c# - 如何仅从 ViewModel 以编程方式突出显示 DataGrid 行？

Question

SelectedItem 属性绑定(bind)不会导致其 DataGrid 行在初始加载时突出显示。

我有一个绑定(bind)到 SelectedItem 的 DataGrid，在我再次单击它之前它不会突出显示。我想我有一个操作顺序问题——因为所有 ViewModel 代码都在 View 呈现之前运行。单击一行(即使是已在 SelectedAccount Prop 中的同一行)后它工作正常，但我需要能够突出显示 VM 中的一行。

我可以轻松验证 SelectedAccount 属性不为空，因为还有其他 ViewModel 通过 PubSubEvents 显示它的值。

我已经尝试了几种解决方法，到目前为止我唯一能够让它工作的方法感觉很脏:

using ApplicationName.UI.ViewModels;
public partial class AccountsView : UserControl
{
    public AccountsView()
    {
        InitializeComponent();
        Loaded += AccountsView_Loaded;
    }

    private void AccountsView_Loaded(object sender, RoutedEventArgs e)
    {
        AccountsViewModel viewModel = (AccountsViewModel)DataContext;
        AccountsDataGrid.SelectedItem = viewModel.SelectedAccount;
        AccountsDataGrid.Focus();
        UpdateLayout();
    }   
}

我不喜欢这样，因为它会导致 OnPropertyChanged 事件触发两次，一次是在 View 加载之前，一次是在上述 hack 之后。这会触发 SQL 调用，所以我想避免这种情况。我还认为 MVVM 的目的是将 View 与 View 模型分离，但也许我没有像我想的那样理解这一点。

这是 DataGrid 的 XAML:

<ScrollViewer Grid.Row="1"
              Grid.Column="0"
              Grid.ColumnSpan="3"
              Margin="5,0">
    <DataGrid Name="AccountsDataGrid"
              ItemsSource="{Binding Accounts}"
              SelectedItem="{Binding SelectedAccount}"
              AutoGenerateColumns="False"
              CanUserResizeColumns="True"
              SelectionMode="Single"
              SelectionUnit="FullRow">
        <DataGrid.Columns>
            <DataGridTextColumn Header="ClinicId" 
                                TextBlock.TextAlignment="Center"
                                Width="75"
                                Binding="{Binding ClinicId}" />
            <DataGridTextColumn Header="Account#"
                                Width="75"
                                Binding="{Binding AccountNumber}"/>
            <DataGridTextColumn Header="LastName"
                                Width="1*"
                                Binding="{Binding LastName}" />
            <DataGridTextColumn Header="FirstName"
                                Width="1*"
                                Binding="{Binding FirstName}" />
            <DataGridTextColumn Header="Balance"
                                Width="Auto"
                                Binding="{Binding Balance}" />
            <DataGridTextColumn Header="Follow Up"
                                Width="100"
                                Binding="{Binding FollowUpDate}"/>
        </DataGrid.Columns>
    </DataGrid>
</ScrollViewer>

还有 ViewModel 中的初始 Load 方法，这是我要设置突出显示行的地方。

public void Load()
{
    RefreshGrid();
    SelectedAccount = Accounts.First();
    _accountId = SelectedAccount.Id;
}

编辑

这个问题很微妙，但现在很有意义。

private Account _selectedAccount;

public Account SelectedAccount
{
    get => _selectedAccount;
    set => SetSelectedAccount(value);
}

private void SetSelectedAccount(Account value)
{
    _selectedAccount = value;
    OnPropertyChanged("_selectedAccount");  // <= whoops
    if (_selectedAccount != null)
        OnAccountSelected(
           _selectedAccount.PrimaryKeyFields);
}

为私有(private)属性引发此事件没有意义，因为 View 看不到它，并且绑定(bind)到 SelectedAccount。将其更改为 OnPropertyChanged("SelectedAccount") 就可以了。

Answer 1

实现 INotifyPropertyChanged 应该足够了，这段代码对我有效，我正在使用 Command 调用 Load() 方法但您的代码中可能不需要它。

ViewModel 和 C# 代码:

public partial class MainWindow : Window
{
    public MainWindow()
    {
        InitializeComponent();

        DataContext = new ViewModel();
    }
}

public class ViewModel : INotifyPropertyChanged
{
    public event PropertyChangedEventHandler PropertyChanged;

    public ViewModel()
    {
        Accounts = new List<Account>();

        Accounts.AddRange(
            Enumerable.Range(0, 10)
                .Select(r => new Account
                {
                    AccountNumber = r,
                    FirstName = $"First{r}",
                    LastName = $"Last{r}"
                }));

        LoadedCommand = new WpfCommand((param) => Load());
    }

    private void Load()
    {
        SelectedAccount = Accounts.FirstOrDefault(a => a.AccountNumber == 2);
    }

    public WpfCommand LoadedCommand { get; set; }

    public List<Account> Accounts { get; set; }

    private Account _selectedAccount = null;
    public Account SelectedAccount
    {
        get { return _selectedAccount; }
        set
        {
            _selectedAccount = value;
            PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(nameof(SelectedAccount)));
        }
    }
}

public class Account
{
    public int AccountNumber { get; set; }
    public string FirstName { get; set; }
    public string LastName { get; set; }
}

public class WpfCommand : ICommand
{
    private Action<object> _execute;
    private Func<object, bool> _canExecute;

    public event EventHandler CanExecuteChanged;

    public WpfCommand(Action<object> execute, Func<object, bool> canExecute = null)
    {
        _execute = execute;
        _canExecute = canExecute;
    }

    public void Execute(object parameter)
    {
        _execute?.Invoke(parameter);
    }

    public bool CanExecute(object parameter)
    {
        return _canExecute?.Invoke(parameter) ?? true;
    }
}

XAML:

   <!--System.Windows.Interactivity.WPF nuget package-->
   xmlns:i="http://schemas.microsoft.com/expression/2010/interactivity"

    <DataGrid 
        ItemsSource="{Binding Accounts}"
        SelectedItem="{Binding SelectedAccount}">

        <i:Interaction.Triggers>
            <i:EventTrigger EventName="Loaded">
                <i:InvokeCommandAction Command="{Binding LoadedCommand}" />
            </i:EventTrigger>
        </i:Interaction.Triggers>

        <DataGrid.Columns>
            <DataGridTextColumn Binding="{Binding AccountNumber}"/>
            <DataGridTextColumn Binding="{Binding LastName}" />
            <DataGridTextColumn Binding="{Binding FirstName}" />
        </DataGrid.Columns>
    </DataGrid>