Xamarin Forms: BoxViews Color get’s lost when updating CornerRadius

In Version 4.8.0.1451 of Xamarin Forms NuGet package, when you update the BoxView’s Corner Radius, the Color property will be cleared.

Issue opened here:
https://github.com/xamarin/Xamarin.Forms/issues/12061

This content has 3 years. Some of the information in this post may be out of date or no longer work. Please, read this page keeping its age in your mind.

Xamarin Forms: Infinite scrolling ListView

To get a dynamic “paged” loading for your list view, follow the steps below:

Make a new usercontrol in your forms project. Derive from ContentView instead from ListView. By deriving from listview, you simply can not Count the items binded to the ItemsSource property, which is the base of the Fetching logic.

public class InfiniteScrollListView : ContentView

Make a countable ItemsSource bindable property for your new usercontrol.

		public static readonly BindableProperty ItemsSourceProperty = BindableProperty.Create(
														propertyName: "ItemsSource",
														returnType: typeof(IList),
														declaringType: typeof(View),
														defaultValue: null,
														defaultBindingMode: BindingMode.TwoWay,
														propertyChanged: null);

		public IList ItemsSource
		{
			get { return (IList)GetValue(ItemsSourceProperty); }
			set { SetValue(ItemsSourceProperty, value); }
		}

We need to get the usercontrol to display a listview for us. Make a new instance of a listview. You can specify a caching strategy for the listview, which can be useful on lists have a lot of items. Set the contenview’s content to the new listview instance.

		public InfiniteScrollListView()
		{
			_listViewInstance = new ListView(cachingStrategy: ListViewCachingStrategy.RecycleElement);
			_listViewInstance.HorizontalOptions = LayoutOptions.Fill;
			_listViewInstance.VerticalOptions = LayoutOptions.Fill;
			_listViewInstance.ItemAppearing += InfiniteScrollListView_ItemAppearing;
			_listViewInstance.SetBinding(ListView.ItemsSourceProperty, new Binding(nameof(ItemsSource), BindingMode.TwoWay, source: this));
			Content = _listViewInstance;
		}

		~InfiniteScrollListView()
		{
			if (_listViewInstance != null)
				_listViewInstance.ItemAppearing -= InfiniteScrollListView_ItemAppearing;
		}

The ItemAppearing event is the most important event in our Infinite scrolling listview instance. It’s called, when an item is displayed “phisically” on the screen. Let’s make an eventhandler for it. We are using a new Bindable Property for fetching data command, which will be called, when the last item of the ItemsSource has been displayed, and an another Bindable property, to turn off the fetching if the Data access layer could not provide more elements for the query. The _lastElementIndex will be the e.ItemIndex.

if (_lastItemDisplayedIndex == (ItemsSource?.Count - 1 ?? int.MinValue))
			{
				if (HasMoreItems)
				{
					if (FetchDataCommand?.CanExecute(null) == true)
					{
						FetchDataCommand?.Execute(null);
					}
				}
			}

This content has 3 years. Some of the information in this post may be out of date or no longer work. Please, read this page keeping its age in your mind.

Xamarin Android: Dismiss lock screen or show activity on lock screen

To gain an Activity to be showed on the lock screen, or bypass the phone’s lock screen (aka Keyguard) for important notification handling, for example an Incoming VOIP call, you need to do the following:

Set the permission for disabling keyguard. Add the following permission to the AndroidManifest.xml:

  <uses-permission android:name="android.permission.DISABLE_KEYGUARD"/>

Add flags to the Activity’s Window in order to show the activity on the lock screen, or to bypass the lock screen.

this.Window.AddFlags(WindowManagerFlags.DismissKeyguard | WindowManagerFlags.ShowWhenLocked);

Dismiss the keyguard if needed. (CrossCurrentActivity plugin is used to get the current activity):

KeyguardManager keyguardManager = (KeyguardManager)CrossCurrentActivity.Current.Activity?.GetSystemService(Context.KeyguardService);
if (keyguardManager != null)
{	
	keyguardManager.RequestDismissKeyguard(CrossCurrentActivity.Current.Activity, null);
}

This content has 3 years. Some of the information in this post may be out of date or no longer work. Please, read this page keeping its age in your mind.

Xamarin: Android bindings library could not build

It seems, the new Visual Studio 2019 release with version 16.7 could not build the AndroidBindings projects. (For further information about what is an android binding proj, see: https://docs.microsoft.com/en-us/xamarin/android/platform/binding-java-library/)

The compiler gives the following error message:

...\MSBuild\Xamarin\Android\Xamarin.Android.Bindings.targets(327,5): warning MSB6002: The command-line for the "BindingsGenerator" task is too long. Command-lines longer than 32000 characters are likely to fail. Try reducing the length of the command-line by breaking down the call to "BindingsGenerator" into multiple calls with fewer parameters per call.

Workarounds like: Change the path of the soulution to shorter one does not seems to work.
The only solution for the problem was to downgrade VisualStudio to 16.5.4 (to the last working one for me)

This content has 4 years. Some of the information in this post may be out of date or no longer work. Please, read this page keeping its age in your mind.

Xamarin Android: Native image scaling, images are pixelated

If you use Android’s native image scaling, from ldpi, mdpi, hdpi, to xxxhdpi, and have all the image resource in the right directory of your Xamarin.Android project folder, and find the pictures displaying pixelated: Make sure, you are correctly set the Build action for each images to AndroidResource. When adding an existing item to the resources folder from Windows version of VisualStudio’s browse dialog, the Build action will be set to BundleResource, and won’t appear in the Resources.designer.cs file, so it will be unavailable to use from code. If the picture is displaying, but it is pixelated, you may check the higher DPI version image files, have the correct buid action

This content has 4 years. Some of the information in this post may be out of date or no longer work. Please, read this page keeping its age in your mind.