AnimationDrawable animationDrawable= (AnimationDrawable) iv_guide_animation_1.getBackground();
animationDrawable.start();
一加上 .start(); 就闪退，三个 一个都不行，动画不显示。
错误信息：Attempt to invoke virtual method ‘void android.graphics.drawable.AnimationDrawable.start()’ on a null object reference
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2947)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3082)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method ‘void android.graphics.drawable.AnimationDrawable.start()’ on a null object reference