模拟新闻APP显示界面滑动优化

转载请注明出处：http://blog.csdn.net/mr_leixiansheng/article/details/65435266

模拟新闻APP显示界面：http://blog.csdn.net/mr_leixiansheng/article/details/64906462

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>