Android AlertDialog背景设置有问题

写了一个包含Listview的AlertDialog，设置完背景透明之后，还是有黑色包裹着Listview
如图

下面是具体的代码实现

背景样式

<style name="QRCodeDialogStyle" parent="@android:style/Theme.Dialog">
        <item name="android:windowFrame">@null</item><!--边框-->
        <item name="android:background">#00000000</item>
        <item name="android:windowIsFloating">true</item><!--是否浮现在activity之上-->
        <item name="android:windowIsTranslucent">true</item><!--半透明-->
        <item name="android:windowNoTitle">true</item><!--无标题-->
        <item name="android:windowBackground">@android:color/transparent</item><!--背景透明-->
        <item name="android:backgroundDimEnabled">true</item><!--背后的Activity是否模糊-->
        <item name="android:backgroundDimAmount">0.5</item>
    </style>

布局文件

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:id="@+id/qr_ll"
    android:layout_width="100dp"
    android:layout_height="wrap_content"
    android:layout_gravity="center"
    android:background="#ffffff"
    android:orientation="vertical" >

    <ListView
        android:layout_width="100dp"
        android:layout_height="wrap_content"
        android:background="#ffffff"
        android:id="@+id/qrcode_listview">

    </ListView>


</LinearLayout>

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:gravity="center_horizontal"
    android:background="#00000000"
    android:orientation="vertical" >

    <TextView
        android:id="@+id/qr_text_item"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="保存图片"
        android:textSize="20sp" />

</LinearLayout>

Java代码

arrayAdapter = new ArrayAdapter<String>(getApplicationContext(), R.layout.qrcode_dialog_item, R.id.qr_text_item);
                    arrayAdapter.add("保存到本地");
                    arrayAdapter.add("保存到本地");
                    LayoutInflater inflater = getLayoutInflater();
                    View layout = inflater.inflate(R.layout.qrcode_dialog1_layout, null);
                    ListView listView = (ListView) layout.findViewById(R.id.qrcode_listview);
                    listView.setAdapter(arrayAdapter);

                    builder.setView(layout);
                    alertDialog = builder.create();
                    alertDialog.getWindow().setBackgroundDrawable(new ColorDrawable(0));
                    //alertDialog.setTitle("选择教室类型");
                    //alertDialog.setView(listView);
                    alertDialog.show();

若将
style里面的background改为白色这变成下图

<item name="android:background">#ffffff</item>

把你ListView的背景透明化

AlertDialog.Builder builder = new AlertDialog.Builder(MainActivity.this,R.style.QRCodeDialogStyle);
                View viewDialog = View.inflate(MainActivity.this, R.layout.dialog_transfer, null);
                ListView lv = viewDialog.findViewById(R.id.qrcode_listview);
                builder.setView(viewDialog);
                final AlertDialog alertDialog = builder.create();
                alertDialog.create();
                alertDialog.show();

                ArrayAdapter arrayAdapter = new ArrayAdapter<String>(getApplicationContext(), R.layout.tv_item, R.id.qr_text_item);
                arrayAdapter.add("保存到本地");
                arrayAdapter.add("保存到本地");
                lv.setAdapter(arrayAdapter);

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:gravity="center"
    android:orientation="vertical">

    <ListView
        android:id="@+id/qrcode_listview"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content" />


</LinearLayout>

 <?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:gravity="center_vertical">

    <TextView
        android:id="@+id/qr_text_item"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="保存图片"
        android:textSize="20sp" />

</LinearLayout>

 <style name="QRCodeDialogStyle" parent="@android:style/Theme.Dialog">
        <item name="android:background">#00000000</item>
        <item name="android:windowIsFloating">true</item><!--是否浮现在activity之上-->
        <item name="android:windowBackground">@android:color/transparent</item><!--背景透明-->
    </style>