Good evening everyone.
For some time now I have been to Xamarin. My first tests are rather conclusive. I decided to try to make a small application that retrieves information in a database via an API and then update this data via a ListView.
When I launch the application on my emulator everything works but as soon as I install the application on my phone it crashes. I thought this was because the API but I have an API that I use to check the Login / password that works correctly.
The API that returns the data reviews a lot of line about 3500/4000, can this be the reason?
So I passed the loading of the data in my viewModel in an async method but the problem now is that the view loads before the data is loaded correctly. Is there a way to get the view initialized after the data is loaded?
Below my code.
Initializing my viewModel
class ManageInventViewModel
{
public ObservableCollection<InventViewModel> InventProduct { get; set; }
public Command<InventViewModel> UpdateCommand
{
get
{
return new Command<InventViewModel>(invent =>
{
var index = invent.IndexLigneInventaire;
InventProduct.Remove(invent);
InventProduct.Insert(index, invent);
});
}
}
public Command<InventViewModel> ResetStock
{
get
{
return new Command<InventViewModel>(invent =>
{
var index = InventProduct.IndexOf(invent);
InventProduct.Remove(invent);
invent.RealStockProduct = 0;
InventProduct.Insert(index, invent);
});
}
}
public ManageInventViewModel()
{
LoadInventaire();
}
private async void LoadInventaire()
{
var listMvt = await Utils.Utils.GetListMouvementUntilDate();
var listStock = Utils.Utils.GetStockByProduct(listMvt).Take(20);
InventProduct = new ObservableCollection<InventViewModel>();
var indexLine = 0;
foreach (var stock in listStock)
{
var inventViewModel = new InventViewModel
{
LibelleProduit = stock.LibelleProduit,
PrCodeProduit = stock.PrCodeProduit,
UpCodeProduit = stock.UpCodeProduit,
RealStockProduct = stock.StockTheoProdct,
StockTheoProdct = stock.StockTheoProdct,
IndexLigneInventaire = indexLine
};
++indexLine;
InventProduct.Add(inventViewModel);
}
}
}
Initializinz my view
public partial class InventPage : ContentPage
{
public InventPage()
{
InitializeComponent();
TableInvent.ItemSelected += (sender, e) =>
{
if (TableInvent.SelectedItem != null)
{
if (TableInvent.SelectedItem is InventViewModel item)
{
PopupNavigation.Instance.PushAsync(new ChangeStockModal(item, this));
}
TableInvent.SelectedItem = null;
}
};
}
private void Reset_Stock(object sender, EventArgs e)
{
var input = sender as Button;
var inventViewModel = input?.BindingContext as InventViewModel;
var listViewModel = BindingContext as ManageInventViewModel;
listViewModel?.ResetStock.Execute(inventViewModel);
}
public void Update_Stock_List(InventViewModel dataStockUpdate)
{
var listViewModel = BindingContext as ManageInventViewModel;
listViewModel?.UpdateCommand.Execute(dataStockUpdate);
PopupNavigation.Instance.PopAsync();
}
}
Thanks
I managed to create the ActivityIndicator but I can not get my data loaded while I'm displaying the wait screen.
Regarding this issue, I don't see you useActivityIndicator from your code,maybe you didn't update your code, I think if you use useActivityIndicator , You can bind one property to ActivityIndicator IsRunning and IsVisible, then you can solve your issue.
Related use ActivityIndicator step, you can take a look:
ActivityIndicator
Related
I'm new to Xamarin, I have an app in Xamarin-Form that it's fetching data from web api and getting user input from Entry control.
The web api service class is working fine and reaches the deserialization in the getCourses method as seen below in Code Snippet 1.
The Entry control as well is working fine until it retrieves the user input on the MainPage class, OnOkGetCourseButton method as seen below Code Snippet 2.
What I want to achieve is, inside MainPage.xaml.cs, I create a method that takes the user input data and check agaisnt the deseriaized json data (the Id specially),
if it finds the Id in deserialized List of data, then it can send the found data to another ViewPage and display them.
if It cannot find the data, it shows a dialog box.
