MVVM分页和排序

Question

我正在努力寻找一个适当的解决方案来实现符合MVVM P&P的WPF DataGrid的排序和分页.

以下示例说明了实现按照MVVM实践进行的分页的有效方法,但排序的自定义实现(在实现分页后需要)不遵循MVVM:

http://www.eggheadcafe.com/tutorials/aspnet/8a2ea78b-f1e3-45b4-93ef-32b2d802ae17/wpf-datagrid-custom-pagin.aspx

我目前有一个DataGrid绑定到一个CollectionViewSource(在XAML中使用GroupDescriptions和SortDescritptions定义)绑定到我的ViewModel中的ObservableCollection.一旦通过限制DataGrid每页获取的项目数来实现Paging,它就会破坏CollectionViewSource中定义的排序,因为它只对项目的子集进行排序.MVVM下实施分页和排序的最佳方法是什么？

谢谢,

亚伦

Answer 1

前几天我写了一个PagingController类来帮助分页,所以在这里你去:

• PagingController.cs
• CurrentPageChangedEventArgs.cs

你需要清理一下这些资源,因为它们使用了MS Code Contracts,它们引用了Prism等的一些(非常基本的)实用程序.

用法示例(codebehind - ViewModel.cs):

private const int PageSize = 20;

private static readonly SortDescription DefaultSortOrder = new SortDescription("Id", ListSortDirection.Ascending);

private readonly ObservableCollection<Reservation> reservations = new ObservableCollection<Reservation>();

private readonly CollectionViewSource reservationsViewSource = new CollectionViewSource();

public ViewModel()
{
    this.reservationsViewSource.Source = this.reservations;

    var sortDescriptions = (INotifyCollectionChanged)this.reservationsViewSource.View.SortDescriptions;
    sortDescriptions.CollectionChanged += this.OnSortOrderChanged;

    // The 5000 here is the total number of reservations
    this.Pager = new PagingController(5000, PageSize);
    this.Pager.CurrentPageChanged += (s, e) => this.UpdateData();

    this.UpdateData();

}

public PagingController Pager { get; private set; }

public ICollectionView Reservations
{
    get { return this.reservationsViewSource.View; }
}

private void UpdateData()
{
    var currentSort = this.reservationsViewSource.View.SortDescriptions.DefaultIfEmpty(DefaultSortOrder).ToArray();

    // This is the "fetch the data" method, the implementation of which
    // does not directly interest us for this example.
    var data = this.crsService.GetReservations(this.Pager.CurrentPageStartIndex, this.Pager.PageSize, currentSort);
    this.reservations.Clear();
    this.reservations.AddRange(data);
}

private void OnSortOrderChanged(object sender, NotifyCollectionChangedEventArgs e)
{
    if (e.Action == NotifyCollectionChangedAction.Add) {
        this.UpdateData();
    }
}

使用示例(XAML - View.xaml):

<DataGrid ... ItemSource="{Binding Reservations}" />

<!-- all the rest is UI to interact with the pager -->
<StackPanel>
    <StackPanel Orientation="Horizontal" HorizontalAlignment="Center" Margin="4">
        <StackPanel.Resources>
            <Style TargetType="{x:Type Button}">
                <Setter Property="FontFamily" Value="Webdings" />
                <Setter Property="Width" Value="60" />
                <Setter Property="Margin" Value="4,0,4,0" />
            </Style>
            <Style TargetType="{x:Type TextBlock}">
                <Setter Property="Margin" Value="4,0,4,0" />
                <Setter Property="VerticalAlignment" Value="Center" />
            </Style>
            <Style TargetType="{x:Type TextBox}">
                <Setter Property="Margin" Value="4,0,4,0" />
                <Setter Property="Width" Value="40" />
            </Style>
        </StackPanel.Resources>
        <Button Content="9" Command="{Binding Path=Pager.GotoFirstPageCommand}" />
        <Button Content="3" Command="{Binding Path=Pager.GotoPreviousPageCommand}" />
        <TextBlock Text="Page" />
        <TextBox Text="{Binding Path=Pager.CurrentPage, ValidatesOnExceptions=True}" />
        <TextBlock Text="{Binding Path=Pager.PageCount, StringFormat=of {0}}" />
        <Button Content="4" Command="{Binding Path=Pager.GotoNextPageCommand}" />
        <Button Content=":" Command="{Binding Path=Pager.GotoLastPageCommand}" />
    </StackPanel>
    <ScrollBar Orientation="Horizontal" Minimum="1" Maximum="{Binding Path=Pager.PageCount}" Value="{Binding Path=Pager.CurrentPage}"/>
</StackPanel>

简短说明:

如您所见,ViewModel并没有真正做多少.它保留表示当前页面的项目集合,并向View 公开CollectionView(用于数据绑定)和a PagingController.然后它所做的就是CollectionView每次PagingController指示某些内容发生变化时更新集合中的数据项(并因此更新).当然,这意味着您需要一个方法,给定起始索引,页面大小,并SortDescription[]返回这些参数描述的数据切片.这是您的业务逻辑的一部分,我在这里没有包含代码.

在XAML方面,所有工作都是通过绑定到PagingController.我已经暴露在这里的全部功能(绑定到一/上一页/下一页/尾的命令,直接绑定的按钮TextBox来CurrentPage,和一个结合ScrollBar到CurrentPage).通常,您不会同时使用所有这些.

Answer 2

您应该ListCollectionView在 ViewModel 中使用类型的集合属性，并将 Grid 绑定到它。这样，CollectionView 定义就不会位于 View 中，而是位于 ViewModel（它所属的位置）中，这将帮助您在 ViewModel 中轻松进行所有想要的操作（无论是分页、排序还是过滤）