Develop Reference

How to intercept "a redirect URL" from webview in Xamarin Forms

I'm displaying an OAtuh2 HTML page in WebView that returns me, after clicking on a validation button that is on this page, a redirect URL that I would like to intercept to use the information from it.
in XML file
<ContentPage.Content>
<WebView x:Name="browser"></WebView>
</ContentPage.Content>
in CS file
browser.Source = "https://myUrl";
My low knowledge in Xamarin doesn't allow me to know how to do it
Thanks for your help

You can do as ToolmakerSteve mentioned using WebNavigatingEventArgs.
And for details you can implement this on each specific platform with custom renderer .
iOS
[assembly: ExportRenderer(typeof(WebView), typeof(MyRenderer))]
namespace FormsApp.iOS
{
class MyRenderer : WkWebViewRenderer
{
protected override void OnElementChanged(VisualElementChangedEventArgs e)
{
base.OnElementChanged(e);
this.NavigationDelegate = new MyDelegate();
}
}
public class MyDelegate : WKNavigationDelegate
{
public override void DecidePolicy(WKWebView webView, WKNavigationAction navigationAction, Action<WKNavigationActionPolicy> decisionHandler)
{
if(navigationAction.NavigationType == WKNavigationType.Other)
{
if(navigationAction.Request.Url != null)
{
//do something
}
decisionHandler(WKNavigationActionPolicy.Cancel);
return;
}
decisionHandler(WKNavigationActionPolicy.Allow);
}
}
}
Android
[assembly: ExportRenderer(typeof(Xamarin.Forms.WebView), typeof(MyRenderer))]
namespace FormsApp.Droid
{
class MyRenderer : WebViewRenderer
{
public MyRenderer(Context context):base(context)
{
}
protected override void OnElementChanged(ElementChangedEventArgs<Xamarin.Forms.WebView> e)
{
base.OnElementChanged(e);
if (Control != null)
{
Control.SetWebViewClient(new MyClient());
}
}
}
public class MyClient : WebViewClient
{
public override bool ShouldOverrideUrlLoading(Android.Webkit.WebView view, IWebResourceRequest request)
{
//do something
return true;
}
}
}
Refer to
https://stackoverflow.com/a/45604360/8187800
https://stackoverflow.com/a/4066497/8187800

How can I detect the clicking of a tab button in Xamarin.Forms?

Here is the code that I have. I would like to know how I can detect when a user clicks a tab that is already selected as I want to toggle the icon for the aPage between play.png and pause.png plus I also want to call a method on APage.
public partial class MainPage : TabbedPage
{
public MainPage()
{
InitializeComponent();
var aPage = new NavigationPage(new APage())
{
Title = "Play",
Icon = "play.png"
};
var bPage = new NavigationPage(new BPage())
{
Title = "Settings",
Icon = "b.png"
};
Children.Add(aPage);
Children.Add(bPage);
}
}
Note that if possible I would like to find a solution that does not involve custom renderers for both iOS and Android. I'm wondering can I redefine the TabbedPage and put the logic in that class?

