DialogActivity

 <?xml version="1.0" encoding="utf-8"?>
 <resources>

 <style name="MyDialogStyle">
 <item name="android:windowBackground">@android:color/transparent</item>
 <item name="android:windowFrame">@null</item>
 <item name="android:windowNoTitle">true</item>
 <item name="android:windowIsFloating">true</item>
 <item name="android:windowIsTranslucent">true</item>
 <item name="android:windowContentOverlay">@null</item>
 <item name="android:windowAnimationStyle">@android:style/Animation.Dialog</item>
 <item name="android:backgroundDimEnabled">true</item>
 </style>

 </resources>

styles.xml

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
                xmlns:tools="http://schemas.android.com/tools"
                android:layout_width="match_parent"
                android:layout_height="match_parent">

    <RelativeLayout
            android:layout_width="match_parent"
            android:layout_height="180dp"
            android:layout_centerInParent="true"
            android:background="#fff" >

        <LinearLayout
                android:layout_width="fill_parent"
                android:layout_height="fill_parent"
                android:layout_alignParentLeft="true"
                android:layout_alignParentTop="true"
                android:gravity="center"
                android:orientation="vertical" >

            <ProgressBar
                    android:id="@+id/progressBar1"
                    style="?android:attr/progressBarStyleLarge"
                    android:layout_width="wrap_content"
                    android:layout_height="wrap_content"
                    android:layout_gravity="center_horizontal" />

            <TextView
                    android:layout_width="wrap_content"
                    android:layout_height="wrap_content"
                    android:layout_marginTop="10dp"
                    android:text="正在登录"
                    android:textColor="#fff"
                    android:textSize="20sp" />
        </LinearLayout>

    </RelativeLayout>

</RelativeLayout>