Binding to resource key, WPF

问题

I have a ResourceDictionary with some images:

<BitmapImage UriSource="..\Images\Bright\folder-bright.png"
             x:Key="FolderItemImage" />

I've create a HierarchicalTemplate for treeview items like the following:

<HierarchicalDataTemplate ItemsSource="{Binding VisibleChildren}"
                          DataType="{x:Type st:StructureTreeItem}">
    <StackPanel Orientation="Horizontal">
        <TextBlock Text="{Binding ImageResourceKey}" />
        <Image x:Name="iIcon2" Source="{DynamicResource FolderItemImage}"/>
        <Image x:Name="iIcon"
               Source="{DynamicResource {Binding ImageResourceKey}}"/>
    </StackPanel>
</HierarchicalDataTemplate>

Now, when item is displayed:

Textblock displays FolderItemImage
First image is shown
Second image is not shown.

The whole idea is to set item images to ones stored in resources, but the technique presented above unfortunately won't work and now I know, why:

<Image x:Name="iIcon3" Width="16" Height="16" Margin="0, 1, 3, 1" >
    <Image.Source>
        <DynamicResource ResourceKey="{Binding ImageResourceKey}" />
    </Image.Source>
</Image>

Result:

An unhandled exception of type 'System.Windows.Markup.XamlParseException' occurred in PresentationFramework.dll

Additional information: A 'Binding' cannot be set on the 'ResourceKey' property of type 'DynamicResourceExtension'. A 'Binding' can only be set on a DependencyProperty of a DependencyObject.

So I have to rephrase my question: how can I convert some data (a resource key, perhaps?) stored in model to a dynamic resource? It has to be a dynamic resource, because I'm certain it may change during runtime.

回答1:

I write following markup extension to allow binding to resourceKey in general case

using System;
using System.ComponentModel;
using System.Globalization;
using System.Windows;
using System.Windows.Data;
using System.Windows.Markup;

namespace Mersoft.Mvvm.MarkupExtensions
{

    public class ResourceBinding : MarkupExtension
    {
        #region Helper properties

        public static object GetResourceBindingKeyHelper(DependencyObject obj)
        {
            return (object)obj.GetValue(ResourceBindingKeyHelperProperty);
        }

        public static void SetResourceBindingKeyHelper(DependencyObject obj, object value)
        {
            obj.SetValue(ResourceBindingKeyHelperProperty, value);
        }

        // Using a DependencyProperty as the backing store for ResourceBindingKeyHelper.  This enables animation, styling, binding, etc...
        public static readonly DependencyProperty ResourceBindingKeyHelperProperty =
            DependencyProperty.RegisterAttached("ResourceBindingKeyHelper", typeof(object), typeof(ResourceBinding), new PropertyMetadata(null, ResourceKeyChanged));

        static void ResourceKeyChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
        {
            var target = d as FrameworkElement;
            var newVal = e.NewValue as Tuple<object, DependencyProperty>;

            if (target == null || newVal == null)
                return;

            var dp = newVal.Item2;

            if (newVal.Item1 == null)
            {
                target.SetValue(dp, dp.GetMetadata(target).DefaultValue);
                return;
            }

            target.SetResourceReference(dp, newVal.Item1);

        }

        #endregion

        public ResourceBinding()
        {

        }

        public ResourceBinding(string path)
        {
            this.Path = new PropertyPath(path);
        }

        public override object ProvideValue(IServiceProvider serviceProvider)
        {
            var provideValueTargetService = (IProvideValueTarget)serviceProvider.GetService(typeof(IProvideValueTarget));
            if (provideValueTargetService == null)
                return null;

            if (provideValueTargetService.TargetObject != null &&
                provideValueTargetService.TargetObject.GetType().FullName == "System.Windows.SharedDp")
                return this;


            var targetObject = provideValueTargetService.TargetObject as FrameworkElement;
            var targetProperty = provideValueTargetService.TargetProperty as DependencyProperty;
            if (targetObject == null || targetProperty == null)
                return null;



            var binding = new Binding();

            #region binding

            binding.Path = this.Path;
            binding.XPath = this.XPath;
            binding.Mode = this.Mode;
            binding.UpdateSourceTrigger = this.UpdateSourceTrigger;
            binding.Converter = this.Converter;
            binding.ConverterParameter = this.ConverterParameter;
            binding.ConverterCulture = this.ConverterCulture;

            if (this.RelativeSource != null)
                binding.RelativeSource = this.RelativeSource;

            if (this.ElementName != null)
                binding.ElementName = this.ElementName;

            if (this.Source != null)
                binding.Source = this.Source;

            binding.FallbackValue = this.FallbackValue;

