模拟新闻APP显示界面

johnsoncodehk · 发表于 2023-2-9 14:07

推荐关联文章：模拟新闻APP显示界面滑动优化

image

内容：
1、异步加载（此处进行耗时操作，更新UI）
2、JSON解析，获取网络资源
3、缓存LruCache的应用
4、ViewHolder 实现控件优化
5、消除listview 快速滑动出现错位现象
6、获取最大内存
7、数据流读取
8、http请求图片
9、Bitmap 使用
10、Handler使用
11、线程
代码如下：
1、布局文件设置

<?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><?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>2、异步获取数据

public class NewsBean { public String view; public String title; public String content;}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.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.view = 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

public class NewsAdapter extends BaseAdapter { private List<NewsBean> newsBeanList; private LayoutInflater inflater; private ImageLoader imageLoader; public NewsAdapter(Context context, List<NewsBean> newsBeanList) {       this.newsBeanList = newsBeanList;       inflater = LayoutInflater.from(context);       imageLoader = new ImageLoader(); } @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).view;       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; }}
图片加载类
public class ImageLoader { private ImageView mImageView; private String mUrl; //*&*创建缓存 private LruCache<String, Bitmap> lruCache; public ImageLoader() {       //*&*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) {          new NewsAsyncTask(imageView, url).execute(url);       } else {          imageView.setImageBitmap(bitmap);       } } private class NewsAsyncTask extends AsyncTask<String, Void, Bitmap> {       private ImageView imageView;       private String url;       public NewsAsyncTask(ImageView imageView, 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);          if (imageView.getTag().equals(url)) {             imageView.setImageBitmap(bitmap);          }       } }}4、listview添加适配器（在2步骤中已经添加）

5、权限声明

<?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>
补充：
本地图片加载出现错位，直接在adapter中用if()else对图片设置进行区分
      if ("xxx") {//根据条件修改图片          viewHolder.imageView.setImageResource("要改变成的图片");       } else {          viewHolder.imageView.setImageResource("默认图片");       }<hr>
赠人玫瑰，手有余香。您的支持是我创作最大的动力!

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模拟新闻APP显示界面

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