Android的布局图毛刺

我写一个机器人比赛，我已经创建了具有这种XML主菜单的布局：Android的布局图毛刺

import android.app.Activity; 
import android.content.Intent; 
import android.os.Bundle; 
import android.view.View.OnClickListener; 
import android.view.View; 
import android.view.Window; 
import android.view.WindowManager; 
import android.widget.*; 

public class MainActivity extends Activity { 


    @Override 
    protected void onCreate(Bundle savedInstanceState) { 
     super.onCreate(savedInstanceState); 

     //Get rid of the stuff around the edges 
     requestWindowFeature(Window.FEATURE_NO_TITLE); 
     getWindow().setFlags(WindowManager.LayoutParams.FLAG_FULLSCREEN, 
           WindowManager.LayoutParams.FLAG_FULLSCREEN); 

     //show layout 
     setContentView(R.layout.main_menu); 
     Button btnStart = (Button)findViewById(R.id.btnStartSurvive); 
     btnStart.setOnClickListener(oclStart); 
    } 

    private OnClickListener oclStart = new OnClickListener() { 

     @Override 
     public void onClick(View v) { 
      // TODO Auto-generated method stub 
      Intent intent = new Intent(MainActivity.this, GameActivity.class); 
      intent.putExtra("gametype", 'S'); 
      startActivity(intent); 
     } 
    }; 

}

：

<?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:orientation="vertical" > 

    <TextView 
     android:id="@+id/tvStats" 
     android:layout_width="wrap_content" 
     android:layout_height="wrap_content" 
     android:layout_gravity="center_horizontal" 
     android:text="Large Text" 
     android:textAppearance="?android:attr/textAppearanceLarge" /> 

    <LinearLayout 
     android:layout_width="match_parent" 
     android:layout_height="wrap_content" 
     android:layout_gravity="fill_horizontal" 
     android:gravity="fill_horizontal" > 

     <Button 
      android:id="@+id/btnStartSurvive" 
      android:layout_width="wrap_content" 
      android:layout_height="wrap_content" 
      android:layout_gravity="fill_horizontal" 
      android:gravity="center_vertical|center_horizontal" 
      android:text="Start Survival Mode" /> 

     <Button 
      android:id="@+id/btnStartChall" 
      android:layout_width="wrap_content" 
      android:layout_height="wrap_content" 
      android:layout_gravity="fill_horizontal" 
      android:text="Start Callenge Mode" /> 

    </LinearLayout> 

</LinearLayout>

使用此活动在屏幕上显示的布局

当我我的手机上运行这个（安卓4.2.2），我得到的东西看起来是这样的：