Bug 56333 - PropertyChanged of custom Bindable property of a Custom view is called before InitializeComponent is called
Summary: PropertyChanged of custom Bindable property of a Custom view is called before...
Alias: None
Product: Forms
Classification: Xamarin
Component: Forms ()
Version: 2.3.4
Hardware: PC Windows
: --- normal
Target Milestone: ---
Assignee: Stephane Delcroix
Depends on:
Reported: 2017-05-13 09:12 UTC by Gagik Kyurkchyan
Modified: 2017-06-19 19:18 UTC (History)
5 users (show)

Tags: xaml styles ac
Is this bug a regression?: Yes
Last known good build:

Sample project to reproduce the issue (178.65 KB, application/x-rar)
2017-05-16 07:11 UTC, Gagik Kyurkchyan

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Description Gagik Kyurkchyan 2017-05-13 09:12:25 UTC
I have multiple custom views with custom bindable properties in my project. Before Xamarin 2.3.4 everything was working Ok. After updating to 2.3.4 my custom views stopped working. Take a look here

 public partial class RightIconButton
        public RightIconButton()

        public static readonly BindableProperty TextProperty = BindableProperty.Create(nameof(Text),

        public string Text
            get { return (string) GetValue(TextProperty); }
            set { SetValue(TextProperty, value); }

        private static void OnTextChanged(BindableObject bindable, object oldvalue, object newvalue)
            var button = (RightIconButton) bindable;
            button.TitleLabel.Text = Text;

My custom view has a backing xaml. So the TitleLabel is inside the xaml. The issue is when I use this view and set the Text property, the OnTextChanged method is getting called even before InitializeComponent is called. Thus TitleLabel is never initiated and I get a null reference exception. Same thing happens for all other views. This has been a breaking change on Xamarin.Forms 2.3.4.
Comment 1 Gagik Kyurkchyan 2017-05-16 07:11:24 UTC
Created attachment 22186 [details]
Sample project to reproduce the issue


I found what is the exact issue and have attached sample project through which you can 100% reproduce the issue. The issue is that if you have custom view with custom bindable property let's say It's Color, and you set default style in the App.xaml, the style is applied event before InitializeComponent is called.
Comment 2 Jimmy [MSFT] 2017-05-19 21:52:03 UTC
Thank you for filing this report! I am able to reproduce the crash using the attached repro project.

As mentioned in comment 1, the issue does appear to be that in 2.3.4 the implicit style is applied _before_ InitializeComponent(), so none of the view's children are instantiated at that point. This is different behavior than in 2.3.3 and therefore a possible regression.

### Version Test   BAD
2.3.5-pre3  BAD   BAD   GOOD
Comment 3 Jon Scalet 2017-05-19 22:46:22 UTC

I'm having the same issue. Any suggestions from the XForms team on how we can work around this? As Gagik mentioned, we too, have reusable controls with properties set globally. 

It's a pretty big pain for us.

Comment 4 Stephane Delcroix 2017-05-23 09:46:51 UTC
> Any suggestions from the XForms team on how we can work around this?

use bindings from the Xaml to the BP

instead of doing this in code-behind:

    button.TitleLabel.Text = Text;

do this in the Xaml

    <Button Text="{Binding Text, Source={x:Reference rightIconButton}}" />

this will work if you set a x:Name="rightIconButton" on the top level element of your Xaml file:

    <RightIconButton ... x:Name="rightIconButton" >
Comment 5 Ryan 2017-06-08 17:46:53 UTC
Stephane, I don't quite understand this solution

What source am I referencing that has the Text property to bind to?

I have a page with an instance of my custom control that has bindable properties bound from the view model and from static references ( text, colors, commands, etc.) and I don't quite understand how I can reference those bindings in the custom control xaml file. 

this is my custom control xaml. It uses property change events to set its bindable properties:

<ContentView xmlns="http://xamarin.com/schemas/2014/forms" xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml" x:Class="CiiCommon.Controls.SvgButton"
    <StackLayout x:Name="SVGStackLayout">
      <Frame Padding="0" HasShadow="false" HorizontalOptions="Fill" VerticalOptions="Fill" x:Name="Frame">
        <StackLayout Orientation="Horizontal" Padding="10,5,10,5" HorizontalOptions="FillAndExpand" x:Name="Layout">
          <svg:SvgImage Svg="res:Images.icon_logEntry.svg" HorizontalOptions="Center" VerticalOptions="Center" WidthRequest="50" x:Name="SvgImage" Clicked="SvgImage_Clicked" >

          <Label TextColor="White" VerticalOptions="Center" HorizontalOptions="CenterAndExpand" FontSize="14" x:Name="Label"/>
            <TapGestureRecognizer x:Name="TapGesture"
                CommandParameter="{Binding .}" Tapped="SvgImage_Clicked"/>

Upgrading Xamarin on our build machine has forced us to upgrade xamarin.forms to 2.3.4 and this issue is breaking all of our pages :((