Sqlite缓存及查询

最新推荐文章于 2024-03-26 05:30:00 发布

原创最新推荐文章于 2024-03-26 05:30:00 发布 · 1.3k 阅读

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当网络不可用时，该应用通过SQLite数据库查询新闻数据。首先判断网络状态，若无网络则从本地数据库中获取`NewsBean.DataBean`列表，并使用自定义适配器显示数据。如果有网络，应用执行异步任务从服务器获取数据。

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@SuppressLint(“StaticFieldLeak”)
private void initData() {
//做一个网络判断
if (!NetWork.isnetwork(MainActivity.this)) {
Toast.makeText(MainActivity.this, “无网络”, Toast.LENGTH_SHORT).show();
//调用dao层查询方法
List<NewsBean.DataBean> list = dao.list();
//判断是否为空
if (list.size() != 0) {
Madapter madapter = new Madapter(MainActivity.this, list);
plv.setAdapter(madapter);
}
return;
}
new AsyncTask<String, Void, List<NewsBean.DataBean>>() {
@Override
protected List<NewsBean.DataBean> doInBackground(String… strings) {
try {
URL url = new URL(strings[0]);
HttpURLConnection connection = (HttpURLConnection) url.openConnection();
connection.setRequestMethod(“GET”);
int responseCode = connection.getResponseCode();
if (responseCode == 200) {
InputStream inputStream = connection.getInputStream();
Gson gson = new Gson();
NewsBean newsBean = gson.fromJson(new BufferedReader(new InputStreamReader(inputStream)), NewsBean.class);
List<NewsBean.DataBean> data = newsBean.getData();
return data;
}
} catch (Exception e) {
e.printStackTrace();
}
return null;
}

        @Override
        protected void onPostExecute(List<NewsBean.DataBean> dataBeans) {
            super.onPostExecute(dataBeans);
            if (page == 1) {
                //集合必须创建
                list = new ArrayList<>();
                //清除数据库
                dao.delete();
                //添加数据库
                dao.insert(dataBeans);
                Toast.makeText(MainActivity.this, "缓存成功", Toast.LENGTH_SHORT).show();
            }
            list.addAll(dataBeans);
            Madapter madapter = new Madapter(MainActivity.this, list);
            plv.setAdapter(madapter);
        }
    }.execute(apiurl + page);
}
数据库
 //添加数据库
public void insert(List<NewsBean.DataBean> list) {
    for (int i = 0; i < list.size(); i++) {
        ContentValues values = new ContentValues();
        values.put("news_title", list.get(i).getNews_title());
        values.put("news_summary", list.get(i).getNews_summary());
        values.put("pic_url", list.get(i).getPic_url());
        db.insert("news", null, values);
    }
}

public List<NewsBean.DataBean> list() {
    List<NewsBean.DataBean> list = new ArrayList<>();
    Cursor cursor = db.query("news", null, null, null, null, null, null);
    while (cursor.moveToNext()) {
        //创建对象
        NewsBean.DataBean dataBean = new NewsBean.DataBean();
        String news_title = cursor.getString(cursor.getColumnIndex("news_title"));
        String news_summary = cursor.getString(cursor.getColumnIndex("news_summary"));
        dataBean.setNews_title(news_title);
        dataBean.setNews_summary(news_summary);
        //添加到集合
        list.add(dataBean);
    }
    return list;
}

//删除
public void delete() {
    db.delete("news", null, null);
}