namespace WpfApp1
{
     class MyLocator
     {
          public MainWindowViewModel myMainWindowViewModel { get; } = new MainWindowViewModel();
     }
}

namespace WpfApp1
{
     class MainWindowViewModel
     {
          public MainWindowViewModel()
          {
               BookName = "Hello";
          }

          public string BookName { get; set; }
     }
}

<Application x:Class="WpfApp1.App"
          xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
          xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
          xmlns:local="clr-namespace:WpfApp1"
          StartupUri="MainWindow.xaml">

     <Application.Resources>
          <ResourceDictionary>
               <local:MyLocator x:Key="KeyForMyLocator" />
          </ResourceDictionary>
     </Application.Resources>

</Application>

<Window x:Class="WpfApp1.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:WpfApp1"
          mc:Ignorable="d"
          DataContext="{Binding Source={StaticResource KeyForMyLocator}, Path=myMainWindowViewModel}"
          Title="MainWindow" Height="450" Width="800">
     <StackPanel>

          <TextBlock
               Text="{Binding BookName}"
               HorizontalAlignment="Left"
               FontSize="22">
          </TextBlock>
         
     </StackPanel>
</Window>