I know you want to avoid using custom renderers, but this is only possible by using a Custom Renderer.
Code
Xamarin.Android Custom Renderer
using Android.Content;
using Android.Support.Design.Widget;
using Xamarin.Forms;
using Xamarin.Forms.Platform.Android;
using Xamarin.Forms.Platform.Android.AppCompat;
[assembly: ExportRenderer(typeof(MainPage), typeof(MainPageRenderer))]
namespace YourNameSpace
{
public class MainPageRenderer : TabbedPageRenderer, TabLayout.IOnTabSelectedListener
{
MainPage _page;
public MainPageRenderer(Context context) : base(context) { }
protected override void OnElementChanged(ElementChangedEventArgs<TabbedPage> e)
{
base.OnElementChanged(e);
if (e.NewElement != null)
_page = e.NewElement as MainPage;
else
_page = e.OldElement as MainPage;
}
void TabLayout.IOnTabSelectedListener.OnTabReselected(TabLayout.Tab tab)
{
System.Diagnostics.Debug.WriteLine("Tab Reselected");
//Handle Tab Reselected
}
}
}
Xamarin.iOS Custom Renderer
using System;
using System.Diagnostics;
using UIKit;
using Xamarin.Forms;
using Xamarin.Forms.Platform.iOS;
[assembly: ExportRenderer(typeof(MainPage), typeof(MainPageRenderer))]
namespace YourNameSpace
{
public class MainPageRenderer : TabbedRenderer
{
MainPage _page;
protected override void OnElementChanged(VisualElementChangedEventArgs e)
{
base.OnElementChanged(e);
if (e.NewElement != null)
_page = e.NewElement as MainPage;
else
_page = e.OldElement as MainPage;
try
{
if (ViewController is UITabBarController tabBarController)
tabBarController.ViewControllerSelected += OnTabbarControllerItemSelected;
}
catch (Exception exception)
{
Debug.WriteLine(exception);
}
}
void OnTabbarControllerItemSelected(object sender, UITabBarSelectionEventArgs eventArgs)
{
if (_page?.CurrentPage?.Navigation != null && _page.CurrentPage.Navigation.NavigationStack.Count > 0)
{
Debug.WriteLine("Tab Tapped");
//Handle Tab Tapped
}
}
}
}
Code credit: #Kyle https://stackoverflow.com/a/42909203/5953643

If you want to get selected tab then you need to use ItemSource and SelectedItem property like ListView.

You can do this easily in iOS, but in Android you need a custom renderer. Just check this blog
http://motzcod.es/post/162985782667/dynamically-changing-xamarin-forms-tab-icons-when-select

You can't. TabbedPage interited from MultiPage that you can check the source from here. All select, deselect, update, template and logic is implemented here. You suppose to watch CurrentPage property but it has value check if already selected, so you cannot use.

this.PropertyChanging += async (object sender, PropertyChangingEventArgs e) =>
{
if (e.PropertyName == "CurrentPage")
{
if (this.CurrentPage == null)
return;
}
};

How to access method from view inside a Xamarin Forms custom renderer?

I have the following code:
public partial class PhrasesFrameRendererClass : Frame
{
.....
void getRandomWords() {
// more code here that involves getting random numbers
// and updating a grid's bindingcontext
}
}
In my custom renderer I want to be able to call the getRandomWords on swipe left gesture like below:
public class PhraseFrameCustomRenderer : FrameRenderer
{
UISwipeGestureRecognizer leftSwipeGestureRecognizer;
protected override void OnElementChanged(ElementChangedEventArgs<Frame> e)
{
base.OnElementChanged(e);
leftSwipeGestureRecognizer = new UISwipeGestureRecognizer();
leftSwipeGestureRecognizer.Direction = UISwipeGestureRecognizerDirection.Left;
leftSwipeGestureRecognizer.NumberOfTouchesRequired = 1;
leftSwipeGestureRecognizer.AddTarget((obj) =>
{
// Call getRandomWords() here
});
}
}
Is this possible? Any ideas on how this could be done?

base.OnElementChanged(e);
leftSwipeGestureRecognizer = new UISwipeGestureRecognizer();
leftSwipeGestureRecognizer.Direction = UISwipeGestureRecognizerDirection.Left;
leftSwipeGestureRecognizer.NumberOfTouchesRequired = 1;
leftSwipeGestureRecognizer.AddTarget((obj) =>
{
// Call getRandomWords() here
var frame = Element as PhrasesFrameRendererClass ;
if(frame!=null){
frame.getRandomWords();
}
});

