如何使装订方面的DependencyProperty值强制？ [英] How do I make Binding respect DependencyProperty value coercion?

问题描述

我有一个CoerceValueCallback一个DependencyProperty的控制。
此属性绑定到一个模型对象的属性。

在设置控件属性，导致强制绑定推动的不受胁迫价值模型对象的值。在控件的属性值正确强制。

我怎么绑定到强制值推到模型对象？

 无效初始化（）
{
    UIObject的UI =新UIObject类（）;
    ModelObject M =新ModelObject（）;
    熔点= 4;    结合B =新绑定（P）;
    b.Source =米;
    b.Mode = BindingMode.TwoWay;
    的Debug.WriteLine（SetBinding）;
    //设置绑定将模型值推到UI
    ui.SetBinding（UIObject.PProperty，B）;    //设置UI值会导致强迫，但只有在UI中。
    //通过结合推到模型中的值不强制。
    的Debug.WriteLine（设置到-4）;
    ui.P = -4;    Debug.Assert的（ui.P == 0）;
    //绑定是双向的DP值被强制为0。
    Debug.Assert的（熔点== 0）; // 不对。这将是-4。为什么？？？
}类UIObject类：FrameworkElement的
{
    公共静态只读的DependencyProperty PProperty =
        DependencyProperty.Register（P的typeof（INT）的typeof（UIObject类），
        新FrameworkPropertyMetadata（
            新PropertyChangedCallback（OnPChanged）
            新CoerceValueCallback（CoerceP）））​​;    公众诠释P
    {
        {返回（INT）的GetValue（PProperty）; }
        集合{的SetValue（PProperty，值）; }
    }    私有静态无效OnPChanged（DependencyObject的D，DependencyPropertyChangedEventArgs E）
    {
        的Debug.WriteLine（typeof运算（UIObject类）+ + + e.OldValue到+ e.NewValue.P从）;
    }    私有静态对象CoerceP（DependencyObject的发件人，对象的值）
    {
        INT P =（int）的值;
        如果（第℃，）
        {
            的Debug.WriteLine（typeof运算（UIObject类）+ P +.P从强制0）;
            p值= 0;
        }
        回磷;
    }
}类ModelObject
{
    私人诠释磷;
    公众诠释P
    {
        得到
        {
            的Debug.WriteLine（这+.P返回+ this.p）;
            返回this.p;
        }
        组
        {
            的Debug.WriteLine（本+ + + this.p.P从+改为到+值）;
            this.p =价值;
        }
    }
}
 

解决方案

我不认为要挟回调意味着是一个双行道。其中一个解决方法是将更新要挟回调的内部模型的价值。

I have a control with a DependencyProperty with a CoerceValueCallback. This property is bound to a property on a model object.

When setting the control property to a value that causes coercion the Binding pushes the uncoerced value to the model object. The property value on the control is coerced correctly.

How do I get the Binding to push the coerced value to the model object?

void Initialize()
{
    UIObject ui = new UIObject();
    ModelObject m = new ModelObject();
    m.P = 4;

    Binding b = new Binding("P");
    b.Source = m;
    b.Mode = BindingMode.TwoWay;
    Debug.WriteLine("SetBinding");
    // setting the binding will push the model value to the UI
    ui.SetBinding(UIObject.PProperty, b);

    // Setting the UI value will result in coercion but only in the UI.
    // The value pushed to the model through the binding is not coerced.
    Debug.WriteLine("Set to -4");
    ui.P = -4;

    Debug.Assert(ui.P == 0);
    // The binding is TwoWay, the DP value is coerced to 0.
    Debug.Assert(m.P == 0); // Not true. This will be -4. Why???
}

class UIObject : FrameworkElement
{
    public static readonly DependencyProperty PProperty =
        DependencyProperty.Register("P", typeof(int), typeof(UIObject), 
        new FrameworkPropertyMetadata(
            new PropertyChangedCallback(OnPChanged), 
            new CoerceValueCallback(CoerceP)));

    public int P
    {
        get { return (int)GetValue(PProperty); }
        set { SetValue(PProperty, value); }
    }

    private static void OnPChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
    {
        Debug.WriteLine(typeof(UIObject) + ".P changed from " + e.OldValue + " to " + e.NewValue);
    }

    private static object CoerceP(DependencyObject sender, object value)
    {
        int p = (int)value;
        if (p < 0)
        {
            Debug.WriteLine(typeof(UIObject) + ".P coerced from " + p + " to 0");
            p = 0;
        }
        return p;
    }
}

class ModelObject
{
    private int p;
    public int P
    {
        get
        {
            Debug.WriteLine(this + ".P returned " + this.p);
            return this.p;
        }
        set
        {
            Debug.WriteLine(this + ".P changed from +" + this.p + " to " + value);
            this.p = value;
        }
    }
}

解决方案

I don't think the coerce callback is meant to be a two-way street. One workaround would be to update the model's value inside of the coerce callback.

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