Preference items being automatically re-set?

Question

This appears like a bug to me: When you load many switch preferences in a preference fragment, they somehow re-set themselves , when you scroll the preferences. I have separately tested this with little demo code:

---

/res/xml/prefs.xml (Just a bunch of switch preferences, just enough to make preferences scroll on screen) :

<PreferenceScreen xmlns:android="http://schemas.android.com/apk/res/android" android:key="my_prefs">
    <PreferenceCategory android:key="my_prefs_cat" android:title="Settings">
        <SwitchPreference android:key="p1" android:title="p1" android:defaultValue="false" />
        <SwitchPreference android:key="p2" android:title="p2" android:defaultValue="false" />
        <SwitchPreference android:key="p3" android:title="p3" android:defaultValue="false" />
        <SwitchPreference android:key="p4" android:title="p4" android:defaultValue="false" />
        <SwitchPreference android:key="p5" android:title="p5" android:defaultValue="false" />
        <SwitchPreference android:key="p6" android:title="p6" android:defaultValue="false" />
        <SwitchPreference android:key="p7" android:title="p7" android:defaultValue="false" />
        <SwitchPreference android:key="p8" android:title="p8" android:defaultValue="false" />
        <SwitchPreference android:key="p9" android:title="p9" android:defaultValue="false" />
        <SwitchPreference android:key="p10" android:title="p10" android:defaultValue="false" />
    </PreferenceCategory>
</PreferenceScreen>

---

/src/Prefs.java (A simple PreferenceFragment) :

package com.example.preflistbug;

import android.os.Bundle;
import android.preference.PreferenceFragment;

public class Prefs extends PreferenceFragment {
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        addPreferencesFromResource(R.xml.prefs);
    }

}

---

/res/layout/main.xml (Placed PreferenceFragment in Activity layout) :

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent">

    <fragment android:name="com.example.preflistbug.Prefs" 
        android:id="@+id/frg_prefs"
        android:layout_width="fill_parent"
        android:layout_height="fill_parent"
        />
</LinearLayout>

---

/src/MyActivity.java (Demo Activity) :

package com.example.preflistbug;

import android.app.Activity;
import android.os.Bundle;

public class MyActivity extends Activity {
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
    }
}

---

Problem: If you change the first switch preference , scroll down, scroll back up, the switch is reset. Same is true for other switch preferences which scroll out of view and are visited later. (specially, in horizontal orientation)

Happens on emulator too. I'm compiling on platform version 15, ICS. As you can see in above code, this is a very simple setup, I can't find anything in this code, that might explain why this is happening.

Update

Bug reported as Issue 26194.

Update 2

It is supposed to be fixed in android L release.

Answer 1

I was able to reproduce this issue. I also found a workaround but I don't know why it works :)

Create a derived class from SwitchPreference like so:

public class Pref extends SwitchPreference {
    public Pref(Context context) {
        super(context);
    }

    public Pref(Context context, AttributeSet attrs) {
        super(context, attrs);
    }

    public Pref(Context context, AttributeSet attrs, int defStyle) {
        super(context, attrs, defStyle);
    }    
}

Then, instead of using these in your prefs.xml:

<SwitchPreference ... />

You can use these instead

<com.example.preflistbug.Pref ... />

The derivation seems to somehow fixes the issue where the view recycling in the ListView-driven preference list is reusing the controls without "freeing" them from their previous Preference object first (or so I think). I'll update this answer if I figure out more.