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>