ArgbEvaluator compatible with JELLY_BEAN (API Level 16, Android 4.1) and lower

ArgbEvaluator.java

/*
 * Copyright (C) 2010 The Android Open Source Project
 *
 * 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.
 */

package com.example;

import android.animation.TypeEvaluator;
import android.os.Build;

/**
 * This evaluator can be used to perform type interpolation between integer
 * values that represent ARGB colors.
 * <p/>
 * <b>Official 4.2 source code. Solution for https://code.google.com/p/android/issues/detail?id=36158.</b>
 */
public class ArgbEvaluator implements TypeEvaluator {

	private android.animation.ArgbEvaluator mDelegate;

	/**
	 * This function returns the calculated in-between value for a color
	 * given integers that represent the start and end values in the four
	 * bytes of the 32-bit int. Each channel is separately linearly interpolated
	 * and the resulting calculated values are recombined into the return value.
	 *
	 * @param fraction   The fraction from the starting to the ending values
	 * @param startValue A 32-bit int value representing colors in the
	 *                   separate bytes of the parameter
	 * @param endValue   A 32-bit int value representing colors in the
	 *                   separate bytes of the parameter
	 * @return A value that is calculated to be the linearly interpolated
	 * result, derived by separating the start and end values into separate
	 * color channels and interpolating each one separately, recombining the
	 * resulting values in the same way.
	 */
	public Object evaluate(float fraction, Object startValue, Object endValue) {

		Object result;

		if (mDelegate != null) {
			result = mDelegate.evaluate(fraction, startValue, endValue);
		} else {
			int startInt = (Integer) startValue;
			int startA = (startInt >> 24) & 0xff;
			int startR = (startInt >> 16) & 0xff;
			int startG = (startInt >> 8) & 0xff;
			int startB = startInt & 0xff;

			int endInt = (Integer) endValue;
			int endA = (endInt >> 24) & 0xff;
			int endR = (endInt >> 16) & 0xff;
			int endG = (endInt >> 8) & 0xff;
			int endB = endInt & 0xff;

			result = (int) ((startA + (int) (fraction * (endA - startA))) << 24) |
				(int) ((startR + (int) (fraction * (endR - startR))) << 16) |
				(int) ((startG + (int) (fraction * (endG - startG))) << 8) |
				(int) ((startB + (int) (fraction * (endB - startB))));
		}

		return result;
	}

	public static ArgbEvaluator getNewInstance() {
		if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.JELLY_BEAN_MR1) {
			return new ArgbEvaluator().withDelegate(new android.animation.ArgbEvaluator());
		} else {
			return new ArgbEvaluator();
		}
	}

	private ArgbEvaluator withDelegate(android.animation.ArgbEvaluator delegate) {
		this.mDelegate = delegate;
		return this;
	}

}