CheckableLinearLayout

package com.example.checkableviews;

/*******************************************************************************
 * Copyright 2013 Chris Banes.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.    
 *******************************************************************************/

import android.content.Context;
import android.util.AttributeSet;
import android.util.Log;
import android.view.View;
import android.widget.Checkable;
import android.widget.LinearLayout;

public class CheckableLinearLayout extends LinearLayout implements Checkable {

    /**
     * Interface definition for a callback to be invoked when the checked state of this View is
     * changed.
     */
    public static interface OnCheckedChangeListener {

        /**
         * Called when the checked state of a compound button has changed.
         *
         * @param checkableView The view whose state has changed.
         * @param isChecked     The new checked state of checkableView.
         */
        void onCheckedChanged(View checkableView, boolean isChecked);
    }

    private static final int[] CHECKED_STATE_SET = {android.R.attr.state_checked};

    private boolean mChecked = false;

    private OnCheckedChangeListener mOnCheckedChangeListener;

    public CheckableLinearLayout(Context context, AttributeSet attrs) {
        super(context, attrs);
    }

    public boolean isChecked() {
        return mChecked;
    }

    public void setChecked(boolean b) {
        if (b != mChecked) {
            mChecked = b;
            refreshDrawableState();

            if (mOnCheckedChangeListener != null) {
                mOnCheckedChangeListener.onCheckedChanged(this, mChecked);
            }
        }
    }

    public void toggle() {
        setChecked(!mChecked);
    }

    @Override
    public int[] onCreateDrawableState(int extraSpace) {
        final int[] drawableState = super.onCreateDrawableState(extraSpace + 1);
        if (isChecked()) {
            mergeDrawableStates(drawableState, CHECKED_STATE_SET);
        }
        return drawableState;
    }

    /**
     * Register a callback to be invoked when the checked state of this view changes.
     *
     * @param listener the callback to call on checked state change
     */
    public void setOnCheckedChangeListener(OnCheckedChangeListener listener) {
        mOnCheckedChangeListener = listener;
    }

}

int[] onCreateDrawableState(int extraSpace)
Is it this method that make the key impact?