Android怎么实现颜色渐变动画效果

本篇内容主要讲解"Android怎么实现颜色渐变动画效果"，感兴趣的朋友不妨来看看。本文介绍的方法操作简单快捷，实用性强。下面就让小编来带大家学习"Android怎么实现颜色渐变动画效果"吧!

效果图：

一、Android中插值器TypeEvaluator

TypeEvaluator是一个接口，在开发中可以自定义该接口实例，利用ValueAnimator的setEvaluator(TypeEvaluator)方法来控制动画的更新计算表达式。在日常开发中，不可能只是需要操纵单一数值的变化，如果需要同时操纵对象的多个属性，如定义动画的x，y移动的坐标等，那就需要对TypeEvaluator有所了解了。

二、案例效果实现

1.利用Android自带的颜色插值器ArgbEvaluator

ValueAnimator colorAnim = ObjectAnimator.ofInt(this, "backgroundColor", RED, BLUE);        colorAnim.setDuration(4000);        colorAnim.setEvaluator(new ArgbEvaluator());        colorAnim.setRepeatCount(ValueAnimator.INFINITE);        colorAnim.setRepeatMode(ValueAnimator.REVERSE);        colorAnim.start();

2.看看Android自带颜色插值器ArgbEvaluator核心代码

@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;        // 将sRGB转化成线性        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);        //在线性空间中计算插值的颜色        float a = startA + fraction * (endA - startA);        float r = startR + fraction * (endR - startR);        float g = startG + fraction * (endG - startG);        float b = startB + fraction * (endB - startB);        //转换回sRGB在[0..255]范围        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);    }

3.根据ArgbEvaluator的实现来自定义一个颜色插值器

public class MyColorEvaluator implements TypeEvaluator

接下来换一种颜色的计算方式，在本人看相关api的过程中，发现Color中有colorToHSV和HSVToColor的方法，于是在网上找了一个HVS的计算方式。（以下代码来源于网络）。

@Override    public Integer evaluate(float fraction, Integer startValue, Integer endValue) {        Color.colorToHSV(startValue,startHsv);        Color.colorToHSV(endValue,endHsv);        int alpha = startValue >> 24 + (int) ((endValue >> 24 - startValue >> 24) * fraction);        // 计算当前动画完成度（fraction）所对应的颜色值        if (endHsv[0] - startHsv[0] > 180) {            endHsv[0] -= 360;        } else if (endHsv[0] - startHsv[0] < -180) {            endHsv[0] += 360;        }        outHsv[0] = startHsv[0] + (endHsv[0] - startHsv[0]) * fraction;        if (outHsv[0] > 360) {            outHsv[0] -= 360;        } else if (outHsv[0] < 0) {            outHsv[0] += 360;        }        outHsv[1]=startHsv[1]+(endHsv[1]-startHsv[1])*fraction;        outHsv[2]=startHsv[2]+(endHsv[2]-startHsv[2])*fraction;        return Color.HSVToColor(alpha,outHsv);    }

4.使用自己定义的颜色插值器MyColorEvaluator

ValueAnimator colorAnim = ObjectAnimator.ofInt(this, "backgroundColor", RED, BLUE);        colorAnim.setDuration(4000);        colorAnim.setEvaluator(new MyColorEvaluator());        colorAnim.setRepeatCount(ValueAnimator.INFINITE);        colorAnim.setRepeatMode(ValueAnimator.REVERSE);        colorAnim.start();

三、源码

ColorGradient.java:

public class ColorGradient extends View {    public ColorGradient(Context context) {        super(context);    }    public ColorGradient(Context context, @Nullable AttributeSet attrs) {        super(context, attrs);        animation();    }    public ColorGradient(Context context, @Nullable AttributeSet attrs, int defStyleAttr) {        super(context, attrs, defStyleAttr);    }    private void animation(){        ValueAnimator colorAnim = ObjectAnimator.ofInt(this, "backgroundColor", RED, BLUE);        colorAnim.setDuration(4000);        colorAnim.setEvaluator(new MyColorEvaluator());        colorAnim.setRepeatCount(ValueAnimator.INFINITE);        colorAnim.setRepeatMode(ValueAnimator.REVERSE);        colorAnim.start();    }    }

MyColorEvaluator.java:

public class MyColorEvaluator implements TypeEvaluator {    float[] startHsv=new float[3];    float[] endHsv=new float[3];    float[] outHsv=new float[3];    @Override    public Integer evaluate(float fraction, Integer startValue, Integer endValue) {        Color.colorToHSV(startValue,startHsv);        Color.colorToHSV(endValue,endHsv);        int alpha = startValue >> 24 + (int) ((endValue >> 24 - startValue >> 24) * fraction);        // 计算当前动画完成度（fraction）所对应的颜色值        if (endHsv[0] - startHsv[0] > 180) {            endHsv[0] -= 360;        } else if (endHsv[0] - startHsv[0] < -180) {            endHsv[0] += 360;        }        outHsv[0] = startHsv[0] + (endHsv[0] - startHsv[0]) * fraction;        if (outHsv[0] > 360) {            outHsv[0] -= 360;        } else if (outHsv[0] < 0) {            outHsv[0] += 360;        }        outHsv[1]=startHsv[1]+(endHsv[1]-startHsv[1])*fraction;        outHsv[2]=startHsv[2]+(endHsv[2]-startHsv[2])*fraction;        return Color.HSVToColor(alpha,outHsv);    }}

到此，相信大家对"Android怎么实现颜色渐变动画效果"有了更深的了解，不妨来实际操作一番吧！这里是网站，更多相关内容可以进入相关频道进行查询，关注我们，继续学习！