I want to apply some validation on the entry input, I went to the docs page of the attached behaviors
and did this:
public enum TextType { Email, Phone, }
public static class Validator
{
public static readonly BindableProperty TextTypeProperty = BindableProperty.CreateAttached(
"TextType", typeof(TextType), typeof(Validator), TextType.Email, propertyChanged: ValidateText);
public static TextType GetTextType(BindableObject view)
{
return (TextType)view.GetValue(TextTypeProperty);
}
public static void SetTextType(BindableObject view, TextType textType)
{
view.SetValue(TextTypeProperty, textType);
}
private static void ValidateText(BindableObject bindable, object oldValue, object newValue)
{
var entry = bindable as Entry;
entry.TextChanged += Entry_TextChanged;
}
private static void Entry_TextChanged(object sender, TextChangedEventArgs e)
{
var entry = sender as Entry;
bool isValid = false;
switch (GetTextType(sender as Entry))
{
case TextType.Email:
isValid = e.NewTextValue.Contains("#");
break;
case TextType.Phone:
isValid = Regex.IsMatch(e.NewTextValue, #"^\d+$");
break;
default:
break;
}
if (isValid)
entry.TextColor = Color.Default;
else
entry.TextColor = Color.Red;
}
}
in XAML:
<Entry beh:Validator.TextType="Email" Placeholder="Validate Email"/>
but it doesn't work, the setter nor the propertyChanged call back are never called,
also what is the difference between this "Attached behavior" and the attached property, the two pages are pretty identical
what does the logic have to do with the propertyChanged method is not called?
From this MSDN Attached Behaviors,you can see that An attached property can define a propertyChanged delegate that will be executed when the value of the property changes.
According to your code, you set TextType=TextType.Email firstly, then you also set
<Entry beh:Validator.TextType="Email" Placeholder="Validate Email"/>
Validator.TextType="Email", the attached property doesn't change, so PropertyChanged method is not call.
You can modify your code like this, then you will find the propertychanged will be called.
<Entry beh:Validator.TextType="Phone" Placeholder="Validate Email"/>
Comparing to the sample you ignore most of the logic from OnAttachBehaviorChanged in your ValidateText and it is quite necessary:
static void OnAttachBehaviorChanged (BindableObject view, object oldValue, object newValue)
{
var entry = view as Entry;
if (entry == null) {
return;
}
bool attachBehavior = (bool)newValue;
if (attachBehavior) {
entry.TextChanged += OnEntryTextChanged;
} else {
entry.TextChanged -= OnEntryTextChanged;
}
}
Considering the differences, attached properties are something that is applied to a specific control, you can apply behavior technically to any control though probably it will work only on some of them but it may work on multiple control types properly.
I am using Xamarin.Forms with Android. I have a form which has 4 Entry controls for a user to enter code. I am using TextChanged event to detect user input and automatically move focus to the next control. This part works fine, i.e. as user types a digit focus automatically jumps to the next entry. However, I need to achieve the opposite, user should be able to tap backspace button and focus should move to the previous control. The problem is that TextChanged is not triggered when entry control is empty. How can I achieve this? Is there a custom renderer I can create for android to capture text input? Maybe there is a way to use 1 entry instead but I need to make it look like distinct 4 boxes.
Finally,I've found a solution for this by implementing a renderer in android.
In shared code(PCL),Create a class like this
public class CustomEntry:Entry
{
public delegate void BackspaceEventHandler(object sender, EventArgs e);
public event BackspaceEventHandler OnBackspace;
public CustomEntry()
{
}
public void OnBackspacePressed()
{
if (OnBackspace != null)
{
OnBackspace(null, null);
}
}
}
And,Then in your android project create a renderer like this:
public class CustomEntryRenderer: EntryRenderer
{
public override bool DispatchKeyEvent(KeyEvent e)
{
if (e.Action == KeyEventActions.Down)
{
if (e.KeyCode == Keycode.Del)
{
if (string.IsNullOrWhiteSpace(Control.Text))
{
var entry = (PasswordBox)Element;
entry.OnBackspacePressed();
}
}
}
return base.DispatchKeyEvent(e);
}
protected override void
OnElementChanged(Xamarin.Forms.Platform.Android.ElementChangedEventArgs<Entry> e)
{
base.OnElementChanged(e);
}
}
And then use it like this:
Entry1.OnBackspace += Entry1BackspaceEventHandler;
public void Entry1BackspaceEventHandler()
{
//things you want to do
}
What events should I listen to on a UWP Xaml Slider to determine when the user begins and ends manipulation.
