ListView的优化

用convertView优化ListView
 1 package com.example.zhangmeng.myliestview;
 2 
 3 import android.os.Bundle;
 4 import android.support.v7.app.AppCompatActivity;
 5 import android.view.View;
 6 import android.view.ViewGroup;
 7 import android.widget.BaseAdapter;
 8 import android.widget.ListView;
 9 import android.widget.TextView;
10 
11 public class MainActivity extends AppCompatActivity {
12 
13     @Override
14     protected void onCreate(Bundle savedInstanceState) {
15         super.onCreate(savedInstanceState);
16         setContentView(R.layout.activity_main);
17         ListView lv=(ListView)findViewById(R.id.lv);
18         MyAdapter adapter=new MyAdapter();
19         lv.setAdapter(adapter);
20     }
21 
22     class MyAdapter extends BaseAdapter{
23 
24         @Override
25         public int getCount() {
26             return 100;
27         }
28 
29         @Override
30         public Object getItem(int position) {
31             return null;
32         }
33 
34         @Override
35         public long getItemId(int position) {
36             return 0;
37         }
38 
39         @Override
40         public View getView(int position, View convertView, ViewGroup parent) {
41 
42             TextView tv=null;
43             if(convertView==null){
44                 tv=new TextView(MainActivity.this);
45             }
46             else{
47                 tv=(TextView) convertView;
48             }
49 
50             tv.setText("Hello"+(position+1));
51             return tv;
52         }
53     }
54 }