So far, I tried to call Task<ObservableCollection> getCourses() method from the MainPage class, inside CheckCourseComplete as seen below but it giving me no value/nothing, some kind of null value.
I don't want to filter the user input against web api json response inside getCourses(),
I want to do that in a separate method to follow S-OLID (Single Responsibility Principle).
If it's not possible in a separate method, then I just need to get it worked.
Please what is the best way to achieve it?
Code Snippet 1
public class CourseService : ICourseService
{
string Base_Url = "https://www.test.com/api/TheCourse";
public async Task<ObservableCollection<Course>> getCourses()
{
try
{
string url = Base_Url;
HttpClient client = new HttpClient();
HttpResponseMessage responseMessage = await client.GetAsync(url);
if (responseMessage.StatusCode == System.Net.HttpStatusCode.OK)
{
var result = await responseMessage.Content.ReadAsStringAsync();
var deserializedClass = JsonConvert.DeserializeObject<ObservableCollection<Course>>(result);
// I don't want to do that here, as it will violate SRP (SOLID)
return deserializedClass;
}
return null;
}
catch (Exception)
{
throw;
}
}
}
Code Snippet 2
namespace CourseMobile
{
public partial class MainPage : ContentPage
{
private string _getEntryText;
private readonly CourseViewModel orderViewModel;
public Course FetchCourse { get; set; }
public MainPage()
{
InitializeComponent();
CheckCourseComplete();
BindingContext = new CourseViewModel();
}
public string GetEntryText
{
get => _getEntryText;
set => _getEntryText = value;
}
public async void OnOkGetCourseButton(object sender, EventArgs e)
{
var inputtedCourseNumber = this.GetEntryText;
if(inputtedCourseNumber == string.Empty)
{
await DisplayAlert("", "Please enter your Course number", "OK 3");
}
else
{
CheckCourseComplete();
this.GetEntryText = inputtedCourseNumber;
await DisplayAlert("New Text", inputtedCourseNumber, "OK 2");
}
}
void Entry_TextChanged(object sender, TextChangedEventArgs e)
{
var newText = e.NewTextValue;
this.GetEntryText = newText;
}
public async void CheckCourseComplete()
{
CourseService myCourse = new CourseService();
await myCourse.getCourses(); // It doesn't return the json data (web api data)
// I need to check user input + (web api data) here
}
}
}
getCourses is async, so you need to use await when calling it
public async void CheckCourseComplete()
{
CourseService myCourse = new CourseService();
var data = await myCourse.getCourses();
// now filter data
}
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'm clicking on a product item in listview in product page viewmodel to show a popup(using rg.plugin popup) for selecting one of the product variants.After selecting variant,i am sending the selected variant to product page using messagingcenter from variant popup page viewmodel,subscribed in product page viewmodel constructor. working fine there.when i navigate to the previous page and then came back to this product page for adding one or more variant to the
same previously selected product,Messagingcenter subscribe called twice and product value increased twice.Tried to subscribe in the product page onappearing and unsubscribe in disappearing method.still calling two times? How to solve this issue?
