android 新闻app 滑动优化 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>