如何綁定WPF中Observable集合的總和

Question

我正在學習WPF，所以請裸露我的問題，如果它是非常新手！我有一個Items集合，我想將該集合綁定到一個Grid並將Sum綁定到一個文本框。在線搜索我發現這個類將會引發事件，即使我們對集合對象的屬性進行了更改。

ObservableCollection not noticing when Item in it changes (even with INotifyPropertyChanged)

但我似乎不能讓它在我的代碼工作。

這裏是我的代碼

SaleItem

public class SaleItem : INotifyPropertyChanged 
{ 
    public int Num { get; set; } 
    public string ItemID { get; set; } 
    public string Name { get; set; } 

    private decimal price; 
    public decimal Price 
    { 
     get { return price; } 
     set 
     { 
      this.price = value; 
      OnPropertyChanged("Total"); 
     } 
    } 
    public int quantity; 
    public int Quantity 
    { 
     get { return quantity; } 
     set 
     { 
      this.quantity = value; 
      OnPropertyChanged("Total"); 
     } 
    } 

    public decimal Total 
    { 
     get { return decimal.Round(Price * Quantity, 2, MidpointRounding.AwayFromZero);} 
    } 

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

售

public class Sale : INotifyPropertyChanged 
{ 
    private Decimal _total; 
    public TrulyObservableCollection<SaleItem> Items { get; set; } 

    public Sale() 
    { 
     Items = new TrulyObservableCollection<SaleItem>(); 
     Items.Add(new SaleItem { ItemID = "1", Name = "Product 1", Price = 10, Quantity = 1 }); 
     Items.Add(new SaleItem { ItemID = "2", Name = "Product 2", Price = 10, Quantity = 1 }); 
     Items.Add(new SaleItem { ItemID = "3", Name = "Product 3", Price = 10, Quantity = 1 }); 

    } 

    public Decimal Total 
    { 
     get 
     { 
      return Items.Sum(x => x.Total); 
     } 
     set 
     { 
      _total = value; 
      OnPropertyChanged("Total"); 
     } 
    } 

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

主窗口

public partial class MainWindow : Window 
{ 
    public Sale Model { get; set; } 

    public MainWindow() 
    { 
     InitializeComponent(); 
     Model = new Sale(); 
     this.DataContext = Model;    
    } 



    private void btnQuantity_Click(object sender, RoutedEventArgs e) 
    { 
     Model.Items.Add(new SaleItem { ItemID = "2", Name = "Product 2", Price = 10, Quantity = 1 }); 

    } 
} 

XAML

<Window x:Class="WpfApplication1.MainWindow" 
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" 
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" 
    xmlns:local ="clr-namespace:WpfApplication1" 
    Title="MainWindow" Height="350" Width="525"> 

<Window.DataContext> 
    <local:Sale /> 
</Window.DataContext> 

<Grid> 
    <StackPanel> 
     <DataGrid x:Name="grdItems" ItemsSource="{Binding Items}"></DataGrid> 
     <TextBlock x:Name="txtTotal" Text="{Binding Total}"/> 
     <Button x:Name="btnQuantity" Content="Update" Click="btnQuantity_Click"/> 
    </StackPanel> 
</Grid> 

我想測試增加一個項目，當我按一下按鈕，並更新項目的網格數量。如果我設置了一個斷點並查看Total的值，那麼它是正確的，但不知何故它不會在UI上更新。我在這裏錯過了什麼？

Answer 1

你想做什麼。當集合本身已被更改時，請致電OnPropertyChanged。重新計算總數。目前，Sale類不知道該集合已更新，並且需要更新其Total屬性。你可以這樣做

的一種方法是，以檢查NotifyCollectionChangedEvent這樣的：

在你的構造出售（）：

public Sale() 
{ 
//Instantiate your collection and add items 

    Items.CollectionChanged += CollectionChanged; 
} 

然後添加事件的處理：

public void CollectionChanged(object sender, NotifyCollectionChangedEventArgs e) 
{ 
    OnPropertyChanged("Total"); 
} 

如果在集合更改與更新Total屬性不同時，您再也無法執行其他任何操作。您可以通過刪除事件處理程序和使用lambda表達式，而不是進一步縮短代碼：

Items.CollectionChanged += (s,e) => OnPropertyChanged("Total"); 

除非你曾經打算明確更新Total自己在Sale類。該setter可以去除：

public Decimal Total 
{ 
    get 
    { 
    return Items.Sum(x => x.Total); 
    } 
} 

Answer 2

在Sales.cs補充：

public void AddItem(SaleItem item) 
    { 
     Items.Add(item); 
     OnPropertyChanged("Total"); 
    } 

在MainWindow.xaml。CS呼叫：

Model.AddItem(new SaleItem { ItemID = "2", Name = "Product 2", Price = 10, Quantity = 1 }); 

而不是

Model.Items.Add(new SaleItem { ItemID = "2", Name = "Product 2", Price = 10, Quantity = 1 }); 

這將更新總。