性能优化ListView

Question

这是我的班级和布局.. testlayout dot java

package com.example.project1;
import android.app.ListActivity;
public class testLayout extends ListActivity 
{
        Project1 mAct; 
        void setNewWindow()
{
    mAct=Project1.getMAct(); //Project1 context (Project1 - MainActivity)
    mAct.setContentView(R.layout.testlayout);
    String[] values = new String[] { "Android", "iPhone", "WindowsMobile",
    "Blackberry", "WebOS", "Ubuntu", "Windows7", "Max OS X",
    "Linux", "OS/2", "Ubuntu", "Windows7", "Max OS X", "Linux",
    "OS/2", "Ubuntu", "Windows7", "Max OS X", "Linux", "OS/2",
    "Android", "iPhone", "WindowsMobile" };
    setListAdapter(new MyPerformanceArrayAdapter(mAct, values));
}
}

testlayout.xml

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent" >

<ListView
    android:id="@+id/listView2"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:layout_alignParentLeft="true"
    android:layout_alignParentTop="true" >
</ListView>

</RelativeLayout>

MyPerformanceArrayAdapter.java

package com.example.project1;

import android.app.Activity;
import android.util.Log;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ArrayAdapter;
import android.widget.ImageView;
import android.widget.TextView;

public class MyPerformanceArrayAdapter extends ArrayAdapter<String> {
      private final Project1 context1;
      private final String[] names1;

      static class ViewHolder {
        public TextView text;
        public ImageView image;
      }

      public MyPerformanceArrayAdapter(Project1 context, String[] names) {
        super(Project1.getMAct(), R.layout.rowlayout, names);
        context1 = Project1.getMAct();
        names1 = names;
        Log.v("4", "GOOD");

      }



      @Override
      public View getView(int position, View convertView, ViewGroup parent) {
        View rowView = convertView;
        Log.v("3", "GOOD");

        // reuse views
        if (rowView == null) {
          LayoutInflater inflater = Project1.getMAct().getLayoutInflater();
          rowView = inflater.inflate(R.layout.rowlayout, null);
          // configure view holder
          ViewHolder viewHolder = new ViewHolder();
          viewHolder.text = (TextView) rowView.findViewById(R.id.label);
          viewHolder.image = (ImageView) rowView.findViewById(R.id.icon);
          rowView.setTag(viewHolder);
        }

        // fill data
        ViewHolder holder = (ViewHolder) rowView.getTag();
        String s = names1[position];
        holder.text.setText(s);
        Log.v("2", "GOOD");

        if (s.startsWith("Windows7") || s.startsWith("iPhone")
            || s.startsWith("Solaris")) {
          holder.image.setImageResource(R.drawable.no);
        } else {
          holder.image.setImageResource(R.drawable.ok);
        }
        Log.v("1", "GOOD");

        return rowView;
      }
    } 

rowlayout.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content" >

    <ImageView
        android:id="@+id/icon"
        android:layout_width="22px"
        android:layout_height="22px"
        android:layout_marginLeft="4px"
        android:layout_marginRight="10px"
        android:layout_marginTop="4px"
        android:layout_weight="21.23"
        android:src="@drawable/ic_launcher" />

    <TextView
        android:id="@+id/label"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="@+id/label"
        android:textSize="20px" />

    <ListView
        android:id="@+id/listView1"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_weight="21.23" >
    </ListView>

</LinearLayout>

和ERROR的

 at android.app.Activity.getSystemService(Activity.java:4410)
    FATAL EXCEPTION: main
    java.lang.NullPointerException
    at android.app.Activity.setContentView(Activity.java:1867)
    at android.app.ListActivity.ensureList(ListActivity.java:312)
    at android.app.ListActivity.setListAdapter(ListActivity.java:263)
    at com.example.project1.testLayout.setNewWindow(testLayout.java:19)
    at com.example.project1.SecondLayout$2.onClick(SecondLayout.java:65)

什么是错的？

那是我的SecondView.java

package com.example.project1;

import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

import android.util.Log;
import android.view.View;
import android.widget.Button;
import android.widget.ListView;
import android.widget.SimpleAdapter;
import android.widget.TextView;

public class SecondLayout 
{
private static Project1 mAct;   
testLayout tL= new testLayout();


public void setNewWindow()
{
    mAct = Project1.getMAct();
    mAct.setContentView(R.layout.secondlayout); 
    TextView textView1 = (TextView) mAct.findViewById(R.id.textView4);
    TextView textView2 = (TextView) mAct.findViewById(R.id.textView5);
    ResClass res = Project1.getMAct().getRes();
    textView1.setText(res.getV1("status"));
    textView2.setText(res.getV1(2,"posts", "author"));
    int len= res.getLen();
    List<Map<String, String>> arList = new ArrayList<Map<String,String>>();
    for (int i=0; i<len; i++)
    {
        Map <String, String> resMap = new HashMap <String, String>();
        resMap.put("authors", res.getV1(i, "posts", "author"));
        resMap.put("titles", res.getV1(i, "posts", "title"));
        arList.add(resMap);
    }
    ListView listView1= (ListView) mAct.findViewById(R.id.listView1);

    SimpleAdapter adp = new SimpleAdapter (mAct, arList,         android.R.layout.simple_list_item_2, new String[] {"authors","titles"}, new int[]         {android.R.id.text1, android.R.id.text2});

    listView1.setAdapter(adp);



    res.resFree();
    Button button1 = (Button) mAct.findViewById(R.id.button4);
    Button button2 = (Button) mAct.findViewById(R.id.button5);


    button1.setOnClickListener(new View.OnClickListener() {

        @Override
        public void onClick(View arg0) {
            mAct.StartWindow();
        }
    });

    button2.setOnClickListener(new View.OnClickListener() {

        @Override
        public void onClick(View arg0) {
            Log.v("ON CLICK", "GOOD");
            tL.setNewWindow();
        }
    });



}

}

Project1是我的MainActivity.java类 我从SecondLayout打电话给TestLayout getMAct - 给出Project1 prj1 = this;

public static Project1 getMAct()
{
return prj1;
}