ObjectAnimatorアニメーションでview色を変更(メモ)

public class MainActivity extends AppCompatActivity {

    MyView2 myView2;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        myView2 = (MyView2) findViewById(R.id.MyView2);
        ObjectAnimator anim = ObjectAnimator.ofObject(myView2, "color", new ColorEvaluator(),
                "#0000FF", "#FF0000");
        //      View  、        &      
        //     ：
        //   1：               
        //   2：  set（）          （              ）
        //   3：  invalidate()    ，   onDraw（）    ，        

        anim.setDuration(8000);
        anim.start();
    }
}

public class ColorEvaluator implements TypeEvaluator {
    //   TypeEvaluator  

    private int mCurrentRed;

    private int mCurrentGreen ;

    private int mCurrentBlue ;

    //   evaluate（）
    //  evaluate（）            :           
    @Override
    public Object evaluate(float fraction, Object startValue, Object endValue) {

        //              
        String startColor = (String) startValue;
        String endColor = (String) endValue;

        //                   RGB    ，  RGB          
        //              0-255
        int startRed = Integer.parseInt(startColor.substring(1, 3), 16);
        int startGreen = Integer.parseInt(startColor.substring(3, 5), 16);
        int startBlue = Integer.parseInt(startColor.substring(5, 7), 16);

        int endRed = Integer.parseInt(endColor.substring(1, 3), 16);
        int endGreen = Integer.parseInt(endColor.substring(3, 5), 16);
        int endBlue = Integer.parseInt(endColor.substring(5, 7), 16);

        //                      
            mCurrentRed = startRed;
            mCurrentGreen = startGreen;
            mCurrentBlue = startBlue;


        //                 
        //              :              ，            ;  ,     
        //                       getCurrentColor() .
        int redDiff = Math.abs(startRed - endRed);
        int greenDiff = Math.abs(startGreen - endGreen);
        int blueDiff = Math.abs(startBlue - endBlue);
        int colorDiff = redDiff + greenDiff + blueDiff;
        if (mCurrentRed != endRed) {
            mCurrentRed = getCurrentColor(startRed, endRed, colorDiff, 0,
                    fraction);
                    // getCurrentColor()                   ->>  1
        } else if (mCurrentGreen != endGreen) {
            mCurrentGreen = getCurrentColor(startGreen, endGreen, colorDiff,
                    redDiff, fraction);
        } else if (mCurrentBlue != endBlue) {
            mCurrentBlue = getCurrentColor(startBlue, endBlue, colorDiff,
                    redDiff + greenDiff, fraction);
        }
        //                
        String currentColor = "#" + getHexString(mCurrentRed)
                + getHexString(mCurrentGreen) + getHexString(mCurrentBlue);

        //                 ，              :  getHexString()->>  2
        //    RGB      ,          
        return currentColor;
    }


    //   1:getCurrentColor()
    //      fraction         。

    private int getCurrentColor(int startColor, int endColor, int colorDiff,
                                int offset, float fraction) {
        int currentColor;
        if (startColor > endColor) {
            currentColor = (int) (startColor - (fraction * colorDiff - offset));
            if (currentColor < endColor) {
                currentColor = endColor;
            }
        } else {
            currentColor = (int) (startColor + (fraction * colorDiff - offset));
            if (currentColor > endColor) {
                currentColor = endColor;
            }
        }
        return currentColor;
    }

    //   2: 10        16  。
    private String getHexString(int value) {
        String hexString = Integer.toHexString(value);
        if (hexString.length() == 1) {
            hexString = "0" + hexString;
        }
        return hexString;
    }

}