Question

我试图通过MVVM中的以下简单公式计算“NetAmount”

GrossAmount + Carriage - Discount = NetAmount

我正在使用MVVM Light Toolkit并声明属性如下

public const string DiscountPropertyName = "Discount";
private double _discount;
public double Discount
{
    get
    {
        return _discount;
    }

    set
    {
        if (_discount == value)
        {
            return;
        }
        _discount = value;
        // Update bindings, no broadcast
        RaisePropertyChanged(DiscountPropertyName);
    }
}

public const string CarriagePropertyName = "Carriage";
private double _carriage;

public double Carriage
{
    get
    {
        return _carriage;
    }
    set
    {
        if (_carriage == value)
        {
            return;
        }
        _carriage = value;
        RaisePropertyChanged(CarriagePropertyName);
    }
}

public const string NetAmountPropertyName = "NetAmount";
private double _netAmount;

public double NetAmount
{
    get
    {
        _netAmount = Carriage + Discount;
        return _netAmount;
    }
    set
    {
        if (_netAmount == value)
        {
            return;
        }
        _netAmount = value;
        RaisePropertyChanged(NetAmountPropertyName);
    }
}

public const string GrossAmountPropertyName = "GrossAmount";
private double _grossAmount;

public double GrossAmount
{
    get
    {
        return _grossAmount;
    }

    set
    {
        if (_grossAmount == value)
        {
            return;
        }
        _grossAmount = value;
        RaisePropertyChanged(GrossAmountPropertyName);
    }
}

我将这些属性绑定在XAML中，文本框如下所示：

<TextBox Text="{Binding GrossAmount, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}"  DataContext="{Binding Mode=OneWay}"/>

<TextBox Text="{Binding Carriage, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}"  DataContext="{Binding Mode=OneWay}"/>

<TextBox Text="{Binding Discount, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}"  DataContext="{Binding Mode=OneWay}"/>

我将文本块与NetAmount属性绑定如下：

<TextBlock Text="{Binding NetAmount}" />

ViewModel为SalesOrderViewModel。

我不知道在哪里放置上面提到的公式，以便在更改任何文本框值时，它会导致更改NetAmount属性。

我不是C＃的新手，但我是MVVM和PropertyChanged事件的新手，我知道有一些非常愚蠢的事情我做错了但是无法理解它。

任何帮助都将受到高度赞赏。

Answer 1

由于NetAmount是一个计算，因此在视图模型中将其建模为只读属性是有意义的。访问该属性实际上执行计算。最后一个技巧是，每当影响RaisePropertyChanged(NetAmountProperty)的任何因素发生变化时，都会调用NetAmount

public const string GrossAmountPropertyName = "GrossAmount";
private double _grossAmount;
public double GrossAmount
{
    get { return _grossAmount; }
    set 
    {
           if (_grossAmount == value)
                return;

           RaisePropertyChanged(GrossAmountPropertyName);
           RaisePropertyChanged(NetAmountPropertyName);
    }
}

public double Discount{} ... //Implement same as above
public double Carriage {} ... //Implement same as above

public const string NetAmountPropertyName = "NetAmount";
public double NetAmount
{
    get { return GrossAmount + Carriage - Discount; }
}

编辑：如果您不想向RaisePropertyChanged添加对每个影响NetAmount的属性的调用，那么您可以修改RaisePropertyChanged，这样它也会引发PropertyChanged事件NetAmount属性。它会导致一些不必要的PropertyChanged事件被提出，但会更易于维护

private void RaisePropertyChanged(string propertyName)
{
     var handler = PropertyChanged;
     if (handler != null)
     {
          handler(this, new PropertyChangedEventArgs(propertyName);
          handler(this, new PropertyChangedEventArgs(NetAmountProperty);
     }
}

计算Property Changed MVVM上的两个值的结果

1 个答案: