<activity android:name="MyDialogActivity"
    android:theme="@android:style/Theme.Dialog">
</activity>

<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>

<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="180dp"
    android:layout_height="180dp"
    android:layout_centerInParent="true"
    android:background="@drawable/loading_bg" >
    <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>

public class DialogActivity extends Activity
{
  @Override
  protected void onCreate(Bundle savedInstanceState)
  {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    // 这里你可以进行一些等待时的操作，我这里用8秒后显示Toast代理等待操作
    new Handler().postDelayed(new Runnable(){
      @Override
      public void run(){
        DialogActivity.this.finish();
        Toast.makeText(getApplicationContext(), "登录成功", Toast.LENGTH_SHORT).show();
      }
    }, 8000);
  }
}

<activity
   android:name="LoadingActivity"
   android:theme="@style/MyDialogStyle" />