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POHow do I make Binding respect DependencyProperty value coercion?
 

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  1. POHow do I make Binding respect DependencyProperty value coercion?
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    <p>I have a control with a DependencyProperty with a CoerceValueCallback. This property is bound to a property on a model object.</p> <p>When setting the control property to a value that causes coercion the Binding pushes the <strong>uncoerced</strong> value to the model object. The property value on the control is coerced correctly.</p> <p>How do I get the Binding to push the <strong>coerced</strong> value to the model object?</p> <pre><code>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 &lt; 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; } } } </code></pre>
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    1. USJesper Larsen-Ledet
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