.net – ‘System.Windows.Data.Binding’类型的对象无法转换为’System.String’类型

[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,如果我在我的xaml中的某个地方使用此控件,那么如果我执行此操作：

<controls:InformationBubble 
        Productimagesource="{Binding SELEctedItem.NormalImagesourcE}"
        ProducttitleText="Test title"
        "/>

但是,如果我尝试将数据绑定到viewmodel中的SELEctedItem对象的title属性的数据：

<controls:InformationBubble 
            Productimagesource="{Binding SELEctedItem.NormalImagesourcE}"
            ProducttitleText="{Binding SELEctedItem.title,Mode=TwoWay"
            "/>

我得到’System.Windows.Data.binding’类型的对象不能转换为’System.String’类型. TextBlock的text属性是DependencyProperty,所​​以我必须在这里遗漏一些明显的东西.

非常感谢任何帮助或见解.

短剑的一种