I created a custom SVG button so that I have a Xamarin Forms button with text and an SVG image. Everything was fine with me, and then I transferred my project to .NET Standard 2.0.
Now, when you change the text on the control, I get a Null Reference Exception inside the Xamarin Forms Framework StackLayout LayoutChildIntoBoundingRegion method in ListDictionaryInternal.
Here is the control. It is pretty simple.
using System.Windows.Input; using FFImageLoading.Svg.Forms; using Core.Interfaceses; using Xamarin.Forms; using Xamarin.Forms.Xaml; namespace CustomControls { [XamlCompilation(XamlCompilationOptions.Compile)] public class SVGImageButton : ContentView { #region Member Variables private readonly Button _button; private readonly SvgCachedImage _svgImage; #endregion #region Bindible Properties public static BindableProperty ButtonPressedCommandProperty = BindableProperty.Create(nameof(ButtonPressedCommand), typeof(ICommand), typeof(SVGImageButton)); public ICommand ButtonPressedCommand { get { return (ICommand)GetValue(ButtonPressedCommandProperty); } set { SetValue(ButtonPressedCommandProperty, value); } } public static BindableProperty CommandParameterProperty = BindableProperty.Create(nameof(CommandParameter), typeof(object), typeof(SVGImageButton)); public object CommandParameter { get { return GetValue(CommandParameterProperty); } set { SetValue(CommandParameterProperty, value); } } public static BindableProperty ButtonTextProperty = BindableProperty.Create(nameof(ButtonText), typeof(string), typeof(SVGImageButton), string.Empty, BindingMode.TwoWay, propertyChanged: (bindable, oldValue, newValue) => { if (newValue == null) return; var control = (SVGImageButton)bindable; control.ButtonText = newValue.ToString(); }); public string ButtonText { get { return _button.Text; } set { _button.Text = value; } } public static BindableProperty ButtonBackgroundColorProperty = BindableProperty.Create(nameof(ButtonBackgroundColor), typeof(Color), typeof(View), Color.Fuchsia, BindingMode.OneWay, propertyChanged: (bindable, oldValue, newValue) => { if (newValue == null) return; var control = (SVGImageButton)bindable; control.ButtonBackgroundColor = (Color)newValue; }); public Color ButtonBackgroundColor { get { return _button.BackgroundColor; } set { _button.BackgroundColor = value; } } public static BindableProperty ButtonTextColorProperty = BindableProperty.Create(nameof(ButtonTextColor), typeof(Color), typeof(View), Color.Fuchsia, BindingMode.OneWay, propertyChanged: (bindable, oldValue, newValue) => { if (newValue == null) return; var control = (SVGImageButton)bindable; control.ButtonTextColor = (Color)newValue; }); public Color ButtonTextColor { get { return _button.TextColor; } set { _button.TextColor = value; } } public static BindableProperty ButtonStyleProperty = BindableProperty.Create(nameof(ButtonBackgroundColor), typeof(Style), typeof(View), null, BindingMode.OneWay, propertyChanged: (bindable, oldValue, newValue) => { if (newValue == null) return; var control = (SVGImageButton)bindable; control.ButtonStyle = (Style)newValue; }); public Style ButtonStyle { get { return _button.Style; } set { _button.Style = value; } } public static BindableProperty ButtonBorderWidthProperty = BindableProperty.Create(nameof(ButtonBorderWidth), typeof(double), typeof(View), 0.0, BindingMode.OneWay, propertyChanged: (bindable, oldValue, newValue) => { if (newValue == null) return; var control = (SVGImageButton)bindable; control.ButtonBorderWidth = (double)newValue; }); public double ButtonBorderWidth { get { return _button.BorderWidth; } set { _button.BorderWidth = value; } } public static BindableProperty ButtonBorderColorProperty = BindableProperty.Create(nameof(ButtonBorderColor), typeof(Color), typeof(View), Color.Fuchsia, BindingMode.OneWay, propertyChanged: (bindable, oldValue, newValue) => { if (newValue == null) return; var control = (SVGImageButton)bindable; control.ButtonBorderColor = (Color)newValue; }); public Color ButtonBorderColor { get { return _button.BorderColor; } set { _button.BorderColor = value; } } #endregion #region Properties public string SVGImageName { get; set; } #endregion #region Life Cycle protected override void OnParentSet() { base.OnParentSet(); _button.Text = ButtonText; _svgImage.Source = SvgImageSource.FromResource(SVGImageName); } protected override SizeRequest OnMeasure(double widthConstraint, double heightConstraint) { _button.HorizontalOptions = (Parent as View).HorizontalOptions; _button.VerticalOptions = (Parent as View).VerticalOptions; if (_button.Text != null) { var size = DependencyService.Get<ITextMeter>().MeasureTextSize(_button.Text.TrimEnd(), 200, _button.FontSize); WidthRequest = size.Width + 60 + _button.Height; } return base.OnMeasure(widthConstraint, heightConstraint); } public SVGImageButton() { var content = new RelativeLayout(); _button = new Button { BackgroundColor = Color.Gray, TextColor = Color.Black }; _svgImage = new SvgCachedImage { IsEnabled = false }; content.Children.Add(_button, Constraint.RelativeToParent((parent) => { return parent.X; }), Constraint.RelativeToParent((parent) => { return parent.Y; }), Constraint.RelativeToParent((parent) => { return parent.Width; }), Constraint.RelativeToParent((parent) => { return parent.Height; })); content.Children.Add(_svgImage, Constraint.RelativeToParent((parent) => { return parent.Width - (parent.Height / 2) - (parent.Height / 4); }), Constraint.RelativeToParent((parent) => { return parent.Height - (parent.Height / 2) - (parent.Height / 4); }), Constraint.RelativeToParent((parent) => { return parent.Height / 2; }), Constraint.RelativeToParent((parent) => { return parent.Height / 2; })); Content = content; _button.Clicked += (sender, e) => { ButtonPressedCommand?.Execute(CommandParameter); }; } #endregion } }
Here is the use of control in XAML.
<customcontrols:SVGImageButton x:Name="TypeSelectionButton" HorizontalOptions="Start" VerticalOptions="Center" ButtonPressedCommand="{Binding TypeButtonClickedCommand}" SVGImageName="SVGImages.ic_triangle_down.svg" CommandParameter="{x:Reference TypeSelectionButton}" ButtonText="{Binding SearchTypeButtonText}" ButtonBackgroundColor="{Binding ButtonBackgroundColor}"/>
Before porting to .NET Standard 2.0, when the text has been resized, the control will resize, it will now receive this failure.
Any help that I can get, understands what is happening, is bewildering!