomePageViewModel();
_connection = DependencyService.Get<ISQLiteDb>().GetConnection();
loadData(BackgroundimgPath);
}
public HomePage(string City, string LocationKey, string StateID)
{
InitializeComponent();
_connection = DependencyService.Get<ISQLiteDb>().GetConnection();
// BindingContext = new HomePageViewModel();
try
{
// Method Calls
}
catch (Exception)
{
DisplayAlert("Error", "There was an error loading this page.", "OK");
}
}
protected override void OnAppearing()
{
this.Title = App.AppTitle;
this.firstStacklayout.Margin = new Thickness(0, (Application.Current.MainPage.Height * 0.25), 0, 0);
base.OnAppearing();
}
you are creating an instance of HomePage and trying to update it, but it is NOT the same instance that is being displayed in your MasterDetail
try something like this
var md = (MasterDetailPage)MainPage;
var nav = (NavigationPage)md.DetailPage;
var home = (HomePage)nav.CurrentPage;
home.ChangeBackgroundImage();
alternately, you could use MessagingCenter to send a message to HomePage requesting that it udpate
Is there any way to check if keyboard is open or not in Xamarin Forms? Are there any events getting fired when the keyboard opens or closes? If so, where can I find an example of it?
I don't believe that there's a Xamarin.Forms way of doing it. Anyway, for the different platforms (at least Android and iOS) there is a way to achieve what you want.
Android
Under android there is InputMethodManager class. You can obtain it from your activity
var inputMethodManager = (InputMethodManager)this.GetSystemService(Context.InputMethodService);
Now you can check if the keyboard is shown with
var keyboardIsShown = inputMethodManager.IsAcceptingText;
According to this article on CodeProject you can use a class derived from IOnGlobalLayoutListener to listen to global layout events. When this event has fired, you can use the code above to check, if the layout has been changed due to the keyboard popping up.
iOS
Under iOS you may use UIKeyboard class which allows you to observe the DidShowNotification (see here).
notification = UIKeyboard.Notifications.ObserveDidShow ((sender, args) => {
Debug.WriteLine("Keyboard is shown.");
// whatever
});
similarly you can observe DidHideNotification (and some others - see here).
Xamarin.Forms
To implement the keyboard-notification in your Xamarin.Forms the easiest way will be to implement platform dependencies which are resolved with the DependencyService. To do this, you'll first have to introduce an interface for the platform service.
public interface IKeyboardService
{
event EventHandler KeyboardIsShown;
event EventHandler KeyboardIsHidden;
}
In your platform specific projects you'll have to implement the functionality in a platform specific way. See the following code section for iOS implementation
[assembly: Xamarin.Forms.Dependency(typeof(Your.iOS.Namespace.KeyboardService))]
namespace Your.iOS.Namespace
{
public class KeyboardService : IKeyboardService
{
public event EventHandler KeyboardIsShown;
public event EventHandler KeyboardIsHidden;
public KeyboardService()
{
SubscribeEvents();
}
private void SubscribeEvents()
{
UIKeyboard.Notifications.ObserveDidShow(OnKeyboardDidShow);
UIKeyboard.Notifications.ObserveDidHode(OnKeyboardDidHide);
}
private void OnKeyboardDidShow(object sender, EventArgs e)
{
KeyboardIsShown?.Invoke(this, EventArgs.Empty);
}
private void OnKeyboardDidHide(object sender, EventArgs e)
{
KeyboardIsHidden?.Invoke(this, EventArgs.Empty);
}
}
}
The Xamarin.Forms.Dependency makes the class visible to the DependencyService. See the following code for Android implementation
[assembly: Xamarin.Forms.Dependency(typeof(Your.Android.Namespace.KeyboardService))]
namespace Your.Android.Namespace
{
public class KeyboardService : IKeyboardService
{
public event EventHandler KeyboardIsShown;
public event EventHandler KeyboardIsHidden;
private InputMethodManager inputMethodManager;
private bool wasShown = false;
public KeyboardService()
{
GetInputMethodManager();
SubscribeEvents();
}
public void OnGlobalLayout(object sender, EventArgs args)
{
GetInputMethodManager();
if(!wasShown && IsCurrentlyShown())
{
KeyboardIsShown?.Invoke(this, EventArgs.Empty);
wasShown = true;
}
else if(wasShown && !IsCurrentlyShown())
{
KeyboardIsHidden?.Invoke(this, EventArgs.Empty);
wasShown = false;
}
}
private bool IsCurrentlyShown()
{
return inputMethodManager.IsAcceptingText;
}
private void GetInputMethodManager()
{
if (inputMethodManager == null || inputMethodManager.Handle == IntPtr.Zero)
{
inputMethodManager = (InputMethodManager)this.GetSystemService(Context.InputMethodService);
}
}
private void SubscribeEvents()
{
((Activity)Xamarin.Forms.Forms.Context).Window.DecorView.ViewTreeObserver.GlobalLayout += this.OnGlobalLayout;
}
}
}
In your Xamarin.Forms app you can now obtain an instance of the correct implementation of IKeyboardService with
var keyboardService = Xamarin.Forms.DependencyService.Get<IKeyboardService>();
In Xamarin Forms in ANDROID CODE change
(InputMethodManager)this.GetSystemService(Context.InputMethodService);
with
(InputMethodManager)Xamarin.Forms.Forms.Context.GetSystemService(Context.InputMethodService);
You need to change:
var inputMethodManager = (InputMethodManager)this.GetSystemService(Context.InputMethodService);
To:
InputMethodManager inputMethodManager = (InputMethodManager)((Activity)Android.App.Application.Context).GetSystemService(Context.InputMethodService);
Situation:
Building an application using Xamarin Forms and MasterDetail component.
Question:
How Can I render a specific page on Android based on a PageRender? and keep the Drawer?
Edit
public class MasterBacASable : MasterDetailPage
{
public MasterBacASable ()
{
Icon = null;
Title = "The title";
Detail = (new FirstPage ());
Master = new AppMenuPage ();
}
}
[assembly:ExportRenderer (typeof(BacASable.FirstPage), typeof(BacASable.Droid.FirstPageContentRennderer))]
namespace BacASable.Droid
{
public class FirstPageContentRennderer : PageRenderer
{
public FirstPageContentRennderer ()
{
}
protected override void OnElementChanged (ElementChangedEventArgs<Page> e)
{
base.OnElementChanged (e);
var activity = this.Context as Activity;
var v = activity.LayoutInflater.Inflate (Resource.Layout.AndroidView,this,false);
AddView (v);
}
}
}
Follow this for Xamarin.Forms Master-Detail Documentation
The base Concept is the following
public class MainPageCS : MasterDetailPage
{
MasterPageCS masterPage;
public MainPageCS ()
{
masterPage = new MasterPageCS ();
Master = masterPage;
Detail = new NavigationPage (new ContactsPageCS ());
...
}
}
Your Master is your drawer and Detail the Page (ContentPage, TabbedPage,NavigationPage,CustomPageRenderer ).
So each time you want to display a different page set the Detail property
Detail = new MyContentPage();
I was just forgetting to override the OnLayout in the Renderer.
Thank you all.