关于AlertDialog设置背景透明的问题

Question

在setView（view）自定义的view里面，外层linearLayout我设置成透明的了，可是运行起来还是白色的，求解

Answer 1

//自定义布局
View layout = getActivity().getLayoutInflater().inflate(R.layout.mydialog,null);
AlertDialog.Builder dialog = new AlertDialog.Builder(DialogActivity.this,AlertDialog.THEME_DEVICE_DEFAULT_DARK);
final AlertDialog dialog = builder.create();
dialog.setView(layout);
//透明
Window window = dialog.getWindow();
WindowManager.LayoutParams lp = window.getAttributes();
lp.alpha = 0.9f;
window.setAttributes(lp);
.......
dialog.show();