Progressdialog在android滑动标签片段

Question

我有一个主活动，它使用以下代码扩展SampleActivityBase

public class MainActivity extends SampleActivityBase {
 protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    if (savedInstanceState == null) {
        FragmentTransaction transaction = getSupportFragmentManager().beginTransaction();
        SlidingTabsBasicFragment fragment = new SlidingTabsBasicFragment();
        transaction.replace(R.id.sample_content_fragment, fragment);
        transaction.commit();
    }
  }
}

我有另一类

public class SlidingTabsBasicFragment extends Fragment {

在这一类中，我有另一个子类

class SamplePagerAdapter extends PagerAdapter {

在覆盖所有必要的功能后，我还有一个功能

public String getJSON(String url) {
        class GetJSON extends AsyncTask<String, Void, String> {
            ProgressDialog loading;
            @Override
            protected void onPreExecute() {
                super.onPreExecute();
                loading = ProgressDialog.show(SlidingTabsBasicFragment.this.getContext(), "Please Wait...", "Checking", true, true);
            }
            @Override
            protected String doInBackground(String... params) {
                Log.d("doInBackground : ", "Function Started");
                String uri = params[0];
                BufferedReader bufferedReader = null;
                try {
                    URL url = new URL(uri);
                    HttpURLConnection con = (HttpURLConnection) url.openConnection();
                    StringBuilder sb = new StringBuilder();
                    bufferedReader = new BufferedReader(new InputStreamReader(con.getInputStream()));
                    String json;
                    while ((json = bufferedReader.readLine()) != null) {
                        sb.append(json + "n");
                    }
                    jsonString = sb.toString().trim();
                    return sb.toString().trim();
                } catch (Exception e) {
                    return new String("Exception: " + e.getMessage());
                }
            }
            @Override
            protected void onPostExecute(String s) {
               if(loading.isShowing()) {
                    loading.dismiss();
                }
                super.onPostExecute(s);
                jsonString = s;
            }
        }
        GetJSON gj = new GetJSON();
        gj.execute(url);
        return jsonString;
    }

当我在SamplePagerAdapter类中调用这个函数时，除了Progress Dialog之外，其他一切都很好。它没有显示。。。

请告诉我我做错了什么，以及如何显示进度对话框。选项卡显示来自在线数据库的数据，我想在数据堆积时启动进度对话框。

Answer 1

保持适配器类独立的try.get（）安装在.execute 中