如何强制更新只读属性？

Question

我正在尝试自动计算我的对象的总价值。假设我的对象是：

public class Sale
{
    public double Amount { get; set; }
    public double Price { get; set; }
    public double Total { get { return Amount * Price; } }
}

我的页面上有两个 Entry，因此用户可以键入 Amount 和 Price 值，以及一个 Label 来显示 Total 值：

<Entry Placeholder="Amount"
       ReturnType="Done"
       Keyboard="Numeric"
       Text="{Binding MySale.Amount, Mode=OneWayToSource, StringFormat='{}{0:N0}'}"/>

<Entry Placeholder="Price"
       ReturnType="Done"
       Keyboard="Numeric"
       Text="{Binding MySale.Price, Mode=OneWayToSource, StringFormat='{}{0:N0}'}"/>

<Label Text="{Binding MySale.Total, StringFormat='{}R$ {0:N2}'}"/>

BindingContext 被正确定义为我的视图模型，MySale 对象实现了 INotifyPropertyChanged:

private Sale _mySale;
public Sale MySale
{
    get { return _mySale; }
    set { SetProperty(ref _mySale, value); } // The SetProperty is defined in my BaseViewModel
}

问题是当我更改条目的值时，标签的值没有更新。当控件未聚焦时，我什至尝试手动将 Amount 和 Price 值分配给条目文本，但它也没有用。

我不确定它是否改变了什么，但我的应用程序是一个 MVVM Xamarin.Forms 应用程序。

-- 编辑 -- 这是我的 BaseViewModel class:

public class BaseViewModel : INotifyPropertyChanged
{
    string title = string.Empty;
    public string Title
    {
        get { return title; }
        set { SetProperty(ref title, value); }
    }

    bool isBusy = false;
    public bool IsBusy
    {
        get { return isBusy; }
        set { SetProperty(ref isBusy, value); }
    }

    public event PropertyChangedEventHandler PropertyChanged;
    protected virtual void OnPropertyChanged([CallerMemberName] string propertyName = null)
    {
        PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
    }

    protected virtual bool SetProperty<T>(ref T storage, T value, [CallerMemberName] string propertyName = "")
    {
        if (EqualityComparer<T>.Default.Equals(storage, value))
            return false;
        storage = value;
        this.OnPropertyChanged(propertyName);
        return true;
    }
}

Answer 1

当您设置 Amount 或 Price 的值时，您可以引发多个 PropertyChanged 事件

public class Sale : BaseViewModel
{
    private double amount;
    private double price;

    public double Amount
        get { return amount; }
        set { SetProperty(ref amount, value);
              this.OnPropertyChanged("Total"); }

    public double Price
        get { return price; }
        set { SetProperty(ref price, value); 
              this.OnPropertyChanged("Total"); } 

    public double Total { get { return Amount * Price; } }
}

如何强制更新只读属性？

How to force update on a read only property?

c#

xamarin.forms

mvvm

data-binding

如何强制更新只读 属性？

How to force update on a read only property?

c#

xamarin.forms

mvvm

data-binding

如何强制更新只读属性？