MVVM event handling - mvvm

Question

I am trying to manage dragdrop events on a "TreeView" object in a view with MVVM approach, thus I don't want write hookevent codes in "FormProjectWorksView.xaml.cs"... And following a tutorial on youtube : https://www.youtube.com/watch?v=Cx6YE86XzYE , I tried to get a custom dependency property being populated in xaml designer code in visual studio...But when I type the name of the customDP which is "DragCommand"; it doesn't get recognised, anywhere in the "xaml" file... In my case I tried to use it inside "" Tag..could you help why it doesn't showup in the IDE popup? and doesn't compile of course? Or am I totally in wrong direction to handle such mouseevents on a view separated from viewmodel...And even further actually I am using view switching from MainWindow.xml, which is the starting View of the application...and any other "UserControl-Views" are switched when necessary.
FormProjectWorksView.xaml
<UserControl x:Class="FullProject.Views.FormProjectWorksView"
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:local="clr-namespace:FullProject.Views"
xmlns:viewmodels="clr-namespace:FullProject.ViewModels"
mc:Ignorable="d"
d:DesignHeight="450" d:DesignWidth="800">
<Grid>
<Grid.ColumnDefinitions>
<ColumnDefinition Width="2*"/>
<ColumnDefinition Width="5*"/>
</Grid.ColumnDefinitions>
<TreeView x:Name="tv1" Grid.Column="0" ItemsSource="{Binding treeView.Items}"
AllowDrop="True"/>
<Grid x:Name="maingrid" Grid.Column="1" Background="Chartreuse">
<TextBlock Grid.Column="0" Margin="10 " Text="{Binding deneme}" FontSize="28"/>
</Grid>
</Grid>
</UserControl>
FormProjectWorksView.xaml.cs
using System.Windows;
using System.Windows.Controls;
using System.Windows.Input;
namespace FullProject.Views
{
/// <summary>
/// Interaction logic for FormProjectWorksView.xaml
/// </summary>
public partial class FormProjectWorksView : UserControl
{
public ICommand DragCommand
{
get { return (ICommand)GetValue(DragCommandProperty); }
set { SetValue(DragCommandProperty, value); }
}
// Using a DependencyProperty as the backing store for command. This enables animation, styling, binding, etc...
public static readonly DependencyProperty DragCommandProperty =
DependencyProperty.Register("DragCommand", typeof(ICommand), typeof(FormProjectWorksView), new PropertyMetadata(null));
public FormProjectWorksView()
{
InitializeComponent();
}
}
}
MainWindow.xaml
<Window x:Class="FullProject.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:FullProject"
xmlns:viewmodels="clr-namespace:FullProject.ViewModels"
xmlns:views="clr-namespace:FullProject.Views"
mc:Ignorable="d"
Title="MainWindow" Height="450" Width="800">
<Window.Resources>
<DataTemplate DataType="{x:Type viewmodels:MainFormViewModel}">
<views:MainFormView/>
</DataTemplate>
<DataTemplate DataType="{x:Type viewmodels:GlobalWorksViewModel}">
<views:GlobalWorksView/>
</DataTemplate>
<DataTemplate DataType="{x:Type viewmodels:GlobalResourcesViewModel}">
<views:GlobalResourcesView/>
</DataTemplate>
<DataTemplate DataType="{x:Type viewmodels:FormProjectWorksViewModel}">
<views:FormProjectWorksView/>
</DataTemplate>
</Window.Resources>
<Grid>
<ContentControl Content="{Binding CurrentViewModel}"/>
</Grid>
</Window>