解决dialog 透明背景

AlertDialog.Builder builder = new AlertDialog.Builder(activity,R.style.NoBackGroundDialog);
        final AlertDialog dialog = builder.create();

        View dialogView = View.inflate(activity, R.layout.dialog_login, null);
        //设置对话框布局
//        dialog.setView(dialogView);

        ImageView btn_qq_login = dialogView.findViewById(R.id.btn_qq_login);
        ImageView btn_weixin_login = dialogView.findViewById(R.id.btn_weixin_login);
//        Button btn_guest_login = dialogView.findViewById(R.id.btn_guest_login);
        dialog.show();
        dialog.setContentView(dialogView); //放在show之后，位置也很重要

关键在于 dialog.setView(dialogView)和dialog.setContentView(dialogView)

<resources>

    <style name="NoBackGroundDialog" parent="@android:style/Theme.Holo.Light.Dialog">
        <item name="android:windowBackground">@android:color/transparent</item>
    </style>

</resources>