Question

如何在MVVM ListView中保存和加载ObservableCollection。错误低于..

未处理的类型＆＃39; System.InvalidOperationException＆＃39;   发生在System.Xml.dll
中
其他信息：Database_MVVM.Model.UserData不能   序列化，因为它没有无参数构造函数。

在我的MainViewModel

中

public ObservableCollection<UserData> _userDataCollection = new ObservableCollection<UserData>();

public ObservableCollection<UserData> UserDataCollection
        {
            get { return _userDataCollection; }
            set { _userDataCollection = value; }
        }

public ICommand SaveCommand
        {
            get
            {
                if (saveCommand == null)
                {
                    saveCommand = new DelegateCommand(Save);
                }
                return saveCommand;
            }
        }

private void Save()
{
    XmlSerializer serializer = new XmlSerializer(typeof(ObservableCollection<UserData>));

   using (var sw = new StreamWriter("output.txt"))
   {
       serializer.Serialize(sw, UserDataCollection);
       sw.Close();
   }
}

我的模特

public class UserData
    {
        #region Declarations

        private string _theEnteredData;
        private string _theRandomData;

        public UserData(string theEnteredData, string theRandomData)
        {
            this._theEnteredData = theEnteredData;
            this._theRandomData = theRandomData; 
        }
        #endregion

        #region Properties
        public string theEnteredData
        {
            get { return _theEnteredData; }
            set { _theEnteredData = value; }
        }

        public string theRandomData
        {
            get { return _theRandomData; }
            set { _theRandomData = value; }
        }
        #endregion
    }

在My Command中，我创建了DelegateCommand.cs

 public class DelegateCommand : ICommand
    {
        private readonly Action _action;

        public DelegateCommand(Action action)
        {
            this._action = action;
        }

        public bool CanExecute(object parameter)
        {
            return true;
        }

        public void Execute(object parameter)
        {
            this._action();
        }

        public event EventHandler CanExecuteChanged
        {
            add
            {
            }
            remove
            {
            }
        }

我在listview中保存项目后会自动清除。加载保存文件（txt文件）并加载它，而不使用openfiledialogbox和openfiledialog框。

我尝试使用streamwriter和foreach循环将其保存为文本文件，但我失败了我只是刚接触MVVM并仍在尝试学习它。

Answer 1

正如异常所述：UserData没有默认构造函数。

序列化程序使用默认构造函数来创建实例，因此如果缺少序列化程序，则无法创建对象。

添加默认构造函数：

public class UserData
{
    #region Declarations

    private string _theEnteredData;
    private string _theRandomData;

    public UserData()
    {
    }

    public UserData(string theEnteredData, string theRandomData)
    {
        this._theEnteredData = theEnteredData;
        this._theRandomData = theRandomData; 
    }
    #endregion

    #region Properties
    public string theEnteredData
    {
        get { return _theEnteredData; }
        set { _theEnteredData = value; }
    }

    public string theRandomData
    {
        get { return _theRandomData; }
        set { _theRandomData = value; }
    }
    #endregion
}

Answer 2

XmlSerializer获取一个对象并将其转换为xml，您可以将其保存到文本文件中。然后可以在需要时对其进行反序列化。

    public void SaveToFile()
    {
        XmlSerializer serializer = new XmlSerializer(typeof(ObservableCollection<UserData>));

        using (var sw = new StreamWriter("output.txt"))
        {
            serializer.Serialize(sw, UserDataCollection);
            sw.Close();
        }

    }

    public void LoadFromFile()
    {
        XmlSerializer serializer = new XmlSerializer(typeof(ObservableCollection<UserData>));

        using (Stream reader = new FileStream("output.txt", FileMode.Open))
        {
            // Call the Deserialize method to restore the object's state.
            UserDataCollection = (ObservableCollection<UserData>)serializer.Deserialize(reader);
        }
    }

Answer 3

您可以在mainViewModel中尝试此设置吗？

public ObservableCollection<UserData> _userDataCollection = new ObservableCollection<UserData>();
public ObservableCollection<UserData> UserDataCollection
{
get { return _userDataCollection; }
set
{
_userDataCollection = value;
RaisePropertyChanged(() => UserDataCollection);
}
}

public ICommand SaveCommand
{
get
{
//Bind UserDataCollection to your List View
LoadDataToListView();
}
}

private void LoadDataToListView()
{
using (var sw = new StreamWriter("output.txt"))
{
//load in UserDataCollection your data from textfile in here
 sw.Close();
}
return UserDataCollection ;
}

只需从文本文件中加载UserDataCollection中的数据，然后将其绑定到列表视图即可。您将使用相同的模型。这对我很好。我希望我帮助你。祝你好运。

您的模型更新

public class UserData
    {
        #region Declarations

        private string _theEnteredData;
        private string _theRandomData;

        public UserData(string theEnteredData, string theRandomData)
        {
            theEnteredData = theEnteredData;
            theRandomData = theRandomData; 
        }
        public UserData(){}
        #endregion

        #region Properties
        public string theEnteredData
        {
            get { return _theEnteredData; }
            set { _theEnteredData = value; }
        }

        public string theRandomData
        {
            get { return _theRandomData; }
            set { _theRandomData = value; }
        }
        #endregion
    }

使用MVVM保存/加载Observable Collection

3 个答案: