I have the following code:
private void CloseOrder(object sender, EventArgs e)
{
Android.Support.V7.App.AlertDialog.Builder alert = new Android.Support.V7.App.AlertDialog.Builder(this);
alert.SetTitle("Cerrar Pedido");
alert.SetMessage("Are you sure?");
alert.SetCancelable(true);
alert.SetPositiveButton("Confirm", delegate { this.Rta = true; });
alert.SetNegativeButton("Cancel", delegate { this.Rta = false; });
Dialog dialog = alert.Create();
dialog.Show();
if (this.Rta)
{
//Some code here
}
}
this.Rta is a property of my class.
The problem is that the alert doesn't show at dialog.show(), it shows once the method CloseOrder() ended, so this.Rta never gets the corresponding value assigned.
I've been searching a lot but I can't find a solution, if anyone can help me that'd be great!
dialog.Show() is asynchronous method, that means CloseOrder(object sender, EventArgs e) and dialog.Show() end up at the same time.
You can not get the 'Rta' assigned value at the CloseOrder function.
You will get the value when you click the confirm or cancel button of the dialog.
I suggest you to use message sender in the delegate{this.Rta = true}
For example:
mHandler handler = new mHandler();
Message message = new Message();
message.What = 1;
alert.SetPositiveButton("Confirm", delegate { this.Rta = true; handler.SendMessage(message); });
alert.SetNegativeButton("Cancel", delegate { this.Rta = false; handler.SendMessage(message); });
//....
class mHandler : Handler{
public override void HandleMessage(Message message) {
switch (message.What) {
case 1:
if (this.Rta)
{
//Some code here
}
break;
}
}
}
Related
I have added Xamarin GestureRecognizers on a SKCanvasView and overridden OnTouch method.
I have some implementations on SKTouchAction.Moved. In order to trigger it after SKTouchAction.Pressed on Android I set e.Handled = true;
Doing so, none of the Xamarin GestureRecognizers seems to be working.
Is there any way to make both of these events work together or any alternative way to achieve this requirement?
Here is my code sample.
public abstract class GestureContainer : SKCanvasView, IViewportable
{
public GestureContainer()
{
var doubleTapGesture = new TapGestureRecognizer();
doubleTapGesture.NumberOfTapsRequired = 2;
doubleTapGesture.Tapped += TapGesture_DoubleTapped;
GestureRecognizers.Add(doubleTapGesture);
var pinchGesture = new PinchGestureRecognizer();
pinchGesture.PinchUpdated += OnPinchUpdated;
GestureRecognizers.Add(pinchGesture);
}
private void TapGesture_DoubleTapped(object sender, EventArgs e)
{
//Double tap action here
}
public void OnPinchUpdated(object sender, PinchGestureUpdatedEventArgs e)
{
//Pinch action here
}
protected override void OnTouch(SKTouchEventArgs e)
{
switch (e.ActionType)
{
case SKTouchAction.Moved:
{
//Move action here
}
break;
case SKTouchAction.Pressed:
{
//Move action here
}
break;
}
e.Handled = false; // Xamarin gesture works when I set this to false
InvalidateSurface();
}
}
How can I avoid invoking of the same event multiple times when a button is clicked rapidly.
Below is the code:
I've created a Custom Delegate Command as below
View Model
namespace TestProject.ViewModels
{
public class TestViewModel
{
public CustomDelegateCommand MenuButtonClickCommand { get; set; }
public TestViewModel()
{
MenuButtonClickCommand = new CustomDelegateCommand (async () => await ShowMenuAction());
}
private async Task ShowMenuAction()
{
//await some stuff
}
}
}
CustomDelegateCommand.cs
public class CustomDelegateTimerCommand : DelegateCommand
{
public CustomDelegateTimerCommand(Action executeMethod, Func<bool> validateMethod, Action onBusy = default(Action)) : base(executeMethod)
{
BackgroundTaskWaitHandle = new EventWaitHandle(true, EventResetMode.ManualReset);
_validateMethod = validateMethod;
_onBusy = onBusy;
}
}
The problem I'm facing is whenever a user clicks on the button rapidly, the menu list popup is opening multiple times.
I have lot of commands in my project and I need a solution that would work globally.
I tried to resolve the issue like below using ObservesCanExecute() but I don't like the idea of creating a separate variable for every command as I've a lot of commands in my project and I don't want the button to go in to disabled state when CanExecute = false.
ViewModel
MenuButtonClickCommand = new CustomDelegateCommand (async () => await ShowMenuAction().ObservesCanExecute(() => CanExecute );
private async Task ShowMenuAction()
{
CanExecute = false;
//await some stuff
CanExecute = true;
}
Any help is much appreciated!
There are 2 solutions to it. One is when you use, MVVM other is when you dont.
