android的ListView图文混搭
16lz
2021-01-23
main4.xml
<?xml version="1.0" encoding="utf-8"?>
main4_item.xml
<?xml version="1.0" encoding="utf-8"?>
MainActivity4
package com.example.listview;import java.util.ArrayList;import java.util.HashMap;import java.util.List;import java.util.Map;import android.R.anim;import android.R.drawable;import android.app.Activity;import android.os.Bundle;import android.widget.ListView;import android.widget.SimpleAdapter;public class MainActivity4 extends Activity{private ListView listView;@Overrideprotected void onCreate(Bundle savedInstanceState) {// TODO Auto-generated method stubsuper.onCreate(savedInstanceState);setContentView(R.layout.main4);listView=(ListView) findViewById(R.id.listView4_1_1);//一个列表项的内容Mapmap=new HashMap ();map.put("p_w_picpath", R.drawable.ic_launcher);map.put("name", "张三");Map map2=new HashMap ();map2.put("p_w_picpath", R.drawable.ic_launcher);map2.put("name", "王五");List
亦可以自定义Adapter
mian5.xml
<?xml version="1.0" encoding="utf-8"?>
main5_item.xml
<?xml version="1.0" encoding="utf-8"?>
MainActivity5
package com.example.listview;import android.app.Activity;import android.os.Bundle;import android.view.LayoutInflater;import android.view.View;import android.view.ViewGroup;import android.widget.BaseAdapter;import android.widget.ImageView;import android.widget.ListView;import android.widget.TextView;public class MainActivity5 extends Activity {private ListView listView;//定义的数据private int [] p_w_picpaths={R.drawable.ic_launcher,R.drawable.ic_launcher};private String [] names={"xiaobai","xiaoming"};@Overrideprotected void onCreate(Bundle savedInstanceState) {// TODO Auto-generated method stubsuper.onCreate(savedInstanceState);setContentView(R.layout.main5);listView=(ListView) findViewById(R.id.listView5_1_1);listView.setAdapter(new MyAdapter());}//自定义适配器class MyAdapter extends BaseAdapter{//获取列表项总数@Overridepublic int getCount() {// TODO Auto-generated method stubreturn names.length;}//获取每一个列表项(根据下标获取)@Overridepublic Object getItem(int position) {// TODO Auto-generated method stubreturn names[position];}//获取每一个列表项的id@Overridepublic long getItemId(int position) {// TODO Auto-generated method stubreturn position;}//@Overridepublic View getView(int position, View convertView, ViewGroup parent) {// TODO Auto-generated method stub//获取布局填充器LayoutInflater layoutInflater=getLayoutInflater();//获取main5_item的布局模板View view=layoutInflater.inflate(R.layout.main5_item, null);//从得到的view查找相应viewImageView p_w_picpathView=(ImageView) view.findViewById(R.id.p_w_picpathView5_1_1);TextView textView=(TextView) view.findViewById(R.id.textView5_1_1);p_w_picpathView.setImageResource(p_w_picpaths[position]);textView.setText(names[position]);return view;}}}
这种方式会多次调用getView()方法
优化方法
main5.xml
<?xml version="1.0" encoding="utf-8"?>
ListView设置成 android:layout_height="fill_parent"
//屏幕一次显示7(假设)条记录,则调用7次getView方法,只负责在屏幕中显示的内容的创建,其他的在滑动显示时才创建//因为ListView的高度设置为 android:layout_height="wrap_content"//调用一次getView,绘制一次,增加子组件时会重新绘制(计算高度),所以会多次调用getView()方法//增加一个组件,重新绘制ListView,//每绘制一次ListView,每一个子组件都重新绘制(有几个子组件调用几次)//ListView设置成 android:layout_height="fill_parent"//只输出0,1,2,3,4,5一次System.out.println("position:"+position);
将activity中代码修改为:
System.out.print("position:"+position);System.out.println(" "+convertView);//获取布局填充器LayoutInflater layoutInflater=getLayoutInflater();//获取main5_item的布局模板,创建布局对象//如果没有空闲的convertView,创建convertView,否则重复利用convertViewif(convertView==null){convertView=layoutInflater.inflate(R.layout.main5_item, null);}
