欢迎您访问程序员文章站本站旨在为大家提供分享程序员计算机编程知识!
您现在的位置是: 首页  >  移动技术

Android 模拟新闻APP显示界面滑动优化实例代码

程序员文章站 2023-11-26 09:52:52
内容: 1、滑动优化(滑动时不加载图片,停止才加载) 2、第一次进入时手动加载 代码如下: 1、界面布局

内容:

1、滑动优化(滑动时不加载图片,停止才加载)

2、第一次进入时手动加载

代码如下:

1、界面布局

<?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> 

2、开启异步解析数据

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; 
 } 
} 

3、自定义适配器(在此处设置滑动监听,以此来判断什么时候加载资源)

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); 
  } 
 } 
} 

4、注册声明权限

<?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> 

以上所述是小编给大家介绍的android 模拟新闻app显示界面滑动优化实例代码,希望对大家有所帮助