Unable to restore the theme last set by user?

Question

App restores the theme when brought to the front from background or when screen orientation is changed but it does not work, when i change the press the middle button to see list of running background apps and clear it from there.

Here is code from my themechanger class:

package com.example.calculator;

import android.content.Intent;
import android.support.v7.app.ActionBarActivity;

public class ThemeChanger 
{
    private static int sTheme;

    public final static int THEME_DARKORANGE = 0;
    public final static int THEME_GREEN = 1;
    public final static int THEME_BLUE = 2;
    public final static int THEME_LIGHT = 3;

    public static void changeToTheme(ActionBarActivity activity, int theme)
    {
        sTheme = theme;
        activity.finish();

        activity.startActivity(new Intent(activity, activity.getClass()));
    }


    public static void onActivityCreateSetTheme(ActionBarActivity activity, int theme)
    {
        switch (sTheme)
        {
        default:
        case THEME_DARKORANGE:
            activity.setTheme(R.style.Theme_Darkorange);
            break;
        case THEME_GREEN:
            activity.setTheme(R.style.Theme_Green);
            break;
        case THEME_BLUE:
            activity.setTheme(R.style.Theme_Blue);
            break;
        case THEME_LIGHT:
            activity.setTheme(R.style.Theme_AppCompat_Light);
        }
    }
    }

Below is my code for storing theme values:

case R.id.bluetheme:
          editor.putInt("mytheme", ThemeChanger.THEME_BLUE);
          editor.commit();
          ThemeChanger.changeToTheme(this, ThemeChanger.THEME_BLUE);
          return true;
      case R.id.darkorangetheme:
          editor.putInt("mytheme", ThemeChanger.THEME_DARKORANGE);
          editor.commit();
          ThemeChanger.changeToTheme(this, ThemeChanger.THEME_DARKORANGE);
          return true;
      case R.id.greentheme:
          editor.putInt("mytheme", ThemeChanger.THEME_GREEN);
          editor.commit();

Here is my onCreate method:

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    preferences = PreferenceManager.getDefaultSharedPreferences(this);      
    int defaultValue = R.drawable.blue;
    int themedefault = ThemeChanger.THEME_BLUE;
    appliedtheme = preferences.getInt("mytheme", themedefault);
    ThemeChanger.onActivityCreateSetTheme(this,appliedtheme);
    setContentView(R.layout.main);

I know i need to restart activity to change my theme but if i write

ThemeChanger.changeToTheme(this, appliedtheme); 

at the beginning my app goes in infinite loop.

Answer 1

If you are using a piece of code that restarts the Activity inside onCreate(), then it makes perfect sense that you are getting a restart loop. Every time your Activity is created, it restarts. Modify your code as such:

public class ThemeChanger
{
    public final static int THEME_DARKORANGE = 0;
    public final static int THEME_GREEN = 1;
    public final static int THEME_BLUE = 2;
    public final static int THEME_LIGHT = 3;

    public static void restartActivity(Activity activity)
    {
        activity.finish();
        activity.startActivity(new Intent(activity, activity.getClass()));
    }


    public static void onActivityCreateSetTheme(Activity activity, int newTheme)
    {
        switch (newTheme)
        {
            default:
            case THEME_DARKORANGE:
            activity.setTheme(R.style.Theme_Darkorange);
            break;
            case THEME_GREEN:
            activity.setTheme(R.style.Theme_Green);
            break;
            case THEME_BLUE:
            activity.setTheme(R.style.Theme_Blue);
            break;
            case THEME_LIGHT:
            activity.setTheme(R.style.Theme_AppCompat_Light);
        }
    }
}

There is no need to use sTheme since the theme is already stored in SharedPrefs. I renamed your changeToTheme() method to restartActivity() so it accurately reflects its purpose.

When you save your values, you should restart your Activity using the method we modified.

 case R.id.bluetheme:
      editor.putInt("mytheme", ThemeChanger.THEME_BLUE);
      editor.commit();
      ThemeChanger.restartActivity(this);
      return true;
  case R.id.darkorangetheme:
      editor.putInt("mytheme", ThemeChanger.THEME_DARKORANGE);
      editor.commit();
      ThemeChanger.restartActivity(this);
      return true;
  case R.id.greentheme:
      editor.putInt("mytheme", ThemeChanger.THEME_GREEN);
      ThemeChanger.restartActivity(this);
      editor.commit();
      return true;
  //etc.

restartActivity() should only be used here, never in onCreate(). This means that onCreate() needs to use onActivityCreateSetTheme()

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    preferences = PreferenceManager.getDefaultSharedPreferences(this);
    int defaultValue = R.drawable.blue;
    int themedefault = ThemeChanger.THEME_BLUE;
    appliedtheme = preferences.getInt("mytheme", themedefault);
    ThemeChanger.onActivityCreateSetTheme(this,appliedtheme);
    setContentView(R.layout.main);
    //rest of code
}