<Window x:Class="ShenJingBingDemo.View.VLoginWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:i="http://schemas.microsoft.com/expression/2010/interactivity"
        xmlns:ei="http://schemas.microsoft.com/expression/2010/interactions"
        xmlns:vm="clr-namespace:ShenJingBingDemo.ViewModel"
        Title="登录" Height="300" Width="300">
    <Window.DataContext>
        <vm:VMLoginWindow />
    </Window.DataContext>

    <i:Interaction.Triggers>
        <i:EventTrigger  EventName="Loaded">
            <ei:CallMethodAction TargetObject="{Binding}" MethodName="MainWindow_Loaded"/>
        </i:EventTrigger>
    </i:Interaction.Triggers>
    <Grid>
        <Button Content="登录" VerticalAlignment="Center" HorizontalAlignment="Center" Width="100" Height="60">
            <i:Interaction.Triggers>
                <i:EventTrigger  EventName="Click">
                    <ei:CallMethodAction TargetObject="{Binding}" MethodName="Btn_Login_Click"/>
                </i:EventTrigger>
            </i:Interaction.Triggers>
        </Button>
    </Grid>
</Window>

using System.Windows;

namespace ShenJingBingDemo.ViewModel
{
    public class VMLoginWindow : NotificationObject
    {
        #region 变量
        Window win;
        #endregion 变量

        #region 事件
        public void MainWindow_Loaded(object sender, RoutedEventArgs e)
        {
            win = sender as Window;

           // e.Handled = true;
        }

        public void Btn_Login_Click(object sender, RoutedEventArgs e)
        {
            MainWindow mainwin = new MainWindow();
            win.Close();
            mainwin.ShowDialog();

          //  e.Handled = true;
        }

        #endregion 事件

    }
}

using System;
using System.ComponentModel;
using System.Linq.Expressions;
using System.Reflection;
namespace ShenJingBingDemo
{
    public abstract class NotificationObject : INotifyPropertyChanged
    {

        public event PropertyChangedEventHandler PropertyChanged;

        protected virtual void RaisePropertyChanged(string propertyName)
        {
            PropertyChangedEventHandler handler = this.PropertyChanged;
            if (handler != null)
            {
                handler(this, new PropertyChangedEventArgs(propertyName));
            }
        }

        protected void RaisePropertyChanged(params string[] propertyNames)
        {
            if (propertyNames == null) throw new ArgumentNullException("propertyNames");

            foreach (var name in propertyNames)
            {
                this.RaisePropertyChanged(name);
            }
        }

        protected void RaisePropertyChanged<T>(Expression<Func<T>> propertyExpression)
        {
            var propertyName = ExtractPropertyName(propertyExpression);
            this.RaisePropertyChanged(propertyName);
        }

        public static string ExtractPropertyName<T>(Expression<Func<T>> propertyExpression)
        {
            if (propertyExpression == null)
            {
                throw new ArgumentNullException("propertyExpression");
            }

            var memberExpression = propertyExpression.Body as MemberExpression;
            if (memberExpression == null)
            {
                throw new ArgumentException("PropertySupport_NotMemberAccessExpression_Exception", "propertyExpression");
            }

            var property = memberExpression.Member as PropertyInfo;
            if (property == null)
            {
                throw new ArgumentException("PropertySupport_ExpressionNotProperty_Exception", "propertyExpression");
            }

            var getMethod = property.GetGetMethod(true);
            if (getMethod.IsStatic)
            {
                throw new ArgumentException("PropertySupport_StaticExpression_Exception", "propertyExpression");
            }

            return memberExpression.Member.Name;
        }

    }
}