来自Prism的DelegateCommand没有开火

Question

如果我使用Prism的DelegateCommand，则不会触发按钮单击。如果我为按钮点击编写命令类而不使用Prism，那么它可以工作。这是我的Prism代码：

这是我的View XAML：

<Window x:Class="MVVMPractice2.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:prism="http://prismlibrary.com/"
        prism:ViewModelLocator.AutoWireViewModel="True"
        Title="MainWindow" Height="350" Width="525">
    <Grid>
        <Label Content="Customer Name" HorizontalAlignment="Left" Margin="0,0,0,292.8"></Label>
        <Label Name="lblName"  HorizontalAlignment="Left" Margin="108,0,0,292.8" Width="37" Content="{Binding TxtCustomerName}"></Label>

        <Label Content="Sales Amount" HorizontalAlignment="Left" Margin="0,28,0,264.8"></Label>
        <TextBox Name="lblAmount"  HorizontalAlignment="Left" Margin="101,28,0,264.8" Width="44" Text="{Binding TxtAmount}"></TextBox>

        <Label Content="Buying Habits" HorizontalAlignment="Left" Margin="0,56,0,236.8"></Label>
        <Label Name="lblBuyingHabits" HorizontalAlignment="Left" Margin="108,56,0,236.8" Width="52" Background="{Binding LblAmountColor}"></Label>

        <Label Content="Married" HorizontalAlignment="Left" Margin="0,84,0,208.8" Width="62"></Label>
        <CheckBox Name="chkMarried" HorizontalAlignment="Left" Margin="102,84,0,208.8" IsChecked="{Binding IsMarried}"></CheckBox>

        <Label Content="Tax" HorizontalAlignment="Left" Margin="0,112,0,180.8"></Label>
        <TextBlock Name="lblTax" HorizontalAlignment="Left" Margin="108,117,0,175.8" Width="37" Text="{Binding TaxAmount}"></TextBlock>

        <Button Name="btnTax" Content="Calculate Tax" Margin="118,158,287.4,123.8" Command="{Binding UpdateCommand}"
></Button>

    </Grid> </Window>

ViewModel：

 public class MainWindowViewModel : BindableBase 
    {
        //instantiate the model
        private Customer customer = new Customer();

        //property for button click command
        private DelegateCommand UpdateCommand;


        //constructor to instantiate the buttons click command
        public MainWindowViewModel()
        {
            UpdateCommand = new DelegateCommand(customer.CalculateTax, customer.IsValid);

        }



        //this property maps customer name from model to the view
        public string TxtCustomerName
        {
            get { return customer.CustomerName; }
            set { customer.CustomerName = value; }
        }

        //this property maps amount from model to the view
        public string TxtAmount
        {
            get { return Convert.ToString(customer.Amount); }
            set { customer.Amount = Convert.ToDouble(value); }
        }


        //this property maps and transforms color from model to the view
        public string LblAmountColor
        {
            get
            {
                if (customer.Amount > 2000)
                {
                    return "Blue";
                }
                else if (customer.Amount > 1500)
                {
                    return "Red";
                }
                return "Yellow";
            }
        }

        //this property maps and transforms married from model to the view
        public bool IsMarried
        {
            get
            {
                if (customer.Married == "Married")
                {
                    return true;
                }

                else if (customer.Married == "UnMarried")
                {
                    return false;
                }

                return false;

            }

            set 
            {
                if (value)
                {
                    customer.Married = "Married";
                }

                else
                {
                    customer.Married = "UnMarried";
                }
            }



        }

        //this property maps tax from model to the view
        public string TaxAmount
        {
            get { return Convert.ToString(customer.Tax); }
            set { customer.Tax = Convert.ToDouble(value); }


        }



    }

和模型：

public class Customer
    {
        //model property
        private string customerName = "Ivan";
        public string CustomerName 
        {
            get { return customerName; }

            set { customerName = value; }
        }

        //model property
        private double amount = 2000;
        public double Amount
        {
            get { return amount; }

            set { amount = value; }
        }

        //model property
        private string married = "Married";
        public string Married
        {
            get { return married; }

            set { married = value; }
        }


        //model property
        private double tax;
        public double Tax
        {
            get { return tax; }
            set { tax = value; }

        }

        //this modifier calculates the tax
        public void CalculateTax()
        {
            if (amount > 2000)
            {
                tax = 20;
            }

            else if (amount > 1000)
            {
                tax = 10;
            }

            else
            {
                tax = 5;
            }
        }


        //this modifier validates the amount
        public bool IsValid()
        {
            if (amount < 0)
            {
                return false;
            }

            else
            {
                return true;
            }
        }


    }

Answer 1

正如上面的评论中指出的那样，将字段更改为属性会有所帮助，并触发NotifyPropertyChanged（删除不相关的部分）：

public class MainWindowViewModel : BindableBase 
{
    //property for button click command
    public DelegateCommand UpdateCommand { get; }

    //constructor to instantiate the buttons click command
    public MainWindowViewModel()
    {
        UpdateCommand = new DelegateCommand(() => {
           customer.CalculateTax();
           OnPropertyChanged( () => TaxAmount );
        }, customer.IsValid);
    }

    //this property maps tax from model to the view
    public string TaxAmount
    {
        get { return Convert.ToString(customer.Tax); }
        set { customer.Tax = Convert.ToDouble(value); }
    }
}

或者，让Customer实施INotifyPropertyChanged并使用PropertyObserver之类的内容将事件传递给视图。