“System.Windows.Data.Binding”类型的对象无法转换为“System.String”类型

Question

我想知道是否有人可以帮忙。我已经在这个问题上敲了半天了，我一定是做错了什么。我有一个带有许多依赖属性的自定义控件。

    [TemplatePart(Name = InformationBubble.InformationBubbleTitlePart, Type = typeof(TextBlock))]
    [TemplatePart(Name = InformationBubble.InformationBubbleProductImagePart, Type=typeof(Image))]

    public class InformationBubble : Control 
    {
        #region Template Parts Name Constants

        /// <summary>
        /// Name constant for the Information Bubble Title Part
        /// </summary>
        public const string InformationBubbleTitlePart = "InformationBubbleTitleText";

        /// <summary>
        /// Name constant for the Information Bubble Product Image Part
        /// </summary>
        public const string InformationBubbleProductImagePart = "InformationBubbleProductImage";

        #endregion

        #region TemplateParts

        private TextBlock _Title;

        internal TextBlock Title
        {
            get { return _Title; }
            private set
            {
                _Title = value;

                if (_Title != null)
                {
                    _Title.Text = this.ProductTitleText;       
                }
            }
        }

        private Image _ProductImage;

        internal Image ProductImage
        {
            get { return _ProductImage; }
            private set
            {
                _ProductImage = value;

                if (_ProductImage != null)
                {
                    _ProductImage.Source = this.ProductImageSource;
                }
            }
        }

        #endregion

        #region Public String Product Title 

        // Dependency properties declaration
        public static readonly DependencyProperty ProductTitleProperty = DependencyProperty.Register(
            "ProductTitle",
            typeof(string),
            typeof(InformationBubble),
            new PropertyMetadata(string.Empty, new PropertyChangedCallback(OnProductTitleChanged)));

        public static void OnProductTitleChanged(DependencyObject sender, DependencyPropertyChangedEventArgs e)
        {
            InformationBubble iBubble = sender as InformationBubble;

            if (iBubble.Title != null)
            {
                iBubble.Title.Text = e.NewValue as string;
            }
        }

        public string ProductTitleText
        {
            get { return GetValue(ProductTitleProperty) as string; }
            set { SetValue(ProductTitleProperty, value); }
        }

        #endregion

        #region Public Image Source Product Image

        public static readonly DependencyProperty ProductImageSourceProperty = DependencyProperty.Register(
            "ProductImageSource",
            typeof(ImageSource),
            typeof(InformationBubble),
            new PropertyMetadata(null, new PropertyChangedCallback(OnProductImageSourceChanged)));

        public static void OnProductImageSourceChanged(DependencyObject sender, DependencyPropertyChangedEventArgs e)
        {
            InformationBubble iBubble = sender as InformationBubble;

            if (iBubble.ProductImage != null)
            {
                iBubble.ProductImage.Source = e.NewValue as ImageSource;
            }
        }

        public ImageSource ProductImageSource
        {
            get { return GetValue(ProductImageSourceProperty) as ImageSource; }
            set { SetValue(ProductImageSourceProperty, value); }
        }

        #endregion

        public InformationBubble()
        {
             this.DefaultStyleKey = typeof(InformationBubble);
        }

        #region Overrides

        public override void OnApplyTemplate()
        {       
            base.OnApplyTemplate();

            Title = GetTemplateChild(InformationBubble.InformationBubbleTitlePart) as TextBlock;
            ProductImage = GetTemplateChild(InformationBubble.InformationBubbleProductImagePart) as Image;
        }

        #endregion

        #region Private Methods

        private void GoToState(string stateName, bool useTransitions)
        {
            VisualStateManager.GoToState(this, stateName, useTransitions);
        }

        #endregion
    }

现在，如果我在 xaml 中的某处使用此控件，如果我这样做，它就会起作用：

<controls:InformationBubble 
        ProductImageSource="{Binding SelectedItem.NormalImageSource}"
        ProductTitleText="Test Title"
        "/>

但是如果我尝试将产品标题文本数据绑定到 ViewModel 中 SelectedItem 对象的 title 属性：

<controls:InformationBubble 
            ProductImageSource="{Binding SelectedItem.NormalImageSource}"
            ProductTitleText="{Binding SelectedItem.Title, Mode=TwoWay"
            "/>

我得到“System.Windows.Data.Binding”类型的对象无法转换为“System.String”类型。 TextBlock 的文本属性是 DependencyProperty 所以我一定在这里遗漏了一些明显的东西。

Answer 1

难道是房产名称写错了。下面代码中的“ProductTitle”应该是“ProductTitleText”吗？

public static readonly DependencyProperty ProductTitleProperty = DependencyProperty.Register(
    "ProductTitle",  // "ProductTitleText" ?
    typeof(string),
    typeof(InformationBubble),
    new PropertyMetadata(string.Empty, new PropertyChangedCallback(OnProductTitleChanged)));

我想象当您使用字符串常量时，WPF 使用反射直接访问属性“public string ProductTitleText”。 DependencyProperty 被忽略，因为属性名称不匹配（“ProductTitle”与“ProductTitleText”）。

因此，对于标题，您有一个名为“ProductTitle”的依赖属性和一个名为“ProductTitleText”的（字符串）属性。 对于 ProductImage，您有一个名为“ProductImageSource”的依赖属性和一个也称为“ProductImageSource”的属性（ImageSource 类型）。

有道理吗？

Answer 2

当

ownerType

的

DependencyProperty

不正确时，您也会收到此错误。

public static readonly DependencyProperty ProductTitleProperty = DependencyProperty.Register(
    "ProductTitle",
    typeof(string),
    typeof(SomeOtherType), // In my case, this was the wrong type.
    new PropertyMetadata(string.Empty, new PropertyChangedCallback(OnProductTitleChanged)));

（当您在类之间复制并粘贴 same

DependencyProperty

时，可能会发生这种情况。）

Answer 3

如果 DependendyProperty 的名称不是 完全是实现 get/set 的属性的名称（带有后缀 Property

），您也可能会收到此错误

public static readonly DependencyProperty MyPropertyNameProperty = [...]
public string MyPropertyName // in my case, this was a different name
{
    get { return GetValue(MyPropertyName) as string; }
    set { SetValue(MyPropertyName, value); }
}