WPF DataGrid DataBinding 不显示

Question

我当前的 WPF 应用程序中有一个 DataGrid，我想将它绑定到一个包含 ObservableCollection 的 ViewModel。用户可以在某些 TextBoxes 中输入搜索值，并且在输入被击中后，我正在对我们的数据库执行查询，以返回记录表。从这些记录中，我为 ObservableCollection 填充数据。我现在正在苦苦挣扎，因为数据网格没有显示数据。

我已经阅读了一堆关于绑定的帖子，但我仍然错过了一些我认为的东西。

Product.cs

public class Product : InotifyPropertyChanged, IEditableObject
{
    public string Title { get; set; } = "";

    //public Product()
    //{

    //}
    private ProductViewModel _productViewModel = new ProductViewModel();
    public ProductViewModel productViewModel { get { return _productViewModel; } set { _productViewModel = value; } }

    public DataTable ProductsTable { get; set; }

    public void GetProducts(string filter)
    {
        //< --doing some stuff to fill the table-->

        foreach (DataRow row in ProductsTable.Rows)
        {
            productViewModel.Products.Add(new Product
            {

                Title = (string)row["TITLE"],

            });
        }
    }
}

ProductViewModel.cs

public class ProductViewModel : INotifyPropertyChanged
{
    public event PropertyChangedEventHandler PropertyChanged;
    private Product _SelectedProduct;
    private ObservableCollection<Product> _Products = new ObservableCollection<Product>();
    public ObservableCollection<Product> Products { get { return _Products; } set { _Products = value; } }

    public ProductViewModel()
    {
    }

    public void NotifyPropertyChanged(string propertyName)
    {

        PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
    }
}

ProductWindow.xaml

<DataGrid 
    Name="ProductsGrid" 
    AutoGenerateColumns="False" 
    ItemsSource="{Binding Products, Mode=TwoWay, NotifyOnSourceUpdated=True}" 
    SelectedItem="{Binding SelectedProduct, Mode=TwoWay}"  
    CanUserAddRows="False" SelectionUnit="FullRow"  
    VerticalAlignment="Stretch" 
    Grid.Row="0" 
    Margin="10,10,10,10" 
    >
    <DataGrid.Columns>
        <DataGridTextColumn Binding="{Binding Title}" Header="Title"></DataGridTextColumn>
    </DataGrid.Columns>
</DataGrid>

ProductWindow.xaml.cs

    public partial class ProductWindow : Page
{
    public object DialogResult { get; private set; }
    //public ProductViewModel ProductViewModel;
    public ProductWindow()
    {

        InitializeComponent();

        DataContext = new ProductViewModel();//stackflow
        //var ProductViewModel = products.ProductViewModel;
        //ProductsGrid.DataContext = new ProductViewModel();

    }

    public ProductViewModel ViewModel => DataContext as ProductViewModel;

    private void OnKeydownHandler(object sender, KeyEventArgs e)
    {
        if (e.Key == Key.Enter)
        {
            var tb = sender as TextBox;
            Product products = new Product();
            string filter = "";//performing some ifelse to create filter
            products.GetProducts(filter);
            //ProductsGrid.DataContext = products.ProductsTable;
            //ProductsGrid.DataContext = products.productViewModel;

        }
        else if (e.Key == Key.Escape)
        {
            ProductsGrid.DataContext = null;
            foreach (TextBox tb in FindVisualChildren<TextBox>(this))
            {
                // do something with tb here
                tb.Text = "";
            }
        }
    }

}

Answer 1

如果DataContext 是ProductViewModel，并且填充了该ProductViewModel 的Products 集合，您将在DataGrid 中看到行。我已经测试过了。您提供的视图模型似乎没有任何行。

也就是说，你的设计有问题：

Product 创建一个ProductViewModel。 ProductViewModel 创建Product 的集合。正如我刚才所说，每个Product 创建一个ProductViewModel。它创建了Product 的集合。他们不断创造彼此，直到您获得StackOverflowException。如果您没有看到，您一定是从其他地方调用 GetProducts()。

但是Product 没有必要拥有ProductViewModel 的副本。这就像在汽车的每个车轮上添加一辆车。

所以让我们改为这样做：ProductViewModel 拥有Product 的集合。只是。我们将调用GetProducts() 以确保我们在网格中获得了一些项目。你的绑定没问题。你只是没有填充集合。

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

        DataContext = new ProductViewModel();
    }

    //  Now you can call ViewModel.GetProducts(filterString) from an event handler. 
    //  It would be more "correct" to use a Command, but let's take one step at a time. 
    public ProductViewModel ViewModel => DataContext as ProductViewModel;
}

视图模型

//  You didn't include any implementation of IEditableObject. I presume 
//  you can add that back in to this version of the class. 
public class Product : INotifyPropertyChanged, IEditableObject
{
    //  You weren't raising PropertyChanged here, or anywhere at all. 
    //  In every setter on a viewmodel, you need to do that. 
    private string _title = "";
    public string Title {
        get => _title;
        set
        {
            if (_title != value)
            {
                _title = value;
                NotifyPropertyChanged(nameof(Title));
            }
        }
    }

    public Product()
    {
    }

    public event PropertyChangedEventHandler PropertyChanged;

    public void NotifyPropertyChanged(string propertyName)
    {

        PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
    }
}

public class ProductViewModel : INotifyPropertyChanged
{
    public ProductViewModel()
    {
        GetProducts("");
    }

    public event PropertyChangedEventHandler PropertyChanged;
    private Product _SelectedProduct;

    public Product SelectedProduct
    {
        get { return _SelectedProduct; }
        set
        {
            if (value != _SelectedProduct)
            {
                _SelectedProduct = value;
                NotifyPropertyChanged(nameof(SelectedProduct));
            }
        }
    }


    public DataTable ProductsTable { get; set; }

    public void GetProducts(string filter)
    {
        //< --doing some stuff to fill the table-->

        Products.Clear();

        foreach (DataRow row in ProductsTable.Rows)
        {
            Products.Add(new Product
            {
                Title = (string)row["TITLE"],
            });
        }
    }

    private ObservableCollection<Product> _Products = new ObservableCollection<Product>();
    //  This setter MUST raise PropertyChanged. See the Title property above for example. 
    public ObservableCollection<Product> Products { get { return _Products; } private set { _Products = value; } }

    public void NotifyPropertyChanged(string propertyName)
    {
        PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
    }
}

更新

问题出在：您创建了一个新的Product，它创建了自己的ProductsViewModel。 没有任何东西绑定到该视图模型的任何属性。您填充了它的集合，而 DataGrid 不知道也不关心，因为您将它的 ItemsSource 绑定到了不同对象的属性。

所以请使用我上面的建议，尤其是窗口的ViewModel 属性。 我刚刚在 ProductsViewModel.GetProducts() 中进行了更改，您需要复制该更改：现在它在填充集合之前调用 Products.Clear()。

    if (e.Key == Key.Enter)
    {
        var tb = sender as TextBox;

        //  Don't create this
        //Product products = new Product();

        string filter = "";//performing some ifelse to create filter
        ViewModel.GetProducts(filter);

    }
    else if (e.Key == Key.Escape)
    {
        //  Setting the DataContext to null breaks everything. Never do that. 
        //ProductsGrid.DataContext = null;

        //  Instead, just clear the collection. It's an ObservableCollection so it will 
        //  notify the DataGrid that it was cleared. 
        ViewModel.Products.Clear();

        foreach (TextBox tb in FindVisualChildren<TextBox>(this))
        {
            // do something with tb here
            tb.Text = "";
        }
    }