Bug 8765 - Crash happen when implement custom scrollview
Summary: Crash happen when implement custom scrollview
Alias: None
Product: Android
Classification: Xamarin
Component: BCL Class Libraries ()
Version: 4.2.x
Hardware: PC Windows
: --- normal
Target Milestone: ---
Assignee: Bugzilla
Depends on:
Reported: 2012-12-05 04:45 UTC by Low
Modified: 2012-12-05 21:06 UTC (History)
2 users (show)

Is this bug a regression?: ---
Last known good build:

Crash logcat (339.86 KB, text/plain)
2012-12-05 04:45 UTC, Low

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Description Low 2012-12-05 04:45:00 UTC
Created attachment 3058 [details]
Crash logcat

When I implement a custom scrollview and override onTouch event, sometimes it will crash. Refer to the attachment for the crash logcat. This crash issue is happen SOMETIMES only. I need to keep on touch and scroll the screen for sometime then only it will crash. Please help to look into this issue.

Activity code:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

using Android.App;
using Android.Content;
using Android.OS;
using Android.Runtime;
using Android.Views;
using Android.Widget;
using Android.Util;

namespace HelloM4A
    [Activity (Label = "Activity2", MainLauncher = true)]            
    public class Activity2 : Activity
        protected override void OnCreate (Bundle bundle)
            base.OnCreate (bundle);


            LinearLayout v = (LinearLayout)FindViewById(Resource.Id.layout);
            CustomScrollView scrollView = new CustomScrollView(this);
            LinearLayout ll = new LinearLayout(this);
            TextView tv = new TextView(this);
            tv.Text = "aksdjhaskudhasiurgqwkebegbsewkrhqwakdnkabsrkawdksbjfbadaskfbaskdhasl;dasdkbaskdbasdhasldhnasldhqaowehqwkjfbkgfbeklrhwqaohlawndsl;dhiaowhrwqan";
            scrollView.AddView(ll, new ViewGroup.LayoutParams(ViewGroup.LayoutParams.MatchParent, ViewGroup.LayoutParams.MatchParent));
            v.AddView(scrollView, new ViewGroup.LayoutParams(ViewGroup.LayoutParams.MatchParent, ViewGroup.LayoutParams.MatchParent));

        class CustomScrollView : ScrollView
            int mMarginThreshold;
            public CustomScrollView(Context context)
                : base(context)
                mMarginThreshold = (int)TypedValue.ApplyDimension(ComplexUnitType.Dip,
                                                                  40, this.Resources.DisplayMetrics);
            public override bool OnTouchEvent(MotionEvent ev)
                int x = (int)ev.GetX();
                Console.WriteLine("x: " + x + ", margin: " + mMarginThreshold);
                Console.WriteLine("x: " + ev.GetX() + ", y: " + ev.GetY() + ", index: " + ev.ActionIndex);
                if (x <= mMarginThreshold)
                    return false;
                return base.OnTouchEvent(ev);

Layout file:

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
Comment 1 Jonathan Pryor 2012-12-05 16:31:03 UTC
The cause for the crash is in the logcat output you attached:

> UNHANDLED EXCEPTION: Java.Lang.IllegalArgumentException: Exception of type 'Java.Lang.IllegalArgumentException' was thrown.
> at Android.Runtime.JNIEnv.CallNonvirtualBooleanMethod (intptr,intptr,intptr,Android.Runtime.JValue[]) <0x00090>
> at Android.Views.View.OnTouchEvent (Android.Views.MotionEvent) <0x001e7>
> at HelloM4A.Activity2/CustomScrollView.OnTouchEvent (Android.Views.MotionEvent) <0x0029f>
> at Android.Views.View.n_OnTouchEvent_Landroid_view_MotionEvent_ (intptr,intptr,intptr) <0x00057>
> at (wrapper dynamic-method) object.bafd36d0-07bf-490c-960a-0a5f29f00733 (intptr,intptr,intptr) <0x00033>
>   --- End of managed exception stack trace ---
> java.lang.IllegalArgumentException: pointerIndex out of range
> 	at android.view.MotionEvent.nativeGetAxisValue(Native Method)
> 	at android.view.MotionEvent.getY(MotionEvent.java:1996)
> 	at android.widget.ScrollView.onTouchEvent(ScrollView.java:588)
> 	at hellom4a.Activity2_CustomScrollView.n_onTouchEvent(Native Method)

From the stack trace, we see that your `base.OnTouchEvent(ev)` invokes ScrollView.onTouchEvent():


ScrollView.onTouchEvent() then calls MotionEvent.getY(), which calls MotionEvent.nativeGetAxisValue():


The C++ `pointerIndex` parameter is always `0` (from the Java invocation), and the C++ `event->getPointerCount()` invocation should (hopefully!) be identical to the Java MotionEvent.getPointerCount() method.

In short, you get the IllegalArgumentException because (somehow...) MotionEvent.getPointerCount() is returning 0, thus causing `size_t(0) >= pointerCount` to fail.

To confirm, please add a debug message to your OnTouchEvent() and print out the value of `ev.PointerCount`: is it ever 0?

If it is ever 0, this is clearly an Android bug -- it should never be 0, especially since they document that it's always >= 1:

Comment 2 Low 2012-12-05 21:06:49 UTC
Updated onTouchEvent methods to the following:

public override bool OnTouchEvent(MotionEvent ev)
	int x = (int)ev.GetX();
	if (x <= mMarginThreshold)
		return false;

	bool flag = false;
		flag = base.OnTouchEvent(ev);
	catch(Java.Lang.IllegalArgumentException e)
		Console.WriteLine("Execption catch. pointer count: " + ev.PointerCount);
		Console.WriteLine("Execption catch. action index: " + ev.ActionIndex);
		int activePointerId = MotionEventCompat.GetActionIndex(ev);
		int activePointerIndex = MotionEventCompat.FindPointerIndex(ev, activePointerId);

		Console.WriteLine("Execption catch. pointer id: " + activePointerId);
		Console.WriteLine("Execption catch. pointer index: " + activePointerIndex);

		Console.WriteLine("Exception: " + e.Message);

	return flag;

And I get the output of:

Execption catch. pointer count: 2
Execption catch. action index: 0
Execption catch. pointer id: 0
Execption catch. pointer index: 0
Exception: pointerIndex out of range
Execption catch. pointer count: 2
Execption catch. action index: 0
Execption catch. pointer id: 0
Execption catch. pointer index: 0
Exception: pointerIndex out of range
Execption catch. pointer count: 2
Execption catch. action index: 0
Execption catch. pointer id: 0
Execption catch. pointer index: 0
Exception: pointerIndex out of range
Execption catch. pointer count: 1
Execption catch. action index: 0
Execption catch. pointer id: 0
Execption catch. pointer index: -1
Exception: pointerIndex out of range

It seems like Android is throwing exception even though the pointer count is not 0. And I have test it with native Android code, it seems to be crash on the same point. So, this is confirm to be an Android bug. So for now, I will catch the exception in order to prevent crash.