使用ComboBox为DataGrid选择数据

Question

在我的XAML中，我有一个选择父元素的ComboBox。在ComboBox中选择一个项目时，应该用子元素填充DataGrid，这些子元素属于来自ComboBox的选择父元素(我希望这是有意义的)。

<!-- Select here to populate datagrid -->
<ComboBox ItemsSource="{Binding ContactGroups}"
          DisplayMemberPath="Name"
          SelectedValuePath="Id"
          SelectedValue="{Binding ContactGroup}" />

<!-- ComboBox selection loads data to the grid -->
<DataGrid ItemsSource={Binding Contacts}">
    <DataGrid.Columns>
        <DataGridTextColumn Binding="{Binding FirstName}" Header="First Name" />
        <DataGridTextColumn Binding="{Binding LastName}" Header="Last Name" />
    </DataGrid.Columns>
</DataGrid>

我本来只想使用数据库和ViewModel来完成这个任务，但老实说，我不知道如何将选定的ContactGroup Id传递给我的ViewModel，这是我用以下方法设置的：

public class ContactsViewModel
{
    private readonly ObservableCollection<Contact> _Contacts
        = new ObservableCollection<Contact>();
    public IEnumerable<Contact> Contacts
    {
        get { return _Contacts; }
    }

    private ObservableCollection<ContactGroup> _ContactGroups 
        = new ObservableCollection<ContactGroup>();
    private IEnumerable<ContactGroup> ContactGroups
    {
        get { return _ContactGroupsViewModel; }
    }

    // Binding for ContactGroups ComboBox
    public ICommand ListContactGroupsCommand
    {
        get
        {
            return new MyDelegateCommand(ListContactGroups);
        }
    }
    private void ListContactGroups()
    {
        using (ApplicationDbContext Context = new ApplicationDbContext())
        {
            var ContactGroups = Context.ContactGroups.Where
            (
                x => x.Deleted == false
            );

            foreach (var c in ContactGroups)
            {
                AddToContactGroups(c);
            }
        }
    }
    private void AddToContactGroups(ContactGroup group)
    {
        if (!_ContactGroups.Contains(group))
            _ContactGroups.Add(group);
    }

    // Handle selection of a ContactGroup.
    public ICommand ListContactsForGroupCommand
    {
        get
        {
            return new MyDelegateCommand((ContactGroupId) =>
                { ListContacts((int)ContactGroupId); });
        }
    }

   private void ListContacts(int contactGroupId)
    {
        using (ApplicationDbContext db = new ApplicationDbContext())
        {
            var Contacts = db.Contacts.Where
            (
                x => x.ContactGroupId == contactGroupId &&
                x.Deleted == false
            );
            foreach (var c in Contacts)
            {
                AddToContacts(c);
            }
        }
    }
    private void AddToContacts(Contact contact)
    {
        if (!_Contacts.Contains(contact))
            _Contacts.Add(contact);
    }
}

如何在ListContactsForGroupCommand上执行ComboBox？

我想我可以将它连接到SelectionChanged事件中，但现在我看到了提供参数值的方法。

我能从代码背后做这个吗？

Answer 1

我会这样执行：

视图模型

public class ContactsViewModel
{    
    public IEnumerable<Contact> Contacts
    {
        get 
        { 
            return db.Contacts.Where
            (
                x => x.ContactGroupId == ContactGroup.Id &&
                x.Deleted == false
            ); 
        }
    }

    private ContactGroup _contactGroup = new ContactGroup();
    private ContactGroup ContactGroup
    {
        get { return _contactGroup; }
        set
        {
            _contactGroup = value;
            RaisePropertyChangedEvent("ContactGroup");
            RaisePropertyChangedEvent("Contacts");
        }
    }  

    private ObservableCollection<ContactGroup> _ContactGroups 
    = new ObservableCollection<ContactGroup>();
    private IEnumerable<ContactGroup> ContactGroups
    {
        get { return _ContactGroupsViewModel; }
    }  
}

XAML

<!-- Select here to populate datagrid -->
<ComboBox ItemsSource="{Binding ContactGroups}"
          DisplayMemberPath="Name"
          SelectedItem="{Binding ContactGroup}" />

<!-- ComboBox selection loads data to the grid -->
<DataGrid ItemsSource={Binding Contacts}">
    <DataGrid.Columns>
        <DataGridTextColumn Binding="{Binding FirstName}" Header="First Name" />
        <DataGridTextColumn Binding="{Binding LastName}" Header="Last Name" />
    </DataGrid.Columns>
</DataGrid>

Answer 2

在视图模型中添加一个ContactGroup属性，并在此模型的setter中执行命令或直接调用ListContactGroups()方法：

private int _contactGroup;
public int ContactGroup
{
    get { return _contactGroup; }
    set
    {
        _contactGroup = value;
        ListContactGroups();
    }
}

这应该可以工作，因为您正在将ComboBox的ComboBox属性绑定到XAML中的ContactGroup：

SelectedValue="{Binding ContactGroup}" />

这意味着，无论何时在ComboBox中选择项，都将设置此属性。