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();
}
}
Related
I am kind of new to Xamarin development. I tried to change the back button behavior with a binding command, but that didn't seem to work. This is the code for the view:
<Shell.BackButtonBehavior>
<BackButtonBehavior Command="{Binding GoBack}"/>
</Shell.BackButtonBehavior>
And this is the code for the view model:
public CreatePasswordVM()
{
_goBack = new Command(GoBackButton);
}
private ICommand _goBack;
public ICommand GoBack
{
get { return _goBack; }
}
public async void GoBackButton()
{
await Shell.Current.GoToAsync("../..");
}
When I pressed the back button, the method "GoBackButton" didn't call. I want to mention that on Android works.
Shell BackButtonBehavior command binding not working in UWP
Derive from Xamarin Form source code. BackButtonBehavior has not implemented for UWP platform, we could find Android and IOS implementation here and here. But for uwp there is not such tracker and there is not such value in the UWP ShellRenderer. For this scenario, we suggest your post new feature request in the Xamarin Forms github.
In my Xamarin app, I create a button (Xamarin.Forms.Button) programmatically. I need this button to show a different background image under normal vs hovered state. I have created a style resource similar to what is described at How to indicate currently selected control in Xamarin?. However, I cannot figure out how to apply this style to the button.
The Button class exposes a property called Image that is of FileImageSource type. The closest API I found to load my style resource is ImageSource.FromResource static method. However, this method seems to return StreamImageSource instance which is not what we need.
Class Button does not seem to provide any Style property.
Can you please suggest how I can programmatically associate a style to the button? Regards.
To achieve this request you need custom renderers.
To be able to apply your style f.e.: "myButtonStyle.xml" you have to create a custom renderer for your target platform:
Android:
[assembly: ExportRenderer (typeof (YourExtendedButtonClass), typeof (MyCustomButtonRenderer))]
namespace YourApp.Droid
{
public class MyCustomButtonRenderer : ButtonRenderer
{
protected override void OnElementChanged(ElementChangedEventArgs<Button> e)
{
base.OnElementChanged(e);
var myButton = this.Control as Android.Widget.Button;
myButton?.SetBackgroundResource(Resource.Drawable.myButtonStyle);
}
}
}
In XAMARIN FORMS ButtonRenderer only provide two methods which i can override: OnElementChanged and OnElementPropertyChanged. Which method do I want to override to handle button clicks?
You have a reference to the button in your Renderer (search for the proeprty Control). Just add the click-event/listener/command for this Control (but be carefull, it may be that the Control is NULL, depending on your renderer implementation).
Quick code sample for ios (depends on your renderer):
protected override void OnElementChanged(ElementChangedEventArgs<MyButtonRenderer> e)
{
var mybutton = Control as UIButton;
mybutton.TouchUpInside += (s, args) => { /* your logic */};
}
For android you can find a sample on this page.
I have recently updated xamarin forms to 1.5.1-pre1 so that I can use the beautiful AppCompat themes. It works and looks very nice.
I do have one problem, in my old FormsApplicationActivity I used to override the OnOptionsItemSelected method to intercept when the user was clicking on the back arrow icon and do some viewmodel cleanup. Apparently this method is not being called after using the FormsAppCompatActivity.
How can I intercept the "soft" back button press (toolbar icon not hard back button) ?
I also tried to override the Xamarin.Forms.Platform.Android.AppCompat.NavigationPageRenderer but i can't seem to override it :(
Does anyone have a clue how I can intercept this?
You can add the following to your custom renderer. You can either user current activity plugin or cast your context to activity.
var toolbar = CrossCurrentActivity.Current?.Activity?.FindViewById<Toolbar>(Resource.Id.toolbar);
toolbar.NavigationClick += ToolbarNavigationClick;
Have a look at the last two lines of the OnCreate() After adding them OnOptionsItemSelected was called as expected).
https://raw.githubusercontent.com/UdaraAlwis/Xamarin-Playground/master/XFNavBarBackBtnClickOverride/XFNavBarBackBtnClickOverride/XFNavBarBackBtnClickOverride.Droid/MainActivity.cs
Toolbar toolbar = this.FindViewById<Toolbar>(Resource.Id.toolbar);
SetSupportActionBar(toolbar);
In Xamarin.Forms there's a better way to intercept the NavigationBar back button pressed and the hardware back button pressed, which is creating your own NavigationRenderer and overriding the method OnPopViewAsync:
[assembly: ExportRenderer(typeof(NavigationPage), typeof(CustomNavigationRenderer))]
namespace YourApp.Droid
{
public class CustomNavigationRenderer : NavigationPageRenderer
{
public CustomNavigationRenderer(Context context) : base(context)
{
}
protected override async Task<bool> OnPopViewAsync(Page page, bool animated)
{
// Write your code here
}
}
}
Hope this helps
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