ViewIdGenerator.java

package com.example;

import android.os.Build;
import android.view.View;

import java.util.concurrent.atomic.AtomicInteger;

/**
 * Created by srokowski.maciej@gmail.com on 16.11.16.
 */

public class ViewIdGenerator {

    /**
     * Unique view id generator, like the one used in {@link View} class for view id generation.
     * Since we can't access the generator within the {@link View} class before API 17, we create
     * the same generator here. This creates a problem of two generator instances not knowing about
     * each other, and we need to take care that one does not generate the id already generated by other one.
     * <p>
     * We know that all integers higher than 16 777 215 are reserved for aapt-generated identifiers
     * (source: {@link View#generateViewId()}, so we make sure to never generate a value that big.
     * We also know that generator within the {@link View} class starts at 1.
     * We set our generator to start counting at 15 000 000. This gives us enough space
     * (15 000 000 - 16 777 215), while making sure that generated IDs are unique, unless ILocationChooserView generates
     * more than 15M IDs, which should never happen.
     */
    private static final AtomicInteger viewIdGenerator = new AtomicInteger(15000000);

    /**
     * Generate a value suitable for use in {@link View#setId(int)}.
     * This value will not collide with ID values generated at build time by aapt for R.id.
     *
     * @return a generated ID value
     */
    public static int generateViewId() {
        if (Build.VERSION.SDK_INT < Build.VERSION_CODES.JELLY_BEAN_MR1) {
            return generateUniqueViewId();
        } else {
            return View.generateViewId();
        }
    }

    private static int generateUniqueViewId() {
        while (true) {
            final int result = viewIdGenerator.get();
            // aapt-generated IDs have the high byte nonzero; clamp to the range under that.
            int newValue = result + 1;
            if (newValue > 0x00FFFFFF) newValue = 1; // Roll over to 1, not 0.
            if (viewIdGenerator.compareAndSet(result, newValue)) {
                return result;
            }
        }
    }

}

ViewIdRestorer.java

package com.example;

import android.os.Bundle;
import android.support.annotation.NonNull;
import android.support.annotation.Nullable;

import java.util.HashMap;

/**
 * Created by srokowski.maciej@gmail.com on 16.11.16.
 */

public class ViewIdRestorer {

    private static final String TAG_ID_MAP_KEY = "TAG_ID_MAP_KEY";

    private HashMap<String, Integer> tagIdMap = new HashMap<>();

    public int getId(String tag) {
        if (tagIdMap.containsKey(tag)) {
            return tagIdMap.get(tag);
        } else {
            final int viewId = ViewIdGenerator.generateViewId();
            tagIdMap.put(tag, viewId);
            return viewId;
        }
    }


    public void onCreate(@Nullable Bundle savedInstanceState) {
        if (savedInstanceState != null) {
            final HashMap<String, Integer> savedTagIdMap = (HashMap<String, Integer>) savedInstanceState.getSerializable(TAG_ID_MAP_KEY);
            tagIdMap.putAll(savedTagIdMap);
        }
    }

    public void onRestoreInstanceState(@NonNull Bundle savedInstanceState) {
        final HashMap<String, Integer> savedTagIdMap = (HashMap<String, Integer>) savedInstanceState.getSerializable(TAG_ID_MAP_KEY);
        tagIdMap.putAll(savedTagIdMap);
    }

    public void onSaveInstanceState(@NonNull Bundle outState) {
        outState.putSerializable(TAG_ID_MAP_KEY, tagIdMap);
    }


}