Android：ListView、BaseAdapter、convertView、ListView优化及事件、notifyDataSetChanged()
@Override
protected void onCreate(Bundle savedInstanceState)
{
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
final ArrayList<String> title = new ArrayList<String>();
for (int i = 0; i < 20; i++)
{
title.add("标题" + i);
}
ListView listView = (ListView) findViewById(R.id.listView1);
listView.setAdapter(new BaseAdapter()
{
@Override
public View getView(int position, View convertView, ViewGroup parent)//执行数等于当前页面出现的行数,convertView指滚动消失的layout
{
Log.e("getView", "调用getView"+ i++ + "convertView:" + convertView);
LayoutInflater inf = getLayoutInflater();//通过LayoutInflater将布局id转换到对象
RelativeLayout relativeLayout = (RelativeLayout) inf.inflate(R.layout.relat, null);
TextView titleview = (TextView) relativeLayout.findViewById(R.id.textView1);//通过布局找到里面的控件
titleview.setText(title.get(position));//得到容器内的内容
return relativeLayout;
}
@Override
public long getItemId(int position)
{
return 0;
}
@Override
public Object getItem(int position)
{
return null;
}
@Override
//先执行getCount再执行getView，出现新行数时再次执行getCount
//listview清单里要设置高度match_parent
//每次点击屏幕一次都会先执行getCount
public int getCount()
{
Log.e("getCount", "调用getCount"+ j++);
return title.size();
}
});
}
复用converview：
ListView listView = (ListView) findViewById(R.id.listView1);
listView.setAdapter(new BaseAdapter()
{
@Override
public View getView(int position, View convertView, ViewGroup parent)//执行数等于当前页面出现的行数,convertView指滚动消失的layout
{
//复用converview
RelativeLayout relativeLayout = null;
if(convertView == null)
{
LayoutInflater inf = getLayoutInflater();
relativeLayout = (RelativeLayout) inf.inflate(R.layout.relat, null);
}
else
{
relativeLayout = (RelativeLayout) convertView;
}
TextView titleView = (TextView) relativeLayout.findViewById(R.id.textView1);
titleView.setText(title.get(position));
return relativeLayout;
}
继续优化：
public class MainActivity extends Activity
{
int imID = 0;
class Msg//内容
{
String mTitle;
String mSubtitle;
String mTime;
int mImagID;
public Msg(String mTitle, String mSubtitle, String mTime, int mImagID)
{
super();
this.mTitle = mTitle;
this.mSubtitle = mSubtitle;
this.mTime = mTime;
this.mImagID = mImagID;
}
}
class ViewHolder//控件
{
TextView viewTitle;
TextView viewSubtitle;
TextView viewTime;
ImageView viewImage;
}
@Override
protected void onCreate(Bundle savedInstanceState)
{
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
Date timeNow = new Date();
SimpleDateFormat timeFormat = new SimpleDateFormat("HH:mm:ss");
String time = timeFormat.format(timeNow);
final ArrayList<Msg> msgList = new ArrayList<Msg>();
for (int i = 0; i < 30; i++)//选择图片
{
if(i % 4 == 0)
{
imID = R.drawable.ic_launcher;
}
if(i % 4 == 1)
{
imID = R.drawable.ic_1;
}
if(i % 4 == 2)
{
imID = R.drawable.ic_2;
}
if(i % 4 == 3)
{
imID = R.drawable.ic_3;
}
Msg msg = new Msg("标题" + i, "内容" + i, time ,imID);
msgList.add(msg);
}
ListView listView = (ListView) findViewById(R.id.listView1);
listView.setAdapter(new BaseAdapter()
{
ViewHolder holder = null;
@Override
public View getView(int position, View convertView, ViewGroup parent)
{
RelativeLayout relout = null;
if (convertView == null)//创建首页时才find控件
{
LayoutInflater layoutInflater =getLayoutInflater();
relout = (RelativeLayout) layoutInflater.inflate(R.layout.relaout, null);
holder = new ViewHolder();
holder.viewTitle= (TextView) relout.findViewById(R.id.textView_title);
holder.viewSubtitle = (TextView) relout.findViewById(R.id.textView_subtitle);
holder.viewTime = (TextView) relout.findViewById(R.id.textView_time);
holder.viewImage = (ImageView) relout.findViewById(R.id.imageView1);
relout.setTag(holder);
}
else//否则复用layout和view
{
relout = (RelativeLayout) convertView;
holder = (ViewHolder) relout.getTag();//记得得到holder
}
Msg msg = msgList.get(position);
holder.viewTitle.setText(msg.mTitle);
holder.viewSubtitle.setText(msg.mSubtitle);
holder.viewTime.setText(msg.mTime);
holder.viewImage.setImageResource(msg.mImagID);//设置图片的方法
return relout;
}
@Override
public long getItemId(int position)
{
return 0;
}
@Override
public Object getItem(int position)
{
return null;
}
@Override
public int getCount()
{
return msgList.size();
}
});
}
@Override
public boolean onCreateOptionsMenu(Menu menu)
{
getMenuInflater().inflate(R.menu.activity_main, menu);
return true;
}
}
点击按钮更新listview：Adapter使用notifyDataSetChanged()通知listview更新
3private void btn1Click()//增加一行信息
{
i++;
data.add("内容" + i );
arrAdapter.notifyDataSetChanged();//Adapter通知listview做更新
}
private void btn2Click()//删除第一行信息
{
if(data.size() < 1)
{
Toast.makeText(this, "信息已删除完毕！", Toast.LENGTH_LONG).show();
}
else
{
data.remove(0);
arrAdapter.notifyDataSetChanged();//Adapter通知listview做更新
}
}
private void btnsortClick()//对列表进行排序
{
Collections.sort(data);
arrAdapter.notifyDataSetChanged();
}
注：
1.LayoutInflater inflater = getLayoutInflater();
layout = (RelativeLayout) inflater.inflate(R.layout.relayout, null);
layout要通过LayoutInflater拿到。
2.getView返回layout，getCount()返回int。
3.layout.getTag()要转换为holder = (ViewHolder)。
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