Question

I’ve created a custom control based on Expander class:

public partial class HideableExpander : Expander
{
    public new double Height
    {
        get
        {
            if (Visibility== System.Windows.Visibility.Hidden)
            {
                return 0;
            }
            return base.Height;
        }
        set
        {
            base.Height = value;
        }
    }

    public new double Width
    {
        get
        {
            if (Visibility == System.Windows.Visibility.Hidden)
            {
                return 0;
            }
            return base.Width;
        }
        set
        {
            base.Width = value;
        }
    }

    public new Thickness Margin
    {
        get
        {
            if (Visibility== System.Windows.Visibility.Hidden)
            {
                return new Thickness();
            }
            return base.Margin;
        }
        set
        {
            base.Margin = value;
        }
    }

    public HideableExpander()
    {

        this.InitializeComponent();

    }
}

XAML:

<Expander
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
mc:Ignorable="d"
x:Class="leartWPF.HideableExpander"
x:Name="UserControl"
d:DesignWidth="640" d:DesignHeight="480">

<Grid x:Name="LayoutRoot"/>
</Expander>

Now, when I’m trying to use it with Width=”Auto” property:

            <local:HideableExpander Header="{Binding Expander1Name, ElementName=Window}"  Margin="10" Width="Auto" Background="#00F19494" VerticalAlignment="Top" >
                <WrapPanel Height="Auto" Margin="0" Width="Auto" >
                      <TextBlock Text="Please, enter the name of this expander:       " VerticalAlignment="Center"/>
                      <TextBox Width="150" Text="{Binding Expander1Name, ElementName=Window, Mode=TwoWay, NotifyOnValidationError=True, UpdateSourceTrigger=PropertyChanged, ValidatesOnDataErrors=True, ValidatesOnExceptions=True}" Background="#FFF5EECC"/>  
                </WrapPanel>
            </local:HideableExpander>

I get an exception about not being able convert “Auto” to double:

Unhandled Exception: System.Windows.Markup.XamlParseException: 'Provide value on 'System.Windows.Baml2006.TypeConverterMarkupExtension' threw an exception.' Line number '10' and line position '8'. ---> System.Exception: Auto is not a valid value for Double. ---> System.FormatException: Input string was not in a correct format.
   at System.Number.ParseDouble(String value, NumberStyles options, NumberFormatInfo numfmt)
   at System.Double.Parse(String s, NumberStyles style, IFormatProvider provider)
   at System.ComponentModel.DoubleConverter.FromString(String value, NumberFormatInfo formatInfo)
   at System.ComponentModel.BaseNumberConverter.ConvertFrom(ITypeDescriptorContext context, CultureInfo culture, Object value)
   --- End of inner exception stack trace ---
   at System.ComponentModel.BaseNumberConverter.ConvertFrom(ITypeDescriptorContext context, CultureInfo culture, Object value)
   at MS.Internal.Xaml.Runtime.ClrObjectRuntime.CallProvideValue(MarkupExtension me, IServiceProvider serviceProvider)
   --- End of inner exception stack trace ---
   at System.Windows.Markup.WpfXamlLoader.Load(XamlReader xamlReader, IXamlObjectWriterFactory writerFactory, Boolean skipJournaledProperties, Object rootObject, XamlObjectWriterSettings settings, Uri baseUri)
   at System.Windows.Markup.WpfXamlLoader.LoadBaml(XamlReader xamlReader, Boolean skipJournaledProperties, Object rootObject, XamlAccessLevel accessLevel, Uri baseUri)
   at System.Windows.Markup.XamlReader.LoadBaml(Stream stream, ParserContext parserContext, Object parent, Boolean closeStream)
   at System.Windows.Application.LoadBamlStreamWithSyncInfo(Stream stream, ParserContext pc)
   at System.Windows.Application.LoadComponent(Uri resourceLocator, Boolean bSkipJournaledProperties)
   at System.Windows.Application.DoStartup()
   at System.Windows.Application.<.ctor>b__1(Object unused)
   at System.Windows.Threading.ExceptionWrapper.InternalRealCall(Delegate callback, Object args, Int32 numArgs)
   at MS.Internal.Threading.ExceptionFilterHelper.TryCatchWhen(Object source, Delegate method, Object args, Int32 numArgs, Delegate catchHandler)
   at System.Windows.Threading.Dispatcher.WrappedInvoke(Delegate callback, Object args, Int32 numArgs, Delegate catchHandler)
   at System.Windows.Threading.DispatcherOperation.InvokeImpl()
   at System.Threading.ExecutionContext.runTryCode(Object userData)
   at System.Runtime.CompilerServices.RuntimeHelpers.ExecuteCodeWithGuaranteedCleanup(TryCode code, CleanupCode backoutCode, Object userData)
   at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean ignoreSyncCtx)
   at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state)
   at System.Windows.Threading.DispatcherOperation.Invoke()
   at System.Windows.Threading.Dispatcher.ProcessQueue()
   at System.Windows.Threading.Dispatcher.WndProcHook(IntPtr hwnd, Int32 msg, IntPtr wParam, IntPtr lParam, Boolean& handled)
   at MS.Win32.HwndWrapper.WndProc(IntPtr hwnd, Int32 msg, IntPtr wParam, IntPtr lParam, Boolean& handled)
   at MS.Win32.HwndSubclass.DispatcherCallbackOperation(Object o)
   at System.Windows.Threading.ExceptionWrapper.InternalRealCall(Delegate callback, Object args, Int32 numArgs)
   at MS.Internal.Threading.ExceptionFilterHelper.TryCatchWhen(Object source, Delegate method, Object args, Int32 numArgs, Delegate catchHandler)
   at System.Windows.Threading.Dispatcher.WrappedInvoke(Delegate callback, Object args, Int32 numArgs, Delegate catchHandler)
   at System.Windows.Threading.Dispatcher.InvokeImpl(DispatcherPriority priority, TimeSpan timeout, Delegate method, Object args, Int32 numArgs)
   at MS.Win32.HwndSubclass.SubclassWndProc(IntPtr hwnd, Int32 msg, IntPtr wParam, IntPtr lParam)
   at MS.Win32.UnsafeNativeMethods.DispatchMessage(MSG& msg)
   at System.Windows.Threading.Dispatcher.PushFrameImpl(DispatcherFrame frame)
   at System.Windows.Application.RunInternal(Window window)
   at System.Windows.Application.Run()
   at leartWPF.App.Main() in d:\Users\menkaur\Documents\Expression\Blend 4\Projects\leartWPF\leartWPF\obj\Debug\App.g.cs:line 0

What should I do to be able to accept Auto as a value?

Answer 1

Try adding following attribute, I think that should help, and of course, “new” to hide parent’s Width…

[TypeConverterAttribute(typeof(LengthConverter))]
public new double Width
{
  ......your getter and setter

// EDIT
per comment: -“what is a getter and setter?”

   //getter and setter sample(grabbing them from the question)
    get
    {
        if (Visibility == System.Windows.Visibility.Hidden)
        {
            return 0;
        }
        return base.Width;
    }
    set
    {
        base.Width = value;
    }
}