Capture touch events in Xamarin.Forms for Android - xamarin

I am creating an app that allows the user to drag and drop to put one image on top of another using Xamarin.Forms.
On iOS I managed to hack together a workable gesture recognizer renderer by creating a custom ContentView and a custom renderer for it, which then attaches native gesture recognizers to itself based on the GestureRecognizers elements. To do that I disable the default EventTracker and implement my own, with overridden GetNativeRecognizer method
in the custom renderer:
public InteractiveContentViewRenderer () : base ()
{
AutoTrack = false;
events = new InteractiveEventTracker (this);
}
in the custom event tracker:
public InteractiveEventTracker (IVisualElementRenderer renderer) : base (renderer)
{
this.Renderer = renderer;
}
protected override MonoTouch.UIKit.UIGestureRecognizer GetNativeRecognizer (Xamarin.Forms.IGestureRecognizer recognizer)
{
var gestureRecognizer = base.GetNativeRecognizer (recognizer);
if (gestureRecognizer == null) {
// here I find my own native recognizer and return it
}
}
On Android, however, so far I haven't figured out how to achieve the same thing. There's no EventTracker in Android, I think I'll have to implement some Android View for this to work but I haven't figured it out so far.
Has anyone managed to hack together touch events in Xamarin.Forms for Android? I'd like to know at least the basic structure of the hack?

Read this: http://blog.twintechs.com/cross-platform-compositional-gesture-advanced-xamarin-forms-techniques-for-flexible-and-performant-cross-platform-apps-part-4
There's a lot about custom gestures in Xamarin.Forms
The source is here: https://github.com/twintechs/TwinTechsFormsLib/tree/master/TwinTechsForms/TwinTechsForms.Droid/TwinTechs/Gestures

Related

Xamarin ios map circle overlay click

I'm following the maps example https://developer.xamarin.com/samples/xamarin-forms/customrenderers/map/circle/ to create custom renderer to overlay circles. It seems to be working fine for all 3 platforms except I am unable to find any click event for iOS.
I am building a xamarin forms app and able to find out the click event on both Android and UWP but iOS seems to be far fetched.
Is there any way to do it?
iOS doesn't provide the API which detects the click event.
As a alternative workaround, we can add UITapGestureRecognizer on the mapview and judge if the tap point locates inside the circle.
Solution
//xxx
nativeMap.AddOverlay(circleOverlay);
nativeMap.AddGestureRecognizer(new UITapGestureRecognizer(TapHandle));
void TapHandle(UITapGestureRecognizer tap)
{
MKMapView mapView = tap.View as MKMapView;
CGPoint tapPoint = tap.LocationInView(mapView);
CLLocationCoordinate2D tapCoordinate = mapView.ConvertPoint(tapPoint, tap.View);
MKMapPoint point = MKMapPoint.FromCoordinate(tapCoordinate);
foreach(IMKOverlay overlay in mapView.Overlays)
{
MKCircleRenderer render = GetOverlayRenderer(mapView, overlay) as MKCircleRenderer;
CGPoint datPoint = render.PointForMapPoint(point);
render.InvalidatePath();
if (render.Path.ContainsPoint(datPoint,false))
{
break;
}
}
}

Override Fragment functions on Xamarin Android if fragment is created using Forms Embedding

I have created a forms page in Xamarin and used that page as a fragment using Xamarin Forms Embedding.
var fragment = new FormsPage().CreateFragment(context);
I would like to override the OnBackPressed() control in Android version of the app.
What's the best possible way to do it as I can't override it inside the Xamarin Forms Page.
I would like to override the OnBackPressed() control in Android version of the app.
You could override OnBackButtonPressed in Xamarin.Forms, this event also be raised when the hardware back button is pressed in Android and this event is not raised on iOS.
If you want remove fragment from the stack in OnBackPressed() method, you could override this method in your Activity like this :
public override void OnBackPressed()
{
base.OnBackPressed();
if (FragmentManager.BackStackEntryCount != 0)
{
FragmentManager.PopBackStack();
}
else
{
base.OnBackPressed();
}
}