You can create a BindableProperty of type Command in your custom frame class, call that Command from your renderer and bind your ViewModel's getRandomWords method as a Command
//Your custom control in your PCL project
public partial class PhrasesFrameRendererClass : Frame
{
public static readonly BindableProperty SwipeLeftCommandProperty =
BindableProperty.Create(nameof(SwipeLeftCommand), typeof(ICommand), typeof(PhrasesFrameRendererClass ), null);
public ICommand SwipeLeftCommand
{
get { return (ICommand)GetValue(CommandProperty); }
set { SetValue(CommandProperty, value); }
}
}
//Your custom control renderer
public class PhraseFrameCustomRenderer : FrameRenderer
{
UISwipeGestureRecognizer leftSwipeGestureRecognizer;
protected override void OnElementChanged(ElementChangedEventArgs<Frame> e)
{
base.OnElementChanged(e);
leftSwipeGestureRecognizer = new UISwipeGestureRecognizer();
leftSwipeGestureRecognizer.Direction = UISwipeGestureRecognizerDirection.Left;
leftSwipeGestureRecognizer.NumberOfTouchesRequired = 1;
leftSwipeGestureRecognizer.AddTarget((obj) =>
{
var myFrame = Element as PhrasesFrameRendererClassl
if(myFrame != null){
if(myFrame.SwipeLeftCommand != null && myFrame.SwipeLeftCommand.CanExecute()){
myFrame.SwipeLeftCommand.Execute();
}
}
});
}
}
//Your ViewModel
public class PhrasesViewModel{
public Command GetRandomWordsCommand {get;set;}
public PhrasesViewModel(){
GetRandomWordsCommand = new Command(ExecuteGetRandomWords);
}
private void ExecuteGetRandomWords(){
//Your method goes here
}
}
//Your XAML
<yourControls:PhrasesFrameRendererClass SwipeLeftCommand="{Binding GetRandomWordsCommand }"/>
It may seem more complicated this way, but using commands allows you to separate your application code (Such as getting random phrases) from your rendering code

How can I get Google Glass gestures working with Xamarin?

I'm using Xamarin to build a Google Glass application, and haven't been able to get the GestureDetector to fire any OnGesture events. Here is what I've tried so far:
In my Activity:
using Gesture = Android.Glass.Touchpad.Gesture;
using GestureDetector = Android.Glass.Touchpad.GestureDetector;
private GestureDetector _gestureDetector;
protected override void OnCreate(Bundle bundle)
{
base.OnCreate(bundle);
this._gestureDetector = new GestureDetector(this);
this._gestureDetector.SetBaseListener(new GestureListener());
}
public override bool OnGenericMotionEvent(MotionEvent e)
{
if (this._gestureDetector != null)
{
return this._gestureDetector.OnMotionEvent(e);
}
return false;
}
The IBaseListener implementation:
class GestureListener : GestureDetector.IBaseListener
{
public bool OnGesture(Gesture gesture)
{
if (gesture == Gesture.SwipeRight)
{
// do something on right (forward) swipe
return true;
}
else if (gesture == Gesture.SwipeLeft)
{
// do something on left (backwards) swipe
return true;
}
return false;
}
public void Dispose()
{
}
public IntPtr Handle { get; set; }
}
I tried setting a breakpoint just inside the OnGesture method, but it is never triggered. Is there something missing from my IBaseListener implementation?

