AS報錯：Could not find class 'android.graphics.drawable.RippleDrawable', referenced from method android.support.v7.widget.AppCompatImageHelper.hasOverlappingRendering
問題：在替換fragment時候出錯
FragmentTransaction記得在同一個activity切換activity的時候，
fragmentTransaction.replace(R.id.ll_container,frag2).commit();再次初始化，
方式為：fragmentTransaction=fm.beginTransaction();。