How to present an iOS Modal View in MvvmCross

How can I present a modal view on iOS using MvvmCross?
Using Xamarin Studio on iOS and the MvvmCross NuGet version 4.2.2, none of the MvxModalSupportTouchViewPresenter, MvxModalNavSupportTouchViewPresenter or IMvxModalTouchView are even available.
Does the ViewModel even need to know about the fact that a particular view is presented as a modal view on iOS?
MvvmCross is a strong Page navigation framework. Default navigation using ShowViewModel<AViewModel> will use the stack metaphor: one on top of another on Android, slide atop each other on iOS, and use < on either platform to go back.
You can tell the ViewPresenter that a given view is modal by giving it a hint, in the form of an interface marker, by adopting IMvxModalIosView.
At the View Level
Adopt the IMvxModalIosView protocol:
public partial class AView : MvxViewController, IMvxModalIosView
At the AppDelegate Level
Replace var setup = new Setup(this, Window) by:
var presenter = new MvxModalSupportIosViewPresenter(this, Window);
var setup = new Setup(this, presenter);
setup.Initialize();
At the ViewModel Level
No change required. The ViewModel is actually not made aware of the modal presentation. Invoke:
ShowViewModel<AViewModel> // May be modal on certain platforms
To close a Page and go back to the previous one, regardless of your presentation style, use Close(this) on that very ViewModel. This will close a modal dialog, or pop a pushed view. A complete, bindable ICommand may look like this:
public ICommand BackCommand {
get { return new MvxCommand(() => Close(this)); }
}
Notes: In MvvmCross 4.2.2, Touch has been renamed iOS, so IMvxModalTouchView is now IMvxModalIosView. The new using are:
using MvvmCross.iOS.Platform;
using MvvmCross.iOS.Views.Presenters;
Using MvvmCross 5.5.2 all I had to get a modal was to add the following MvxModalPresentation attribute to my iOS view:
[Register("ExampleModalView")]
[MvxModalPresentation(
ModalPresentationStyle = UIModalPresentationStyle.PageSheet,
ModalTransitionStyle = UIModalTransitionStyle.CoverVertical
)]
public class ExampleModalView : MvxViewController
{
public ExampleModalView() {
}
...
}
Launching the modal is simple with the IMvxNavigationService service
await _navigationService.Navigate<ExampleModalViewModel>();
ExampleModalViewModel just needs to be a plain MvvmCross view model inheriting from MvxViewModel.
A useful reference for this is ModalView.cs in the iOS playground project: https://github.com/MvvmCross/MvvmCross/blob/develop/TestProjects/Playground/Playground.iOS/Views/ModalView.cs#L12

Disable ScrollView bounce NativeScript

Looking for a way to disable the ScrollView bounce or overflow that happens when scrolling reaches the top or bottom of the scroll view.
here how to set the settings in android.
Android scrollview remove blue light
Here is a code snippet that might do the trick for you:
if (this.content.ios instanceof UIScrollView) {
this.content.ios.alwaysBounceVertical = false;
}
Of course you need to get an instance of the <ScrollView> component from NativeScript and then the native iOS instance.
I have a small utility library that has this function and some other handy functions baked into it.
https://github.com/TheOriginalJosh/nativescript-swiss-army-knife
import {SwissArmyKnife} from 'nativescript-swiss-army-knife/nativescript-swiss-army-knife';
...
let scrollView = page.getViewById('myScrollView');
SwissArmyKnife.disableScrollBounce(scrollView);
Here is how to do it on iOS and Android.
let scrollView = page.getViewById('myScrollView');
if (app.android) {
scrollView.android.setOverScrollMode(2);
}
else if (app.ios) {
scrollView.ios.bounces = false;
}

How to handle screen rotation/orientation in Xamarin Forms?

Is there a (half) generic way to handle rotation/orientation in Xamarin Forms for different views and platforms (Android, iOS, WinPhone)?
The UI does rotate, and that is nice enough, though it wreaks havoc to my layout (absolute layout right now). I suppose with a Stacklayout I could make it a litte more flexible, but would then hit a road block somewhere else when the layout is more intricate.
Can I somehow display different views for portrait and landscape, with the same ViewModel? (I am using XLABs based MVVM.)
Possible solutions I have found:
http://blog.rthand.com/post/2014/07/24/Different-XAML-layouts-for-different-device-orienations-in-XamarinForms.aspx is lacking iOS and I wonder if it will handle MVVM too well, seems good though and I am investigating it right now
http://www.jimbobbennett.io/orientation-with-xamarin-forms/ sounds promising but the sample is iOS only, the linked GIT repository has no documentation at all, it just says "Xamarin Helpers"
http://www.sellsbrothers.com/posts/Details/13740 might also be a possibility for programmatically created views. Though in my tests I did not get a size changed event (though I listened at a different code place) for ios simulator when rotating. (The solution is based on size changed to detect rotation.)
If you are already using XLabs then you could use IXFormsApp and property 'Orientation' and event handler 'Rotation'. You would have to add the native observers per platform and set IXFormsApp's 'Orientation' there which would cause the event handler to invoke.
For example on iOS:
public override bool FinishedLaunching(UIApplication app, NSDictionary options)
{
var xapp = new XFormsAppiOS();
xapp.Init(this);
var resolverContainer = new SimpleContainer();
resolverContainer.Register<IXFormsApp>(xapp);
Resolver.SetResolver(resolverContainer.GetResolver());
var a = new App();
LoadApplication(a);
UIDevice.Notifications.ObserveOrientationDidChange((s, e) =>
{
xapp.Orientation = ... // set orientation here
});
Now you can monitor orientation changes by resolving IXFormsApp:
xapp = Resolver.Resolve<IXFormsApp>();
if (xapp.Orientation == Orientation.Landscape) { ... } else { ... }
xapp.Rotation += (sender, args) =>
{
switch (args.Value)
{
case Orientation.LandscapeLeft:
break;
default:
// etc.
break;
}
};
As for layouts I would imagine RelativeLayout would be the most convenient choice as you could put the orientation inside the Constraint's. On rotation make the layout refresh itself.

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