Xamarin.Forms.Map CameraChanged event

[roubachof]

Description of Change

Added a "camera changed" event to be notified when the maps is moved or zoomed. With the proper CameraChangedEventArgs and the Camera property, it allows developers to add customs overlays with SkiaSharp, or even hide or show some controls while the map is changing.

Issues Resolved

Collaterally fixes an issue on Android.

• fixes Map renderer giving 0 size with MoveToRegion #1852. If map size is 0, and a call to MoveCamera is made an IllegalStateException will be thrown

API Changes

Added:

• event EventHandler<CameraChangedEventArgs> CameraChanged;
• Camera Camera { get; }

Platforms Affected

• Core/XAML (all platforms)
• iOS
• Android
• UWP

Behavioral/Visual Changes

None.

Before/After Screenshots

Not applicable.

Testing Procedure

I tested the 3 platforms with the RunAway! app:

https://github.com/roubachof/SkiaSharpnado/tree/xamarin-maps

in the SessionMap.xaml.cs (naming is bad :):

GoogleMap.CameraChanged += GoogleMapCameraChanged;

private void GoogleMapCameraChanged(object sender, CameraChangedEventArgs e)
{
    Debug.WriteLine($"CameraChanged: pos: {e.Camera.Position.Latitude}, {e.Camera.Position.Longitude}");

    if (!_isCameraInitialized)
    {
        _isCameraInitialized = true;
    }

    if (_drawingCount == 0)
    {
        MapOverlay.InvalidateSurface();
    }
}

Then checked that I can indeed move and zoom the map and the overlay is updated accordingly.

Platforms specific comments

Core

I created a Camera class with Zoom and Position to represent the current view photo settings.

For the Camera property, I wasn't sure how to propagate a change from the renderer to the core class for a read only property.
I reproduced the same pattern that the VisibleRegion property.

Android

I added some code in the OnLayout method to return if the map size is 0, since the MoveToRegion call will fail if it's the case.

iOS

MkMapView has no Zoom property, so I had to implement its own zoom.

UWP

The zoom given by the MapControl is not consistent with the Google Maps and iOS custom zooms. To have the same behavior as the others platforms, I had to compute it manually (it uses the same code as the iOS one).

I added a OnSizeChanged delegate for the initial Camera assignement. It fixes also a scenario when MoveToRegion is called before the layout pass is made, and then the region set by the user is not taken into account.

Issues to solve on UWP before merge

1. The zoom computation on uwp seems to be a little unaccurate, I don't really understand why. I would need a Bing maps expert for this :)

2. The ActualCameraChanging event seems to be aggressively invoked and seems to take a lot of UI thread time. I tried numerous tactics without much success... It works but it is a bit laggy in my sharpnado example.

PR Checklist

• Has automated tests
• Rebased on top of the target branch at time of PR
• Changes adhere to coding standard

[samhouts]

@roubachof What's the status of this PR? Your last comment mentions that there is still work to be done. Is that still the case? Thanks!

[roubachof]

@samhouts It's fine for iOS and Android, but I would need some help of someone from the uwp team maybe to solve the uwp issues I met... Maybe I should split the uwp version out so you could merge the iOS and Android version?

[samhouts]

@roubachof That sounds like a good idea! Thanks!

[roubachof]

@samhouts removed the UWP implementation.

[AlonRom]

Hi, @samhouts what is the status about this merge?

[nbsoftware]

Hello.
What's the status of this one?
I'm waiting on a fix for #1852

[AlonRom]

@samhouts @hartez Hi, any status regarding this would be great. thanks

[baneageorge]

Hi, any chance to have some progress on this?

[jfversluis]

Closing this as we won't be adding anything new to Forms. Adding a tag to put it on the list to look into this for .NET MAUI.