WPF中DataGrid选中行无法写入SQL表的问题求助

核心问题分析 #

• 按钮始终启用：RelayCommand的CanExecute状态未随SelectedItems的变化而自动更新
• 方法未按预期触发：DataGrid选中项未正确同步到ViewModel的SelectedItems集合，且数据写入逻辑缺少提交操作

分步解决 #

1. 修复DataGrid选中项与ViewModel的同步问题 #

DataGrid的SelectedItems是只读集合，直接绑定无法实现双向同步，可通过以下两种方式解决：

方式一：通过SelectionChanged事件手动同步

在XAML的DataGrid中添加事件绑定：

<DataGrid ItemsSource="{Binding DataGridItems}"
          SelectionMode="Extended"
          SelectionChanged="DataGrid_SelectionChanged"/>

在视图后台实现事件处理逻辑：

private void DataGrid_SelectionChanged(object sender, SelectionChangedEventArgs e)
{
    var viewModel = DataContext as DataGridViewModel;
    viewModel.SelectedItems.Clear();
    foreach (var item in (sender as DataGrid).SelectedItems)
    {
        viewModel.SelectedItems.Add(item as States);
    }
}

方式二：使用附加属性（MVVM友好方案）

创建附加属性来实现SelectedItems的双向绑定：

public class DataGridSelectionHelper
{
    public static readonly DependencyProperty SelectedItemsProperty =
        DependencyProperty.RegisterAttached("SelectedItems", typeof(ObservableCollection<object>), typeof(DataGridSelectionHelper),
            new PropertyMetadata(null, OnSelectedItemsChanged));

    public static ObservableCollection<object> GetSelectedItems(DependencyObject obj)
    {
        return (ObservableCollection<object>)obj.GetValue(SelectedItemsProperty);
    }

    public static void SetSelectedItems(DependencyObject obj, ObservableCollection<object> value)
    {
        obj.SetValue(SelectedItemsProperty, value);
    }

    private static void OnSelectedItemsChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
    {
        if (d is DataGrid dataGrid)
        {
            dataGrid.SelectionChanged += (s, args) =>
            {
                var selectedItems = GetSelectedItems(dataGrid);
                selectedItems.Clear();
                foreach (var item in dataGrid.SelectedItems)
                {
                    selectedItems.Add(item);
                }
            };
        }
    }
}

在XAML中引用该附加属性：

<DataGrid ItemsSource="{Binding DataGridItems}"
          local:DataGridSelectionHelper.SelectedItems="{Binding SelectedItems}"/>

2. 修复RelayCommand的CanExecute状态更新问题 #

当SelectedItems集合内容变化时，需要主动通知RelayCommand重新评估CanExecute状态：

首先确保你的RelayCommand实现包含触发CanExecuteChanged的方法：

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

    public event EventHandler CanExecuteChanged;

    public RelayCommand(Action<object> execute, Func<object, bool> canExecute = null)
    {
        _execute = execute ?? throw new ArgumentNullException(nameof(execute));
        _canExecute = canExecute;
    }

    public bool CanExecute(object parameter)
    {
        return _canExecute == null || _canExecute(parameter);
    }

    public void Execute(object parameter)
    {
        _execute(parameter);
    }

    public void RaiseCanExecuteChanged()
    {
        CanExecuteChanged?.Invoke(this, EventArgs.Empty);
    }
}

然后在ViewModel中监听SelectedItems的集合变化，触发命令状态更新：

public DataGridViewModel()
{
    DataGridItems = new ObservableCollection<States>();
    SelectedItems = new ObservableCollection<States>();
    // 监听集合元素变化事件
    SelectedItems.CollectionChanged += SelectedItems_CollectionChanged;
    
    LoadDataFromDatabase();
    SendSelectedRowsToSQLCommand = new RelayCommand(SendSelectedRowsToSQL, CanSendSelectedRows);
}

private void SelectedItems_CollectionChanged(object sender, NotifyCollectionChangedEventArgs e)
{
    // 通知命令重新评估CanExecute状态
    (SendSelectedRowsToSQLCommand as RelayCommand)?.RaiseCanExecuteChanged();
}

3. 修复数据写入SQL的逻辑问题 #

SendSelectedRowsToSQL方法中缺少SaveChanges()调用，导致数据仅在内存中添加，未提交到数据库：

public void SendSelectedRowsToSQL(object parameter)
{
    using (var context = new DbProjectEntities())
    {
        foreach (var item in SelectedItems)
        {
            context.orderedStateTbl.Add(new orderedStateTbl
            {
                orderStateId = item.StateID,
                oStateName = item.StateName
            });
        }
        // 添加此行提交数据库更改
        context.SaveChanges();
    }
}

验证要点 #

• 确认DataGrid的SelectionMode设置为Single或Extended（默认值为Single）
• 检查ViewModel的SelectedItems在选中行时是否正确添加了对应元素
• 测试按钮状态：未选中行时禁用，选中后启用；点击按钮后验证数据是否成功写入SQL表

内容的提问来源于stack exchange，提问作者farzad