有关WPF依赖属性验证的问题

[亲爱的大狗]

自己写了一个小Demo,遇到了一些问题.搞不明白,希望能在这里得到解答.
这是我的demo结构


这是依赖属性的全部实现:

        public string MyObserver
        {
            get { return (string)GetValue(MyObserverProperty); }
            set { SetValue(MyObserverProperty, value); }
        }

        static FrameworkPropertyMetadata myPropertyMetadata = new FrameworkPropertyMetadata("default hello", FrameworkPropertyMetadataOptions.BindsTwoWayByDefault, PropertyChangedCallback, CoerceValueCallback, false, UpdateSourceTrigger.PropertyChanged);

        private static object CoerceValueCallback(DependencyObject d, object baseValue)
        {
            MessageBox.Show("I am forced to do this. and the baseValue is :"  + baseValue.ToString());
            return baseValue+"~~~";
        }

        private static void PropertyChangedCallback(DependencyObject d, DependencyPropertyChangedEventArgs e)
        {
            MessageBox.Show("I am going to tell you the propertyChanged \r\ne.OldValue is: "+e.OldValue+"\r\ne.NewValue is: "+e.NewValue);
        }

        // Using a DependencyProperty as the backing store for MyObserver.  This enables animation, styling, binding, etc...
        public static readonly DependencyProperty MyObserverProperty =
            DependencyProperty.Register("MyObserver", typeof(string), typeof(MyObserverControl), myPropertyMetadata,ValidateValueCallback);

        private static bool ValidateValueCallback(object value)
        {
            string input = value as string;
            foreach (char item in input)
            {
                if (item=='A')
                {
                    MessageBox.Show("I am going to validate your inputs not containing letter \"A\". and now i am returning False");
                    return false;
                }
            }
            MessageBox.Show("I am going to validate your inputs not containing letter \"A\". and now i am returning True");
            return true;
        }

前台绑定的代码

        <TextBox Grid.Row="0" Text="{Binding ElementName=uc_MyObserver,Path=MyObserver,UpdateSourceTrigger=PropertyChanged,Mode=TwoWay}" Height="40" Width="400"></TextBox>
        <local:MyObserverControl x:Name="uc_MyObserver" Grid.Row="1"/>

问题就来了,如果我去掉ValidateValueCallback() 一切正常

.当改动值时,能够正常跳出Messbox通知.
可是如果我在Register中添加了ValidateValueCallback(),绑定就失效了,改动textbox也不会触发CoerceValueCallback()了.只有初始化的时候会跳两个
MessageBox.Show("I am going to validate your inputs not containing letter \"A\". and now i am returning True");


请问是什么原因?添加了ValidateValueCallback()和不添加的区别在哪里?希望能给个解决办法!谢谢了~

[亲爱的大狗]

顶下 要到6个字符

[亲爱的大狗]

有没有帮忙解答一下.

[q107770540]

http://www.cnblogs.com/mgen/archive/2012/01/03/2311206.html

[亲爱的大狗]

引用 4 楼 q107770540 的回复:

http://www.cnblogs.com/mgen/archive/2012/01/03/2311206.html

我看过这个帖子,我也照着做过.没有问题.不加ValidateValueCallback()委托的时候,执行顺序也是正确的.加了以后那个TextBox和TextBlock之间的绑定好像就断了,CoerceValueCallback也不会执行了.