Android 模拟新闻APP显示界面滑动优化实例代码

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网站的支持！

来源：http://blog.csdn.net/mr_leixiansheng/article/details/65435266