按钮命令上的 WPF 新 DataGrid 行参数 NULL

Question

这里是 WPF 的新手。我正在构建的第一个应用程序使用 RelayCommand 和 DataGrid 和 ButtonCommand 来编辑或输入新用户。对于在打开的行中输入值的新用户，按下时会调用 OneditButtonCommand，但作为参数传递的 Item 始终为 null。我尝试在 XAML 中切换 Command 和 CommandParameter 的顺序，以查看是否在定义的参数之前设置了 Command，但按钮命令对象仍然为 NULL。有什么解决方案跳出来给任何人吗？非常感谢！

视图模型：

public partial class UsersViewModel : INotifyPropertyChanged
{
    public RelayCommand<UserViewModel> editButton_Click_Command { get; set; }

    public UsersViewModel()
    {
        editButton_Click_Command = new RelayCommand<UserViewModel>(OneditButton_Click_Command);

        this.Users = new ObservableCollection<UserViewModel>();

        this.Users.Add(new UserViewModel() { FirstName = "John", LastName = "Doe", EMail = "JohnDoe@yahoo.com", EndDate = new DateTime(2016,2,1), Position = "Developer", UserID = 0 });
    }

    private ObservableCollection<UserViewModel> _Users;
    public ObservableCollection<UserViewModel> Users
    {
        get { return _Users; }
        set { _Users = value; NotifyPropertyChanged("Users"); }
    }

    private void OneditButton_Click_Command(UserViewModel obj)
    {
        //Parameter object is always NULL here!!!
    }

    public event PropertyChangedEventHandler PropertyChanged;

    private void NotifyPropertyChanged(String info)
    {
        if (PropertyChanged != null)
        {
            PropertyChanged(this, new PropertyChangedEventArgs(info));
        }
    }
}

XAML：

<Window x:Name="Base_V"
    x:Class="DbEntities.UsersWindow"
    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:DbEntities"
    xmlns:ViewModels="clr-namespace:DbEntities"
    xmlns:staticData="clr-namespace:DbEntities"
    mc:Ignorable="d"
    Title="UsersWindow" Height="Auto" Width="900">
    <Window.Resources>
        <staticData:PositionsList x:Key="PositionsList" />
    </Window.Resources>
    <Window.DataContext>
        <ViewModels:UsersViewModel/>
    </Window.DataContext>
    <Grid>
        <FrameworkElement x:Name="dummyElement" Visibility="Collapsed" />
        <DataGrid Name="DataGrid1" ItemsSource="{Binding Users}" HorizontalAlignment="Stretch" HorizontalContentAlignment="Stretch"
              ColumnWidth="*" AutoGenerateColumns="False">
            <DataGrid.Columns>
                <DataGridTemplateColumn>
                    <DataGridTemplateColumn.CellTemplate>
                        <DataTemplate>
                            <Button Command="{Binding DataContext.editButton_Click_Command, ElementName=Base_V}" CommandParameter="{Binding}" >Edit</Button>
                        </DataTemplate>
                    </DataGridTemplateColumn.CellTemplate>
                </DataGridTemplateColumn>
                <DataGridTextColumn Header="User ID" Binding="{Binding UserID}" IsReadOnly="True" />
                <DataGridTextColumn Header="Last Name" Binding="{Binding LastName}" />
                <DataGridTextColumn Header="First Name" Binding="{Binding FirstName}" />
                <DataGridTextColumn Header="E-Mail" Binding="{Binding EMail}" />
                <DataGridTemplateColumn>
                    <DataGridTemplateColumn.HeaderTemplate>
                        <DataTemplate>
                            <Label Content="Position" />
                        </DataTemplate>
                    </DataGridTemplateColumn.HeaderTemplate>
                    <DataGridTemplateColumn.CellTemplate>
                        <DataTemplate>
                            <ComboBox ItemsSource="{StaticResource PositionsList}" SelectedItem="{Binding Position}" />
                        </DataTemplate>
                    </DataGridTemplateColumn.CellTemplate>
                </DataGridTemplateColumn>
                <DataGridTextColumn Header="End Date" Binding="{Binding EndDate, StringFormat={}{0:MM/dd/yyyy}}" />
            </DataGrid.Columns>
        </DataGrid>
    </Grid>
</Window>

RelayCommand 取自这里：http://www.kellydun.com/wpf-relaycommand-with-parameter/

编辑： 建议发布 UserViewModel 以查看问题是否可以在此处或其他问题中解决。还从数据库中提取了几个测试用户。

用户视图模型：

public class UserViewModel : INotifyPropertyChanged
{
    private string _FirstName;
    public string FirstName
    {
        get { return _FirstName; }
        set { _FirstName = value; NotifyPropertyChanged("FirstName"); }
    }

    private string _LastName;
    public string LastName
    {
        get { return _LastName; }
        set { _LastName = value; NotifyPropertyChanged("LastName"); }
    }

    private string _EMail;
    public string EMail
    {
        get { return _EMail; }
        set { _EMail = value; NotifyPropertyChanged("EMail"); }
    }

    private int _UserID;
    public int UserID
    {
        get { return _UserID; }
        set { _UserID = value; NotifyPropertyChanged("UserID"); }
    }

    private string _Position;
    public string Position
    {
        get { return _Position; }
        set { _Position = value; NotifyPropertyChanged("Position"); }
    }

    private DateTime? _EndDate;
    public DateTime? EndDate
    {
        get { return _EndDate; }
        set { _EndDate = value; NotifyPropertyChanged("EndDate"); }
    }

    public event PropertyChangedEventHandler PropertyChanged;

    private void NotifyPropertyChanged(String info)
    {
        if (PropertyChanged != null)
        {
            PropertyChanged(this, new PropertyChangedEventArgs(info));
        }
    }
}

在首页：

UsersViewModel Usersvm = new UsersViewModel();
Usersvm.Users = new ObservableCollection<UserViewModel>();
DbEntities db = new DbEntities();
var pulledUsers = db.uspGetNonAdminUsers().ToList();
foreach (var result in pulledUsers)
{
    var pulledUser = new UserViewModel
    {
        FirstName = result.FirstName,
        LastName = result.LastName,
        EMail = result.Email,
        UserID = result.UserID,
        Position = result.Position,
        EndDate = result.EndDate
    };
    Usersvm.Users.Add(pulledUser);
}
new UsersWindow(Usersvm).Show();

用户窗口：

public partial class UsersWindow : Window
{
    public UsersWindow(UsersViewModel uvm)
    {
        InitializeComponent();
        DataContext = uvm;
    }
}

Answer 1

你需要做几件事：

将您的属性更新为object：

   public RelayCommand<object> editButton_Click_Command { get; set; }

更新您的实例以使用 object

editButton_Click_Command = new RelayCommand<object>(OneditButton_Click_Command);

然后，将您的事件处理程序更新为具有参数 object 并进行相应的转换。

private void OneditButton_Click_Command(object obj)
{
    var associatedViewModel = obj as UserViewModel;
    if (associatedViewModel != null)
    {

    }
}