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1.首先，让日落可逆。也就是说，点击屏幕，等太阳落下后，再次点击屏幕，让太阳升起来。 动画集不能逆向执行，因此，你需要新建一个AnimatorSet。
2.第二个挑战是添加太阳动画特效，让它有规律地放大、缩小或是加一圈旋转的光线。（这实际是反复执行一段动画特效，可考虑使用ObjectAnimator的setRepeatCount(int)方法。） 另外，海面上要是有太阳的倒影就更真实了。
3.最后，再来看个颇具挑战的练习。在日落过程中实现动画反转。在太阳慢慢下落时点击屏幕， 让太阳无缝回升至原来所在的位置。或者，在太阳落下进入夜晚时点击屏幕，让太阳重新升回天 空，就像日出。
一、日落可逆
这部分比较简单，根据提示新建新的动画和动画集就可以，直接上代码
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| //上升动画
sun_upAnimator = ObjectAnimator.ofFloat(mSunView, "y", sunYFirstEnd,sunYFirstStart).setDuration(3000);
sun_upAnimator.setInterpolator(new AccelerateInterpolator());
//上升动画集
sun_upAnimatorSet = new AnimatorSet();
sun_upAnimatorSet.play(sun_upAnimator)
.with(sunsetSkyAnimator)
.before(nightSkyAnimator);
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二、太阳动画特效
这部分主要涉及缩放动画、旋转动画，提示使用ObjectAnimator的setRepeatCount(int)方法，但是我并未使用，我的代码如下
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| //变大
bigXAnimator = ObjectAnimator.ofFloat(mSunView,"scaleX",1.0f,2.0f).setDuration(3000);
bigYAnimator = ObjectAnimator.ofFloat(mSunView,"scaleY",1.0f,2.0f).setDuration(3000);
//变小
smallXAnimator = ObjectAnimator.ofFloat(mSunView,"scaleX",2.0f,1.0f).setDuration(3000);
smallYAnimator = ObjectAnimator.ofFloat(mSunView,"scaleY",2.0f,1.0f).setDuration(3000);
//旋转特效
//顺时针
clockwiseAnimator = ObjectAnimator.ofFloat(mSunView,"rotation",0f,720f).setDuration(3000);
//逆时针
anti_clockwiseAnimator = ObjectAnimator.ofFloat(mSunView,"rotation",360f,0f).setDuration(3000);
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旋转动画特别说明：通过旋转sun来实现旋转的光线的效果，所以修改sun.xml给sun加上边框间断线
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| <?xml version="1.0" encoding="utf-8"?>
<shape xmlns:android = "http://schemas.android.com/apk/res/android"
android:shape="oval">
<solid android:color="@color/bright_sun"/>
<stroke
android:width="2dp"
android:color="@color/huawei_red"
android:dashWidth="25dp"
android:dashGap="8dp"/>
</shape>
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以上动画直接.with()加到动画集即可。
One more thing：
为了让太阳更真实，添加倒影效果
①在布局文件中，再添加一个FrameLayout，记得android:layout_weight调成0.5，这样sky和sea各一半。
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| <?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical"
android:layout_width="match_parent"
android:layout_height="match_parent">
<FrameLayout
android:id="@+id/sky"
android:layout_width="match_parent"
android:layout_height="0dp"
android:layout_weight="0.5"
android:background="@color/blue_sky">
<ImageView
android:id="@+id/sun"
android:layout_width="100dp"
android:layout_height="100dp"
android:layout_gravity="center"
android:src="@drawable/sun"
android:contentDescription="@string/todo" />
&l 大专栏 Android编程权威指南第三版 第32章t;/FrameLayout>
<FrameLayout
android:id="@+id/sea"
android:layout_width="match_parent"
android:layout_height="0dp"
android:layout_weight="0.5"
android:background="@color/sea">
<ImageView
android:id="@+id/little_sun"
android:layout_width="100dp"
android:layout_height="100dp"
