Question

我是mvvm的新手，我尝试使用方法＆＃34; SaveAll＆＃34;将observablecollection保存到数据库中，我想通过后面的代码中的buttonclick事件调用它看来，但它似乎不可能。

这是我到目前为止的代码。 NetworkViewModel.SaveAll（person）

中发生错误

namespace MyProject
{
    using Model;

    public class NetworkViewModel : INotifyPropertyChanged
    {
        private ObservableCollection<Person> _networkList1 = new ObservableCollection<Person>();
        public ObservableCollection<Person> NetworkList1
        {
            get { return _networkList1; }
            set { _networkList1 = value; RaisePropertyChanged("NetworkList1"); }
        }

        public NetworkViewModel()
        { }

        public void SaveAll(Person person)
        {
            String dbConnectionString = @"Data Source =movieprepper.sqlite;";

            SQLiteConnection sqliteCon = new SQLiteConnection(dbConnectionString);
            sqliteCon.Open();
            var transaction = sqliteCon.BeginTransaction();

            String DeleteQuery = "delete from networking";
            SQLiteCommand DeleteCommand = new SQLiteCommand(DeleteQuery, sqliteCon);
            DeleteCommand.ExecuteNonQuery();

            foreach (Person p in _networkList1)
            {
                String Query = "insert into networking (firstname, lastname) values ('" + p.FirstName + "','" + p.LastName + "')";
                SQLiteCommand Command = new SQLiteCommand(Query, sqliteCon);
                Command.ExecuteNonQuery();
            }

            transaction.Commit();
            sqliteCon.Close();
        }
    }
}

在代码隐藏视图中我得到了这个

namespace MyProject
{
   public partial class Networking : Window
   {
      public Networking()
      {
        InitializeComponent();
        this.DataContext = new NetworkViewModel();
       }

    private void btn_save_network_Click(object sender, RoutedEventArgs e)
    {
        NetworkViewModel.SaveAll(Person);// This is where error occurs
    }
   }
}

这似乎无法正常工作

"an object reference is required for the non static field, method or property"

我对这一切都很陌生，并试着在我走的时候解决问题，但似乎无法找到这种特殊情况的答案。

Answer 1

技术上的正确答案是NetworkViewModel是一个类名，你需要一个类实例来调用你的方法。例如，您之前放入DataContext的那个。

((NetworkViewModel)this.DataContext).SaveAll(Person);

但是最好阅读一篇关于Microsoft希望您使用WPF的command pattern。 MVVM比后面的代码好多了。

Answer 2

如上所述，您应该遵循命令模式。您可以通过更新您的视图模型来执行此操作：

    public class NetworkViewModel : INotifyPropertyChanged, ICommand
    {
        private ObservableCollection<Person> _networkList1 = new ObservableCollection<Person>();


        public event EventHandler CanExecuteChanged;

        public ObservableCollection<Person> NetworkList1
        {
            get { return _networkList1; }
            set { _networkList1 = value; RaisePropertyChanged("NetworkList1"); }
        }

        public NetworkViewModel()
        { }

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

        public void Execute(object parameter)
        {
            String dbConnectionString = @"Data Source =movieprepper.sqlite;";

            SQLiteConnection sqliteCon = new SQLiteConnection(dbConnectionString);
            sqliteCon.Open();
            var transaction = sqliteCon.BeginTransaction();

            String DeleteQuery = "delete from networking";
            SQLiteCommand DeleteCommand = new SQLiteCommand(DeleteQuery, sqliteCon);
            DeleteCommand.ExecuteNonQuery();

            foreach (Person p in _networkList1)
            {
                String Query = "insert into networking (firstname, lastname) values ('" + p.FirstName + "','" + p.LastName + "')";
                SQLiteCommand Command = new SQLiteCommand(Query, sqliteCon);
                Command.ExecuteNonQuery();
            }

            transaction.Commit();
            sqliteCon.Close();
        }
    }

由于您的SaveAll方法实际上并未使用Person（您在集合中循环遍历所有这些方法），因此我不会传递People参数。

然后，不要让你的代码隐藏调用方法。您可以将按钮绑定到视图模型。你的XAML看起来像这样：

<Button x:Name="SavButton"
        Command="{Binding }"
        Content="Save All People" />

如果您想要保存您选择的特定人员，您也可以在绑定中传递它们

<Button x:Name="SavButton"
        Command="{Binding }"
        CommandParameter="{Binding Path=SelectedPerson}"
        Content="Save All People" />

public void Execute(object person)
{
     People p = (People)person;
     // save......
}

假设您有数据将所选人员绑定到名为SelectedPerson的视图模型上的属性。

希望这有帮助。

在视图

2 个答案: