WPF可编辑的主-细节与数据网格更新保存

我对WPF非常陌生，所以我想我应该从简单的东西开始:一个允许用户管理用户的窗口。该窗口包含一个DataGrid以及几个用于添加或编辑用户的输入控件。当用户在网格中选择一条记录时，数据将绑定到输入控件。然后，用户可以进行所需的更改&点击"保存"按钮保存更改。

然而，发生的事情是，一旦用户在其中一个输入控件中进行更改，在单击"保存"按钮之前，DataGrid中相应的数据也得到更新。我希望DataGrid只在用户单击"保存"后更新。

下面是视图的XAML:

<Window x:Class="LearnWPF.Views.AdminUser"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:vms="clr-namespace:LearnWPF.ViewModels"
        Title="User Administration" Height="400" Width="450" 
        ResizeMode="NoResize">
    <Window.DataContext>
        <vms:UserViewModel />
    </Window.DataContext>
    <StackPanel>
        <GroupBox x:Name="grpDetails" Header="User Details" DataContext="{Binding CurrentUser, Mode=OneWay}">
            <Grid>
                <Grid.RowDefinitions>
                    <RowDefinition Height="Auto" />
                    <RowDefinition Height="Auto" />
                    <RowDefinition Height="Auto" />
                    <RowDefinition Height="Auto" />
                    <RowDefinition Height="Auto" />
                    <RowDefinition Height="*" />
                </Grid.RowDefinitions>
                <Grid.ColumnDefinitions>
                    <ColumnDefinition />
                    <ColumnDefinition />
                </Grid.ColumnDefinitions>
                <Label Grid.Column="0" Grid.Row="0">First Name:</Label>
                <TextBox Grid.Column="1" Grid.Row="0" Style="{StaticResource TextBox}" Text="{Binding FirstName}"></TextBox>
                <Label Grid.Column="0" Grid.Row="1">Surname:</Label>
                <TextBox Grid.Column="1" Grid.Row="1" Style="{StaticResource TextBox}" Text="{Binding LastName}"></TextBox>
                <Label Grid.Column="0" Grid.Row="2">Username:</Label>
                <TextBox Grid.Column="1" Grid.Row="2" Style="{StaticResource TextBox}" Text="{Binding Username}"></TextBox>
                <Label Grid.Column="0" Grid.Row="3">Password:</Label>
                <PasswordBox Grid.Column="1" Grid.Row="3" Style="{StaticResource PasswordBox}"></PasswordBox>
                <Label Grid.Column="0" Grid.Row="4">Confirm Password:</Label>
                <PasswordBox Grid.Column="1" Grid.Row="4" Style="{StaticResource PasswordBox}"></PasswordBox>
            </Grid>
        </GroupBox>
        <StackPanel Orientation="Horizontal">
            <Button Style="{StaticResource Button}" Command="{Binding SaveCommand}" CommandParameter="{Binding CurrentUser}">Save</Button>
            <Button Style="{StaticResource Button}">Cancel</Button>
        </StackPanel>
        <DataGrid x:Name="grdUsers" AutoGenerateColumns="False" CanUserAddRows="False" CanUserResizeRows="False"
                  Style="{StaticResource DataGrid}" ItemsSource="{Binding Users}" SelectedItem="{Binding CurrentUser, Mode=OneWayToSource}">
            <DataGrid.Columns>
                <DataGridTextColumn Header="Full Name" IsReadOnly="True" Binding="{Binding FullName}" Width="2*"></DataGridTextColumn>
                <DataGridTextColumn Header="Username" IsReadOnly="True" Binding="{Binding Username}" Width="*"></DataGridTextColumn>
            </DataGrid.Columns>
        </DataGrid>
    </StackPanel>
</Window>

模型中没有什么特别的东西(基类仅仅实现了INotifyPropertyChanged接口&触发关联事件):

public class UserModel : PropertyChangedBase
{
    private int _id;
    public int Id
    {
        get { return _id; }
        set
        {
            _id = value;
            RaisePropertyChanged("Id");
        }
    }
    private string _firstName;
    public string FirstName
    {
        get { return _firstName; }
        set
        {
            _firstName = value;
            RaisePropertyChanged("FirstName");
            RaisePropertyChanged("FullName");
        }
    }
    private string _lastName;
    public string LastName
    {
        get { return _lastName; }
        set
        {
            _lastName = value;
            RaisePropertyChanged("LastName");
            RaisePropertyChanged("FullName");
        }
    }
    private string _username;
    public string Username
    {
        get { return _username; }
        set
        {
            _username = value;
            RaisePropertyChanged("Username");
        }
    }
    public string FullName
    {
        get { return String.Format("{0} {1}", FirstName, LastName); }
    }
}

ViewModel (IRemoteStore提供对底层记录存储的访问):

public class UserViewModel : PropertyChangedBase
{
    private IRemoteStore _remoteStore = Bootstrapper.RemoteDataStore;
    private ICommand _saveCmd;
    public UserViewModel()
    {
        Users = new ObservableCollection<UserModel>();
        foreach (var user in _remoteStore.GetUsers()) {
            Users.Add(user);
        }
        _saveCmd = new SaveCommand<UserModel>((model) => {
            Users[Users.IndexOf(Users.First(e => e.Id == model.Id))] = model;
        });
    }
    public ICommand SaveCommand
    {
        get { return _saveCmd; }
    }
    public ObservableCollection<UserModel> Users { get; set; }
    private UserModel _currentUser;
    public UserModel CurrentUser
    {
        get { return _currentUser; }
        set
        {
            _currentUser = value;
            RaisePropertyChanged("CurrentUser");
        }
    }
}

为了完整起见，这里是我的Save ICommand的实现(这实际上还没有坚持任何东西，因为我想让数据绑定首先正确工作):

public class SaveCommand<T> : ICommand
{
    private readonly Action<T> _saved;
    public SaveCommand(Action<T> saved)
    {
        _saved = saved;
    }
    public bool CanExecute(object parameter)
    {
        return true;
    }
    public event EventHandler CanExecuteChanged;
    public void Execute(object parameter)
    {
        _saved((T)parameter);
    }
}

显而易见，我希望使用纯MVVM模式实现这一点。我尝试将DataGrid中的绑定设置为OneWay，但这会导致更改未反映在网格中(尽管添加了新条目)。

我也看了一下这个SO问题，它建议在ViewModel上使用"selected"属性。我最初的实现，如上所述，已经有了这样一个属性(称为"CurrentUser")，但是在当前的绑定配置中，网格仍然会随着用户的更改而更新。

任何帮助都将是非常感激的，因为我已经为这个问题绞尽脑汁好几个小时了。如果我遗漏了什么，请评论&我会更新帖子的。谢谢你。

Text="{Binding UserName}"></TextBox>

private string _username;
public string Username
{
    get { return _username; }
    set
    {
        _username = value;
        RaisePropertyChanged("Username"); // notification
    }
}

<DataGridTextColumn Header="Username" IsReadOnly="True" Binding="{Binding Username}" Width="*"></DataGridTextColumn>

<GroupBox x:Name="GroupBoxDetails" Header="User Details" DataContext="{Binding Path=TemporarySelectedUser, Mode=TwoWay, UpdateSourceTrigger=LostFocus}">
...
<Button Content="Save"
                    Command="{Binding Path=SaveCommand}"
                    CommandParameter="{Binding Path=TemporarySelectedUser}"/> // CommandParameter is optional if you'll use SaveCommand with no input members.

...
public UserModel TemporarySelectedUser { get; private set; }
...
TemporarySelectedUser = new UserModel(); // once in the constructor.
...
private UserModel _currentUser;
public UserModel CurrentUser
{
    get { return _currentUser; }
    set
    {
        _currentUser = value;
        if (value != null)
            value.CopyTo(TemporarySelectedUser);
        RaisePropertyChanged("CurrentUser");
    }
}
...
private ICommand _saveCommand;
public ICommand SaveCommand
{
    get
    {
        return _saveCommand ??
                (_saveCommand = new Command<UserModel>(SaveExecute));
    }
}
public void SaveExecute(UserModel updatedUser)
{
    UserModel oldUser = Users[
        Users.IndexOf(
            Users.First(value => value.Id == updatedUser.Id))
        ];
    // updatedUser is always TemporarySelectedUser.
    updatedUser.CopyTo(oldUser);
}
...

public void CopyTo(UserModel target)
{
    if (target == null)
        throw new ArgumentNullException();
    target.FirstName = this.FirstName;
    target.LastName = this.LastName;
    target.Username = this.Username;
    target.Id = this.Id;
}