java - 如何将字符串值传递给 fragment 上的 AsyncTask

Question

如何将 ProductFragment、lv 和 urlAddress 传递给 AsyncTask。当我继承到AppCompatActivity时，没有错误，但是如果我继承到Fragment，就会出现错误行中的错误

new Downloader(ProductFragment.this,urlAddress,lv).execute();

这是我的产品 fragment

    import android.app.Fragment;
    import android.app.ListFragment;
    import android.os.Bundle;
    import android.support.design.widget.FloatingActionButton;
    import android.support.v4.app.FragmentActivity;
    import android.support.v7.app.AppCompatActivity;
    import android.support.v7.widget.Toolbar;
    import android.view.LayoutInflater;
    import android.view.View;
    import android.view.ViewGroup;
    import android.widget.ListView;

    import com.wawi.wawireg.m_MySQL.Downloader;


    public class ProductFragment extends Fragment {

        final static String urlAddress = "http://**.**.**.**/**/****.php";

        public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {

            View view = inflater.inflate(R.layout.calendar_main, container, false);





            Toolbar toolbar = (Toolbar) view.findViewById(R.id.toolbar);
            setSupportActionBar(toolbar);

            FloatingActionButton fab = (FloatingActionButton)view.findViewById(R.id.fab);

            final ListView lv = (ListView)view.findViewById(R.id.lv);

            fab.setOnClickListener(new View.OnClickListener() {
                @Override
                public void onClick(View view) {
                    new Downloader(ProductFragment.this,urlAddress,lv).execute();
                }
            });


            return view;  }

    }

This is my AsyncTask

    public class Downloader extends AsyncTask<Void,Void,String> {


    Context c;
    String urlAddress;
    ListView lv;

    ProgressDialog pd;



    public Downloader(Context c, String urlAddress, ListView lv) {
     this.c = c;
       this.urlAddress = urlAddress;
      this.lv = lv;   }


    @Override
    protected void onPreExecute() {
        super.onPreExecute();

        pd=new ProgressDialog(c);
        pd.setTitle("Retrieve");
        pd.setMessage("Retrieving...Please wait");
        pd.show();
    }

    @Override
    protected String doInBackground(Void... params) {
        return downloadData();
    }

    @Override
    protected void onPostExecute(String jsonData) {
        super.onPostExecute(jsonData);

        pd.dismiss();

        if(jsonData==null)
        {
            Toast.makeText(c,"Unsuccessful, No data Retrieved",Toast.LENGTH_SHORT).show();
        }else {
            //PARSE
            DataParser parser=new DataParser(c,jsonData,lv);
            parser.execute();

        }
    }

    private String downloadData()
    {
        HttpURLConnection con=Connector.connect(urlAddress);
        if(con==null)
        {
            return null;
        }

        try
        {
            InputStream is=new BufferedInputStream(con.getInputStream());
            BufferedReader br=new BufferedReader(new InputStreamReader(is));

            String line;
            StringBuffer jsonData=new StringBuffer();


            while ((line=br.readLine()) != null)
            {
                jsonData.append(line+"\n");
            }

            br.close();
            is.close();

            return jsonData.toString();

        } catch (IOException e) {
            e.printStackTrace();
        }


        return null;
    }
}

Answer 1

这将解决错误，

new Downloader(getActivity(), urlAddress, lv).execute();

您的下载器需要一个Context作为第一个参数。

public Downloader(Context c, String urlAddress, ListView lv) {
    this.c = c;
    this.urlAddress = urlAddress;
    this.lv = lv;
}

您不需要两个 AsyncTasks 来下载和解析数据。您可以使用单个 AsyncTask 来完成此操作。