An exception of type 'System.Reflection.TargetInvocation

我正在构建一个笔记应用程序。在笔记编辑页面上，当用户创建新的笔记和文本类型时，然后按手机的返回按钮，代码应该创建一个新的笔记，我尝试用新行替换回车。当我在应用中尝试这个时，我得到这个异常。类型为System.Reflection的未处理异常。TargetInvocationException'在System.Windows.ni.dll中发生，并打开一个新的文件选项卡，显示System.Windows.pdb未加载这是它中断

的代码

protected async override void OnNavigatedFrom(NavigationEventArgs e)
    {
        base.OnNavigatedFrom(e);
        // we are suppose to save the note, when user navigates away from the page
        ourNote.Note = editorTextBox.Text.Replace("'r", "'n");
        await App.ViewModel.UpdateNotes();
    }

有谁知道我错了什么吗?这是notemmodel类，ourNote变量就是这种类型。

public class NoteModel : INotifyPropertyChanged
{
    public event PropertyChangedEventHandler PropertyChanged;
    private void NotifyPropertyChanged(String propertyName)
    {
        PropertyChangedEventHandler handler = PropertyChanged;
        if (null != handler)
        {
            handler(this, new PropertyChangedEventArgs(propertyName));
        }
    }
    private string _id;
    public string ID 
    {
        get 
        { 
            return _id;
        }
        set 
        {
            // check to see if the value isn't the same with _id if not raise a propertychanged event via the method
            if (value != _id)
            {
                _id = value;
                NotifyPropertyChanged("ID");
            }
        } 
    }
    private string _modDate;
    public string ModifiedDate
    {
        get
        {
            return _modDate;
        }
        set
        {
            // check to see if the value isn't the same with _id if not raise a propertychanged event via the method
            if (value != _modDate)
            {
                _modDate = value;
                NotifyPropertyChanged("ModifiedDate");
            }
        }
    }
    private string _note;
    public string Note
    {
        get
        {
            return _note;
        }
        set
        {
            // check to see if the value isn't the same with _id if not raise a propertychanged event via the method
            if (value != _note)
            {
                _note = value;
                string[] lines = _note.Split(''n'); // we change this from ''r' to ''n' because of winRT serializaiton and deserialization ends up with line feeds only, removes carriage returns
                if (lines.Length > 0)
                {
                    FirstLine = lines[0]; // we removed .Replace("'n", ""); since no more carriage returns
                }
                else
                {
                    // what if there is no first line
                    FirstLine = "(empty)";
                }
                NotifyPropertyChanged("Note");
            }
        }
    }
    private string _firstLine;
    public string FirstLine
    {
        get
        {
            return _firstLine;
        }
        set
        {
            // check to see if the value isn't the same with _id if not raise a propertychanged event via the method
            if (value != _firstLine)
            {
                _firstLine = value;
                NotifyPropertyChanged("FirstLine");
            }
        }
    }
}