The non MVVM solution is delaying the execution of method for certain amount of time, like this:
public class SingleClickListener
{
private bool hasClicked;
private Action<object, EventArgs> _setOnClick;
public SingleClickListener(Action<object, EventArgs> setOnClick)
{
_setOnClick = setOnClick;
}
public void OnClick(object v, EventArgs e)
{
if (!hasClicked)
{
_setOnClick(v, e);
hasClicked = true;
}
reset();
}
private void reset()
{
Android.OS.Handler mHandler = new Android.OS.Handler();
mHandler.PostDelayed(new Action(() => { hasClicked = false; }), 500);
}
}
And then when you subscribe the onclick event:
var buttonNa = new Button { Text = "Test Button" };
buttonNa.Clicked += new SingleClickListener((sender, e) =>
{
//DO something
}).OnClick;
The Mvvm solution is bit more complicated, but its not as hacky.
TestCommand = new Command(
execute: async () =>
{
IsEditing = true;
RefreshCanExecutes();
//Fire Method
TestMethod();
},
canExecute: () =>
{
return !IsEditing;
});
public void RefreshCanExecutes()
{
(TestCommand as Command).ChangeCanExecute();
}
public void TestMethod()
{
//DO something
IsEditing = false;
RefreshCanExecutes();
}
Obviously dont forget to bind your commands to xaml :)
also second solution actually disables the button, so user cannot even tap it, first one however only ignores further taps, till time delay has finished.
Create a new class which inherits from Xamarin.Forms.Button with delay in click event, than add it to your xmal.
public class DelayedButton : Xamarin.Forms.Button
{
public DelayedButton()
{
this.Clicked += DelayedButton_Clicked;
}
async private void DelayedButton_Clicked(object sender, EventArgs e)
{
this.IsEnabled = false;
await Task.Delay(Delay);
this.IsEnabled = true;
}
public int Delay { get; set; } = 500;
}
In XAML：
<yourNameSpace:DelayedButton Delay="300" Text="DelayedButton" Command="{Binding ClickCommand}"/>
I have this timer in my code:
Device.StartTimer(TimeSpan.FromSeconds(100), () =>
{
Device.BeginInvokeOnMainThread(() =>
{
if (detailGrid.IsVisible == true)
{
getRandomPhase();
}
});
return false;
});
Is there a way that I could (through a gesture) cancel the timer from running or abort the timer in some way?
The return value of the Timer callback is a boolean that determines if the timer should keep running or stop. You can use a private variable to keep track if the timer should keep running and return it from the callback.
Please check this sample
private bool _isTimerStart = true;
private void StartTimers()
{
try
{
Device.StartTimer(new TimeSpan(0, 0, 1), () =>
{
// do some code here
return _isTimerStart;
});
}
catch {}
} private void BtnStart_OnClicked(object sender, EventArgs e)
{
_isTimerStart = true;
StartTimers();
}
private void BtnStop_OnClicked(object sender, EventArgs e)
{
_isTimerStart = false;
}
This code was taken from the following blog post which shows a more detailed example : http://www.c-sharpcorner.com/article/quick-start-tutorial-creating-universal-apps-via-xamarin-device-classcont/
I'm trying to implement Azure Active Directory B2C in Xamarin.Forms. If I just copy their example, I can get it to work without a problem. But when I try to use Prism, I run into problems.
I took this code that was sitting in the codebehind of the XAML:
protected override async void OnAppearing ()
{
base.OnAppearing ();
App.PCApplication.PlatformParameters = platformParameters;
try {
var ar = await App.PCApplication.AcquireTokenSilentAsync(
AuthenticationInfo.Scopes, string.Empty, AuthenticationInfo.Authority,
AuthenticationInfo.SignUpSignInpolicy, false);
AuthenticationInfo.UserAuthentication = ar;
} catch {
}
}
async void OnSignUpSignIn(object sender, EventArgs e)
{
try {
var ar = await App.PCApplication.AcquireTokenAsync(
AuthenticationInfo.Scopes, string.Empty, UiOptions.SelectAccount,
string.Empty, null, AuthenticationInfo.Authority,
AuthenticationInfo.SignUpSignInpolicy);
AuthenticationInfo.UserAuthentication = ar;
} catch (Exception ex) {
if (ex != null) {
}
}
}
and moved it to the ViewModel's OnNavigatedTo:
public async void OnNavigatedTo (NavigationParameters parameters)
{
if (parameters.ContainsKey ("title"))
Title = (string)parameters ["title"];
listen2asmr.App.PCApplication.PlatformParameters = platformParameters;
try {
var ar = await listen2asmr.App.PCApplication.AcquireTokenSilentAsync(
AuthenticationInfo.Scopes, string.Empty, AuthenticationInfo.Authority,
AuthenticationInfo.SignUpSignInpolicy, false);
AuthenticationInfo.UserAuthentication = ar;
} catch {
}
}
This is in the Bootstrapper:
protected override Xamarin.Forms.Page CreateMainPage ()
{
return Container.Resolve<LoginPage> ();
}
protected override void RegisterTypes ()
{
Container.RegisterTypeForNavigation<LoginPage>();
}
OnNavigatedTo never seems to get called though. Is there some other method I should be using, or did I miss something else? The only other thing I could think of was to call the code in OnNavigatedTo from the ViewModel constructor, but the async/await does work with the constructor.
