c# - 在 WPF 中使用 ICommand——返回 null 的命令

Question

我正在 WPF 中处理一个示例 ViewModel，我目前将 View 中的 3 个文本框绑定(bind)到 Id、FirstName 和 LastName .然后，我在 xaml.cs 文件中有一个按钮单击事件，该事件执行更新示例数据库表的方法。我正在尝试围绕 MVVM 和 WPF 进行思考。我想取消按钮单击事件并改为绑定(bind)到命令。我正在使用 Linq to Sql 进行数据库连接。

当我调试代码时，一切都返回 null。我走在正确的道路上吗？

谢谢!

这是 VM 的一部分(我不想发布所有代码。)

public class People
{
    public Guid Id {get; set;}
    public string FirstName {get; set;}
    public string LastName {get; set;}
}

private People mPeople = null;
private Guid mId = Guid.empty;

public People people
{
    get {return mPeople;}
    set {mPeople = value; OnPropertyChanged("people");}
}


public overide void Refresh()    
{      
    Using (DatabaseDataContext dc = new DatabaseDataContext())      
    {
        mId = CurrentUser.Identity;

        var query = from person in dc.PeopleTables 
            where person.PId = mId
            select new People()
            {
                Id = person.PId,
                    FirstName = person.FirstName,
                LastName = person.LastName
            };

        mPeople = query.First();
    }
}

在 VM 中，这是我正在尝试使用的命令

private RelayCommand mUserUpdate = null;

public ICommand UserUpdate
{
    get
    {
        if(mUserUpdate == null) mUserUpdate = new RelayCommand(p => UpdateUser(p));
        return mUserUpdate;
    }
}

private void UpdateUser(object parameter)
{
    People pe = parameter as People;
    UpdateUser(pe.Id, pe.FirstName, pe.LastName);
}

public static void UpdateUser(Guid Id, string FirstName, string LastName)
{
    DatabaseDataContext DC = new DatabaseDatacontext();

    var User = (from c in DC.GetTable<PeopleTable>()
                where c.PId = mId
            select c).SingleOrDefault();

    if (User == null
    {
        //Do my inserts here 
    }
    else
    {
        try
        {
            User.Id = Id;
        User.FirstName = FirstName;
        User.LastName = LastName;

        DC.SubmitChanges();
        }
        catch
        {
            throw ex;
        }
    }
}

这是我使用的点击事件

private void btnSave_Click(object sender, RoutedEventArgs e)
{
    UserViewModel.UpdateUser(txtId.Text, txtFirstName.Text, txtLastName.Text);
}

---

是的，我把点击事件去掉，换成了

<Button Command="{Binding Path=UserUpdate}"/>

我是这样绑定(bind)文本框的

<TextBox Width="250" Text="{Binding Path=Id}"/> 
</StackPanel> 
<StackPanel Orientation="Horizontal" Margin="0,5,0,0"> 
<Label Content="First Name:" Margin="0,0,4,0"/> 
<TextBox Width="250" Text="{Binding Path=FirstName}"/> 
</StackPanel> 
<StackPanel Orientation="Horizontal" Margin="0,5,0,0"> 
<Label Content="Last Name:" Margin="35,0,4,0"/> 
<TextBox Width="250" Text="{Binding Path=LastName}"/>

Answer 1

命令旨在替换按钮的Click 事件处理程序。

您应该删除事件处理程序并执行

<Button Command="{Binding UserUpdate}"/>