使用Josh Smith的WPF MVVM演示应用程序实现ListView过滤器

Question

我一直在尝试扩展Josh Smith的演示MVVM应用程序,以便更好地理解它背后的原理,并且当我尝试使用ListView在View上实现过滤器功能时,我遇到了障碍.

我花了几个小时研究和涉猎,但它只是没有用.

我的第一步是将视图中的文本框绑定到ViewModel中的属性:

<TextBox Height="25" Name="txtFilter" Width="150" Text="{Binding Path=Filter, UpdateSourceTrigger=PropertyChanged}"/>

这在我的VM中匹配:

public string Filter
    {
        get { return this.filter; }
        set
        {
            this.filter = value;
            OnFilterChanged();
        }
    }

我的VM使用ObservableCollection作为数据源,但我在阅读教程后尝试将其转换为ICollectionView:

internal ObservableCollection<StaffViewModel> InnerStaff { get; set; }
    internal CollectionViewSource CvsStaff { get; set; }
    public ICollectionView AllStaff
    {
        get { return CvsStaff.View; }
    }

在我的构造函数中,我指定:

CvsStaff = new CollectionViewSource();
CvsStaff.Source = this.InnerStaff;
CvsStaff.Filter += ApplyFilter;

当我的Filter属性更新时,它调用OnFilterChanged,它是:

private void OnFilterChanged()
    {
        CvsStaff.View.Refresh();
    }

我的ApplyFilter函数是:

void ApplyFilter(object sender, FilterEventArgs e)
    {
        StaffViewModel svm = (StaffViewModel)e.Item;

        if (this.Filter.Length == 0)
        {
            e.Accepted = true;
        }
        else
        {
            e.Accepted = svm.LastName.Contains(Filter);
        }
    }

我做过一个愚蠢的错误,任何人都可以帮我发现吗？我是WPF和MVVM模式的新手,所以我还在学习!

编辑

在视图中我将集合绑定到:

<CollectionViewSource
  x:Key="StaffGroup"
  Source="{Binding Path=AllStaff}"
  />

和ListView是这样的:

<ListView
      Name="staffList"
      AlternationCount="2" 
      DataContext="{StaticResource StaffGroup}" 
      ItemContainerStyle="{StaticResource StaffItemStyle}"
      ItemsSource="{Binding}"
        Grid.Row="1">

Answer 1

绑定不正确.你需要做一些改变.首先要确保正确设置DataContext.通常,您将在ListView的父级上执行此操作,而不是直接在ListView控件上设置它.这可能是UserControl/Window /等.

所以假设你有一个视图模型:

public class MainViewModel
{
    public MainViewModel()
    {
        //Create some fake data 
        InnerStaff = new ObservableCollection<StaffViewModel>();
        InnerStaff.Add(new StaffViewModel {FirstName = "Sue", LastName = "Bucknell"});
        InnerStaff.Add(new StaffViewModel {FirstName = "James", LastName = "Bucknell"});
        InnerStaff.Add(new StaffViewModel {FirstName = "John", LastName = "Harrod"});

        CvsStaff = new CollectionViewSource();
        CvsStaff.Source = this.InnerStaff;
        CvsStaff.Filter += ApplyFilter;
    }

    private string filter;

    public string Filter
    {
        get { return this.filter; }
        set
        {
            this.filter = value;
            OnFilterChanged();
        }
    }

    private void OnFilterChanged()
    {
        CvsStaff.View.Refresh();
    }

    internal ObservableCollection<StaffViewModel> InnerStaff { get; set; }
    internal CollectionViewSource CvsStaff { get; set; }
    public ICollectionView AllStaff
    {
        get { return CvsStaff.View; }
    }

    void ApplyFilter(object sender, FilterEventArgs e)
    {
        StaffViewModel svm = (StaffViewModel)e.Item;

        if (string.IsNullOrWhiteSpace(this.Filter) || this.Filter.Length == 0)
        {
            e.Accepted = true;
        }
        else
        {
            e.Accepted = svm.LastName.Contains(Filter);
        }
    }
}

假设你有一个Window MainWindow.cs(后面的代码),你可以(对于这个例子)在这里连接DataContext.

public partial class MainWindow : Window
{
    public MainWindow()
    {
        InitializeComponent();
        DataContext = new MainViewModel();
    }
}

然后你有几个选择来进行绑定,你可以在XAML或代码中指定你的CollectionViewSource,但你已经做到了.即xaml one,键x:key ="StaffGroup",VM为CvsStaff.假设我们完全摆脱了xaml并使用VM one,这是正确设置的.然后你将使用ItemsSource属性绑定,如下所示:

<ListView Name="staffList" 
      AlternationCount="2" 
      ItemsSource="{Binding AllStaff}" 
      Grid.Row="1" />

同样小的事情,我已经更改过滤器来检查空值和空格.您可能还需要将其更改为不区分大小写.

我在这里没有提到但另一件事是至关重要的是在你的StaffViewModel上实现INotifyPropertyChanged - 我假设你有,如果不是这里有一些代码.您通常也会在大多数视图模型上执行此操作,以通知视图属性的更改.

internal class StaffViewModel : INotifyPropertyChanged
{
    private string _firstName;
    public string FirstName
    {
        get { return _firstName; }
        set
        {
            _firstName = value;
            OnPropertyChanged("FirstName");
        }
    }

    private string _lastName;
    public string LastName
    {
        get { return _lastName; }
        set
        {
            _lastName = value;
            OnPropertyChanged("LastName");
        }
    }
    public override string ToString()
    {
        return string.Format("{0} {1}", FirstName, LastName);
    }

    public event PropertyChangedEventHandler PropertyChanged;

    public void OnPropertyChanged(string propertyName)
    {
        var handler = PropertyChanged;
        if (handler != null) handler(this, new PropertyChangedEventArgs(propertyName));
    }
}