c#绑定前更改属性值

我不确定以前是否有人问过这个问题，但我目前的情况是将控件的属性绑定到

DependencyProperty

。但是，

属性返回的值是
Double
类型。设置绑定时，如何从属性中减去
20
或给定值，然后绑定控件？我是否需要为此实施
IValueConverter
？我仍在学习WPF，因此任何帮助都将不胜感激

依赖项属性

public static readonly DependencyProperty ProgressbarValueDependency = DependencyProperty.Register("PrValue", typeof(double),     typeof(LinearProgressBar));

public double PrValue
{
    get
    {
        return System.Convert.ToDouble(GetValue(ProgressbarValueDependency));
    }
    set
    {
        SetValue(ProgressbarValueDependency, value);
    }
}

 {
MainGrid = GetTemplateChild("MainGrid");
Binding MainGridWidthBinding = new Binding("PrValue")
{
    Source = this,
    Mode = BindingMode.TwoWay
};
MainGrid.SetBinding(Grid.WidthProperty, MainGridWidthBinding);
}

绑定到属性

public static readonly DependencyProperty ProgressbarValueDependency = DependencyProperty.Register("PrValue", typeof(double),     typeof(LinearProgressBar));

public double PrValue
{
    get
    {
        return System.Convert.ToDouble(GetValue(ProgressbarValueDependency));
    }
    set
    {
        SetValue(ProgressbarValueDependency, value);
    }
}

 {
MainGrid = GetTemplateChild("MainGrid");
Binding MainGridWidthBinding = new Binding("PrValue")
{
    Source = this,
    Mode = BindingMode.TwoWay
};
MainGrid.SetBinding(Grid.WidthProperty, MainGridWidthBinding);
}

为了达到您的目的，您需要编写一个类实现
IValueConverter
接口

public class MyConverter : IValueConverter
{
    public object Convert(object value, Type targetType, 
        object parameter, string language)
    {
        // Contain your source to target convertion logic. 
    }

    public object ConvertBack(object value, Type targetType, 
        object parameter, string language)
    {
        // Contain your target to source convertion logic.
        // Only needed if using TwoWay or OneWayToSource Binding Mode. 
    }
}

然后在调用之前将其实例设置为
Binding.Converter
属性　<代码>设置绑定

方法

Binding MainGridWidthBinding = new Binding("PrValue")
{
    Source = this,
    Mode = BindingMode.TwoWay,
    Converter = new MyConverter(),
};
MainGrid.SetBinding(Grid.WidthProperty, MainGridWidthBinding);

---

最好的方法是实现IValueConverter，下面是一个示例

using System;
using System.Windows.Data;

namespace WpfApp1
{
    public class DoubleModifierConverter : IValueConverter
    {
        public double Modifier { get; set; }
        public Operator Operator { get; set; } = Operator.Addition;

        public object Convert(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
        {
            if (!(value is double doubleValue))
                throw new InvalidCastException();

            switch (Operator)
            {
                case Operator.Addition:
                    return doubleValue + Modifier;
                case Operator.Substraction:
                    return doubleValue - Modifier;
                case Operator.Multiplication:
                    return doubleValue * Modifier;
                case Operator.Division:
                    return doubleValue / Modifier;
                default:
                    throw new ArgumentOutOfRangeException();
            }
        }

        public object ConvertBack(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
        {
            if (!(value is double doubleValue))
                throw new InvalidCastException();

            switch (Operator)
            {
                case Operator.Addition:
                    return doubleValue - Modifier;
                case Operator.Substraction:
                    return doubleValue + Modifier;
                case Operator.Multiplication:
                    return doubleValue / Modifier;
                case Operator.Division:
                    return doubleValue * Modifier;
                default:
                    throw new ArgumentOutOfRangeException();
            }
        }
    }

    public enum Operator
    {
        Addition = 0,
        Substraction = 1,
        Multiplication = 2,
        Division = 3,
    }
}

这就是你使用它的方式

MainGrid = GetTemplateChild("MainGrid");
Binding MainGridWidthBinding = new Binding(nameof(PrValue)){
    Source = this,
    Mode = BindingMode.TwoWay,
    Converter = new DoubleModifierConverter 
    { 
        Modifier = 20.0, 
        Operator = Operator.Substraction 
    }
};
MainGrid.SetBinding(Grid.WidthProperty, MainGridWidthBinding);

---

是的，你应该实施IVlaueConverter@user1672994，我以前从未使用过它…您能否发布有关此问题的答案，以便我能够解决此问题并让我们了解IValueConverter的工作原理？@user1672994，如果我想使用IValueConverter，是否需要保留上述代码？您可以参考和