This has been fixed in the latest preview version of Prism for Xamarin.Forms. Try using these packages instead:
https://www.nuget.org/packages/Prism.Forms/6.1.0-pre4
https://www.nuget.org/packages/Prism.Unity.Forms/6.2.0-pre4
Also the bootstrapping process has changed. Read this for more information:
Prism.Forms 5.7.0 Preview - http://brianlagunas.com/first-look-at-the-prism-for-xamarin-forms-preview/
Prism.Forms 6.2.0 Preview - http://brianlagunas.com/prism-for-xamarin-forms-6-2-0-preview/
Prism.Forms 6.2.0 Preview 3 - http://brianlagunas.com/prism-for-xamarin-forms-6-2-0-preview-3/
Preview 4 Post Coming Soon
My advice is use your View events as triggers for your ViewModel.
For Instance:
View.xaml.cs
protected override async void OnAppearing () {
base.OnAppearing ();
viewModel.OnAppearing();
}
async void OnSignUpSignIn(object sender, EventArgs e) {
viewModel.OnSignUpSignIn(sender, e);
}
ViewModel.cs
protected override async void OnAppearing () {
App.PCApplication.PlatformParameters = platformParameters;
try {
var ar = await App.PCApplication.AcquireTokenSilentAsync(
AuthenticationInfo.Scopes, string.Empty,
AuthenticationInfo.Authority,
AuthenticationInfo.SignUpSignInpolicy, false);
AuthenticationInfo.UserAuthentication = ar;
} catch {
}
}
async void OnSignUpSignIn(object sender, EventArgs e) {
try {
var ar = await App.PCApplication.AcquireTokenAsync(
AuthenticationInfo.Scopes, string.Empty,
UiOptions.SelectAccount,
string.Empty, null, AuthenticationInfo.Authority,
AuthenticationInfo.SignUpSignInpolicy);
AuthenticationInfo.UserAuthentication = ar;
} catch (Exception ex) {
if (ex != null) {
}
}
}
Reasons:
View should only involve visuals, and the events your page receives. Logic should be forwarded to the ViewModel, unless it deals with representation of information (for instance, logic to use a toggle-box for 2 choices but a combo-box for 3+).
Nearly vice-versa, the ViewModel should keep track of "model state" (ex. the user still needs to enter their payment information) as opposed to "view state" (ex. the user has navigated to the payment page).
I'm developing an app and have run into a problem with asynchronous calls... Here's what i'm trying to do.
The app consumes a JSON API, and, when run, fills the ListBox within a panorama item with the necessary values (i.e. a single news article). When a user selects a ListBox item, the SelectionChanged event is fired - it picks up the articleID from the selected item, and passes it to an Update method to download the JSON response for the article, deserialize it with JSON.NET, and taking the user to the WebBrowser control which renders a html page from the response received.
The problem with this is that I have to wait for the response before I start the NavigationService, but I'm not sure how to do that properly. This way, the code runs "too fast" and I don't get my response in time to render the page.
The event code:
private void lstNews_SelectionChanged(object sender, SelectionChangedEventArgs e)
{
if (lstNews.SelectedIndex == -1)
{
return;
}
ShowArticle _article = new ShowArticle();
ListBox lb = (ListBox)sender;
GetArticles item = (GetArticles)lb.SelectedItem;
string passId = ApiRepository.ApiEndpoints.GetArticleResponseByID(item.Id);
App.Current.JsonModel.JsonUri = passId;
App.Current.JsonModel.Update();
lstNews.SelectedIndex = -1;
NavigationService.Navigate(new Uri("/View.xaml?id=" + item.Id, UriKind.Relative));
}
OnNavigatedTo method in the View:
protected override void OnNavigatedTo(System.Windows.Navigation.NavigationEventArgs e)
{
base.OnNavigatedTo(e);
long sentString = long.Parse(NavigationContext.QueryString["id"]);
string articleUri = ApiRepository.ApiEndpoints.GetArticleResponseByID(Convert.ToInt32(sentString));
//this throws an error, runs "too fast"
_article = App.Current.JsonModel.ArticleItems[0];
}
The update method:
public void Update()
{
ShowArticle article = new ShowArticle();
try
{
webClient.DownloadStringCompleted += (p, q) =>
{
if (q.Error == null)
{
var deserialized = JsonConvert.DeserializeObject<ShowArticle>(q.Result);
_articleItems.Clear();
_articleItems.Add(deserialized);
}
};
}
catch (Exception ex)
{
//ignore this
}
webClient.DownloadStringAsync(new Uri(jsonUri));
}
async callback pattern:
public void Update(Action callback, Action<Exception> error)
{
webClient.DownloadStringCompleted += (p, q) =>
{
if (q.Error == null)
{
// do something
callback();
}
else
{
error(q.Error);
}
};
webClient.DownloadStringAsync(new Uri(jsonUri));
}
call:
App.Current.JsonModel.Update(() =>
{
// executes after async completion
NavigationService.Navigate(new Uri("/View.xaml?id=" + item.Id, UriKind.Relative));
},
(error) =>
{
// error handling
});
// executes just after async call above