android:layout_gravity="center"
android:src="@drawable/sun"
android:contentDescription="@string/todo"
android:alpha="0.7"/>
</FrameLayout>
</LinearLayout>
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②倒影需要有位移动画、缩放动画、旋转动画、渐变透明动画。代码如下
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| //--------------------------------倒影--------------------------------//
//透明度
alphaAnimator = ObjectAnimator.ofFloat(mLittleSunView, "alpha", 0.7f, 0.0f).setDuration(3000);
unalphaAnimator = ObjectAnimator.ofFloat(mLittleSunView,"alpha",0.0f,0.7f).setDuration(3000);
//大小
little_bigXAnimator = ObjectAnimator.ofFloat(mLittleSunView,"scaleX",1.0f,2.0f).setDuration(3000);
little_bigYAnimator = ObjectAnimator.ofFloat(mLittleSunView,"scaleY",1.0f,2.0f).setDuration(3000);
little_smallXAnimator = ObjectAnimator.ofFloat(mLittleSunView,"scaleX",2.0f,1.0f).setDuration(3000);
little_smallYAnimator = ObjectAnimator.ofFloat(mLittleSunView,"scaleY",2.0f,1.0f).setDuration(3000);
//旋转特效
little_clockwiseAnimator = ObjectAnimator.ofFloat(mLittleSunView,"rotation",0f,720f).setDuration(3000);
little_anti_clockwiseAnimator = ObjectAnimator.ofFloat(mLittleSunView,"rotation",360f,0f).setDuration(3000);
//位移
little_upAnimator = ObjectAnimator.ofFloat(mLittleSunView, "y", littlesunYFirstStart, littlesunYFirstEnd).setDuration(3000);
little_upAnimator.setInterpolator(new AccelerateInterpolator());
little_downAnimator = ObjectAnimator.ofFloat(mLittleSunView, "y", littlesunYFirstEnd, littlesunYFirstStart).setDuration(3000);
little_downAnimator.setInterpolator(new AccelerateInterpolator());
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分别定义太阳下降、太阳上升、倒影下降、倒影上升动画集，再合并为上升、下降总动画集
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| //太阳下降动画集
sun_downAnimatorSet = new AnimatorSet();
sun_downAnimatorSet.play(sun_downAnimator)
.with(sunsetSkyAnimator)
.with(bigXAnimator).with(bigYAnimator)
.with(clockwiseAnimator)
.before(nightSkyAnimator);
//太阳上升动画集
sun_upAnimatorSet = new AnimatorSet();
sun_upAnimatorSet.play(sun_upAnimator)
.with(sunsetSkyAnimator)
.with(smallXAnimator).with(smallYAnimator)
.with(anti_clockwiseAnimator)
.before(nightSkyAnimator);
//倒影上升动画集、
little_upAnimatorSet = new AnimatorSet();
little_upAnimatorSet
.play(little_anti_clockwiseAnimator)
.with(little_bigXAnimator).with(little_bigYAnimator)
.with(alphaAnimator)
.with(little_upAnimator);
//倒影下降动画集
little_downAnimatorSet = new AnimatorSet();
little_downAnimatorSet
.play(little_clockwiseAnimator)
.with(little_smallXAnimator).with(little_smallYAnimator)
.with(little_downAnimator)
.with(unalphaAnimator);
//总动画集
downAnimatorSet = new AnimatorSet();
downAnimatorSet.play(sun_downAnimatorSet).with(little_upAnimatorSet);
upAnimatorSet = new AnimatorSet();
upAnimatorSet.play(sun_upAnimatorSet).with(little_downAnimatorSet);
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三、日落动画反转
目前暂时还没做。
推荐文章
关于Android动画用法，推荐这篇https://blog.csdn.net/qq_40881680/article/details/82378391，写得很好，在我学动画部分的时候，对我帮助很大。