convertView的使用,主要优化加载布局问题
增加优化二:内部类ViewHolder的使用。
主要优化getView方法中每次回调用findviewByID()方法来获取一次控件的代码。
新增加内部类ViewHolder,用于对控件的实力存储进行缓存。
package com.example.listview;import android.app.Activity;import android.os.Bundle;import android.view.LayoutInflater;import android.view.View;import android.view.ViewGroup;import android.widget.BaseAdapter;import android.widget.ImageView;import android.widget.ListView;import android.widget.TextView;public class MainActivity5 extends Activity {private ListView listView;//定义的数据private int [] p_w_picpaths={R.drawable.ic_launcher,R.drawable.ic_launcher,R.drawable.ic_launcher,R.drawable.ic_launcher,R.drawable.ic_launcher,R.drawable.ic_launcher,R.drawable.ic_launcher,R.drawable.ic_launcher,R.drawable.ic_launcher,R.drawable.ic_launcher,R.drawable.ic_launcher,R.drawable.ic_launcher};private String [] names={"xiaobai","xiaoming","xiaobai","xiaoming","xiaobai","xiaoming","xiaobai","xiaoming","xiaobai","xiaoming","xiaobai","xiaoming"};@Overrideprotected void onCreate(Bundle savedInstanceState) {// TODO Auto-generated method stubsuper.onCreate(savedInstanceState);setContentView(R.layout.main5);listView=(ListView) findViewById(R.id.listView5_1_1);listView.setAdapter(new MyAdapter());}//自定义适配器//ListView的优化://1.重复使用convertView对象//2.使用viewHolder提高在容器中查找组件的效率class MyAdapter extends BaseAdapter{//获取列表项总数@Overridepublic int getCount() {// TODO Auto-generated method stubreturn names.length;}//获取每一个列表项(根据下标获取)@Overridepublic Object getItem(int position) {// TODO Auto-generated method stubreturn names[position];}//获取每一个列表项的id@Overridepublic long getItemId(int position) {// TODO Auto-generated method stubreturn position;}//@Overridepublic View getView(int position, View convertView, ViewGroup parent) {// TODO Auto-generated method stub//屏幕一次显示7(假设)条记录,则调用7次getView方法,只负责在屏幕中显示的内容的创建,其他的在滑动显示时才创建//因为ListView的高度设置为 android:layout_height="wrap_content"//调用一次getView,绘制一次,增加子组件时会重新绘制(计算高度),所以会多次调用getView()方法//增加一个组件,重新绘制ListView,//每绘制一次ListView,每一个子组件都重新绘制(有几个子组件调用几次)//ListView设置成 android:layout_height="fill_parent"//只输出0,1,2,3,4,5一次System.out.print("position:"+position);System.out.println(" "+convertView);//获取布局填充器LayoutInflater layoutInflater=getLayoutInflater();//获取main5_item的布局模板,创建布局对象//如果没有空闲的convertView,创建convertView,否则重复利用convertViewViewHolder viewHolder;if(convertView==null){convertView=layoutInflater.inflate(R.layout.main5_item, null);viewHolder=new ViewHolder();viewHolder.p_w_picpathView=(ImageView) convertView.findViewById(R.id.p_w_picpathView5_1_1);viewHolder.textView=(TextView) convertView.findViewById(R.id.textView5_1_1);convertView.setTag(viewHolder);}else {viewHolder=(ViewHolder) convertView.getTag();}//View convertView=layoutInflater.inflate(R.layout.main5_item, null);//从得到的view查找相应view/*ImageView p_w_picpathView=(ImageView) convertView.findViewById(R.id.p_w_picpathView5_1_1);TextView textView=(TextView) convertView.findViewById(R.id.textView5_1_1);p_w_picpathView.setImageResource(p_w_picpaths[position]);textView.setText(names[position]);*/viewHolder.p_w_picpathView.setImageResource(p_w_picpaths[position]);viewHolder.textView.setText(names[position]);return convertView;}}class ViewHolder{ImageView p_w_picpathView;TextView textView;}}
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