如何在.java代码中启用禁用的（在xml中）ListPreference对象？

Question

EDIT 3

Here's how I determine if the device is a tablet in onCreate for main Activity :

  public static boolean isTablet(Context ctx){
    return (ctx.getResources().getConfiguration().screenLayout
        & Configuration.SCREENLAYOUT_SIZE_MASK
    )
        >= Configuration.SCREENLAYOUT_SIZE_LARGE;
  }

I don't know if that's a hack and not reliable, but in any event, I don't know how to use it in onCreate in the Fragment (below) because I don't know what Context to pass to isATablet .

  @Override
  public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    addPreferencesFromResource(R.xml.preferences);Preference p = getPreferenceManager().findPreference("orientation");
    p.setEnabled(isTablet(????????????????));

EDIT showing arrays as defined in strings.xml as requested:

<string-array name="modes">
    <item>0</item>
    <item>1</item>
    <item>2</item>
</string-array>
<string-array name="indices">
    <item>Portrait</item>
    <item>Landscape</item>
    <item>Rotate</item>
</string-array>

* END EDIT *

How do I enable this ListPreference object in .java code?

<PreferenceCategory>
    <ListPreference
        android:key="orientation"
        android:title="Orientation (for tablets only)"
        android:enabled="false"
        android:summary="Lock in portrait or landscape mode or neither (allow rotation to determine)?"
        android:defaultValue="0"
        android:entries="@array/indices"
        android:entryValues="@array/modes"
        >
    </ListPreference>
</PreferenceCategory>

I can't make Android Studio 1.1.0 let me give it an id ; but if there's a way, there's my solution--how do I do it?

EDIT

Workaround:

android:enabled="true"

if(isATablet) { // ***************************
  switch (preferences.getString(ORIENTATION, "0")) {
    case "0":
      setRequestedOrientation(ActivityInfo.SCREEN_ORIENTATION_PORTRAIT);
      break;
    case "1":
      setRequestedOrientation(ActivityInfo.SCREEN_ORIENTATION_LANDSCAPE);
      break;
    case "2":
      setRequestedOrientation(ActivityInfo.SCREEN_ORIENTATION_SENSOR);
      break;
    default:
      Toast.makeText(getApplicationContext(), "Bad orientation", Toast.LENGTH_SHORT).show();
  }
}
else{ // ***************************
  editor = preferences.edit(); // ***************************
  editor.putString(ORIENTATION,"0"); // ***************************
  editor.commit(); // ***************************
  setRequestedOrientation(ActivityInfo.SCREEN_ORIENTATION_PORTRAIT);

}

Very lame. Please help!

Answer 1

It looks like you can just use the PreferenceManager and get the Preference based on the key . See documentation here and here .

You could use the method described here to determine if it's a tablet or not.

Then, it's just as simple as getting the preference, and enabling it if it's a tablet!

Edit:

In order to use your method and give it a valid Context , you could do it like this. Note that I used a modified version of the code posted here for the isTablet() method:

 public class SettingsFragment extends PreferenceFragment implements OnSharedPreferenceChangeListener {
        @Override
        public void onCreate(Bundle savedInstanceState) {
            super.onCreate(savedInstanceState);
            addPreferencesFromResource(R.xml.preferences);

            Preference p = getPreferenceManager().findPreference("orientation");
            p.setEnabled(isTablet(getActivity()));
        }

        private boolean isTablet(Context context) {
            int screenLayout = context.getResources().getConfiguration().screenLayout;
            screenLayout &= Configuration.SCREENLAYOUT_SIZE_MASK;

            switch (screenLayout) {
                case Configuration.SCREENLAYOUT_SIZE_SMALL:
                    return false;
                case Configuration.SCREENLAYOUT_SIZE_NORMAL:
                    return false;
                case Configuration.SCREENLAYOUT_SIZE_LARGE:
                    return true;
                case 4: // Configuration.SCREENLAYOUT_SIZE_XLARGE is API >= 9
                    return true;
                default:
                    return false;
            }
        }
        //...................

Answer 2

Thanks to incredible generosity of Daniel Nugent, here's what finally worked.

preferences.xml (don't enable or disable orientation):

    <PreferenceCategory>
        <ListPreference
            android:key="orientation"
            android:title="Orientation (for tablets only)"
            android:summary="Lock in portrait or landscape mode or neither (allow rotation to determine)?"
            android:defaultValue="0"
            android:entries="@array/indices"
            android:entryValues="@array/modes"
            >
        </ListPreference>
    </PreferenceCategory>
</PreferenceScreen>

SettingsFragment.java :

public class SettingsFragment extends PreferenceFragment implements OnSharedPreferenceChangeListener {

  @Override
  public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    addPreferencesFromResource(R.xml.preferences);
//  next two lines ****************************************************
    Preference p = getPreferenceManager().findPreference("orientation");
    p.setEnabled(isTablet(getActivity()));
//  Let java code enable or disable orientation ***********************
  }

  @Override
  public void onResume() {
    super.onResume();
    getPreferenceScreen().getSharedPreferences().registerOnSharedPreferenceChangeListener(this);
  }
  @Override
  public void onPause() {
    super.onPause();
    getPreferenceScreen().getSharedPreferences().unregisterOnSharedPreferenceChangeListener(this);
  }
  @Override
  public void onSharedPreferenceChanged(SharedPreferences sharedPreferences, String key) {
    SharedPreferences sharedPref = PreferenceManager.getDefaultSharedPreferences(getActivity());

  }
}

isTablet.java :

  private boolean isTablet(Context context) {
    int screenLayout = context.getResources().getConfiguration().screenLayout;
    screenLayout &= Configuration.SCREENLAYOUT_SIZE_MASK;

    switch (screenLayout) {
      case Configuration.SCREENLAYOUT_SIZE_SMALL:
        return false;
      case Configuration.SCREENLAYOUT_SIZE_NORMAL:
        return false;
      case Configuration.SCREENLAYOUT_SIZE_LARGE:
        return true;
      case 4: // Configuration.SCREENLAYOUT_SIZE_XLARGE is API >= 9
        return true;
      default:
        return false;
    }
  }