This functionality is important when you have a slider that represents some continuously changing app state (say, an animation time) and you want to pause the update when the user interacts with the slider.
This question has been answered for WPF and Windows Phone, but not UWP. The other solutions do not work, or are incomplete, for UWP.
You need to listen to interaction events from a couple of the elements of the Slider template: the Thumb, and the Container. This is because the user can manipulate the thumb directly by clicking and dragging it, but also they can click anywhere on the slider and the thumb will jump to that location (even though it looks like you are then manipulating the Thumb, actually the thumb is just being relocated every time the mouse moves - you are still interacting with the container).
There are a couple caveats:
the thumb and container both process their input events and do not pass them on, so you need to use the AddHandler method of attaching RoutedEvent handlers so that you get events which have already been processed.
you need to attach the event handlers after the control template has been applied, which means you need to subclass the Slider to override a protected method.
The RoutedEvent handler information is covered here: https://learn.microsoft.com/en-us/windows/uwp/xaml-platform/events-and-routed-events-overview#registering-handlers-for-already-handled-routed-events
The following SliderEx class adds some events which can be used to detect when the user begins/ends interacting with the slider:
public class SliderEx : Slider
{
public event EventHandler SliderManipulationStarted;
public event EventHandler SliderManipulationCompleted;
public event EventHandler SliderManipulationMoved;
private bool IsSliderBeingManpulated
{
get
{
return this.isContainerHeld || this.isThumbHeld;
}
}
private bool isThumbHeld = false;
private bool isContainerHeld = false;
protected override void OnApplyTemplate()
{
base.OnApplyTemplate();
var thumb = base.GetTemplateChild("HorizontalThumb") as Thumb;
if (thumb == null)
{
thumb = base.GetTemplateChild("VerticalThumb") as Thumb;
}
if (thumb != null)
{
thumb.DragStarted += this.Thumb_DragStarted;
thumb.DragCompleted += this.Thumb_DragCompleted;
thumb.DragDelta += this.Thumb_DragDelta;
}
var sliderContainer = base.GetTemplateChild("SliderContainer") as Grid;
if (sliderContainer != null)
{
sliderContainer.AddHandler(PointerPressedEvent,
new PointerEventHandler(this.SliderContainer_PointerPressed), true);
sliderContainer.AddHandler(PointerReleasedEvent,
new PointerEventHandler(this.SliderContainer_PointerReleased), true);
sliderContainer.AddHandler(PointerMovedEvent,
new PointerEventHandler(this.SliderContainer_PointerMoved), true);
}
}
private void SliderContainer_PointerMoved(object sender,
Windows.UI.Xaml.Input.PointerRoutedEventArgs e)
{
this.InvokeMove();
}
private void SliderContainer_PointerReleased(object sender,
Windows.UI.Xaml.Input.PointerRoutedEventArgs e)
{
this.SetContainerHeld(false);
}
private void SliderContainer_PointerPressed(object sender,
Windows.UI.Xaml.Input.PointerRoutedEventArgs e)
{
this.SetContainerHeld(true);
}
private void Thumb_DragDelta(object sender, DragDeltaEventArgs e)
{
this.InvokeMove();
}
private void Thumb_DragCompleted(object sender, DragCompletedEventArgs e)
{
this.SetThumbHeld(false);
}
private void Thumb_DragStarted(object sender, DragStartedEventArgs e)
{
this.SetThumbHeld(true);
}
private void SetThumbHeld(bool held)
{
bool wasManipulated = this.IsSliderBeingManpulated;
this.isThumbHeld = held;
this.InvokeStateChange(wasManipulated);
}
private void SetContainerHeld(bool held)
{
bool wasManipulated = this.IsSliderBeingManpulated;
this.isContainerHeld = held;
this.InvokeStateChange(wasManipulated);
}
private void InvokeMove()
{
this.SliderManipulationMoved?.Invoke(this, EventArgs.Empty);
}
private void InvokeStateChange(bool wasBeingManipulated)
{
if (wasBeingManipulated != this.IsSliderBeingManpulated)
{
if (this.IsSliderBeingManpulated)
{
this.SliderManipulationStarted?.Invoke(this, EventArgs.Empty);
}
else
{
this.SliderManipulationCompleted?.Invoke(this, EventArgs.Empty);
}
}
}
}
So I have a searchbar(My searchbar all have a custom renderer) on one page. When a user fills in their search term they get redirect to searchpage where their results get shown.
The problem I have here is that suddenly the searchbar on the new page gets focussed (because I pass the search term from the previous page into this searchbar) and the software keyboard shows.
