Cannot Hide Scrollview Bar on Android when Horizontal

[Axemasta]

Description

The scroll bar of a horizontal scroll view cannot be removed on android using the following code:

scrollView.HorizontalScrollBarEnabled = false;

I have tested this issue with the use of Custom Renderers & Platform Effects, and successfully recreated in a sample repository.

The scrollview code can be seen here (although i've had this issue in other projects that look different to this)

<ContentPage ...>
    <StackLayout ...>      
        ...
        <ScrollView Orientation="Horizontal" HeightRequest="200">
            <ScrollView.Effects>
                <effects:RemoveScrollBarEffect/>
            </ScrollView.Effects>
            ...
        </ScrollView>
        ...
    </StackLayout>
</ContentPage>

Steps to Reproduce

1. Create a custom renderer or platform effect (verify this works before continuing)
2. Acquire access to the scrollview and set the following property:

scrollView.HorizontalScrollBarEnabled = false;

3. Set the scrollview orientation to horizontal
4. Run the app on Android

Expected Behavior

The scrollbar has no horizontal indicator

Actual Behavior

The scrollbar has a horizontal indicator

This issue is not encountered on iOS, it behaves as usual (but obviously its a different platform & implementation).

Basic Information

• Version with issue: 3.3.0.912540, 3.1.0.637273
• Last known good version: ?
• IDE: Visual Studio for Mac
• Platform Target Frameworks:
  • Android: API 24,25
• Android Support Library Version: 27.0.2.0
• Nuget Packages: Fresh Project
• Affected Devices:Android simulator + physical device (tested on Motorola Moto4G)

Screenshots

Reproduction Link

I have created a standalone project demonstrating this issue, with a readme to guide you in setting up the issue.

https://github.com/Axemasta/ScrollView-Bug-Example

[petermajor]

It's not possible to use an effect for this...

If you look at the ScrollViewRenderer for Android, you'll see that it's actually TWO scroll views - an external vertical ScrollView (this is the Control instance that you will get in the renderer/effect) and a subview (which is a HoriztonalScrollView instance) that you don't have access to.

However, you don't need to worry about this, because there is a property on the Xamarin Forms ScrollView element call "HorizontalScrollBarVisibility" that you can set to "Never".

[hartez]

Ah, petermajor beat me to it..

He's right about why your Effect doesn't work, and that you can just use the HorizontalScrollBarVisibility property to achieve the desired result.

But if you really, really need to access the horizontal ScrollView from an Effect, it is possible (if a bit cumbersome):

private void HideScrollBar(bool hide)
{
	try
	{
		var scrollView = (Android.Widget.ScrollView)Control;
		
		if (scrollView != null)
		{
			scrollView.VerticalScrollBarEnabled = false;

			// Dig into the Container to find the horizontal scroll view
			for (int n = 0; n < Container.ChildCount; n++)
			{
				if (Container.GetChildAt(n) is AHorizontalScrollView hsv)
				{
					hsv.HorizontalScrollBarEnabled = false;
					break;
				}
			}
		}
	}
	catch (Exception ex)
	{
		System.Diagnostics.Debug.WriteLine($"RemoveScrollBarEffect - Android - HideScrollBar - Error:'{ex.Message}'");
	}
}

[Axemasta]

@petermajor Hi Peter Thanks for the response, I was suspecting that this was something to do with the underthehood implementation, I would like to know why the HorizontalScrollBarEnabled does not have a warning associated with it.

I feel a bit dumb that I didn't see the solution that forms offers me but nevertheless I still see this as a bug because the API exists & won't work (without telling you why).

I might submit a request to have the docs updated to reflect this!

[Axemasta]

@hartez Thanks a ton! It's nice to know that I can access it that way, this begs the question... Should this method be updated to call what you just wrote & to perform the task?

In my opinion having the method in Forms is a bad idea because it's essentially android specific code within a supposedly 'platform agnostic' project. Obviously I see this as a bug because I can quickly whip it up on iOS, and then it only half works on Android.

But I guess a doc change would suffice!
Thanks again.