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系列文章目录
Android颜色渐变动画效果的实现
文章最后有源码
前言
案例效果的实现比较简单，利用Android自带的颜色估值器ArgbEvaluator()进行计算即可，而本文的重点就是讲讲估值器。
效果图：
一、Android中估值器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自带的颜色估值器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();
复制代码2.看看Android自带颜色估值器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);
}
复制代码3.根据ArgbEvaluator的实现来自定义一个颜色估值器
public class MyColorEvaluator implements TypeEvaluator
复制代码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);
}
复制代码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();
复制代码三、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();
}
}
复制代码MyColorEvaluator.java:
public class MyColorEvaluator implements TypeEvaluator<Integer> {
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);
}
}
复制代码