            #endregion

            var multiBinding = new MultiBinding();
            multiBinding.Converter = HelperConverter.Current;
            multiBinding.ConverterParameter = targetProperty;

            multiBinding.Bindings.Add(binding);

            multiBinding.NotifyOnSourceUpdated = true;

            targetObject.SetBinding(ResourceBindingKeyHelperProperty, multiBinding);

            return null;

        }


        #region Binding Members

        /// <summary> The source path (for CLR bindings).</summary>
        public object Source
        {
            get;
            set;
        }

        /// <summary> The source path (for CLR bindings).</summary>
        public PropertyPath Path
        {
            get;
            set;
        }

        /// <summary> The XPath path (for XML bindings).</summary>
        [DefaultValue(null)]
        public string XPath
        {
            get;
            set;
        }

        /// <summary> Binding mode </summary>
        [DefaultValue(BindingMode.Default)]
        public BindingMode Mode
        {
            get;
            set;
        }

        /// <summary> Update type </summary>
        [DefaultValue(UpdateSourceTrigger.Default)]
        public UpdateSourceTrigger UpdateSourceTrigger
        {
            get;
            set;
        }

        /// <summary> The Converter to apply </summary>
        [DefaultValue(null)]
        public IValueConverter Converter
        {
            get;
            set;
        }

        /// <summary>
        /// The parameter to pass to converter.
        /// </summary>
        /// <value></value>
        [DefaultValue(null)]
        public object ConverterParameter
        {
            get;
            set;
        }

        /// <summary> Culture in which to evaluate the converter </summary>
        [DefaultValue(null)]
        [TypeConverter(typeof(System.Windows.CultureInfoIetfLanguageTagConverter))]
        public CultureInfo ConverterCulture
        {
            get;
            set;
        }

        /// <summary>
        /// Description of the object to use as the source, relative to the target element.
        /// </summary>
        [DefaultValue(null)]
        public RelativeSource RelativeSource
        {
            get;
            set;
        }

        /// <summary> Name of the element to use as the source </summary>
        [DefaultValue(null)]
        public string ElementName
        {
            get;
            set;
        }


        #endregion

        #region BindingBase Members

        /// <summary> Value to use when source cannot provide a value </summary>
        /// <remarks>
        ///     Initialized to DependencyProperty.UnsetValue; if FallbackValue is not set, BindingExpression
        ///     will return target property's default when Binding cannot get a real value.
        /// </remarks>
        public object FallbackValue
        {
            get;
            set;
        }

        #endregion



        #region Nested types

        private class HelperConverter : IMultiValueConverter
        {
            public static readonly HelperConverter Current = new HelperConverter();

            public object Convert(object[] values, Type targetType, object parameter, CultureInfo culture)
            {
                return Tuple.Create(values[0], (DependencyProperty)parameter);
            }
            public object[] ConvertBack(object value, Type[] targetTypes, object parameter, CultureInfo culture)
            {
                throw new NotImplementedException();
            }
        }

        #endregion
    }
}

Usage

<Image Source="{local:ResourceBinding ImageResourceKey}"/>

回答2:

It cannot be done directly. There's another way though involving an attached property:

public static class ImageHelper {

    private static void SourceResourceKeyChanged(DependencyObject d, DependencyPropertyChangedEventArgs e) {

        var element = d as Image;
        if (element != null) {

            element.SetResourceReference(Image.SourceProperty, e.NewValue);
        }
    }

    public static readonly DependencyProperty SourceResourceKeyProperty = DependencyProperty.RegisterAttached("SourceResourceKey",
        typeof(object),
        typeof(ImageHelper),
        new PropertyMetadata(String.Empty, SourceResourceKeyChanged));

    public static void SetSourceResourceKey(Image element, object value) {

        element.SetValue(SourceResourceKeyProperty, value);
    }

    public static object GetSourceResourceKey(Image element) {

        return element.GetValue(SourceResourceKeyProperty);
    }
}

And then:

<Image local:ImageHelper.SourceResourceKey="{Binding SomeValue}" />

回答3:

I don't think it's possible to use dynamic string value as a key for a dictionary in a way you're trying to do this.

