ObservableCollection.CollectionChanged不触发

Question

我有以下界面： 当一个项目被添加到DataGrid中时，Total列将根据（价格* 数量）进行更新，所有行的总计TextBox也会有全部总和。

然而，当我更改一行的数量时，Total列会更新，但总计TextBox不会。

以下是我的代码，请提前感谢。

 public partial class pgCheckout : Page {

    ObservableCollection<SaleItem> items = new ObservableCollection<SaleItem>();

    public pgCheckout() {
        InitializeComponent();
        dgItems.ItemsSource = items;
        dgItems.Loaded += SetMinWidths;
        items.CollectionChanged += setTotal;
    }

    public void setTotal(object source, EventArgs e) {
        decimal total = 0;
        foreach(SaleItem i in items) {
            total += i.Total;
        }

        txtTotal.Text = total.ToString();
    }


    public void SetMinWidths(object source, EventArgs e) {
        foreach (var column in dgItems.Columns) {
            if (column.DisplayIndex != 0) {
                column.MinWidth = column.ActualWidth;
                column.Width = new DataGridLength(1, DataGridLengthUnitType.Star);
            }
        }
    }

    private void btnRemove_Click(object sender, RoutedEventArgs e) {
        items.RemoveAt(dgItems.SelectedIndex);
    }

    private void btnAdd_Click(object sender, RoutedEventArgs e) {
        bool exist = false;
        foreach (SaleItem i in items) {
            if (i.ItemID.Equals(txtItemID.Text))
                exist = true;
        }

        if (exist) {
            lblErr.Content = "Item already exist";
            txtItemID.Text = "";
        }

        else {

            using (var db = new PoSEntities()) {
                var query = from i in db.Items
                            where i.ItemID.Equals(txtItemID.Text.Trim())
                            select i;
                var itm = query.FirstOrDefault();
                if (itm == null) {
                    lblErr.Content = "Invalid Item";
                    txtItemID.Text = "";
                }
                else {
                    txtItemID.Text = "";
                    lblErr.Content = "";
                    items.Add(new SaleItem() {
                        Num = items.Count + 1,
                        ItemID = itm.ItemID,
                        Name = itm.Name,
                        Price = decimal.Round(itm.Price, 2, MidpointRounding.AwayFromZero),
                        Quantity = 1,
                    });
                }
            }
        }
    }

    private void txtItemID_KeyUp(object sender, KeyEventArgs e) {
        if (e.Key == System.Windows.Input.Key.Enter) {
            btnAdd_Click(txtItemID, e);
        }
    }
}

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));
        }
    }
}

- Edwin

---

你能展示一下 SaleItem 类吗？ - Hossein Narimani Rad

SaleItem类已包含在代码的底部附近。 - Edwin

Answer 1

ObservableCollection.CollectionChanged会在集合中添加或删除内容时触发，而不是在更新单个成员时触发。

...
else 
{
    txtItemID.Text = "";
    lblErr.Content = "";
    SaleItem newItem = new SaleItem() {
                    Num = items.Count + 1,
                    ItemID = itm.ItemID,
                    Name = itm.Name,
                    Price = decimal.Round(itm.Price, 2, MidpointRounding.AwayFromZero),
                    Quantity = 1 };
     newItem.PropertyChanged += 
             new PropertyChangedEventHandler(newSaleItem_PropertyChanged);

    items.Add(newItem);
 }
 ...

这是 newSaleItem_PropertyChanged：

void newSaleItem_PropertyChanged(object sender, PropertyChangedEventArgs e)
{
    setTotal(null, null);
}

- Hossein Narimani Rad

---

我了解了。我该怎么处理这个问题呢？ - Edwin

如果你的SaleItem实现了INotifyPropertyChanged接口，那么你可以为每个SaleItem使用PropertyChanged事件。我将编辑我的帖子。 - Hossein Narimani Rad

Answer 2

 ObservableCollection<SaleItem> items = new ObservableCollection<SaleItem>();

必须是属性

将其更改为

public ObservableCollection<SaleItem> items {get;set;}

在构造函数中实现新功能

或者，如果不存在对象，则使get函数创建新对象

使用绑定必须具有公共getter/setter

- Nahum

Answer 3

你的 SaleItem 必须实现 INotifyPropertyChanged，这样你才会拥有 PropertyChanged 事件并可以订阅它。使用 INotifyPropertyChanged 对于绑定非常有用。

- Dilshod