如何把dialog的圆角改为直角啊

package com.bxdm.xwplayer.online.util;import com.example.httptext.R;import android.app.Activity;  import android.app.AlertDialog;  import android.app.ProgressDialog;   import android.os.Bundle;  import android.view.LayoutInflater;  import android.view.View;    public class test extends Activity {      /** Called when the activity is first created. */      ProgressDialog p_dialog;        @Override      public void onCreate(Bundle savedInstanceState) {          super.onCreate(savedInstanceState);          setContentView(R.layout.dialog);        LayoutInflater factory = LayoutInflater                  .from(test.this);          final View DialogView = factory.inflate(                  R.layout.dialog, null);          AlertDialog dlg = new AlertDialog.Builder(                  test.this)//                .setTitle("")  //                .setMessage("") //                .setView(DialogView)                  .create();        dlg.setView(DialogView, 0, 0, 0, 0);        dlg.show();        }  } 

<?xml version="1.0" encoding="utf-8"?><LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"    android:layout_width="fill_parent"    android:layout_height="fill_parent"    android:orientation="vertical"    android:background="#FFFFFF" >    <RelativeLayout        android:layout_width="fill_parent"        android:layout_height="fill_parent"        android:orientation="horizontal" >        <TextView            android:layout_width="wrap_content"            android:layout_height="wrap_content"            android:text="" />        <ImageView            android:layout_width="wrap_content"            android:layout_height="wrap_content"            android:layout_alignParentRight="true"            android:layout_alignParentTop="true"            android:layout_marginRight="15dp"            android:src="@drawable/close" />    </RelativeLayout>    <TextView         android:layout_margin="100dip"        android:layout_width="wrap_content"        android:layout_height="wrap_content"        /></LinearLayout>