如何让HorizonScrollView中的子控件居中

package com.example.usinghorizontalview;

import android.app.Activity;
import android.os.Bundle;
import android.view.View;
import android.widget.HorizontalScrollView;
import android.widget.LinearLayout;

public class MainActivity extends Activity {

	private LinearLayout mLl;
	private HorizontalScrollView mHsv;
	//屏幕宽度
	private int mScreenWidth;

	@Override
	protected void onCreate(Bundle savedInstanceState) {
		super.onCreate(savedInstanceState);
		setContentView(R.layout.activity_main);
		//获取屏幕宽度
		mScreenWidth = getResources().getDisplayMetrics().widthPixels;
		initViews();
		initEvents();
	}

	private void initEvents() {
		int childCount = mLl.getChildCount();
		for (int i = 0; i < childCount; i++) {
			final int curIndex = i;
			View child = mLl.getChildAt(i);
			// 添加点击事件
			child.setOnClickListener(new View.OnClickListener() {
				@Override
				public void onClick(View v) {
					selectTab(curIndex);
				}
			});
		}
	}
	/**
	 * 选中索引值为curIndex的tab
	 * @param curIndex
	 */
	protected void selectTab(int curIndex) {
		int childCount = mLl.getChildCount();
		for (int i = 0; i < childCount; i++) {
			View child = mLl.getChildAt(i);
			//设置选中状态
			child.setSelected(i == curIndex);
		}
		
		
		View curTabView = mLl.getChildAt(curIndex);
		//获取x的值
		int left = curTabView.getLeft();
		int width = curTabView.getMeasuredWidth();
		int toX =  left + width/2 - mScreenWidth/2 ;
		//滚动
		mHsv.smoothScrollTo(toX, 0);
	}

	private void initViews() {
		mHsv = (HorizontalScrollView) findViewById(R.id.hsv);
		mLl = (LinearLayout) findViewById(R.id.ll);
		// 默认选中第一个
		mLl.getChildAt(0).setSelected(true);
	}
}