calling popup:
var result = await dataService.Get_product_variant(store_id, product_id);
if (result.status == "success")
{
ind_vis = false;
OnPropertyChanged("ind_vis");
App.Current.Properties["product_variant_result"] = result;
App.Current.Properties["cartitems"] = purchaselist;
App.Current.Properties["selected_product"] = product_List2 ;
await PopupNavigation.Instance.PushAsync(new Popup_variant());
}
popup viewmodel: sending message
public Popup_variant_vm()
{
Radio_btn = new Command<Product_variant_list2>(Radio_stk_tapped);
product_variant_list = new List<Product_variant_list2>();
purchaselist = new ObservableCollection<Product_list2>();
show_variants();
}
internal void Confirm_variant()
{
if(App.Current.Properties.ContainsKey("selected_variant"))
{
MessagingCenter.Send<Popup_variant_vm, object>(this, "selected_variant", App.Current.Properties["selected_variant"]); //Message send from popup to product page
}
else
{
DependencyService.Get<IToast>().LongAlert("Please select any size");
}
}
product page viewmodel: subscribed here..called twice when navigating from previous page to this
public Store_page()
{
InitializeComponent();
}
protected override void OnAppearing()
{
base.OnAppearing();
var vm = new store_page_vm();
vm.Navigation = Navigation;
BindingContext = vm;
MessagingCenter.Unsubscribe<Popup_variant_vm, object>(this, "selected_variant");
MessagingCenter.Subscribe<Popup_variant_vm, object>(this, "selected_variant",async (sender, selected_variant) =>
{
var vm1 = BindingContext as store_page_vm;
vm1?.Addcart2(selected_variant);// called twice
});
}
unsubscribed in product cs page
protected override void OnDisappearing()
{
var vm = BindingContext as store_page_vm;
vm?.Save_cart();
MessagingCenter.Unsubscribe<Popup_variant_vm>(this, "selected_variant");
}
Your unsubscription should look something like below and it should work :
MessagingCenter.Unsubscribe<Popup_variant_vm, object>(this, "selected_variant");
https://stackoverflow.com/a/44753021/10937160
try this, and make sure you do not call Subscribe more than once.
My solution:
put unsubscribe sentence into subscribe body !!
MessagingCenter.Subscribe<object, string>(this, "IdSearch", (sender, arg) =>
{
listView.ItemsSource = arg;
MessagingCenter.Unsubscribe<object, string>(this, "IdSearch");
}, BindingContext);
I have created static counter variable in my app the in subscriber I have done this:
public static class Constants
{
public static int msgCenterSubscribeCounter { get; set; } = 0;
}
MessagingCenter.Subscribe<object, string>(this, "hello", (sender, arg) =>
{
Constants.msgCenterSubscribeCounter++;
if (arg.Equals("hello") && Constants.msgCenterSubscribeCounter == 1)
{
// handle your logic here
}
});
Reset counter in OnDisappearing() method from where you have called Send.
Changing Messagingcenter in to single subscription.
public class Messagingcenter_singleton
{
private static Messagingcenter_singleton _instance;
private bool isActivated = false;
private Action<string> callBackFun = null;
public static Messagingcenter_singleton Instance()
{
if (_instance == null)
{
_instance = new Messagingcenter_singleton();
}
return _instance;
}
public void setCallBack(Action<string> eventCallBack)
{
callBackFun = eventCallBack;
}
public void startSubscribe()
{
if (!isActivated)
{
isActivated = true;
MessagingCenter.Subscribe<string, string>(this, "Name", eventCallBack);
}
}
private void eventCallBack(string arg1, string arg2)
{
if (callBackFun != null)
{
InvokeMethod(new Action<string>(callBackFun), arg2);
}
}
public static object InvokeMethod(Delegate method, params object[] args)
{
return method.DynamicInvoke(args);
}
}
Use Below Code in you view model class
public void initSubscribe()
{
Messagingcenter_singleton.Instance().startSubscribe();
Messagingcenter_singleton.Instance().setCallBack(eventCallBack)
}
public void eventCallBack(string arg2)
{
// write your code here
}
I'm stuck on getting my DocumentPicker fully working. Right now it presents the view controller but I can't figure out how to wait or get the result.
In swift you just write the void documentPicker(UIDocumentPickerViewController controller, didPickDocumentAtUrl... method and when it's finished it goes to there.
But in Xamarin it must not be that simple. I've written that method, from the class I'm calling it from as well as in my AppDelegate.cs class and as well as in my Main.cs class. None seem to work, unless I've written it wrong.
What I have is this ....
public async Task<string> pickResume()
{
string path = string.Empty;
var controller = new UIViewController();
var docVC = new UIDocumentPickerViewController(new string[] { "org.openxmlformats.wordprocessingml.document", "com.microsoft.word.doc" }, UIDocumentPickerMode.Import);
UIViewController topController = getTopViewController();
topController.PresentViewController(docVC, true, null);
return path;
}
void documentPicker(UIDocumentPickerViewController controller, NSUrl didPickDocumentAtURL)
{
Console.WriteLine("done");
}
getTopViewController() is just a helper method to get the top view controller so I can present the DocumentPicker
Figured it out, and it's a lot easier than I was making it out to be.
