Question

我有一个DataGrid支持后面的代码中手动处理ObservableCollection<T>。当我将新项目添加到支持列表或删除一个项目时，Count已更新，但ItemsSource未通知，因此Price的总和更新。我甚至试过了BindingList<T>，但即使是Count也停止了更新！什么是黑客？

XAML：

<Label>
   <Label.Content>
        <TextBlock>
             <TextBlock.Text>
                <MultiBinding StringFormat="{}Count: {0}, Sum: {1}" NotifyOnTargetUpdated="True" NotifyOnSourceUpdated="True">
                    <Binding ElementName="datagrid" Path="ItemsSource.Count" UpdateSourceTrigger="PropertyChanged"/>
                    <Binding ElementName="datagrid" Path="ItemsSource" Converter="{StaticResource SumConverter}" UpdateSourceTrigger="PropertyChanged" />
                </MultiBinding>
            </TextBlock.Text>
        </TextBlock>
    </Label.Content>
</Label>

SumConverter：

[ValueConversion(typeof(ObservableCollection<DocView>), typeof(String))]
public class SumConverter : IValueConverter
{
    public object Convert(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
    {
        if (value != null && value is ObservableCollection<DocView>)
        {
            ObservableCollection<DocView> items = (ObservableCollection<DocView>)value;
            return items.Sum(x => x.Price);
        }
        else
            return 0;
    }

    public object ConvertBack(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
    {
        throw new NotImplementedException();
    }
}

代码背后：

ObservableCollection<DocView> list = new ObservableCollection<DocView>();

datagrid.DataContext = list;

Answer 1

我认为问题在于您将列表绑定到datagrid并且转换器无法获取ItemSource中的更改，因为该属性未发生变化。该集合不会触发PropertyChanged事件。试试这个：

datagrid.ItemsSource = list;

在你的XAML中使用多重绑定的转换器。绑定到ItemsSource.Count将在集合更改时触发通知。请注意，您不需要将TextBlock嵌入Label。

    <TextBlock Grid.Row="2">
        <TextBlock.Text>
            <MultiBinding Converter="{StaticResource SumConverter}">
                <Binding ElementName="datagrid" Path="ItemsSource" />
                <Binding ElementName="datagrid" Path="ItemsSource.Count"/>
            </MultiBinding>
        </TextBlock.Text>
    </TextBlock>

显然你需要相应地修改你的转换器。

 public class SumConverter : IMultiValueConverter
    {
        public object Convert(object[] values, Type targetType, object parameter, System.Globalization.CultureInfo culture)
        {
            if (values != null && values.Length > 0 && values[0] is ObservableCollection<string>)
            {
                ObservableCollection<DocView> items = (ObservableCollection<DocView>)values[0];
                return string.Format("Count: {0}, Sum: {1}", items.Count, items.Sum(x => x.Price));
            }
            else
                return "Count: 0, Sum: 0";
        }

        public object[] ConvertBack(object value, Type[] targetTypes, object parameter, CultureInfo culture)
        {
            throw new NotImplementedException();
        }
    }

这是一个需要最少更改的解决方案。更好的方法是将集合绑定到ViewModel而不是datagrid.ItemsSource。

Answer 2

完整的解决方案：

在视图模型中包装所有内容，并在每个位置实现INPC
使用BindingList<T>代替ObservableCollection<T>（如果您使用ObservableCollection<T>，则列表中现有项目属性的更新不会在BindingList<T>时触发对UI的更新支持这个）

XAML：

<DataGrid x:Name="datagrid" ItemsSource="{Binding List}" />

    <Label>
       <Label.Content>
            <TextBlock>
                 <TextBlock.Text>
                    <MultiBinding StringFormat="{}Count: {0}, Sum: {1}" NotifyOnTargetUpdated="True" NotifyOnSourceUpdated="True">
                         <Binding ElementName="datagrid" Path="DataContext.Count"/>
                         <Binding ElementName="datagrid" Path="DataContext.Total"/>
                    </MultiBinding>
                </TextBlock.Text>
            </TextBlock>
        </Label.Content>
    </Label>

代码背后：

DocViewModel list= new DocViewModel();
datagrid.DataContext = list;

<强> DocViewModel ：

public class DocViewModel : INotifyPropertyChanged
{
    public DocViewModel()
    {
        this.list = new BindingList<DocView>();
        this.list.ListChanged += list_ListChanged;
    }

    void list_ListChanged(object sender, ListChangedEventArgs e)
    {
        OnPropertyChanged("Total");
        OnPropertyChanged("Count");
    }

    public event PropertyChangedEventHandler PropertyChanged;

    private BindingList<DocView> list;

    public BindingList<DocView> List
    {
        get { return list; }
        set
        {
            list = value;
            OnPropertyChanged("List");
        }
    }

    public decimal Total
    {
        get { return list.Sum(x => x.Price); }
    }

    private void OnPropertyChanged(String propertyName = "")
    {
        if (PropertyChanged != null)
        {
            PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
        }
    }

    public int Count
    {
        get { return list.Count; }
    }
}

<强> DocView：

public class DocView : INotifyPropertyChanged
{
    private decimal price;

    public decimal Price
    {
        get { return price; }
        set
        {
            price = value;
            OnPropertyChanged("Price");
        }
    }

    public event PropertyChangedEventHandler PropertyChanged;

    private void OnPropertyChanged(String propertyName = "")
    {
        if (PropertyChanged != null)
        {
            PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
        }
    }
}

修改

这是一个更具体的视图模型通用实现，让您使用相同的逻辑，使用不同的项目类型来提供自定义的总计数和计数计算器：

public class GenericListViewModel<T> : INotifyPropertyChanged { Func<BindingList<T>, decimal> totalCalculator; Func<BindingList<T>, int> countCalculator; public GenericListViewModel(Func<BindingList<T>, decimal> _totalCalculator, Func<BindingList<T>, int> _countCalculator) { this.list = new BindingList<T>(); this.list.ListChanged += list_ListChanged; this.totalCalculator = _totalCalculator; this.countCalculator = _countCalculator; } void list_ListChanged(object sender, ListChangedEventArgs e) { OnPropertyChanged("Total"); OnPropertyChanged("Count"); } public event PropertyChangedEventHandler PropertyChanged; private BindingList<T> list; public BindingList<T> List { get { return list; } set { list = value; OnPropertyChanged("List"); } } public decimal Total { get { if (totalCalculator != null) return totalCalculator.Invoke(list); else throw new NotImplementedException("Total Func must be impelmented"); } } private void OnPropertyChanged(String propertyName = "") { if (PropertyChanged != null) { PropertyChanged(this, new PropertyChangedEventArgs(propertyName)); } } public int Count { get { if (countCalculator != null) return countCalculator.Invoke(list); else throw new NotImplementedException("Count Func must be implemented"); } } }

用法：

public class MyDocViewModel: GenericListViewModel<DocView> { public MyDocViewModel() : base( (list) => { return list.Sum(x => x.Price); }, (list) => { return list.Count; } ) { } }

ObservableCollection不反映摘要计算的更改

2 个答案: