NPE in ChangeCurrentByOneFromLongPressCommand (on Samsung devices w/ Android 4.3)

Question

Using a couple android.widget.NumberPicker in my Android App view and I get the following message when I hold down on one of the numbers arrows:-

FATAL EXCEPTION: main 
java.lang.NullPointerException at android.widget.NumberPicker$ChangeCurrentByOneFromLongPressCommand.run(NumberPicker.java:2245)
at android.os.Handler.handleCallback(Handler.java:730)
at android.os.Handler.dispatchMessage(Handler.java:92)
at android.os.Looper.loop(Looper.java:137)
at android.app.ActivityThread.main(ActivityThread.java:5419)

Anyone got any ideas on how I can stop this problem?

UPDATE: From the comments so far, it seems that this exception only happened on Samsung devices with Android 4.3 .

Answer 1

So the Samsung NumberPicker is slightly different from AOSP. The code for ChangeCurrentByOneFromLongPressCommand class has some extra logic including

if (!mIsDeviceDefault) {
    // ...
} else if (mDecrementButton.isShown() || mIncrementButton.isShown()) {
    // ...

• where mIsDeviceDefault is true when you're using one of the Theme.DeviceDefault themes (which is the default theme for apps starting Android 4.x)
• where mDecrementButton and mIncrementButton are null if mHasSelectorWheel is true , which happens if the layout resource ID for NumberPicker specified by its style is one of
  • DEFAULT_LAYOUT_RESOURCE_ID / @layout/number_picker
  • TOUCHWIZ_DARK_LAYOUT_RESOURCE_ID / @layout/tw_number_picker_dark
  • TOUCHWIZ_LIGHT_LAYOUT_RESOURCE_ID / @layout/tw_number_picker_light

which suggests that this would happen all the time.

Here are all the possible styles:

<style name="Widget.NumberPicker">
    <item name="orientation">1</item>
    <item name="fadingEdge">2000</item>
    <item name="fadingEdgeLength">50dp</item>
    <item name="internalLayout">@layout/number_picker</item>
</style>

<style name="Widget.Holo.NumberPicker">
    <item name="solidColor">@color/transparent</item>
    <item name="internalLayout">@layout/number_picker_with_selector_wheel</item>
    <item name="selectionDivider">@drawable/numberpicker_selection_divider</item>
    <item name="selectionDividerHeight">2dp</item>
    <item name="selectionDividersDistance">48dp</item>
    <item name="internalMaxHeight">180dp</item>
    <item name="internalMinWidth">64dp</item>
    <item name="virtualButtonPressedDrawable">?attr/selectableItemBackground</item>
</style>

<style name="Widget.DeviceDefault.NumberPicker">
    <item name="internalLayout">@layout/tw_number_picker_dark</item>
</style>

<style name="Widget.DeviceDefault.Light.NumberPicker">
    <item name="internalLayout">@layout/tw_number_picker_light</item>
</style>

Source: Downloaded Android 4.3 firmware for Samsung Galaxy S3, extracted framework files using ext4 unpacker , decompiled framework.jar and framework2.jar using Universal Deodexer V5 , explored the results including framework-res.apk using JADX .

How to fix

After your NumberPicker is constructed use reflection to check if ImageButton mDecrementButton and ImageButton mIncrementButton are null. If they are use reflection to set them each to a new ImageButton(numberPicker.getContext()) .

Only apply this logic when running on one of the affected devices (check Build constants).

Answer 2

This how I am implementing NumberPicker in my application, and it is working well for me:

java code , in your onCreate() :

NumberPicker numberpicker = (NumberPicker) findViewById(R.id.np_from);
numberpicker.setMaxValue(100);
numberpicker.setMinValue(16);

XML code :

           <NumberPicker
            android:id="@+id/np_from"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_margin="20dp"
            android:width="100dip" />

I hope it helps.

Answer 3

http://grepcode.com/file/repository.grepcode.com/java/ext/com.google.android/android/4.3_r1/android/view/View.java#View.clearAccessibilityFocus%28%29

Looking at all 4.3 versions it's pretty clear the code is most likely calling clearAccessibilityFocus().

Assuming accurate line numbers I'd search in there for a likely cause. Nothing jumps out at me, in fact most of the accesses have good null checks.