The UIDocumentPickerViewController has two EventHandlers, DidPickDocument and WasCancelled so I just assigned those to two different methods and done.
public async Task<string> pickResume()
{
string path = string.Empty;
var controller = new UIViewController();
var docVC = new UIDocumentPickerViewController(new string[] { "org.openxmlformats.wordprocessingml.document", "com.microsoft.word.doc" }, UIDocumentPickerMode.Import);
docVC.DidPickDocument += DocVC_DidPickDocument;
docVC.WasCancelled += DocVC_WasCancelled;
UIViewController topController = getTopViewController();
topController.PresentViewController(docVC, true, null);
return await GetDocPath(new CancellationTokenSource());
}
private void DocVC_WasCancelled(object sender, EventArgs e)
{
//Handle being cancelled
}
private void DocVC_DidPickDocument(object sender, UIDocumentPickedEventArgs e)
{
//Handle document selection
}
Using Xamarin.Forms how can I use make an async method that waits for the form to dismiss? If I use
await Navigation.PushModalAsync(page);
it will return once the animation is finished not when the page is dismissed.
I want a to create modal Task SignInAsync method that return true if sign-in is successful.
You can do this by triggering an event in your login page and listen for that event before going on, but you want the full TAP support and I second you there. Here's a simple yet working 2 page app that does just this. You'll obviously want to use ContentPage custom subclass and have proper methods instead of my quick Commands, but you get the idea, and it saves me typing.
public static Page GetFormsApp ()
{
NavigationPage navpage = null;
return navpage = new NavigationPage (new ContentPage {
Content = new Button {
Text = "Show Login dialog",
Command = new Command (async o => {
Debug.WriteLine ("Showing sign in dialog");
var result = await SignInAsync (navpage);
Debug.WriteLine (result);
})
}
});
}
static Task<bool> SignInAsync (NavigationPage navpage)
{
Random rnd = new Random ();
var tcs = new TaskCompletionSource<bool> ();
navpage.Navigation.PushModalAsync (new ContentPage {
Content = new Button {
Text = "Try login",
Command = new Command ( o => {
var result = rnd.Next (2) == 1;
navpage.Navigation.PopModalAsync ();
tcs.SetResult (result);
})
}
});
return tcs.Task;
}
The minor drawback is that the Task<bool> returns before the end of the pop modal animation, but that's:
easy to fix
only an issue if you're awaiting that result to push a new modal Page. Otherwise, meh, just go on.
Override OnAppearing
Firstly, it's worth noting that simply overriding OnAppearing in the calling Page may suffice in many circumstances.
protected override void OnAppearing()
{
base.OnAppearing();
...
// Handle any change here from returning from a Pushed Page
}
(note that the pushed page's OnDisappearing override is called after the caller's OnAppearing - seems a bit backwards to me!)
