Could not find class 'android.graphics.drawable.RippleDrawable'

 AS报错：Could not find class ‘android.graphics.drawable.RippleDrawable‘, referenced from method android.support.v7.widget.AppCompatImageHelper.hasOverlappingRendering

问题：在替换fragment时候出错

FragmentTransaction记得在同一个activity切换activity的时候，

fragmentTransaction.replace(R.id.ll_container,frag2).commit();再次初始化，
方式为：fragmentTransaction=fm.beginTransaction();。