ListView 遇到问题

package cn.huiyuan.words;



import java.util.ArrayList;

import java.util.HashMap;

import java.util.List;



import android.app.Activity;

import android.content.Intent;

import android.database.DataSetObserver;

import android.os.Bundle;

import android.view.View;

import android.view.ViewGroup;

import android.view.Window;

import android.view.View.OnClickListener;

import android.widget.ArrayAdapter;

import android.widget.Button;

import android.widget.ListAdapter;

import android.widget.ListView;

import android.widget.SimpleAdapter;



public class SentenceBook extends Activity

{

	@Override

	protected void onCreate(Bundle savedInstanceState)

	{

		requestWindowFeature(Window.FEATURE_NO_TITLE);

		super.onCreate(savedInstanceState);

		setContentView(R.layout.sentencebook);

		Button backToMain = (Button)findViewById(R.id.btn_back);

		backToMain.setOnClickListener(new OnClickListener()

		{

			

			@Override

			public void onClick(View v)

			{

				Intent intent = new Intent();

				intent.setClass(getApplicationContext(), OneDayOneWord.class);

				startActivity(intent);

				finish();

			}

		});

		List<HashMap<String, String>> data = new ArrayList<HashMap<String, String>>();

		for (int i = 0; i < 3; i++)

		{

			HashMap<String, String> hashMap = new HashMap<String, String>();

			hashMap.put("bindsentence", "ttttteeeeesssssttttt!");

			data.add(hashMap);

		}

		System.out.println("Data"+data);

		SimpleAdapter sentenceListAdapter = new SimpleAdapter(this, data,

				R.layout.sentencebook_item,

				new String[] { "bindsentence"},

				new int[] { R.id.item});

		ListView listView = (ListView) findViewById(R.layout.sentencebook);

		System.out.println(listView);  

		listView.setAdapter(sentenceListAdapter);



	}



}

<?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:background="@drawable/whatsnew_bg"

    android:orientation="vertical" >



    <RelativeLayout

        android:id="@+id/titlebar_setting"

        android:layout_width="match_parent"

        android:layout_height="wrap_content"

        android:background="@drawable/titlebar_bg" >



        <Button

            android:id="@+id/btn_back"

            android:layout_width="wrap_content"

            android:layout_height="wrap_content"

            android:layout_alignParentLeft="true"

            android:layout_marginLeft="5.0dp"

            android:layout_marginTop="8.0dp"

            android:background="@drawable/titlebar_btn_back_selector"

            android:text="@string/menu_back" />



        <TextView

            android:layout_width="wrap_content"

            android:layout_height="wrap_content"

            android:layout_centerHorizontal="true"

            android:layout_centerVertical="true"

            android:text="@string/book"

            android:textSize="20sp" />

    </RelativeLayout>



    <ListView

        android:id="@+id/sentencelist"

        android:layout_width="wrap_content"

        android:layout_height="wrap_content" >

    </ListView>



</LinearLayout>

<?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/item"

        android:layout_width="fill_parent"

        android:layout_height="wrap_content"

        android:text="测试用~~~~~~~~~~"

         />



</LinearLayout>