Android 模拟新闻APP显示界面滑动优化实例代码

<?xml version="1.0" encoding="utf-8"?> 
<linearlayout xmlns:android="http://schemas.android.com/apk/res/android" 
 android:orientation="horizontal" android:layout_width="match_parent" 
 android:layout_height="wrap_content" 
 android:gravity="center"> 
 <imageview 
  android:id="@+id/image" 
  android:src="@mipmap/ic_launcher" 
  android:layout_width="60dp" 
  android:layout_height="60dp" /> 
 <linearlayout 
  android:orientation="vertical" 
  android:layout_marginleft="10dp" 
  android:layout_width="match_parent" 
  android:layout_height="wrap_content"> 
  <textview 
   android:id="@+id/title_tv" 
   android:text="title" 
   android:textsize="15dp" 
   android:maxlines="1" 
   android:layout_width="match_parent" 
   android:layout_height="wrap_content" /> 
  <textview 
   android:id="@+id/content_tv" 
   android:text="content" 
   android:textsize="10dp" 
   android:maxlines="3" 
   android:layout_width="match_parent" 
   android:layout_height="wrap_content" /> 
 </linearlayout> 
</linearlayout> 

<?xml version="1.0" encoding="utf-8"?> 
<relativelayout xmlns:android="http://schemas.android.com/apk/res/android" 
 xmlns:tools="http://schemas.android.com/tools" 
 android:id="@+id/activity_main" 
 android:layout_width="match_parent" 
 android:layout_height="match_parent" 
 android:paddingbottom="@dimen/activity_vertical_margin" 
android:paddingleft="@dimen/activity_horizontal_margin" android:paddingright="@dimen/activity_horizontal_margin" android:paddingtop="@dimen/activity_vertical_margin" 
tools:context="com.example.leixiansheng.news.mainactivity"> 
 <listview 
  android:id="@+id/list_view" 
  android:layout_width="match_parent" 
  android:layout_height="match_parent"> 
 </listview> 
</relativelayout> 

package com.example.leixiansheng.news; 
 
/** 
 * created by leixiansheng on 2017/3/21. 
 */ 
public class newsbean { 
 public string viewurl; 
 public string title; 
 public string content; 
} 
package com.example.leixiansheng.news; 
import android.os.asynctask; 
import android.support.v7.app.appcompatactivity; 
import android.os.bundle; 
import android.util.log; 
import android.widget.listview; 
import org.json.jsonarray; 
import org.json.jsonexception; 
import org.json.jsonobject; 
import java.io.bufferedreader; 
import java.io.ioexception; 
import java.io.inputstream; 
import java.io.inputstreamreader; 
import java.io.unsupportedencodingexception; 
import java.net.url; 
import java.util.arraylist; 
import java.util.list; 
public class mainactivity extends appcompatactivity { 
 private listview listview; 
 private static string url = "http://www.imooc.com/api/teacher?type=4&num=30"; 
 @override 
 protected void oncreate(bundle savedinstancestate) { 
  super.oncreate(savedinstancestate); 
  setcontentview(r.layout.activity_main); 
  listview = (listview) findviewbyid(r.id.list_view); 
  new newsasynctask().execute(url); 
 } 
 //*&*异步加载，处理耗时任务,ui更新 
 class newsasynctask extends asynctask<string, void, list<newsbean>> { 
  @override 
  protected list<newsbean> doinbackground(string... strings) { 
   return getjsondata(strings[0]); 
  } 
  @override 
  protected void onpostexecute(list<newsbean> newsbeen) { 
   super.onpostexecute(newsbeen); 
   newsadapter adapter = new newsadapter(mainactivity.this, newsbeen,listview); 
   listview.setadapter(adapter); 
  } 
 } 
 //*&*json解析网页获取数据 
 private list<newsbean> getjsondata(string url) { 
  list<newsbean> newsbeanlist = new arraylist<>(); 
  try { 
   string jsonstring = readsteam(new url(url).openstream()); 
   log.i("data", jsonstring); 
   jsonobject jsonobject; 
   newsbean newsbean; 
   try { 
    jsonobject = new jsonobject(jsonstring); 
    jsonarray jsonarray = jsonobject.getjsonarray("data"); 
    for (int i = 0; i < jsonarray.length(); i++) { 
     jsonobject = jsonarray.getjsonobject(i); 
     newsbean = new newsbean(); 
     newsbean.content = jsonobject.getstring("description"); 
     newsbean.title = jsonobject.getstring("name"); 
     newsbean.viewurl = jsonobject.getstring("picsmall"); 
     newsbeanlist.add(newsbean); 
    } 
   } catch (jsonexception e) { 
    e.printstacktrace(); 
   } 
  } catch (ioexception e) { 
   e.printstacktrace(); 
  } 
  return newsbeanlist; 
 } 
 //*&*读取数据流 
 private string readsteam(inputstream is) { 
  inputstreamreader isr; 
  string result = ""; 
  try { 
   string line = ""; 
   isr = new inputstreamreader(is, "utf-8"); 
   bufferedreader br = new bufferedreader(isr); 
   try { 
    while ((line = br.readline()) != null) { 
     result += line; 
    } 
   } catch (ioexception e) { 
    e.printstacktrace(); 
   } 
  } catch (unsupportedencodingexception e) { 
   e.printstacktrace(); 
  } 
  return result; 
 } 
} 

