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// アニメーションの実行(fade_out)
Animation animation= AnimationUtils.loadAnimation(this, R.animator.alpha_fadeout);
imageView.startAnimation(animation);

// アニメーションの実行(fade_in)
Animation animation= AnimationUtils.loadAnimation(this,R.animator.alpha_fadein);
imageView.startAnimation(animation);

<?xml version="1.0" encoding="utf-8"?>

<!-- res/animator/alpha_fadeout.xml -->
<set xmlns:android="http://schemas.android.com/apk/res/android"
    android:duration="5000">
    <alpha android:interpolator="@android:anim/decelerate_interpolator"
           android:fromAlpha="1.0"
           android:toAlpha="0.0"
           android:fillAfter="true"
           android:duration="3000" />
</set>

<?xml version="1.0" encoding="utf-8"?>

<!-- res/animator/alpha_fadein.xml -->
<set xmlns:android="http://schemas.android.com/apk/res/android">
<alpha android:interpolator="@android:anim/decelerate_interpolator"
       android:fromAlpha="0.0"
       android:toAlpha="1.0"
       android:fillAfter="true"
       android:duration="3000"/>
</set>