我正在开发一个WPF-MVVM应用程序。

我有一个空白的dataGrid，用于添加行。最后一列显示价格。

我想显示价格总额作为衡量标准，我添加了行

我的代码不起作用。问题出在哪里？

查看

<DataGrid x:Name="dataGridInvoice" ItemsSource="{Binding Collection}" 
                                   AutoGenerateColumns="False"
                                   SelectedItem="{Binding Selected, Mode=TwoWay}" 
                    <DataGridComboBoxColumn Header="Ref Supplier"
                                        ItemsSource="{Binding DataContext.Reference, Source={StaticResource ProxyElement}}"
                                        DisplayMemberPath="refsup" 
                                        SelectedValueBinding="{Binding refSup, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}" 
                                        SelectedValuePath="refsup"/>
                    <DataGridTextColumn Header="Quantity" Binding="{Binding quantity, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}" Width="*"/>
                    <DataGridTextColumn Header="Price/MOQ" Binding="{Binding unitPrice, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}" Width="*"/>
                    <DataGridTextColumn Header="Total Price" Binding="{Binding totalPrice, Mode=TwoWay, StringFormat=N2, UpdateSourceTrigger=PropertyChanged}" Width="*" IsReadOnly="True"/>
                </DataGrid.Columns>
            </DataGrid>

ViewModel

public class InvoiceViewModel : ViewModelBase
    {
        public Context ctx = new Context();
        Invoice invoice;
        public InvoiceViewModel()
        {
            Collection = new ObservableCollection<PreInvoice>();
        }
        private ObservableCollection<PreInvoice> collection;
        public ObservableCollection<PreInvoice> Collection
        {
            get
            {
                return collection;
            }
            set
            {
                collection = value;
                OnPropertyChanged("Collection");
                Total = Convert.ToString(Collection.Sum(t => t.totalPrice));
            }
        }
        private string _total;
        public string Total
        {
            get
            {
                return _total;
            }
            set
            {
                _total = value;
                OnPropertyChanged("Total");
            }
        }

        private void Save()
        {

        }
        private void Delete()
        {
        }


        #region "Command"
        private ICommand saveCommand;
        private ICommand removeCommand;

        #endregion

我的型号：

        # region wrapper
        public class PreInvoice : ViewModelBase, IDataErrorInfo
        {
            private string _refSup;
            public string refSup
            {
                get
                {
                    return _refSup;
                }
                set
                {
                    _refSup = value;
                    OnPropertyChanged("refSup");
                }
            }
            private decimal _quantity;
            public decimal quantity
            {
                get
                {
                    return _quantity;
                }
                set
                {
                    _quantity = value;
                    OnPropertyChanged("quantity");
                    totalPrice = _quantity * _unitPrice;
                }
            }
            private decimal _unitPrice;
            public decimal unitPrice
            {
                get
                {
                    return _unitPrice;
                }
                set
                {
                    _unitPrice = value;
                    OnPropertyChanged("unitPrice");
                    totalPrice = _quantity * _unitPrice;
                }
            }
            private decimal _totalPrice;
            public decimal totalPrice
            {
                get
                {
                    return _totalPrice;
                }
                set
                {
                    _totalPrice = value;
                    OnPropertyChanged("totalPrice");
                }
            }
    }

    private string _total;
    public string Total
    {
        get
        {
            _total = Convert.ToString(Collection.Sum(t => t.totalPrice));
            return _total;
        }            
    }

    public InvoiceViewModel()
    {
        Collection = new ObservableCollection<PreInvoice>();
        Collection.CollectionChanged += Collection_CollectionChanged;
    }
    void Collection_CollectionChanged(object sender,  System.Collections.Specialized.NotifyCollectionChangedEventArgs e)
    {
        OnPropertyChanged("Total");
    }

public ObservableCollection<PreInvoice> Collection
    {
        get
        {
            return collection;
        }
        set
        {
            collection = value;
            Total = Convert.ToString(Collection.Sum(t => t.totalPrice));
            /*or if the above code is not working
            collection=Collection.Sum(t => t.totalPrice));
            */
            OnPropertyChanged("Collection");
        }
    }