将参数传递给 CollectionViews

Question

我正在尝试以 WPF 形式编写数据绑定的第一个实现。

我已经到了可以成功检索数据以使用所需条目填充组合框的地步，但我仍坚持如何在给定组合框当前选择的情况下填充依赖的 ListView。

为了更好地解释我的问题，这是支持我的应用程序的当前视图。

class SchoolBookViewModel
{
    public SchoolBookViewModel() { }

    //Problem is here... How do I pass in the SelectedSchoolClassID?
    public CollectionView ClassBookListEntries(Guid SelectedSchoolClassID)
    {
        return new CollectionView(SchoolQuoteList.GetSchoolClassQuoteListBySchoolClassID(SelectedSchoolClassID, 2011, "MyConnectionString"));
    }

    public CollectionView SchoolEntries
    {
        get
        {
            return new CollectionView(SchoolList.GetSchoolList("MyConnectionString"));
        }
    }

}

这是 XAML

<StackPanel Height="449" HorizontalAlignment="Left" Margin="12,12,0,0" Name="stackPanel1" VerticalAlignment="Top" Width="650" DataContext="{Binding}">
      <Label Content="School:" Height="28" Name="lblSchoolName" Width="651" />
      <ComboBox Height="23" Name="cmbSchoolNames" Width="644" DisplayMemberPath="SchoolName" ItemsSource="{Binding Path=SchoolEntries}" SelectedValuePath="SelectedSchoolClassID" SelectionChanged="cmbSchoolNames_SelectionChanged" />
      <Label Content="Class booklist:" Height="29" Name="label1" Width="651" />
      <ListView Height="163" Name="lblClassBookList" Width="645" ItemsSource="{Binding Path=ClassBookListEntries}" DisplayMemberPath="QuoteReference" />
</StackPanel>

在我调用的 Window_Loaded 方法中

stackPanel1.DataContext = new Views.SchoolBookViewModel(); 

我是否走在正确的轨道上？任何指导将不胜感激。

Answer 1

要将 ComboBox 的选择返回到 ViewModel，您需要一个属性来绑定到其选择属性之一。如果你不使用它们做任何事情，你也可以摆脱显式的 CollectionViews。只需直接绑定到集合，ICollectionView 实例就会自动为您创建和管理。尝试像这样构造您的虚拟机：

class SchoolBookViewModel : INotifyPropertyChanged
{
    private SchoolList _selectedSchoolClass;
    public SchoolList SelectedSchoolClass
    {
        get { return _selectedSchoolClass; }
        set
        {
            _selectedSchoolClass = value;
            ClassBookListEntries = SchoolQuoteList.GetSchoolClassQuoteListBySchoolClassID(_selectedSchoolClass.Id, 2011, "MyConnectionString");
            NotifyPropertyChanged("SelectedSchoolClass");
        }
    }

    private SchoolQuoteList _classBookListEntries;
    public SchoolQuoteList ClassBookListEntries
    {
        get { return _classBookListEntries; }
        set
        {
            _classBookListEntries = value;
            NotifyPropertyChanged("ClassBookListEntries");
        }
    }

    private SchoolList _schoolEntries;
    public SchoolList SchoolEntries
    {
        get
        {
            if (_schoolEntries == null)
                _schoolEntries = SchoolList.GetSchoolList("MyConnectionString");
            return _schoolEntries;
        }
    }
    ...
}

一般来说，最好不要设置显式的宽度和高度值，而是让布局系统为您调整元素的大小。您还可以摆脱 DataContext="{Binding}" - 这是多余的，因为 DataContext 是继承的，而 {Binding} 表示 DataContext 本身的值。下面是已清理并绑定到上面的新属性的 XAML：

<StackPanel HorizontalAlignment="Left" Margin="12,12,0,0" x:Name="stackPanel1" VerticalAlignment="Top">
    <Label Content="School:" x:Name="lblSchoolName" />
    <ComboBox x:Name="cmbSchoolNames" DisplayMemberPath="SchoolName" ItemsSource="{Binding Path=SchoolEntries}"
              SelectedItem="{Binding SelectedSchoolClass}" />
    <Label Content="Class booklist:" x:Name="label1" />
    <ListView x:Name="lblClassBookList" ItemsSource="{Binding Path=ClassBookListEntries}" DisplayMemberPath="QuoteReference" />
</StackPanel>