android动画之AlphaAnimation（渐变动画，最简单的动画）

AlphaAnimation渐变动画只需要设置从一可见程度，到另一可见程度即可。

示例代码：

package com.hongchou.www.myalphaanimation;import android.app.Activity;import android.support.v7.app.AppCompatActivity;import android.os.Bundle;import android.view.Window;import android.view.animation.AlphaAnimation;import android.widget.ImageView;/** * android AlphaAnimation渐变动画 */public class MainActivity extends Activity {    private ImageView iv;    @Override    protected void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        requestWindowFeature(Window.FEATURE_NO_TITLE);        setContentView(R.layout.activity_main);        iv = findViewById(R.id.iv);        AlphaAnimation alphaAnimation=new AlphaAnimation(0,1);        alphaAnimation.setDuration(2000);        iv.startAnimation(alphaAnimation);    }}

布局文件代码：

<?xml version="1.0" encoding="utf-8"?><android.support.constraint.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"    xmlns:app="http://schemas.android.com/apk/res-auto"    xmlns:tools="http://schemas.android.com/tools"    android:layout_width="match_parent"    android:layout_height="match_parent"    tools:context="com.hongchou.www.myalphaanimation.MainActivity">    <ImageView        android:id="@+id/iv"        android:background="@drawable/bk"        android:layout_width="match_parent"        android:layout_height="match_parent"        android:text="Hello World!"        app:layout_constraintBottom_toBottomOf="parent"        app:layout_constraintLeft_toLeftOf="parent"        app:layout_constraintRight_toRightOf="parent"        app:layout_constraintTop_toTopOf="parent" /></android.support.constraint.ConstraintLayout>

注意设置动画时间，才能看到动画效果

 alphaAnimation.setDuration(2000);