WPF CM框架下点击不同的按钮切换到不同的界面

<UserControl x:Class="WinTab.View.TabControl"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
xmlns:cal="http://www.caliburnproject.org"
xmlns:vm="clr-namespace:WinTab.View"
xmlns:me="clr-namespace:WinTab.ViewModel"
mc:Ignorable="d"
d:DesignHeight="300" d:DesignWidth="300">
<UserControl.DataContext>
<me:TabControlViewModel></me:TabControlViewModel>
</UserControl.DataContext>
<Grid>
<DockPanel>
<Button Height="60" Width="100" DockPanel.Dock="Top" cal:Message.Attach="[Event Click]=[Action Btn1Click($view,$eventArgs)]"></Button>
<Button Height="60" Width="100" DockPanel.Dock="Bottom" cal:Message.Attach="[Event Click]=[Action Btn2Click($view,$eventArgs)]"></Button>
<StackPanel>
<ContentControl Content="{Binding ConVM}"></ContentControl>
</StackPanel>
</DockPanel>
</Grid>
</UserControl>

public class TabControlViewModel:PropertyChangedBase
{
public void Btn1Click(object sender,RoutedEventArgs e)
{

ConVM = new Tab1View();
}

public void Btn2Click(object sender, RoutedEventArgs e)
{
ConVM = new Tab2View();
}

private object conVM;
public object ConVM
{
get { return conVM; }
set
{
conVM = value;
NotifyOfPropertyChange(() => ConVM);
}
}
}