类型\'System.Windows.Data.Binding\'的对象不能转换为类型\'System.String\'

问题描述

|| 我想知道是否有人可以提供帮助。我已经半天不停地解决这个问题了，我一定做错了。我有一个带有多个依赖项属性的自定义控件。

[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),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中的某个地方使用此控件，则可以执行以下操作：

<controls:informationBubble 
        ProductimageSource=\"{Binding SelectedItem.normalImageSource}\"
        ProductTitleText=\"Test Title\"
        \"/>

但是，如果我尝试将产品标题文本与数据绑定到viewmodel中SelectedItem对象的title属性，则：

<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text属性是DependencyProperty，因此我在这里肯定缺少明显的东西。 非常感谢您的帮助或见解。 克里斯     

解决方法

可能是属性名称错误。以下代码中的“ 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)));

我想像一下，当您使用字符串常量时，WPF会使用反射直接访问属性“公共字符串ProductTitleText \”。 DependencyProperty将被忽略，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 \”的依赖项属性和一个名为\“ ProductTitleText \”的（字符串）属性。 对于ProductImage，您有一个名为\“ ProductImageSource \”的依赖项属性和一个也称为\“ ProductImageSource \”的属性（ImageSource类型）。 是否有意义？