package com.example.leixiansheng.news; 
import android.content.context; 
import android.view.layoutinflater; 
import android.view.view; 
import android.view.viewgroup; 
import android.widget.abslistview; 
import android.widget.baseadapter; 
import android.widget.imageview; 
import android.widget.listview; 
import android.widget.textview; 
import java.util.list; 
/** 
 * created by leixiansheng on 2017/3/21. 
 */ 
public class newsadapter extends baseadapter implements abslistview.onscrolllistener{ 
 private list<newsbean> newsbeanlist; 
 private layoutinflater inflater; 
 private imageloader imageloader; //图片加载 
 private int start;  //第一个元素 
 private int end;  //最后一个元素 
 private boolean isfirstin;  //是否第一次进入 
 public static string[] urls;  //所有资源 
 public newsadapter(context context, list<newsbean> newsbeanlist, listview listview) { 
  this.newsbeanlist = newsbeanlist; 
  inflater = layoutinflater.from(context); 
  imageloader = new imageloader(listview); 
  urls = new string[newsbeanlist.size()]; 
  for (int i = 0; i < newsbeanlist.size(); i++) { 
   urls[i] = newsbeanlist.get(i).viewurl; 
  } 
  isfirstin = true; 
  listview.setonscrolllistener(this); 
 } 
 @override 
 public int getcount() { 
  return newsbeanlist.size(); 
 } 
 @override 
 public object getitem(int i) { 
  return newsbeanlist.get(i); 
 } 
 @override 
 public long getitemid(int i) { 
  return i; 
 } 
 @override 
 public view getview(int i, view view, viewgroup viewgroup) { 
  viewholder viewholder = null; 
  if (view == null) { 
   viewholder = new viewholder(); 
   view = inflater.inflate(r.layout.item, null); 
   viewholder.imageview = (imageview) view.findviewbyid(r.id.image); 
   viewholder.title = (textview) view.findviewbyid(r.id.title_tv); 
   viewholder.content = (textview) view.findviewbyid(r.id.content_tv); 
   view.settag(viewholder); 
  } else { 
   viewholder = (viewholder) view.gettag(); 
  } 
  string url = newsbeanlist.get(i).viewurl; 
  viewholder.imageview.setimageresource(r.mipmap.ic_launcher); 
  //*&*设置标签，避免快速滑动listview出现位置误差 
  viewholder.imageview.settag(url); 
//  new imageloader().showimagebythread(viewholder.imageview, url); 
  imageloader.showimageviewbyasynctask(viewholder.imageview,url); 
  viewholder.title.settext(newsbeanlist.get(i).title); 
  viewholder.content.settext(newsbeanlist.get(i).content); 
  return view; 
 } 
 //*&*优化 
 class viewholder { 
  public textview title; 
  public textview content; 
  private imageview imageview; 
 } 
 //滑动监听 
 @override 
 public void onscrollstatechanged(abslistview abslistview, int i) { 
  if (i == scroll_state_idle) { 
   //停止状态：加载图片 
   imageloader.loadimages(start, end); 
  } else { 
   //滑动状态：停止加载 
   imageloader.cancelalltasks(); 
  } 
 } 
 /** 
  * 
  * @param abslistview 
  * @param i  第一个元素 
  * @param i1 元素数量 
  * @param i2 
  */ 
 @override 
 public void onscroll(abslistview abslistview, int i, int i1, int i2) { 
  start = i; 
  end = i + i1; 
  //第一次进入需要手动加载 
  if (isfirstin && i1 > 0) { 
   imageloader.loadimages(start, end); 
   isfirstin = false; 
  } 
 } 
} 