You need to either make a Converter that converts from a string to ImageSource or use DataTrigger to choose Source depending on ImageResourceKey

using Converter:

in resources:

<local:StringToResource x:Key="StringToResource" />

then:

<Image x:Name="iIcon" Source="{Binding ImageResourceKey, Converter={StaticResource StringToResource}}"/>

your converter may look like:

public class StringToResource: IValueConverter
{
    public object Convert(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
    {
        return Application.Current.FindResource(value as string);
    }

    public object ConvertBack(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
    {
        throw new NotImplementedException();
    }
}

not tested

回答4:

public class DynamicResourceBinding : MarkupExtension
{
    public DynamicResourceBinding(string path)
    {
        binding = new Binding(path);
    }

    #region Binding Members

    public PropertyPath Path
    {
        get { return binding.Path; }
        set { binding.Path = value; }
    }
    public string XPath
    {
        get { return binding.XPath; }
        set { binding.XPath = value; }
    }
    [DefaultValue(BindingMode.Default)]
    public BindingMode Mode
    {
        get { return binding.Mode; }
        set { binding.Mode = value; }
    }
    [DefaultValue(UpdateSourceTrigger.Default)]
    public UpdateSourceTrigger UpdateSourceTrigger
    {
        get { return binding.UpdateSourceTrigger; }
        set { binding.UpdateSourceTrigger = value; }
    }
    public IValueConverter Converter
    {
        get { return binding.Converter; }
        set { binding.Converter = value; }
    }
    public object ConverterParameter
    {
        get { return binding.ConverterParameter; }
        set { binding.ConverterParameter = value; }
    }
    [TypeConverter(typeof(CultureInfoIetfLanguageTagConverter))]
    public CultureInfo ConverterCulture
    {
        get { return binding.ConverterCulture; }
        set { binding.ConverterCulture = value; }
    }
    public object Source
    {
        get { return binding.Source; }
        set { binding.Source = value; }
    }
    public string ElementName
    {
        get { return binding.ElementName; }
        set { binding.ElementName = value; }
    }
    public RelativeSource RelativeSource
    {
        get { return binding.RelativeSource; }
        set { binding.RelativeSource = value; }
    }
    public object FallbackValue
    {
        get { return binding.FallbackValue; }
        set { binding.FallbackValue = value; }
    }

    private readonly Binding binding;

    #endregion Binding Members

    public override object ProvideValue(IServiceProvider serviceProvider)
    {
        var provideValueTarget = serviceProvider.GetService(typeof(IProvideValueTarget)) as IProvideValueTarget;
        if (provideValueTarget != null)
        {
            var targetObject = provideValueTarget.TargetObject as FrameworkElement;
            if (targetObject != null)
            {
                var targetProperty = provideValueTarget.TargetProperty as DependencyProperty;
                if (targetProperty != null)
                {
                    targetObject.SetBinding(EnsureResourceKeyProperty(targetProperty), binding);
                }
            }
        }

        return null;
    }

    private static readonly object locker = new object();

    public static DependencyProperty EnsureResourceKeyProperty(DependencyProperty targetProperty)
    {
        DependencyProperty resourceKeyProperty;
        lock (locker)
        {
            if (!DirectMap.TryGetValue(targetProperty, out resourceKeyProperty))
            {
                resourceKeyProperty = RegisterResourceKeyProperty(targetProperty);
                DirectMap.Add(targetProperty, resourceKeyProperty);
                ReverseMap.Add(resourceKeyProperty, targetProperty);
            }
        }
        return resourceKeyProperty;
    }

    private static DependencyProperty RegisterResourceKeyProperty(DependencyProperty targetProperty)
    {
        return DependencyProperty.RegisterAttached(targetProperty.Name + "_ResourceKey", typeof(object), typeof(DynamicResourceBinding),
            new PropertyMetadata(ResourceKeyChanged));
    }

    private static void ResourceKeyChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
    {
        var fe = d as FrameworkElement;
        if (fe != null)
        {
            lock (locker)
            {
                DependencyProperty targetProperty;
                if (ReverseMap.TryGetValue(e.Property, out targetProperty))
                {
                    fe.SetResourceReference(targetProperty, e.NewValue);
                }
            }
        }
    }

    private static readonly Dictionary<DependencyProperty, DependencyProperty> DirectMap = new Dictionary<DependencyProperty, DependencyProperty>();
    private static readonly Dictionary<DependencyProperty, DependencyProperty> ReverseMap = new Dictionary<DependencyProperty, DependencyProperty>();
}

Usage

来源：https://stackoverflow.com/questions/20564862/binding-to-resource-key-wpf

标签

wpf

binding

dynamicresource