It turns out that I needed to make my listener implementation extend Java.Lang.Object, as mentioned in the Xamarin article about Android Callable Wrappers. Below is a fully working sample Activity.
using System;
using Android.App;
using Android.Content;
using Android.Runtime;
using Android.Views;
using Android.Widget;
using Android.OS;
using Gesture = Android.Glass.Touchpad.Gesture;
using GestureDetector = Android.Glass.Touchpad.GestureDetector;
namespace GlassGestureTest
{
using Android.Util;
using Java.Util.Logging;
[Activity(Label = "GlassGestureTest", MainLauncher = true, Icon = "#drawable/icon")]
public class Activity1 : Activity
{
private GestureDetector _gestureDetector;
int count = 1;
protected override void OnCreate(Bundle bundle)
{
base.OnCreate(bundle);
// Set our view from the "main" layout resource
SetContentView(Resource.Layout.Main);
// Get our button from the layout resource,
// and attach an event to it
Button button = FindViewById<Button>(Resource.Id.MyButton);
button.Click += delegate { button.Text = string.Format("{0} clicks!", count++); };
this._gestureDetector = new GestureDetector(this);
this._gestureDetector.SetBaseListener(new GestureListener());
}
public override bool OnGenericMotionEvent(MotionEvent e)
{
if (this._gestureDetector != null)
{
return this._gestureDetector.OnMotionEvent(e);
}
return false;
}
}
// Note - the key part here is to extend Java.Lang.Object in order to properly setup
// the IntPtr field and Dispose method required by IBaseListener
public class GestureListener : Java.Lang.Object, GestureDetector.IBaseListener
{
public bool OnGesture(Gesture gesture)
{
if (gesture == Gesture.SwipeRight)
{
// do something on right (forward) swipe
return true;
}
else if (gesture == Gesture.SwipeLeft)
{
// do something on left (backwards) swipe
return true;
}
else if (gesture == Gesture.SwipeDown)
{
// do something on the down swipe
return true;
}
else if (gesture == Gesture.SwipeUp)
{
// do something on the up swipe
return true;
}
return false;
}
}
}

Why custom control task pane does not update its properties?

I have designed a custom panel which can expand or collapse form at run time.
When I change its height from custom designed task, it does not update it.
Code of my control class:
using System;
using System.Windows.Forms;
using System.ComponentModel;
using System.ComponentModel.Design;
using System.Windows.Forms.Design;
[Designer(typeof(MyControlDesigner))]
public partial class ExpandCollapsePanel : UserControl
{
private bool flag = false;
private Size size;
public int usrVerticalSize;
public ExpandCollapsePanel()
{
InitializeComponent();
}
[DefaultValueAttribute(true)]
public int SetVerticalSize
{
get
{
return usrVerticalSize;
}
set
{
usrVerticalSize = value;
}
}
Code of taskpanedesign class:
namespace ExpandCollapseFormLibrary
{
class CustomDialogue : ControlDesigner
{
private DesignerActionListCollection actionLists;
public override DesignerActionListCollection ActionLists
{
get
{
if (actionLists == null)
{
actionLists = new DesignerActionListCollection();
actionLists.Add(new MyActionListItem(this));
}
return actionLists;
}
}
}
internal class MyActionListItem : DesignerActionList
{
public MyActionListItem(ControlDesigner owner) : base(owner.Component)
{
}
public override DesignerActionItemCollection GetSortedActionItems()
{
var items = new DesignerActionItemCollection();
//items.Add(new DesignerActionTextItem("Hello world", "Misc"));
items.Add(new DesignerActionPropertyItem("Checked", "Vertical Drop Down Size"));
return items;
}
public int Checked
{
get { return ((ExpandCollapsePanel)base.Component).SetVerticalSize; }
set { ((ExpandCollapsePanel)base.Component).SetVerticalSize = value; }
}
}
}
When I change the value the Form1(where drag and dropped) designed class keep it permanently.

the SetVerticalSize property value of your custom pane's is really changed, but the problem is that the designer host does not know about it at all. To notify the designer host about your custom pane changing you should implement something like this (I suggest you read the IComponentChangeService MSDN article for more details):
int usrVerticalSize;
[DefaultValue(true)]
public int SetVerticalSize {
get { return usrVerticalSize; }
set {
FireChanging(); //changing notification
try {
usrVerticalSize = value;
}
finally { FireChanged(); } //changed notification
}
}
void FireChanging() {
IComponentChangeService service = GetComponentChangeService();
if(service != null)
service.OnComponentChanging(this, null);
}
void FireChanged() {
IComponentChangeService service = GetComponentChangeService();
if(service != null)
service.OnComponentChanged(this, null, null, null);
}
IComponentChangeService GetComponentChangeService() {
return GetService(typeof(IComponentChangeService)) as IComponentChangeService;
}