SharedPreferrenceHelper

public class SharedPreferrenceHelper {
    private static final String THEME = "theme";
    public static void settheme(Context context, String theme){
        SharedPreferences sp = context.getSharedPreferences("demo",Context.MODE_PRIVATE);
        SharedPreferences.Editor editor = sp.edit();
        editor.putString(THEME
 
,theme);
        editor.apply();
    }
    public static String gettheme(Context context){
        SharedPreferences sp = context.getSharedPreferences("demo",Context.MODE_PRIVATE);
        return sp.getString(THEME,"1");
    }
}

utils

public class utils {
    public static int getAppTheme(Context context){
        String value = SharedPreferrenceHelper.gettheme
 
(context);
        switch (Integer.valueOf(value)){
            case 1:
                return R.style.AppTheme;
            case 2:
                return R.style.AppThemeDark;
            default:
                return R.style.AppTheme;
        }
    }
    public static void switchAppTheme(Context context){
        String value = SharedPreferrenceHelper.gettheme
 
(context);
        switch (Integer.valueOf(value)){
            case 1:
                SharedPreferrenceHelper.settheme(context,"2");
                break;
            case 2:
                SharedPreferrenceHelper.settheme(context,"1");
                break;
            default:
                SharedPreferrenceHelper.settheme(context,"1");
                break;
        }
    }
}

BaseActivity

public abstract class BaseActivity extends FragmentActivity {
    TextView mTextView;
    private int theme = 0;
    private static final String TAG = "MainActivity";

    @Override
protected void onResume() {
        Log.d(TAG,"onResume");
        super.onResume();
        if(theme==utils.getAppTheme(this)){

        }else{
            reload();
        }
    }

    @Override
protected void onDestroy() {
        super.onDestroy();
        Log.d(TAG,"onDestroy");
    }

    @Override
protected void onSaveInstanceState(Bundle outState) {
        super.onSaveInstanceState(outState);
        outState.putInt("theme",theme);
    }
    @Override
protected void onCreate(Bundle savedInstanceState) {
        if(savedInstanceState==null){
            theme=utils.getAppTheme(this);
        }else{
            theme=savedInstanceState.getInt("theme");
        }
        setTheme(theme);
        super.onCreate(savedInstanceState);
        Log.d(TAG,"onCreate");

        //setContentView(R.layout.activity_main);
setView();

    }
    abstract void setView();
    public void reload() {
        Intent intent = getIntent();
        overridePendingTransition(0, 0);//不設定進入退出動畫
intent.addFlags(Intent.FLAG_ACTIVITY_NO_ANIMATION);
        finish();

        overridePendingTransition(0, 0);
        startActivity(intent);
    }

    @Override
protected void onRestart() {
        super.onRestart();
        Log.d(TAG, "onRestart");
    }

    @Override
protected void onPause() {
        super.onPause();
        Log.d(TAG,"onPause");
    }
}

<resources>

    <!-- Base application theme. -->
<style name="AppTheme" parent="Theme.AppCompat.Light.DarkActionBar">
        <!-- Customize your theme here. -->
<item name="colorPrimary">@color/colorPrimary</item>
        <item name="colorPrimaryDark">@color/colorPrimaryDark</item>
        <item name="colorAccent">@color/colorAccent</item>
    </style>
    <style name="AppThemeDark" parent="Theme.AppCompat"></style>
</resources>

MainActivity

public class MainActivity extends BaseActivity {
    private Button btn1;
    @Override
void setView() {
        setContentView(R.layout.activity_main);
        btn1= (Button) findViewById(R.id.btn);
        btn1.setOnClickListener(new View.OnClickListener() {
            @Override
public void onClick(View view) {
                utils.switchAppTheme(MainActivity.this);
                reload();
            }
        });
    }
}