Xamarin.forms: [Bug] [UWP] Picker control has unwanted margin on top in Xamarin.Forms 4.3.x

[Brosten]

Description

When using a Picker control in UWP you get an unwanted margin on top of the picker.

Steps to Reproduce

<StackLayout>
    <Label Text="Welcome to Xamarin.Forms!" BackgroundColor="Yellow"/>
    <Picker BackgroundColor="Green"/>
</StackLayout>

Expected Behavior

The picker should en up right under the label (it does in xamarin forms 4.2.x)

Actual Behavior

You get a margin (about as high as the picker itself) between the picker and the label

Basic Information

• Version with issue: 4.3.0.908675
• Last known good version: 4.2.0.910310
• IDE: VS 2019 (16.3.5) for Windows
• Platform Target Frameworks:
  
  
  
  • UWP: 1903
  
  

Screenshots

[hartez]

Confirmed.
_8150 Repro.zip

[Depechie]

Seems the Header will always be rendered on UWP even though no Picker Title property is filled in... I submitted PR #8160 to amend this.

[jimmccurdy]

If anyone needs a workaround while waiting for the fix, add the following custom picker renderer in your UWP project:

using AppShack.UWP.Renderers;
using Xamarin.Forms;
using Xamarin.Forms.Internals;
using Xamarin.Forms.Platform.UWP;

[assembly: ExportRenderer(typeof(Picker), typeof(CustomPickerRenderer))]
namespace AppShack.UWP.Renderers
{
[Preserve(AllMembers = true)]
public class CustomPickerRenderer : PickerRenderer
{
protected override void OnElementChanged(ElementChangedEventArgs e)
{
base.OnElementChanged(e);
if (Control != null)
Control.Header = null;
}
}
}

[MitchBomcanhao]

I have this on my project so that the title displays as the placeholder text instead, which is more consistent to what other platforms do in Xamarin.forms

protected override void OnElementChanged(ElementChangedEventArgs<Picker> e)
        {
            base.OnElementChanged(e);

            if (Control != null)
            {
                if (!string.IsNullOrWhiteSpace(Element?.Title))
                {
                    Control.Header = null;
                    Control.PlaceholderText = Element.Title;
                }                
            }
        }

I guess I'll need a variation to include this newer workaround.

[MagicAndre1981]

Your workaround doesn't fix anything for me @jimmccurdy and the workaround from @MitchBomcanhao breaks picker completely.

[slakul]

@MagicAndre1981 I made another workaround in my code. You can try replace

Control.Header = null;

with

if (Control.Header is UIElement tb) { tb.Visibility = Visibility.Collapsed; }

[MagicAndre1981]

ok, with some code of the linked PR it works fine for my case:

    protected override void OnElementChanged(ElementChangedEventArgs<Picker> e)
    {
        base.OnElementChanged(e);
        if (Control != null)
        {
            Control.Header = null;
            Control.HeaderTemplate = string.IsNullOrEmpty(Element.Title) ? null : (Windows.UI.Xaml.DataTemplate)Windows.UI.Xaml.Application.Current.Resources["ComboBoxHeader"];
            Control.DataContext = Element;
        }
    }

I'll use this now until PR gets merged and released in next 4.3 version.

_// Edit, this causes that I can't have empty picker so it is always one entry selected, so not that good as I first thought._

[MagicAndre1981]

I submitted PR #8160 to amend this.

Hi, @Depechie can you respond to the change requests so that it can be merged?

[Depechie]

Talked to Gerald about it. Normally end of this week I will have some time to test the PR again to see if everything is ok to merge it.

[MagicAndre1981]

ok, thanks

[MagicAndre1981]

Is the issue still present in 4.4? Looks like @Depechie was not able to make the changes in his PR.

[Brosten]

Yes, still present in 4.4.0991265 :(

[SoledadIce]

Any info about when this will be fixed?

[Bosch-Eli-Black]

@jimmccurdy's workaround didn't work for me, but got me on the right track.

For me, I had to use the line

Control.HeaderTemplate = new Windows.UI.Xaml.DataTemplate();

instead of

Control.Header = null;

Hope this helps, and thanks to @jimmccurdy for the original workaround :)