AwaitableContentPage
Secondly...this is my take on #Chad Bonthuys answer:
public class AwaitableContentPage : ContentPage
{
// Use this to wait on the page to be finished with/closed/dismissed
public Task PageClosedTask { get { return tcs.Task; } }
private TaskCompletionSource<bool> tcs { get; set; }
public AwaitableContentPage()
{
tcs = new System.Threading.Tasks.TaskCompletionSource<bool>();
}
// Either override OnDisappearing
protected override void OnDisappearing()
{
base.OnDisappearing();
tcs.SetResult(true);
}
// Or provide your own PopAsync function so that when you decide to leave the page explicitly the TaskCompletion is triggered
public async Task PopAwaitableAsync()
{
await Navigation.PopAsync();
tcs.SetResult(true);
}
}
And then call it thus:
SettingsPage sp = new SettingsPage();
await Navigation.PushAsync(sp);
await sp.PageClosedTask; // Wait here until the SettingsPage is dismissed
Just thought I would contribute to this one, although it's been a while since it was asked and answered. I built upon the answer by #noelicus. I wanted a generic way to do this with multiple situations so the Task needs to be able to return not just bool but anything. Then, using generics:
public class AwaitableContentPage<T> : ContentPage
{
// Use this to wait on the page to be finished with/closed/dismissed
public Task<T> PageClosedTask => tcs.Task;
// Children classes should simply set this to the value being returned and pop async()
protected T PageResult { get; set; }
private TaskCompletionSource<T> tcs { get; set; }
public AwaitableContentPage()
{
tcs = new TaskCompletionSource<T>();
}
protected override void OnDisappearing()
{
base.OnDisappearing();
tcs.SetResult(PageResult);
}
}
Now, in the page you want to run as modal, you can do:
public partial class NewPerson : AwaitableContentPage<Person>
and when done, simply do:
base.PageResult = newPerson; // object you created previously
await base.Navigation.PopAsync();
Then, to make it super simple to use, use an extension method:
public static class ExtensionMethods
{
async public static Task<T> GetResultFromModalPage<T>(this INavigation nav, AwaitableContentPage<T> page)
{
await nav.PushAsync(page);
return await page.PageClosedTask;
}
That's all. Now, in your code, in any page where you want to use this, the syntax ends up simply like this:
Person newPerson = await Navigation.GetResultFromModalPage<string>(new NewPersonCreatePage());
if (newPerson != null)
UseNewPersonCreatedByOtherPage();
Hope this helps!
In my implementation I used:
await navigation.PopModalAsync();
Full Example:
private INavigation navigation;
public LoginPageModel(INavigation navigation, LoginPage loginPage)
{
this.navigation = navigation;
this.loginPage = loginPage;
}
public bool IsValid { get; set; }
protected async void ExecuteLoginCommand()
{
var loginResult = await AuthenticationHelper.Authenticate(Email, Password);
var isValid = false;
if (loginResult != null)
{
isValid = true;
}
//return isValid;
AuthenticationResult(isValid);
}
private async void AuthenticationResult(bool isValid)
{
if (isValid)
{
Debug.WriteLine("Logged in");
await navigation.PopModalAsync();
}
else
{
Debug.WriteLine("Failed" + email + password);
await loginPage.DisplayAlert("Authentication Failed", "Incorrect email and password combination","Ok", null);
}
}
The answer selected and given by #Stephane Delcroix above is awesome. But for anybody willing to push this further, by waiting for a page's completion and returning more structured data in a good MVVM fashion, you could do the following:
By calling an event from the page's OnDisapearing method, this event can then be subscribed by the navigation service which you create, and you can then use the "TaskCompletionSource" to wati until your page finishes its work and then complete the task.
For more details about accomplishing this, you can check this blog post.
Here is the base page's implementation, every page in this demo app inherit this page:
public class BasePage<T> : ContentPage
{
public event Action<T> PageDisapearing;
protected T _navigationResut;
public BasePage()
{
}
protected override void OnDisappearing()
{
PageDisapearing?.Invoke(_navigationResut);
if (PageDisapearing != null)
{
foreach (var #delegate in PageDisapearing.GetInvocationList())
{
PageDisapearing -= #delegate as Action<T>;
}
}
base.OnDisappearing();
}
}
Here is an overview of the navigation service you should use:
public async Task<T> NavigateToModal<T>(string modalName)
{
var source = new TaskCompletionSource<T>();
if (modalName == nameof(NewItemPage))
{
var page = new NewItemPage();
page.PageDisapearing += (result) =>
{
var res = (T)Convert.ChangeType(result, typeof(T));
source.SetResult(res);
};
await App.Current.MainPage.Navigation.PushModalAsync(new NavigationPage(page));
}
return await source.Task;
}
To call this page with the navigation service, you can use the following code:
var item = await new SimpleNavigationService().NavigateToModal<Item>(nameof(NewItemPage));
Items.Add(item);