Android动画之帧动画

帧动画，顾名思义就是通过一帧一帧切换图片来实现动画效果。老式电影放映机就是这样的
优点：原理简单，实现也很简单
缺点：占资源，图片多了很容易OOM。
需要用到AnimationDrawable

方式一：xml定义资源

<?xml version="1.0" encoding="utf-8"?>
<animation-list xmlns:android="http://schemas.android.com/apk/res/android"
    android:oneshot="false">
    <item android:drawable="@drawable/dayu1"  android:duration="50" />
    <item android:drawable="@drawable/dayu2"  android:duration="50" />
    <item android:drawable="@drawable/dayu3"  android:duration="50" />
    <item android:drawable="@drawable/dayu4"  android:duration="50" />
    ...
    <item android:drawable="@drawable/dayu100"  android:duration="50" />
</animation-list>

将资源设置为背景

<ImageView
        android:id="@+id/img_show"
        android:layout_width="800px"
        android:layout_height="600px"
        android:background="@drawable/yu_gif"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintRight_toRightOf="parent"
        app:layout_constraintTop_toTopOf="parent" />

通过View获取AnimationDrawable对象

        var annotation: AnimationDrawable = img_show.background as AnimationDrawable

方式二：代码生成对象

class DayuActivity : AppCompatActivity() {
    val list = arrayOf(
        R.drawable.dayu1,
        R.drawable.dayu2,
        R.drawable.dayu3,
        R.drawable.dayu4,
        ...
        R.drawable.dayu100
    )

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_dayu)
        //1 获取 AnimationDrawable对象
        //a xml
        //var annotation: AnimationDrawable = img_show.background as AnimationDrawable
        //b 代码
        var annotation: AnimationDrawable = AnimationDrawable()
        for(id in list){
            annotation.addFrame(resources.getDrawable(id),50)
        }
        img_show.background=annotation
        
        //2 设置动画是否只执行一次
        annotation.isOneShot = false
        //3 开始动画
        annotation.start()
    }
}

dayu.gif