在WPF，MVVM中实现TextBox LostFocus事件 [英] mplement TextBox LostFocus event in WPF , MVVM

问题描述

我想在我的WPF窗口中实现TextBox LostFocus事件，该事件应该在我的ViewModel中触发，以便我可以验证该值。偶数参数应该传递给命令。如果我们可以使用附加命令行为，那么任何人都可以请分享一个例子。



注意：我使用的是MVVM模式。



问候，



Ramana

I want to implement TextBox LostFocus event in my WPF window which should be fired in my ViewModel so that I can validate the value. Even parameter should be passed to the command. If we can use Attached Command Behavior, so anyone can please share an example.

Note: I am using MVVM pattern.

Regards,

Ramana

推荐答案

可以通过创建的附加行为来实现。

Can be achieved by created Attached Behaviour.

public class TextBoxBehavior
    {
        public static DependencyProperty OnLostFocusProperty = DependencyProperty.RegisterAttached(
            "OnLostFocus",
            typeof(ICommand),
            typeof(TextBoxBehavior),
            new UIPropertyMetadata(TextBoxBehavior.OnLostFocus));

        public static void SetOnLostFocus(DependencyObject target, ICommand value)
        {
            target.SetValue(TextBoxBehavior.OnLostFocusProperty, value);
        }

        /// <summary>
        /// PropertyChanged callback for OnDoubleClickProperty.  Hooks up an event handler with the 
        /// actual target.
        /// </summary>
        private static void OnLostFocus(DependencyObject target, DependencyPropertyChangedEventArgs e)
        {
            var element = target as TextBox;
            if (element == null)
            {
                throw new InvalidOperationException("This behavior can be attached to a TextBox item only.");
            }

            if ((e.NewValue != null) && (e.OldValue == null))
            {
                element.LostFocus += OnPreviewLostFocus;
            }
            else if ((e.NewValue == null) && (e.OldValue != null))
            {
                element.LostFocus -= OnPreviewLostFocus;
            }
        }

        private static void OnPreviewLostFocus(object sender, RoutedEventArgs e)
        {
            UIElement element = (UIElement)sender;
            ICommand command = (ICommand)element.GetValue(TextBoxBehavior.OnLostFocusProperty);
            if (command != null)
            {
                command.Execute(e);
            }
        }
    }

xmlns:ACB="clr-namespace:XML_Binding_Sample1.AttachedCommandBehaviour"

<textbox text="{Binding CustomerName}" acb:textboxbehavior.onlostfocus="{Binding  NameChangeCommand}" xmlns:acb="#unknown" />

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