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最新推荐文章于 2021-04-11 19:24:47 发布

weixin_33890526

最新推荐文章于 2021-04-11 19:24:47 发布

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文章标签： json runtime

效果图：

第一步：设计

先实现图文加载到列表

public class MainActivity extends AppCompatActivity {

    private ListView listView;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        listView = (ListView) findViewById(R.id.listview);
        StringTask task = new StringTask(listView,MainActivity.this);
        String url = String.format(Contants.BK_URL,1);
        task.execute(url);
    }
}

public class StringTask extends AsyncTask<String,Void,List<Teas>> {
    private ListView listview;
    private Context context;

    public StringTask(ListView listview, Context context) {
        this.listview = listview;
        this.context = context;
    }

    @Override
    protected List<Teas> doInBackground(String... params) {
        String jsonStr = HttpUtils.getJSONStr(params[0]);
        List<Teas> list = JSONUtils.parseJSON(jsonStr);
        return list;
    }

    @Override
    protected void onPostExecute(List<Teas> teases) {
        TeasAdapter adapter = new TeasAdapter(teases,context);
        listview.setAdapter(adapter);
        super.onPostExecute(teases);
    }
}

public class TeasAdapter extends BaseAdapter {
    private List<Teas> list;
    private Context context;

    public TeasAdapter(List<Teas> list, Context context) {
        this.list = list;
        this.context = context;
    }

    @Override
    public int getCount() {
        return list.size();
    }

    @Override
    public Object getItem(int position) {
        return list.get(position);
    }

    @Override
    public long getItemId(int position) {
        return position;
    }

    @Override
    public View getView(int position, View convertView, ViewGroup parent) {
        LayoutInflater inflater = LayoutInflater.from(context);
        View view = inflater.inflate(R.layout.list_item, null);
        ViewHolder viewHolder = new ViewHolder();
        viewHolder.title = (TextView) view.findViewById(R.id.title);
        viewHolder.create_time = (TextView) view.findViewById(R.id.creat_time);
        viewHolder.image = (ImageView) view.findViewById(R.id.image);
        Teas teas = list.get(position);
        viewHolder.title.setText(teas.getTitle());
        viewHolder.create_time.setText(teas.getCreate_time());
        //下载图片并赋值
        String image_url = teas.getWap_thumb();
        ImageTask task = new ImageTask(viewHolder.image);
        task.execute(image_url);
        return view;
    }

    public class ViewHolder{
        TextView title,create_time;
        ImageView image;
    }
}

public class HttpUtils {
    //下载数据
    public static String getJSONStr(String path){
        try {
            URL url = new URL(path);
            HttpURLConnection conn = (HttpURLConnection) url.openConnection();
            int code = conn.getResponseCode();
            if(code == 200){
                InputStream is = conn.getInputStream();
                ByteArrayOutputStream baos = new ByteArrayOutputStream();
                byte[] buffer = new byte[1024];
                int ret;
                while((ret = is.read(buffer))>0){
                    baos.write(buffer,0,ret);
                }
                return baos.toString();
            }
        } catch (MalformedURLException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }
        return null;
    }

    //下载图片
    public static Bitmap getBitmap(String path){
        try {
            URL url = new URL(path);
            HttpURLConnection conn = (HttpURLConnection) url.openConnection();
            int code = conn.getResponseCode();
            if(code == 200){
                InputStream is = conn.getInputStream();
                return BitmapFactory.decodeStream(is);
            }
        } catch (MalformedURLException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }
        return null;
    }
}

public class JSONUtils {
    //解析json字符串
    public static List<Teas> parseJSON(String jsonStr){
        List<Teas> list = new ArrayList<Teas>();
        try {
            JSONObject object = new JSONObject(jsonStr);
            JSONArray array = (JSONArray) object.get("data");
            for(int i = 0;i<array.length();i++){
                JSONObject object2 = (JSONObject) array.get(i);
                String title = object2.getString("title");
                String create_time = object2.getString("create_time");
                String wap_thumb = object2.getString("wap_thumb");
                Teas teas = new Teas(create_time,title,wap_thumb);
                list.add(teas);
            }
            return list;
        } catch (JSONException e) {
            e.printStackTrace();
        }
        return null;
    }
}

public class ImageTask extends AsyncTask<String,Void,Bitmap> {
    private ImageView image;

    public ImageTask(ImageView image) {
        this.image = image;
    }

    @Override
    protected Bitmap doInBackground(String... params) {
        Bitmap bitmap = HttpUtils.getBitmap(params[0]);
        return bitmap;
    }

    @Override
    protected void onPostExecute(Bitmap bitmap) {
        image.setImageBitmap(bitmap);
        super.onPostExecute(bitmap);
    }
}

第二步：滑动复用内存空间

优化TeasAdapter的getView方法

@Override
public View getView(int position, View convertView, ViewGroup parent) {
    ViewHolder viewHolder;
    if(convertView == null){
        LayoutInflater inflater = LayoutInflater.from(context);
        convertView = inflater.inflate(R.layout.list_item, null);
        viewHolder = new ViewHolder();
        viewHolder.title = (TextView) convertView.findViewById(R.id.title);
        viewHolder.create_time = (TextView) convertView.findViewById(R.id.creat_time);
        viewHolder.image = (ImageView) convertView.findViewById(R.id.image);
        convertView.setTag(viewHolder);
    }
    viewHolder = (ViewHolder) convertView.getTag();
    Teas teas = list.get(position);
    viewHolder.title.setText(teas.getTitle());
    viewHolder.create_time.setText(teas.getCreate_time());
    //下载图片并赋值
    String image_url = teas.getWap_thumb();
    ImageTask task = new ImageTask(viewHolder.image);
    task.execute(image_url);
    return convertView;
}