I want to dismiss keyboard or prevent the keyboard from showing. But when the user clicks inside the searchbar than ofcourse the keyboard can appear.
Note this question has been asked before, the answers I followed were never successfull. Here you can find what I have tried
First try: Unfocus
Just unfocussing my entry, did not work. Tried it both in my constructor and in my OnAppearing code of the page
Second try: Focus other element
Tried focussing my listview, but keyboard stil showed up
Third try: Dependency service
https://forums.xamarin.com/discussion/comment/172077#Comment_172077
Interface:
public interface IKeyboardHelper
{
void HideKeyboard();
}
iOS:
public class iOSKeyboardHelper : IKeyboardHelper
{
public void HideKeyboard()
{
UIApplication.SharedApplication.KeyWindow.EndEditing(true);
}
}
Droid:
public class DroidKeyboardHelper : IKeyboardHelper
{
public void HideKeyboard()
{
var context = Forms.Context;
var inputMethodManager = context.GetSystemService(Context.InputMethodService) as InputMethodManager;
if (inputMethodManager != null && context is Activity)
{
var activity = context as Activity;
var token = activity.CurrentFocus?.WindowToken;
inputMethodManager.HideSoftInputFromWindow(token, HideSoftInputFlags.None);
activity.Window.DecorView.ClearFocus();
}
}
}
Usage in Xamarin Forms:
DependencyService.Get<IKeyboardHelper>().HideKeyboard();
EDIT
My renderer's code for my search page
protected override void OnElementChanged(ElementChangedEventArgs<SearchBar> e)
{
base.OnElementChanged(e);
if (Control != null)
{
var searchView = Control;
searchView.Iconified = true;
searchView.SetIconifiedByDefault(false);
// (Resource.Id.search_mag_icon); is wrong / Xammie bug
int searchIconId = Context.Resources.GetIdentifier("android:id/search_mag_icon", null, null);
var icon = searchView.FindViewById(searchIconId);
(icon as ImageView).SetImageResource(Resource.Drawable.search_zwart);
int cancelIconId = Context.Resources.GetIdentifier("android:id/search_close_btn", null, null);
var eicon = searchView.FindViewById(cancelIconId);
(eicon as ImageView).SetImageResource(Resource.Drawable.close_zwart);
}
}
I tried to use the back navigation by overriding OnBackButtonPressed, but somehow it wasn't get called at all. I am using the ContentPage and the latest 1.4.2 release.
Alright, after many hours I figured this one out. There are three parts to it.
#1 Handling the hardware back button on android. This one is easy, override OnBackButtonPressed. Remember, this is for a hardware back button and android only. It will not handle the navigation bar back button. As you can see, I was trying to back through a browser before backing out of the page, but you can put whatever logic you need in.
protected override bool OnBackButtonPressed()
{
if (_browser.CanGoBack)
{
_browser.GoBack();
return true;
}
else
{
//await Navigation.PopAsync(true);
base.OnBackButtonPressed();
return true;
}
}
#2 iOS navigation back button. This one was really tricky, if you look around the web you'll find a couple examples of replacing the back button with a new custom button, but it's almost impossible to get it to look like your other pages. In this case I made a transparent button that sits on top of the normal button.
[assembly: ExportRenderer(typeof(MyAdvantagePage), typeof
(MyAdvantagePageRenderer))]
namespace Advantage.MyAdvantage.MobileApp.iOS.Renderers
{
public class MyAdvantagePageRenderer : Xamarin.Forms.Platform.iOS.PageRenderer
{
public override void ViewWillAppear(bool animated)
{
base.ViewWillAppear(animated);
if (((MyAdvantagePage)Element).EnableBackButtonOverride)
{
SetCustomBackButton();
}
}
private void SetCustomBackButton()
{
UIButton btn = new UIButton();
btn.Frame = new CGRect(0, 0, 50, 40);
btn.BackgroundColor = UIColor.Clear;
btn.TouchDown += (sender, e) =>
{
// Whatever your custom back button click handling
if (((MyAdvantagePage)Element)?.
CustomBackButtonAction != null)
{
((MyAdvantagePage)Element)?.
CustomBackButtonAction.Invoke();
}
};
NavigationController.NavigationBar.AddSubview(btn);
}
}
}
Android, is tricky. In older versions and future versions of Forms once fixed, you can simply override the OnOptionsItemselected like this
public override bool OnOptionsItemSelected(IMenuItem item)
{
// check if the current item id
// is equals to the back button id
if (item.ItemId == 16908332)
{
// retrieve the current xamarin forms page instance
var currentpage = (MyAdvantagePage)
Xamarin.Forms.Application.
