一、概念

透明度动画，子类：AlphaAnimation，标签：<alpha>
它可以使View具有透明度的动画效果。

二、实现

1. XML实现
<alpha>标签常用属性如下：
android:fromAlpha：透明度起始值，比如0.1；
android:toAlpha：透明度结束值，比如1。

//res/anim/alpha_animation.xml
<?xml version="1.0" encoding="utf-8"?>
<alpha xmlns:android="http://schemas.android.com/apk/res/android"
    android:fillAfter="true"
    android:fromAlpha="0.1"
    android:toAlpha="1"
    android:duration="3000"
    android:repeatCount="2"
    />

//代码，MAinActivity
private void alphaAnimationXML() {
    Animation alphaAnimation = AnimationUtils.loadAnimation(this, R.anim.alpha_animation);
    mAnimate_tv.setAnimation(alphaAnimation);
    mAnimate_tv.startAnimation(alphaAnimation);
}

private void stopAnimation() {
    mAnimate_tv.clearAnimation();
}

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    initView();
    alphaAnimationXML();
}

@Override
protected void onDestroy() {
    super.onDestroy();
    stopAnimation();
}

2. 代码实现
构造方法：
public AlphaAnimation(float fromAlpha, float toAlpha)
参数说明：
fromAlpha：透明度起始值，比如0.1；
toAlpha：透明度结束值，比如1。

//布局
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="500px"
    android:layout_height="500px"
    android:layout_marginLeft="100px"
    android:background="@color/colorAccent">
    <TextView
        android:id="@+id/animate_tv"
        android:layout_width="wrap_content"
        android:layout_height="200px"
        android:gravity="center"
        android:layout_centerInParent="true"
        android:textColor="@color/colorAccent"
        android:text="Hello Android!"
        android:background="@color/colorPrimaryDark"/>
</RelativeLayout>

//代码，MainActivity
private void alphaAnimationCode() {
    mAnimation = new AlphaAnimation(0.1f, 1f);
    mAnimation.setDuration(3000);
    mAnimation.setRepeatCount(2);
    mAnimation.setFillAfter(true);
    mAnimate_tv.setAnimation(mAnimation);
    mAnimate_tv.startAnimation(mAnimation);
}

private void stopAnimation() {
    mAnimate_tv.clearAnimation();
}

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    initView();
    alphaAnimationCode();
}

@Override
protected void onDestroy() {
    super.onDestroy();
    stopAnimation();
}