第三步：滑动分页

优化MainActivity和StringTask类且在TeasAdapter中增加addData方法

public class MainActivity extends AppCompatActivity {

    private TeasAdapter adapter;
    private ListView listView;
    private boolean flag;
    private int index = 1;
    private List<Teas> list = new ArrayList<Teas>();
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        listView = (ListView) findViewById(R.id.listview);
        adapter = new TeasAdapter(list,MainActivity.this);
        listView.setAdapter(adapter);
        StringTask task = new StringTask(adapter);
        String url = String.format(Contants.BK_URL,index);
        task.execute(url);
        //滑动分页
        listView.setOnScrollListener(new AbsListView.OnScrollListener() {
            @Override
            public void onScrollStateChanged(AbsListView view, int scrollState) {
                if (flag) {
                    index++;
                    String new_url = String.format(Contants.BK_URL, index);
                    StringTask new_task = new StringTask(adapter);
                    new_task.execute(new_url);
                }
            }

            @Override
            public void onScroll(AbsListView view, int firstVisibleItem, int visibleItemCount, int totalItemCount) {
                if (firstVisibleItem + visibleItemCount == totalItemCount) {
                    flag = true;
                } else {
                    flag = false;
                }
            }
        });
    }
}

public class StringTask extends AsyncTask<String,Void,List<Teas>> {

    private TeasAdapter adapter;

    public StringTask(TeasAdapter adapter) {
        this.adapter = adapter;
    }

    @Override
    protected List<Teas> doInBackground(String... params) {
        String jsonStr = HttpUtils.getJSONStr(params[0]);
        List<Teas> list = JSONUtils.parseJSON(jsonStr);
        return list;
    }

    @Override
    protected void onPostExecute(List<Teas> teases) {
        adapter.addData(teases);
        super.onPostExecute(teases);
    }
}

public void addData(List<Teas> teas){
        list.addAll(teas);
        notifyDataSetChanged();
    }

第四步：保存图片加缓存，保存到sd卡且防止图片加载错位

（先在缓存查找图片，再去sdcard查找，如果没有，网络下载，然后保存到sdcard，最后保存到缓存）

优化TeasAdapter和ImageTask类

public class TeasAdapter extends BaseAdapter {
    private List<Teas> list;
    private Context context;
    private LruCache<String,Bitmap> cache;
    public TeasAdapter(List<Teas> list, Context context) {
        this.list = list;
        this.context = context;
        long maxMemory = Runtime.getRuntime().maxMemory();
        cache = new LruCache<String,Bitmap>((int) (maxMemory/8)){
            @Override
            protected int sizeOf(String key, Bitmap value) {
                return value.getByteCount()*value.getHeight();
            }
        };
    }

    @Override
    public int getCount() {
        return list.size();
    }

    @Override
    public Object getItem(int position) {
        return list.get(position);
    }

    @Override
    public long getItemId(int position) {
        return position;
    }

    //滑动复用内存空间
    @Override
    public View getView(int position, View convertView, ViewGroup parent) {
        ViewHolder viewHolder;
        if(convertView == null){
            LayoutInflater inflater = LayoutInflater.from(context);
            convertView = inflater.inflate(R.layout.list_item, null);
            viewHolder = new ViewHolder();
            viewHolder.title = (TextView) convertView.findViewById(R.id.title);
            viewHolder.create_time = (TextView) convertView.findViewById(R.id.creat_time);
            viewHolder.image = (ImageView) convertView.findViewById(R.id.image);
            convertView.setTag(viewHolder);
        }
        viewHolder = (ViewHolder) convertView.getTag();
        Teas teas = list.get(position);
        viewHolder.title.setText(teas.getTitle());
        viewHolder.create_time.setText(teas.getCreate_time());
        //下载图片并赋值
        String image_url = teas.getWap_thumb();
        Bitmap bitmap = cache.get("image_url");
        //判断是否在缓存中
        if(bitmap!=null){
            viewHolder.image.setImageBitmap(bitmap);
        }else{
            viewHolder.image.setTag(image_url);
            ImageTask task = new ImageTask(viewHolder.image,context,cache);
            task.execute(image_url);
        }
        return convertView;
    }

    public class ViewHolder{
        TextView title,create_time;
        ImageView image;
    }

    public void addData(List<Teas> teas){
        list.addAll(teas);
        notifyDataSetChanged();
    }
}

public class ImageTask extends AsyncTask<String,Void,Bitmap> {
    private String image_url;

    private ImageView image;
    private Context context;
    private LruCache<String,Bitmap> cache;

    public ImageTask(ImageView image, Context context, LruCache<String, Bitmap> cache) {
        this.image = image;
        this.context = context;
        this.cache = cache;
    }

    @Override
    protected Bitmap doInBackground(String... params) {
        image_url = params[0];
        File file = context.getCacheDir();
        File file2 = new File(file,image_url);
        //判断是否在sdcard中
        if(file2.exists()){
            return BitmapFactory.decodeFile(file2.getAbsolutePath());
        }else{
            Bitmap bitmap = HttpUtils.getBitmap(image_url);
            try {
                //保存到sdcard中
                FileOutputStream fos = new FileOutputStream(file2);
                bitmap.compress(Bitmap.CompressFormat.JPEG,100,fos);
            } catch (FileNotFoundException e) {
                e.printStackTrace();
            }
            return bitmap;
        }
    }

    @Override
    protected void onPostExecute(Bitmap bitmap) {
        if(bitmap!=null){
            //保存到内存中
            cache.put(image_url, bitmap);
            String url = (String) image.getTag();
            if(url.equals(image_url)){
                image.setImageBitmap(bitmap);
            }
        }
        super.onPostExecute(bitmap);
    }
}