Current.MainPage.Navigation.
NavigationStack.LastOrDefault();
// check if the page has subscribed to
// the custom back button event
if (currentpage?.CustomBackButtonAction != null)
{
// invoke the Custom back button action
currentpage?.CustomBackButtonAction.Invoke();
// and disable the default back button action
return false;
}
// if its not subscribed then go ahead
// with the default back button action
return base.OnOptionsItemSelected(item);
}
else
{
// since its not the back button
//click, pass the event to the base
return base.OnOptionsItemSelected(item);
}
}
However, if you are using FormsAppCompatActivity, then you need to add onto your OnCreate in MainActivity this to set your toolbar:
Android.Support.V7.Widget.Toolbar toolbar = this.FindViewById<Android.Support.V7.Widget.Toolbar>(Resource.Id.toolbar);
SetSupportActionBar(toolbar);
But wait! If you have too old a version of .Forms or too new version, a bug will come up where toolbar is null. If this happens, the hacked together way I got it to work to make a deadline is like this. In OnCreate in MainActivity:
MobileApp.Pages.Articles.ArticleDetail.androdAction = () =>
{
Android.Support.V7.Widget.Toolbar toolbar = this.FindViewById<Android.Support.V7.Widget.Toolbar>(Resource.Id.toolbar);
SetSupportActionBar(toolbar);
};
ArticleDetail is a Page, and androidAction is an Action that I run on OnAppearing if the Platform is Android on my page. By this point in your app, toolbar will no longer be null.
Couple more steps, the iOS render we made above uses properties that you need to add to whatever page you are making the renderer for. I was making it for my MyAdvantagePage class that I made, which implements ContentPage . So in my MyAdvantagePage class I added
public Action CustomBackButtonAction { get; set; }
public static readonly BindableProperty EnableBackButtonOverrideProperty =
BindableProperty.Create(
nameof(EnableBackButtonOverride),
typeof(bool),
typeof(MyAdvantagePage),
false);
/// <summary>
/// Gets or Sets Custom Back button overriding state
/// </summary>
public bool EnableBackButtonOverride
{
get
{
return (bool)GetValue(EnableBackButtonOverrideProperty);
}
set
{
SetValue(EnableBackButtonOverrideProperty, value);
}
}
Now that that is all done, on any of my MyAdvantagePage I can add this
:
this.EnableBackButtonOverride = true;
this.CustomBackButtonAction = async () =>
{
if (_browser.CanGoBack)
{
_browser.GoBack();
}
else
{
await Navigation.PopAsync(true);
}
};
That should be everything to get it to work on Android hardware back, and navigation back for both android and iOS.
You are right, in your page class override OnBackButtonPressed and return true if you want to prevent navigation. It works fine for me and I have the same version.
protected override bool OnBackButtonPressed()
{
if (Condition)
return true;
return base.OnBackButtonPressed();
}
Depending on what exactly you are looking for (I would not recommend using this if you simply want to cancel back button navigation), OnDisappearing may be another option:
protected override void OnDisappearing()
{
//back button logic here
}
OnBackButtonPressed() this will be called when a hardware back button is pressed as in android. This will not work on the software back button press as in ios.
Additional to Kyle Answer
Set
Inside YOURPAGE
public static Action SetToolbar;
YOURPAGE OnAppearing
if (Device.RuntimePlatform == Device.Android)
{
SetToolbar.Invoke();
}
MainActivity
YOURPAGE.SetToolbar = () =>
{
Android.Support.V7.Widget.Toolbar toolbar =
this.FindViewById<Android.Support.V7.Widget.Toolbar>(Resource.Id.toolbar);
SetSupportActionBar(toolbar);
};
I use Prism libray and for handle the back button/action I extend INavigatedAware interface of Prism on my page and I implement this methods:
public void OnNavigatedFrom(INavigationParameters parameters)
{
if (parameters.GetNavigationMode() == NavigationMode.Back)
{
//Your code
}
}
public void OnNavigatedTo(INavigationParameters parameters)
{
}
Method OnNavigatedFrom is raised when user press back button from Navigation Bar (Android & iOS) and when user press Hardware back button (only for Android).
