Override view states for flow

FlowUtils.java

package de.dom.android.ui.util;

import android.content.Context;
import android.os.Parcelable;
import android.util.SparseArray;
import android.view.View;

import java.lang.reflect.Field;
import java.util.ArrayDeque;
import java.util.Deque;
import java.util.Iterator;

import flow.Flow;
import flow.History;
import flow.ViewState;

/**
 * Overrides history view states. When we set history with {@code Flow.setHistory} Flow removes view states from history.
 * Use this method to restore these states.
 */
public class FlowUtils {
    public static void updateHistoryViewState(History history, Context context) {
        Iterator<ViewState> iterator = getHistoryEntries(history).iterator();
        Iterator<ViewState> newIterator = getHistoryEntries(Flow.get(context).getHistory()).iterator();

        FlowStateView flowState = new FlowStateView(context);
        while (iterator.hasNext() && newIterator.hasNext()) {
            if (iterator.hasNext() != newIterator.hasNext()) {
                throw new IllegalAccessError("to override history view state, list should be the same");
            }
            ViewState oldViewState = iterator.next();
            ViewState newViewState = newIterator.next();
            oldViewState.restore(flowState);
            newViewState.save(flowState);
        }
    }

    private static Deque<ViewState> getHistoryEntries(History history) {
        try {
            Field historyField = History.class.getDeclaredField("history");
            historyField.setAccessible(true);
            return  (Deque<ViewState>) historyField.get(history);
        } catch (NoSuchFieldException | IllegalAccessException e) {
            e.printStackTrace();
        }
        return new ArrayDeque<>(0);
    }

    /**
     * Hack to restore view state to new history.
     */
    private static class FlowStateView extends View {

        private SparseArray<Parcelable> state;

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

        @Override public void saveHierarchyState(SparseArray<Parcelable> container) {
            if (state == null) {
                return;
            }
            for (int i = 0; i < state.size(); i++) {
                int key = state.keyAt(i);
                container.put(key, state.get(key));
            }
        }

        @Override public void restoreHierarchyState(SparseArray<Parcelable> container) {
            state = container;
        }
    }
}