package com.example.leixiansheng.news; 
import android.graphics.bitmap; 
import android.graphics.bitmapfactory; 
import android.os.asynctask; 
import android.os.handler; 
import android.os.message; 
import android.util.lrucache; 
import android.widget.imageview; 
import android.widget.listview; 
import java.io.bufferedinputstream; 
import java.io.ioexception; 
import java.io.inputstream; 
import java.net.httpurlconnection; 
import java.net.malformedurlexception; 
import java.net.url; 
import java.util.hashset; 
import java.util.set; 
/** 
 * created by leixiansheng on 2017/3/21. 
 */ 
public class imageloader { 
 private imageview mimageview; 
 private string murl; 
 //*&*创建缓存 
 private lrucache<string, bitmap> lrucache; 
 private listview listview; 
 private set<newsasynctask> mtask; 
 public imageloader(listview listview) { 
  this.listview = listview; 
  mtask = new hashset<>(); 
  //*&*获取最大内存 
  int maxmemory = (int) runtime.getruntime().maxmemory(); 
  //设置缓存大小 
  int lrucachesize = maxmemory / 4; 
  lrucache = new lrucache<string, bitmap>(lrucachesize) { 
   @override 
   protected int sizeof(string key, bitmap value) { 
    //获取每个数据大小 
    return value.getbytecount(); 
   } 
  }; 
 } 
 //添加数据到缓存 
 public void addbitmaptolrucache(string url, bitmap bitmap) { 
  if (getbitmapfromlrucache(url) == null) { 
   lrucache.put(url, bitmap); 
  } 
 } 
 //从缓存中获取数据 
 public bitmap getbitmapfromlrucache(string url) { 
  return lrucache.get(url); 
 } 
 private handler handler = new handler() { 
  @override 
  public void handlemessage(message msg) { 
   super.handlemessage(msg); 
   if (mimageview.gettag().equals(murl)) { 
    mimageview.setimagebitmap((bitmap) msg.obj); 
   } 
  } 
 }; 
 public void showimagebythread(imageview imageview, final string url) { 
  mimageview = imageview; 
  murl = url; 
  new thread() { 
   @override 
   public void run() { 
    super.run(); 
    bitmap bitmap = getbitmapfromurl(url); 
    message message = message.obtain(); 
    message.obj = bitmap; 
    handler.sendmessage(message); 
   } 
  }.start(); 
 } 
 public bitmap getbitmapfromurl(string urlstring) { 
  bitmap bitmap; 
  inputstream is = null; 
  try { 
   url url = new url(urlstring); 
   httpurlconnection connection = (httpurlconnection) url.openconnection(); 
   is = new bufferedinputstream(connection.getinputstream()); 
   bitmap = bitmapfactory.decodestream(is); 
   connection.disconnect(); 
   //模拟网速卡顿时 
//   try { 
//    thread.sleep(1000); 
//   } catch (interruptedexception e) { 
//    e.printstacktrace(); 
//   } 
   return bitmap; 
  } catch (malformedurlexception e) { 
   e.printstacktrace(); 
  } catch (ioexception e) { 
   e.printstacktrace(); 
  } finally { 
   try { 
    is.close(); 
   } catch (ioexception e) { 
    e.printstacktrace(); 
   } 
  } 
  return null; 
 } 
 public void showimageviewbyasynctask(imageview imageview, string url) { 
  //判断是否已经缓存 
  bitmap bitmap = getbitmapfromlrucache(url); 
  //没有缓存则从新下载 
  if (bitmap == null) { 
   imageview.setimageresource(r.mipmap.ic_launcher); 
  } else { 
   imageview.setimagebitmap(bitmap); 
  } 
 } 
 //加载从start到end的所有图片 
 public void loadimages(int start, int end) { 
  for (int i = start; i < end; i++) { 
   string url = newsadapter.urls[i]; 
   //判断是否已经缓存 
   bitmap bitmap = getbitmapfromlrucache(url); 
   //没有缓存则从新下载 
   if (bitmap == null) { 
    newsasynctask task = new newsasynctask(url); 
    task.execute(url); 
    mtask.add(task); 
   } else { 
    imageview imageview = (imageview) listview.findviewwithtag(url); 
    imageview.setimagebitmap(bitmap); 
   } 
  } 
 } 
 public void cancelalltasks() { 
  if (mtask != null) { 
   for (newsasynctask task : mtask) { 
    task.cancel(false); 
   } 
  } 
 } 
 private class newsasynctask extends asynctask<string, void, bitmap> { 
//  private imageview imageview; 
  private string url; 
  public newsasynctask(string url) { 
//   this.imageview = imageview; 
   this.url = url; 
  } 
  @override 
  protected bitmap doinbackground(string... strings) { 
   string url = strings[0]; 
   //从网络获取图片 
   bitmap bitmap = getbitmapfromurl(url); 
   if (bitmap != null) { 
    //将不在缓存中的图片加入到缓存 
    addbitmaptolrucache(url, bitmap); 
   } 
   return bitmap; 
  } 
  @override 
  protected void onpostexecute(bitmap bitmap) { 
   super.onpostexecute(bitmap); 
   imageview imageview = (imageview) listview.findviewwithtag(url); 
   if (imageview != null && bitmap != null) { 
    imageview.setimagebitmap(bitmap); 
   } 
   mtask.remove(this); 
  } 
 } 
} 

<?xml version="1.0" encoding="utf-8"?> 
<manifest xmlns:android="http://schemas.android.com/apk/res/android" 
 package="com.example.leixiansheng.news"> 
 <uses-permission android:name="android.permission.internet"/> 
 <application 
  android:allowbackup="true" 
  android:icon="@mipmap/ic_launcher" 
  android:label="@string/app_name" 
  android:supportsrtl="true" 
  android:theme="@style/apptheme"> 
  <activity android:name=".mainactivity"> 
   <intent-filter> 
    <action android:name="android.intent.action.main" /> 
    <category android:name="android.intent.category.launcher" /> 
   </intent-filter> 
  </activity> 
 </application> 
</manifest>