Mastering Modern UI: A Step-by-Step Guide to Creating Metro UI in WPF

To create metro ui you first have to install "Mahapps.metro" from NuGet.To install it right click on project and click on manage NuGet and type Mahapps.metro you will get this package you have to install from here.Now you are ready to create metro ui.Now open you Mainwindow.xaml and add one namespace like bellow

xmlns:Controls="clr-namespace:MahApps.Metro.Controls;assembly=MahApps.Metro" 

and replace Window to Controls:MetroWindow

Now your Mainwindow.xaml become

<Controls:MetroWindow x:Class="ProjectName.MainWindow"

          xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"

          xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"

          xmlns:Controls="clr-namespace:MahApps.Metro.Controls;assembly=MahApps.Metro"

          Title="MainWindow"

          Height="600"

          Width="800">

  <!-- your content -->

</Controls:MetroWindow>

Now you have to modify Mainwindow.xaml.cs file in wpf application before it was inherited from Window.Now to make it metro you have to replace Window to MetroWindow like

  public partial class MainWindow :MetroWindow 

 { 

         public MainWindow() 

         { 

               InitializeComponent(); 

         }

}

Now add some Button and run the application it will display window with black

background.To apply metro default style you have to add some resources.

All of MahApp.Metro’s resources are contained within separate resource dictionaries.

In order for most of the controls to adopt the MahApps.Metro theme,you will need to

add the ResourceDictionaries to your App.xaml

<Application x:Class="WpfApplication.App"

             xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"

             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"

             StartupUri="MainWindow.xaml">

<Application.Resources>

<ResourceDictionary>

<ResourceDictionary.MergedDictionaries>

<!-- MahApps.Metro resource dictionaries. Make sure that all file names are Case Sensitive! -->

 <ResourceDictionary Source="pack://application:,,,/MahApps.Metro;component/Styles/

   Controls.xaml"/>

<ResourceDictionary Source="pack://application:,,,/MahApps.Metro;component/Styles/

  Fonts.xaml"/>

<ResourceDictionary Source="pack://application:,,,/MahApps.Metro;component/Styles/

  Colors.xaml"/>

      <!-- Accent and AppTheme setting -->

   <ResourceDictionary Source="pack://application:,,,/MahApps.Metro;component/Styles/Accents/Blue.xaml" />

<ResourceDictionary Source="pack://application:,,,/MahApps.Metro;component/Styles/Accents/BaseLight.xaml" />

   </ResourceDictionary.MergedDictionaries>

   </ResourceDictionary>

  </Application.Resources>

</Application>

Now if you run the application you will get metro window with default style.
Watch video for more detail