ListPreference: use string-array as Entry and integer-array as Entry Values doesn't work

Question

I'm using in a settings.xml file a ListPreference. I want to show the user a list of 3 options to select. When the user chooses one of the options in the Settings, I get this error:

java.lang.NullPointerException
    at android.preference.ListPreference.onDialogClosed(ListPreference.java:264)
    at android.preference.DialogPreference.onDismiss(DialogPreference.java:381)
    at android.app.Dialog$ListenersHandler.handleMessage(Dialog.java:1228)
    at android.os.Handler.dispatchMessage(Handler.java:99)
    at android.os.Looper.loop(Looper.java:137)
    at android.app.ActivityThread.main(ActivityThread.java:4424)
    at java.lang.reflect.Method.invokeNative(Native Method)
    at java.lang.reflect.Method.invoke(Method.java:511)
    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:784)
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:551)
    at dalvik.system.NativeStart.main(Native Method)

This is the code of the ListPreference:

<ListPreference
    android:entries="@array/date_alignement"
    android:entryValues="@array/date_alignement_values"
    android:key="settings_date_alignement"
    android:summary="@string/settings_date_alignement_summary"
    android:title="@string/settings_date_alignement_title" />

And here are the arrays I use to populate the entries:

<string-array name="date_alignement">
    <item>"Top"</item>
    <item>"Center"</item>
    <item>"Bottom"</item>
</string-array>
<integer-array name="date_alignement_values">
    <item >0</item>
    <item >1</item>
    <item >2</item>
</integer-array>

In my onSharedPreferenceChanged I use those values in this way:

@Override
public void onSharedPreferenceChanged(
            SharedPreferences sharedPreferences, String key) {          

        //Text
        mAlignment =  mPrefs.getInt(PREF_ALIGNMENT, 1);
        switch (mAlignment) {
        case 0:
            offsetY = mHeight/3.0f;
            break;

        case 2:
            offsetY = mHeight*2.0f/3.0f;
            break;

        default:
            offsetY = mHeight/2.0f;
            break;
        }
}

If I use another string-array for the entryValues it works. For example if I use the same string array as values and entries:

    android:entries="@array/date_alignement"
    android:entryValues="@array/date_alignement"

then I have to change my code a little but it works:

        if(mAlignment.equalsIgnoreCase("center")) {
            offsetY = mHeight/2.0f;
        } else if(mAlignment.equalsIgnoreCase("top")) {
            offsetY = mHeight/3.0f;
        } else if(mAlignment.equalsIgnoreCase("bottom")) {
            offsetY = mHeight*2.0f/3.0f;
        }

Why I can't use a string-array and an integer-array for a ListPreference entries and values?

Solution 1

The answer is simple: because the Android is designed this way. It just uses String arrays for both entries and entry values and that's all. And I can't see any problem in this fact, since you can easily convert a String to an int using the Integer.parseInt() method. Hope this helps.

Solution 2

You can convert your entry values to strings to keep ListPreference happy and then convert them to ints when talking to the persistent data store.

1. When setting the entry values, use strings instead of ints: "1", "2", "3" etc
2. Make a custom IntListPreference that persists the values as ints
3. In your preferences.xml file, change the <ListPreference> into a <your.app.package.IntListPreference>

IntListPreference.java

Here's a sample implementation. Tested and working on AndroidX Preference 1.0.0.

public class IntListPreference extends ListPreference {

    public IntListPreference(Context context, AttributeSet attrs, int defStyleAttr, int defStyleRes) {
        super(context, attrs, defStyleAttr, defStyleRes);
    }

    public IntListPreference(Context context, AttributeSet attrs, int defStyleAttr) {
        super(context, attrs, defStyleAttr);
    }

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

    public IntListPreference(Context context) {
        super(context);
    }

    @Override
    protected boolean persistString(String value) {
        int intValue = Integer.parseInt(value);
        return persistInt(intValue);
    }

    @Override
    protected String getPersistedString(String defaultReturnValue) {
        int intValue;

        if (defaultReturnValue != null) {
            int intDefaultReturnValue = Integer.parseInt(defaultReturnValue);
            intValue = getPersistedInt(intDefaultReturnValue);
        } else {
            // We haven't been given a default return value, but we need to specify one when retrieving the value

            if (getPersistedInt(0) == getPersistedInt(1)) {
                // The default value is being ignored, so we're good to go
                intValue = getPersistedInt(0);
            } else {
                throw new IllegalArgumentException("Cannot get an int without a default return value");
            }
        }

        return Integer.toString(intValue);
    }

}

Solution 3

The answer is listed in List Preference Documentation.

int findIndexOfValue (String value)

will return the index for given value and the argument is taken as a String, so the entryValues array should be a string array to get this work.

Comments

[Yarik]

I'm sory for stupid question, but what type of variable mAlignment do you use? and where did you get PREF_ALIGNMENT?

[Santacrab]

In the first case mAlignment is an int. PREF_ALIGNMENT is the name of the entry in the SharedPreferences, where the alignment current value is stored

[Santacrab]

OK, still don't get why it's not supported. Obviousely I can and I will convert it, but if is possible to use a specific structure (integer-array) instead of using the string one and convert it in int, it should work :) Thanks anyway!

[Egor]

@Santacrab, If there were an integer array support, then there should also be float array support, double, char etc. It would be a big mess, so I think it's just easier to convert a String to whatever data type you need. Please accept the answer if you've found it useful.

[Santacrab]

actually the integer-array structure exists. The problem is that it's not work when paired to the string one.

[Tjaart]

@Egor that is a silly reason. Of course you should be able to store different basic types. You can even serialise object types into your configs in .Net. And it isn't a big mess.

[thom_nic]

I've run into the same issue. It's easy make a ListPreference that gives back ints. See: kvance.livejournal.com/1039349.html

[theblang]

@ThomNichols Nice! I was already rolling my own anyway. That was pretty simple nonetheless.

[Muhammad Babar]

The answer is simple: because the Android is designed this way are you telling me android is rigidly designed? I'm sorry but this can be a lame excuse but not an answer!

[njzk2]

typically, JSONObject.getInt tries to coerce values in int, sharedpreferences.getInt could do the same, and that would be sufficient

[nizam.sp]

@thom_nic: You made my day! The most elegant solution for this issue.

[Gavriel]

@thom_nic: unfortunatelly I get a ClassCastException in this line: int intValue = getPersistedInt(0);

[Vivek Maru]

Please describe the issue properly.

[Nolan Amy]

@thom_nic that livejournal link seems to be dead

[HX_unbanned]

Thanks, @kasvith ! Could you add complete code sample, please?