双向绑定在Xamarin表单中不起作用

我正在Xamarin Form Project中工作.表单输入的值未显示在Binding上下文中.绑定上下文始终显示初始值而不是最新值.我已经添加了表单xaml部件和与View相关的View模型类.是否有任何Addition配置可启用双向绑定

I'm working in a Xamarin Form Project . The form entered values are not showing in the Binding context . Binding Context Always shows the Initial value not the Latest Value .I have added my forms xaml part and View related View model class.Is there any Addition configurations to enable 2 way binding

Xaml页面

 <StackLayout Grid.Row="0" Grid.Column="0">
        <Grid x:Name="grid">
          <Grid.RowDefinitions>
            <RowDefinition Height="*"/>
            <RowDefinition Height="*"/>
            <RowDefinition Height="*"/>
            <RowDefinition Height="*"/>
            <RowDefinition Height="*"/>
            <RowDefinition Height="*"/>
            <RowDefinition Height="*"/>
            </Grid.RowDefinitions>
        <Grid.ColumnDefinitions>
            <ColumnDefinition Width="*"/>
            <ColumnDefinition Width="*"/>
         </Grid.ColumnDefinitions>
            <Label x:Name="labelName" Grid.Row="0"  Grid.Column="0" Margin="10" FontSize="6"  VerticalOptions="CenterAndExpand"  HorizontalTextAlignment="Start" Text="Name"/>
                    <Entry  x:Name="textName" Grid.Row="0"  Grid.Column="1"  WidthRequest="100" FontSize="6" VerticalOptions="CenterAndExpand" HorizontalOptions="Start" HorizontalTextAlignment="Start" Text="{Binding Name,Mode=TwoWay}"  />
            <Label x:Name="labelAge" Grid.Row="1"  Grid.Column="0" Margin="10" FontSize="6"  Text="Age" VerticalOptions="CenterAndExpand" HorizontalTextAlignment="Start" />
                    <Entry  x:Name="textAge" Grid.Row="1"  Grid.Column="1" WidthRequest="100" FontSize="6" VerticalOptions="CenterAndExpand" HorizontalOptions="Start" HorizontalTextAlignment="Start" Text="{Binding Age,Mode=TwoWay}" />
            <Label x:Name="labelAddress" Grid.Row="2"  Grid.Column="0" Margin="10" FontSize="6"  Text="Address" VerticalOptions="CenterAndExpand" HorizontalTextAlignment="Start" />
                    <Entry  x:Name="textAddress" Grid.Row="2"  Grid.Column="1" WidthRequest="100" FontSize="6" VerticalOptions="CenterAndExpand" HorizontalOptions="Start" HorizontalTextAlignment="Start"  Text="{Binding Address,Mode=TwoWay}" />
            <Label x:Name="labelNICNumber" Grid.Row="3"  Grid.Column="0" Margin="10" FontSize="6" Text="NIC" VerticalOptions="CenterAndExpand" HorizontalTextAlignment="Start" />
                    <Entry  x:Name="textNIC" Grid.Row="3"  Grid.Column="1" WidthRequest="100" FontSize="6" VerticalOptions="CenterAndExpand" HorizontalOptions="Start" HorizontalTextAlignment="Start" Text="{Binding NIC,Mode=TwoWay}" />
            <Button Grid.Row="4"  Grid.Column="1" HeightRequest = "30"   VerticalOptions="CenterAndExpand" HorizontalOptions="Start" FontSize="6" Text="Save" Clicked="UserSaveClick" />
        </Grid>
    </StackLayout>

ViewModel

ViewModel

public event PropertyChangedEventHandler PropertyChanged;

    private string userName ;
    private string name;
    private int age ;
    private bool isBusy;
    private string address;
    private int nic;


    void OnPropertyChanged([CallerMemberName] string name = "")
    {
        PropertyChanged.Invoke(this, new PropertyChangedEventArgs(name));
    }

    public int NIC
    {
        get { return nic; }
        set
        {
            nic = value;
            OnPropertyChanged();

        }
    }


    public string Name
    {
        get { return name; }
        set
        {
            name = value;
            IsBusy = Name == "aa" ? true : false;
            OnPropertyChanged();
            OnPropertyChanged(nameof(DisplayMessage));
        }
    }



    public int Age
    {
        get { return age; }
        set
        {
            age = value;
            OnPropertyChanged();
        }
    }


    public string Address
    {
        get { return address; }
        set
        {
            address = value;
            OnPropertyChanged();

        }
    }

    public string DisplayMessage
    {
        get
        {
            return "Hi  " + name;
        }

    }




    public bool IsBusy
    {
        get { return isBusy; }
        set { isBusy = value; }
    }


}