For anyone still fighting with this issue - basically you cannot intercept back navigation cross-platform. Having said that there are two approaches that effectively solve the problem:
Hide the NavigationPage back button with NavigationPage.ShowHasBackButton(this, false) and push a modal page that has a custom Back/Cancel/Close button
Intercept the back navigation natively for each platform. This is a good article that does it for iOS and Android: https://theconfuzedsourcecode.wordpress.com/2017/03/12/lets-override-navigation-bar-back-button-click-in-xamarin-forms/
For UWP you are on your own :)
Edit:
Well, not anymore since I did it :) It actually turned out to be pretty easy – there is just one back button and it’s supported by Forms so you just have to override ContentPage’s OnBackButtonPressed:
protected override bool OnBackButtonPressed()
{
if (Device.RuntimePlatform.Equals(Device.UWP))
{
OnClosePageRequested();
return true;
}
else
{
base.OnBackButtonPressed();
return false;
}
}
async void OnClosePageRequested()
{
var tdvm = (TaskDetailsViewModel)BindingContext;
if (tdvm.CanSaveTask())
{
var result = await DisplayAlert("Wait", "You have unsaved changes! Are you sure you want to go back?", "Discard changes", "Cancel");
if (result)
{
tdvm.DiscardChanges();
await Navigation.PopAsync(true);
}
}
else
{
await Navigation.PopAsync(true);
}
}
protected override bool OnBackButtonPressed()
{
base.OnBackButtonPressed();
return true;
}
base.OnBackButtonPressed() returns false on click of hardware back button.
In order to prevent operation of back button or prevent navigation to previous page. the overriding function should be returned as true. On return true, it stays on the current xamarin form page and state of page is also maintained.
The trick is to implement your own navigation page that inherits from NavigationPage. It has the appropriate events Pushed, Popped and PoppedToRoot.
A sample implementation could look like this:
public class PageLifetimeSupportingNavigationPage : NavigationPage
{
public PageLifetimeSupportingNavigationPage(Page content)
: base(content)
{
Init();
}
private void Init()
{
Pushed += (sender, e) => OpenPage(e.Page);
Popped += (sender, e) => ClosePage(e.Page);
PoppedToRoot += (sender, e) =>
{
var args = e as PoppedToRootEventArgs;
if (args == null)
return;
foreach (var page in args.PoppedPages.Reverse())
ClosePage(page);
};
}
private static void OpenPage(Page page)
{
if (page is IPageLifetime navpage)
navpage.OnOpening();
}
private static void ClosePage(Page page)
{
if (page is IPageLifetime navpage)
navpage.OnClosed();
page.BindingContext = null;
}
}
Pages would implement the following interface:
public interface IPageLifetime
{
void OnOpening();
void OnClosed();
}
This interface could be implemented in a base class for all pages and then delegate it's calls to it's view model.
The navigation page and could be created like this:
var navigationPage = new PageLifetimeSupportingNavigationPage(new MainPage());
MainPage would be the root page to show.
Of course you could also just use NavigationPage in the first place and subscribe to it's events without inheriting from it.
Maybe this can be usefull, You need to hide the back button, and then replace with your own button:
public static UIViewController AddBackButton(this UIViewController controller, EventHandler ev){
controller.NavigationItem.HidesBackButton = true;
var btn = new UIBarButtonItem(UIImage.FromFile("myIcon.png"), UIBarButtonItemStyle.Plain, ev);
UIBarButtonItem[] items = new[] { btn };
controller.NavigationItem.LeftBarButtonItems = items;
return controller;
}
public static UIViewController DeleteBack(this UIViewController controller)
{
controller.NavigationItem.LeftBarButtonItems = null;
return controller;
}
Then call them into these methods:
public override void ViewWillAppear(bool animated)
{
base.ViewWillAppear(animated);
this.AddBackButton(DoSomething);
UpdateFrames();
}
public override void ViewWillDisappear(Boolean animated)
{
this.DeleteBackButton();
}
public void DoSomething(object sender, EventArgs e)
{
//Do a barrel roll
}
Another way around is to use Rg.Plugins.Popup Which allows you to implement nice popup. It uses another NavigationStack => Rg.Plugins.Popup.Services.PopupNavigation.Instance.PopupStack. So your page won't be wrap around the NavigationBar.
In your case I would simply
Create a full page popup with opaque background
Override ↩️ OnBackButtonPressed for Android on ⚠️ParentPage⚠️ with something like this:
protected override bool OnBackButtonPressed()
{
return Rg.Plugins.Popup.Services.PopupNavigation.Instance.PopupStack.Any();
}
Since the back-button affect the usual NavigationStack your parent would pop out whenever the user try to use it while your "popup is showing".
Now what? Xaml what ever you want to properly close your popup with all the check you want.
💥 Problem solved for these targets💥
[x] Android
[x] iOS
[-] Windows Phone (Obsolete. Use v1.1.0-pre5 if WP is needed)
[x] UWP (Min Target: 10.0.16299)