WPF DataGridCellInfo DatePicker列的Item属性值

如何解决WPF DataGridCellInfo DatePicker列的Item属性值

在下面的WPF DataGrid中，以下代码成功返回所选行第一列中单元格的值。

对于第一个单元格，下面的数据项DataGridCellInfo.Item是一个TextBlock（默认值）：

DataGridCellInfo cellInfo = dgEvents.SelectedCells[0]; //cell in first column in selected row
string sSubject = (cellInfo.Column.GetCellContent(cellInfo.Item) as TextBlock).Text;

问题：下面的数据项cellInfo.Item应该是什么？该单元格确实具有日期值，但出现错误：cellInfo_1.Column.GetCellContent(cellInfo_1 .Item) as DatePicker returns null

DataGridCellInfo cellInfo_1 = dgEvents.SelectedCells[1]; //cell in second column in selected row
DateTime? mydatetime = (cellInfo_1.Column.GetCellContent(cellInfo_1 .Item) as DatePicker).SelectedDate;

备注：请注意，问题是要获取单元格中选定的新日期值，而不是有关单元格已绑定的旧值。

XAML ：

<Window x:Class="MyWPFProject.DataGrid_control.DataGridColumnsSample"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        Title="DataGridColumnsSample" Height="200" Width="300">
    <Grid Margin="10">
        <DataGrid Name="dgUsers" AutoGenerateColumns="False">
            <DataGrid.Columns>

                <DataGridTextColumn Header="Name" Binding="{Binding Name}" />

                <DataGridTemplateColumn Header="Birthday">
                    <DataGridTemplateColumn.CellTemplate>
                        <DataTemplate>
                            <DatePicker SelectedDate="{Binding Birthday}" BorderThickness="0" />
                        </DataTemplate>
                    </DataGridTemplateColumn.CellTemplate>
                </DataGridTemplateColumn>

            </DataGrid.Columns>
        </DataGrid>
    </Grid>
</Window>

解决方法

您根本不需要通过C＃代码与WPF中的控件进行交互。

相反，您可以将DataGrid绑定到基础集合并与该集合进行交互。

这是一个简单的示例，它如何工作。

数据类

public class User : INotifyPropertyChanged
{
    private string _name;
    private DateTime _birthday = DateTime.Today;

    public string Name
    {
        get => _name;
        set
        {
            _name = value;
            OnPropertyChanged();
        }
    }

    public DateTime Birthday
    {
        get => _birthday;
        set
        {
            _birthday = value;
            OnPropertyChanged();
        }
    }

    public event PropertyChangedEventHandler PropertyChanged;
    protected virtual void OnPropertyChanged([CallerMemberName] string propertyName = null)
        => PropertyChanged?.Invoke(this,new PropertyChangedEventArgs(propertyName));
}

如果更改了某些属性，则

INotifyPropertyChanged可以注释DataGrid。 DataGrid将自动更新其布局。

隐藏代码

public partial class MainWindow : Window,INotifyPropertyChanged
{
    private ObservableCollection<User> _users;
    public ObservableCollection<User> Users 
    { 
        get => _users;
        set 
        {
            _users = value;
            OnPropertyChanged();
        } 
    }

    private ICollectionView usersView;

    public MainWindow()
    {
        InitializeComponent();
        DataContext = this;
    }

    private void Button_Click(object sender,RoutedEventArgs e)
    {
        User selectedUser = usersView.CurrentItem as User;
        MessageBox.Show(selectedUser.Name + Environment.NewLine + selectedUser.Birthday);
    }

    private void Window_Loaded(object sender,RoutedEventArgs e)
    {
        InitUsers();
    }

    private void InitUsers()
    {
        Users = new ObservableCollection<User>();
        Users.Add(new User { Name = "John",Birthday = DateTime.Now });
        Users.Add(new User { Name = "Jane",Birthday = DateTime.Now });
        usersView = CollectionViewSource.GetDefaultView(Users);
    }

    public event PropertyChangedEventHandler PropertyChanged;
    protected virtual void OnPropertyChanged([CallerMemberName] string propertyName = null)
        => PropertyChanged?.Invoke(this,new PropertyChangedEventArgs(propertyName));
}

您可以从集合中添加/删除项目，重新分配Users属性，并以编程方式对数据进行任何处理。 DataGrid将与数据保持同步。

UI

<Window x:Class="WpfApp3.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
        xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
        xmlns:local="clr-namespace:WpfApp3"
        mc:Ignorable="d"
        Title="MainWindow" Height="450" Width="800" Loaded="Window_Loaded">
    <Grid>
        <Grid.RowDefinitions>
            <RowDefinition Height="Auto"/>
            <RowDefinition />
        </Grid.RowDefinitions>
        <StackPanel Orientation="Horizontal">
            <TextBox Margin="5" Width="300" Text="{Binding Users/Name,UpdateSourceTrigger=PropertyChanged}"/>
            <DatePicker SelectedDate="{Binding Users/Birthday,UpdateSourceTrigger=PropertyChanged}" Margin="5"/>
            <Button Content="Show selected" Click="Button_Click" Margin="5" Padding="10,0"/>
        </StackPanel>
        <DataGrid Grid.Row="1" Margin="5" AutoGenerateColumns="False" ItemsSource="{Binding Users}" IsSynchronizedWithCurrentItem="True">
            <DataGrid.Columns>
                <DataGridTextColumn Header="Name" Binding="{Binding Name,UpdateSourceTrigger=PropertyChanged}" Width="*"/>
                <DataGridTemplateColumn Header="Birthday" Width="200">
                    <DataGridTemplateColumn.CellTemplate>
                        <DataTemplate>
                            <DatePicker SelectedDate="{Binding Birthday,UpdateSourceTrigger=PropertyChanged}" BorderThickness="0" />
                        </DataTemplate>
                    </DataGridTemplateColumn.CellTemplate>
                </DataGridTemplateColumn>
            </DataGrid.Columns>
        </DataGrid>
    </Grid>
</Window>

确实，这不是实现“选定项”的唯一方法，但可以肯定地将这种确切方法直接用在零行C＃代码的UI中。

进一步建议的步骤是了解MVVM编程模式。

试玩示例，在有和没有UpdateSourceTrigger s的情况下尝试