What is LayoutInflater and what does it do?

You mean the LayoutInflater , actually inflater is the name of the variable that is generally used to inflate a layout in Android:

LayoutInflater inflater = (LayoutInflater)this.GetSystemService(Context.LayoutInflaterService);
 var layout = inflater.Inflate(Resource.Layout.layout_elemento, layoutImages) as LinearLayout;

To establish a difference it is necessary to know the definitions:

LayoutInflater Instantiates a layout XML file into its corresponding view objects. It is never used directly. Instead, use Context.getSystemService(Class)to retrieve a standard LayoutInflater instance that is already attached to the current context and configured correctly for the device it is running on.

FindViewById() Finds the first descendant view with the given ID, the view itself if the ID matches, or null if the ID is invalid (<0) or if there is no matching view in the hierarchy.

Regarding your questions:

they compare a Layoutinflater with a beach inflator, I understand the metaphor that the XML goes inside like gas and the beach ball would be the view/View type variable where that XML is loaded

This is so? I know it may seem simple, but there is something that squeaks me in all this.

It's a good comparison, the "inflator" inflates the beach layout:

 View view =  LayoutInflater.Inflate(Resource.Layout.layout_playa, null);

but inside this view (layout_playa) you can find elements like pelota, sombrilla, lentes_sol:

<?xml version="1.0" encoding="utf-8" ?>
    <RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
        android:layout_width="match_parent"
        android:layout_height="wrap_content">


        <ImageView
            android:id="@+id/pelota"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"/>
        <TextView
            android:id="@+id/sombrilla"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"/>
        <TextView
            android:id="@+id/lentes_sol"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"/>

    </RelativeLayout >

To access these elements, you search in the view that you previously inflated by means of their id using FindViewById() , since these elements are inside the view:

 View view =  LayoutInflater.Inflate(Resource.Layout.layout_playa, null);
 ImageView img_pelota = view.FindViewById<ImageView>(Resource.Id.pelota);
 TextView tv_sombrilla = view.FindViewById<TextView>(Resource.Id.sombrilla);
 TextView tv_lentes = view.FindViewById<TextView>(Resource.Id.lentes_sol);

It's important that the view references you get via FindViewById() must exist, otherwise you'll get null values.

What advantages can it have? When would it be more convenient for me to use Layoutinflater than to assign a FindViewById() to a variable and pass the layout directly?

Actually its use is different, LayoutInflater creates an instance of a layout XML file in its corresponding view objects and this view does not need to exist in the layout of your activity but in the resources while to use FindViewById() you use to search for views that are in a previously inflated layout:

Another example of LayoutInflater imagines that you have to "inflate" one type of cell when your list cell is even and another type when it is odd:

public override View GetView(int position, View convertView, ViewGroup parent) {

   View view = convertView;
   if (view == null) // no view to re-use, create new

    if (position % 2 == 1) {
       view  =  LayoutInflater.Inflate(Resource.Layout.layout_par, null);
    } else {
       view  =  LayoutInflater.Inflate(Resource.Layout.layout_impar, null);
    }

   }

    return view ;
}

As an example of FindViewById() , you search inside a layout ( layout_app) for the reference of a view ( TextView) by means of its id ( Resource.Id.tv_titulo) and modify some property, in this case you assign a text.

 public override View GetView(int position, View convertView, ViewGroup parent)
        {

       View view = convertView;
       if (view == null) // no view to re-use, create new   
           view  =  LayoutInflater.Inflate(Resource.Layout.layout_par, null);
           TextView tv_sombrilla = view.FindViewById<TextView>(Resource.Id.sombrilla);

        tv_sombrilla.SetText("Aplicación Aritzbn");  
       }

        return view ;
    }

The LayoutInflater , basically what it does is to have a reference/instantiate an axml layout to be able to use the views within it. When you go to load content on a screen, for example, a Activity, you do SetContentViewthis to indicate that the content of that screen points to a specific layout. This means that the references that you are going to search for FindViewByIdin that Activity should only be attached to that layout that you have loaded.

Normally, the main view of a Layout is a ViewGroup (for example, LinearLayout, FrameLayout, etc...), a layout type parent that contains children, so if you try to make FindViewByIda view or child that does not belong to that ViewGroup , for example, that it is in another axml layout than the one loaded for a specific screen Activity, then it will return a reference to you null.

Let's take the following example: Let's say you want to create different screens. Using the same layout that contains a Buttonwith the id buttonand a TextViewwith the id textView. Doing this via axml has many alternatives, such as using the include tag . However, if you want to do it programmatically, you should use LayoutInflater here.

For example: Xamarin.Android (C#), using LayoutInflater in a Activity:

// Esta es la referencia que tiene el Button y el TextView
View layoutReutilizable = LayoutInflater.Inflate(Resource.Layout.layout_reutilizable, null);

// Esta es la referencia a la vista de tu Activity donde quieres cargar el layout
View layoutPadre = FindViewById<LinearLayout>(Resource.Id.llContainer));
layoutPadre.AddView(layoutReutilizable);

This way you already have that layout loaded inside your LinearLayout. If you want to access that Buttonand the TextViewto modify them, you can simply do:

Button button = layoutReutilizable.FindViewById<Button>(Resource.Id.button);
TextView textView = layoutReutilizable.FindViewById<Button>(Resource.Id.textView);

and you can now customize it and assign the properties you want.