Update readme (#4)

Update README.md

README.md

@@ -6,7 +6,122 @@
 
 # Android Nested Scroll WebView
 
-Android WebView implementation for nested scrolling layouts
+Android WebView implementation for nested scrolling layouts.
+
+## Introduction
+
+In case you have a native application that uses a collapsing toolbar layout, you may need to wrap your webview into a [NestedScrollingView](https://developer.android.com/reference/androidx/core/widget/NestedScrollView) to handle correctly nested scrolling to expand/collapse the toolbar.
+
+This is usually done like this:
+```xml
+<androidx.core.widget.NestedScrollView
+    android:layout_width="match_parent"
+    android:layout_height="match_parent"
+    app:layout_behavior="@string/appbar_scrolling_view_behavior">
+
+    <WebView
+        android:id="@+id/webView"
+        android:layout_width="match_parent"
+        android:layout_height="match_parent"/>
+
+</androidx.core.widget.NestedScrollView>
+```
+
+You may quickly realize that **webview viewport height takes all content size height**. So, for all effects, you are using a browser window with an infinite viewport height, which has important implications:
+* If page content is long, this may suppose performance penalties as whole page must be rendered.
+* In case of scrolling pages where new content is continuously loaded as user scrolls down the page, it will trigger all these loads automatically, this could end on serious performance problems. Think about a "infinite" news feed for example.
+* Page content based on viewport height may be displayed wrongly. Think about on fixed footer elements for example, these will be always displayed at the end of the scrollable content.
+
+If you are thinking on using the `android:fillViewport="false"` property for your NestedScrollView, you won't be able to perform any scroll on your webview content...
+
+NestedScrollWebview implementation avoids this "height issue", making webview to have correct viewport size, while working with a collapsable toolbar layout.
+
+## How to use it?
+
+Just include directly the `NestedScrollWebView` in your layout:
+
+```xml
+<?xml version="1.0" encoding="utf-8"?>
+<androidx.coordinatorlayout.widget.CoordinatorLayout
+    xmlns:android="http://schemas.android.com/apk/res/android"
+    xmlns:app="http://schemas.android.com/apk/res-auto"
+    android:layout_width="match_parent"
+    android:layout_height="match_parent">
+
+    <com.google.android.material.appbar.AppBarLayout
+        android:id="@+id/app_bar"
+        android:layout_width="match_parent"
+        android:layout_height="@dimen/app_bar_height"
+        android:theme="@style/Theme.NestedScrollWebViewDemo.AppBarOverlay">
+
+        <com.google.android.material.appbar.CollapsingToolbarLayout
+            android:id="@+id/toolbar_layout"
+            style="@style/Widget.MaterialComponents.Toolbar.Primary"
+            android:layout_width="match_parent"
+            android:layout_height="match_parent"
+            app:contentScrim="?attr/colorPrimary"
+            app:layout_scrollFlags="scroll|exitUntilCollapsed"
+            app:toolbarId="@+id/toolbar">
+
+            <androidx.appcompat.widget.Toolbar
+                android:id="@+id/toolbar"
+                android:layout_width="match_parent"
+                android:layout_height="?attr/actionBarSize"
+                app:layout_collapseMode="pin"
+                app:popupTheme="@style/Theme.NestedScrollWebViewDemo.PopupOverlay" />
+
+        </com.google.android.material.appbar.CollapsingToolbarLayout>
+    </com.google.android.material.appbar.AppBarLayout>
+
+    <com.telefonica.nestedscrollwebview.NestedScrollWebView
+        android:id="@+id/webView"
+        android:layout_width="match_parent"
+        android:layout_height="match_parent"
+        app:layout_behavior="@string/appbar_scrolling_view_behavior" />
+
+</androidx.coordinatorlayout.widget.CoordinatorLayout>
+```
+
+## Configuration
+
+When expanding toolbar inside a CoordinatorLayout, instead of resizing the space left by the toolbar, it pushes down the content below.
+
+This may be an issue for example for pages where a fixed footer element is displayed. So, in order to correctly resize the webview viewport on these expands you can add this attribute to the NestedScrollWebView.
+
+`app:coordinatorBottomMatchingEnabled={"true"|"false"}`
+
+This is disabled by default, as webview resizing is expensive.
+
+```xml
+<com.telefonica.nestedscrollwebview.NestedScrollWebView
+    android:id="@+id/webView"
+    android:layout_width="match_parent"
+    android:layout_height="match_parent"
+    app:coordinatorBottomMatchingEnabled="true"
+    app:layout_behavior="@string/appbar_scrolling_view_behavior" />
+```
+
+## How we do it?
+
+Implementation extends [WebView](https://developer.android.com/reference/android/webkit/WebView) applying nested scrolling code logic from androidx.core [NestedScrollView](https://developer.android.com/reference/androidx/core/widget/NestedScrollView).
+
+## Known issues, considerations and Future improvements
+
+* As implementation relies on NestedScrollView touch events interception, in cases there are web content elements that intercept movement events, for example a map view or a horizontal carousel, these movement events will be interpreted also as scrolling events for nested scrolling. We are thinking on a solution to prevent this. 
+
+## Videos
+<table>
+<tr>
+<td>
+<video src="https://user-images.githubusercontent.com/5360064/198062480-4f3d6908-fdcf-446f-bc8c-625635b308f9.mp4" />
+</td>
+<td>
+<video src="https://user-images.githubusercontent.com/5360064/198062613-f77eaf9b-bf6b-48aa-b514-b86ccc910102.mp4" />
+</td>
+</tr>
+</table>
+
+# Usage
 
 To include the library add to your app's `build.gradle`: