Custom view with scroll in Xamarin.Android - xamarin

Question

I have to display a large diagram in a Xamarin.Android application and the user must be able to scroll it horizontally and/or vertically.
A. My first thought was to create a custom view (inheriting from View) that handles the drawing in OnDraw and then place the custom view in a ScrollView. But in this situation I do not know:
how to tell the ScrollView how much content it has to scroll;
how do I know inside my custom view where the scroll is so that I can draw the corresponding part of the diagram (I want to draw only what is visible).
Just for testing I tried the layout below but I cannot get it to scroll:
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical"
android:layout_width="match_parent"
android:layout_height="match_parent"
>
<Button
android:id="#+id/btnLoadDiagram"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:text="Load Diagram" />
<ScrollView
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:fillViewport="true"
android:scrollbars = "vertical"
android:scrollbarStyle="insideInset" >
<my.namespace.DiagramView
android:layout_width="2000dp"
android:layout_height="2000dp"
android:id="#+id/diagramView" />
</ScrollView>
</LinearLayout>
B. The second thought was to inherit from ScrollView but I need to scroll both on horizontal and on vertical.
What is the recommended approach here?

Answer 1

In the end I implemented a solution based on option A.
I implemented a custom view that inherits from Android.Views.View. The view implements the GestureDetector.IOnGestureListener and ScaleGestureDetector.IOnScaleGestureListener interfaces for scrolling and zooming. Internally I keep track of current content position and draw only the content that fits inside the view area.