MainWindow.xaml

<Window x:Class="WPFMvvMTest.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
        xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
        xmlns:local="clr-namespace:WPFMvvMTest"
        mc:Ignorable="d"
        Title="MainWindow" Height="450" Width="800">
    <DockPanel>
        <ToolBar DockPanel.Dock="Top">
            <Button Content="-" Width="50"
                    Command="{Binding MinusCommand}" IsEnabled="{Binding MinusEnable}"></Button>
            <TextBox Width="50" Background="#FF8F8F8A"
                     Text ="{Binding Number, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}"></TextBox>
            <Button Content="+" Width="50"
                    Command="{Binding PlusCommand}" IsEnabled="{Binding PlusEnable}"></Button>
        </ToolBar>
        <TextBox Text="{Binding PageContents}"></TextBox>
    </DockPanel>
</Window>