纯色图片颜色渐变动画

纯色图片颜色渐变动画的实现，主要有两点：

1、纯色图片颜色的改变，使用的方法为ImageView里的setColorFilter(int color)；

2、动画使用ValueAnimator，配合相应的颜色TypeEvalutor。

代码实现如下：

public class ImageActivity extends AppCompatActivity {

    private ImageView imageView;

    @Override
    protected void onCreate(@Nullable Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_image);
        imageView = findViewById(R.id.imageView);

        ValueAnimator valueAnimator=new ValueAnimator();
        valueAnimator.setIntValues(Color.RED,Color.GRAY);
        valueAnimator.setEvaluator(new ColorEvaluator());
        valueAnimator.setDuration(5000);
        valueAnimator.addUpdateListener(new ValueAnimator.AnimatorUpdateListener() {
            @Override
            public void onAnimationUpdate(ValueAnimator animation) {
                imageView.setColorFilter((Integer) animation.getAnimatedValue());
            }
        });
        valueAnimator.start();
    }

    private class ColorEvaluator implements TypeEvaluator{

        @Override
        public Object evaluate(float fraction, Object startValue, Object endValue) {
            int startInt = (Integer) startValue;
            float startA = ((startInt >> 24) & 0xff) / 255.0f;
            float startR = ((startInt >> 16) & 0xff) / 255.0f;
            float startG = ((startInt >>  8) & 0xff) / 255.0f;
            float startB = ( startInt        & 0xff) / 255.0f;

            int endInt = (Integer) endValue;
            float endA = ((endInt >> 24) & 0xff) / 255.0f;
            float endR = ((endInt >> 16) & 0xff) / 255.0f;
            float endG = ((endInt >>  8) & 0xff) / 255.0f;
            float endB = ( endInt        & 0xff) / 255.0f;

            // convert from sRGB to linear
            startR = (float) Math.pow(startR, 2.2);
            startG = (float) Math.pow(startG, 2.2);
            startB = (float) Math.pow(startB, 2.2);

            endR = (float) Math.pow(endR, 2.2);
            endG = (float) Math.pow(endG, 2.2);
            endB = (float) Math.pow(endB, 2.2);

            // compute the interpolated color in linear space
            float a = startA + fraction * (endA - startA);
            float r = startR + fraction * (endR - startR);
            float g = startG + fraction * (endG - startG);
            float b = startB + fraction * (endB - startB);

            // convert back to sRGB in the [0..255] range
            a = a * 255.0f;
            r = (float) Math.pow(r, 1.0 / 2.2) * 255.0f;
            g = (float) Math.pow(g, 1.0 / 2.2) * 255.0f;
            b = (float) Math.pow(b, 1.0 / 2.2) * 255.0f;

            return Math.round(a) << 24 | Math.round(r) << 16 | Math.round(g) << 8 | Math.round(b);
        }
    }
}

最后再上传一张纯色图片！