WPF中用MVVM绑定ContentControl界面无变化

[kee_]

在WPF中使用MVVM绑定ContentControl，调试的时候Query和Refund方法都是进的去的，问题就在
ViewModel = _vMQueryPayListCtrl这些东西都无效，界面没有变化，仔细对比了别人的demo，也没找到问题。
VMMainWindow中继承了INotifyPropertyChanged，由于代码较多，只贴了主要部分代码。
xaml部分

 <Window.Resources>
        <v:VMMainWindow x:Key="MainViewModel" />
        <DataTemplate DataType="{x:Type v:VMNumberArea}">
            <c:NumberArea />
        </DataTemplate>
        <DataTemplate DataType="{x:Type v:VMQueryPayListCtrl}">
            <c:QueryPayListCtrl/>
        </DataTemplate>
        <DataTemplate DataType="{x:Type v:VMRefundCtrl}">
            <c:RefundCtrl/>
        </DataTemplate>
        
    </Window.Resources>
    <Grid DataContext="{StaticResource MainViewModel}">
 <ContentControl x:Name="workArea" Background="White" Content="{Binding ViewModel}"  HorizontalAlignment="Left" Height="{Binding Wheight}"  Width="850" Grid.Row="2" VerticalAlignment="Top"/>

        <UserCtrl:ShadeCtrl  Tag="查询" HorizontalAlignment="Left" Grid.Row="0" VerticalAlignment="Top" Height="85" Margin="131,0,0,0" Width="58">
            <i:Interaction.Triggers>
                <i:EventTrigger EventName="MouseLeftButtonUp">
                    <i:InvokeCommandAction Command="{Binding TextBlockCommand}"  CommandParameter="查询"  />
                </i:EventTrigger>
            </i:Interaction.Triggers>
        </UserCtrl:ShadeCtrl>
 <UserCtrl:ShadeCtrl  Tag="退款" HorizontalAlignment="Left" Grid.Row="0" VerticalAlignment="Top" Height="85" Margin="63,0,0,0" Width="68" >
            <i:Interaction.Triggers>
                <i:EventTrigger EventName="MouseLeftButtonUp">
                    <i:InvokeCommandAction Command="{Binding TextBlockCommand}"  CommandParameter="退款"  />
                </i:EventTrigger>
            </i:Interaction.Triggers>
        </UserCtrl:ShadeCtrl>

VM部分

 
   private readonly VMNumberArea _vMNumberArea = new VMNumberArea();
        private readonly VMQueryPayListCtrl _vMQueryPayListCtrl = new VMQueryPayListCtrl();
        private readonly VMRefundCtrl _vMRefundCtrl = new VMRefundCtrl();
     private object _viewModel;

        public object ViewModel
        {
            get { return _viewModel; }
            set
            {
                if (_viewModel == value)
                {
                    return;
                }
                _viewModel = value;
                OnPropertyChanged("ViewModel");
            }
        }
        public DelegateCommand TextBlockCommand { get; set; }

 public VMMainWindow()
        {
            this.TextBlockCommand = new DelegateCommand();
            this.TextBlockCommand.ExecuteAction = new Action<object>(ShowTextBlock);
        }

        private void ShowTextBlock(object obj)
        {
            switch (obj.ToString())
            {
                case "收款":
                    Receivables();
                    break;
                case "退款":
                    Refund();
                    break;
                case "查询":
                    Query();
                    break;
                case "统计":
                    Statistics();
                    break;
                case "解绑":
                    Untying();
                    break;
                case "设置":
                    Setup();
                    break;
                case "账户":
                    Account();
                    break;
                case "退出":
                default:
                    Closed?.Invoke();
                    break;
            }
        }
   private void Query()
        {
            Height = new GridLength(0);
            Wheight = 475;
            ViewModel = _vMQueryPayListCtrl;
        }

        private void Refund()
        {
            ViewModel = new VMRefundCtrl();
        }

[exception92]

ViewModel = _vMQueryPayListCtrl这些东西都无效 -》都不清楚“这些东西”是干什么用的么？ 既然不知道 就要重新学一下MVVM了。

[kee_]

问题已经解决了，因为在v的后台中给ContentControl的content绑定了一个值，因为这个值导致vm中的切换无效的，lz需要重新学习下MVVM了