Question

我是Android的新手，从昨天开始面对这个问题。在查看列表项的详细信息后按后退按钮时，我的列表项会重复。我正在使用片段列表。此外，我正在以JSON格式从api加载数据。

下面是我的ListFragment代码，我把它命名为BlankFragment

package com.equity99.equity99.learningrestjsonwithlistfragment;
import android.content.Context;
import android.os.Bundle;
import android.support.v4.app.Fragment;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.BaseAdapter;
import android.widget.ListView;

import org.json.JSONArray;
import org.json.JSONException;
import org.json.JSONObject;

import java.util.ArrayList;

import com.equity99.equity99.learningrestjsonwithlistfragment.Download_data.download_complete;

/**
 * A simple {@link Fragment} subclass.
 */
public class BlankFragment extends Fragment implements download_complete{

    public ListView list;
    public ArrayList<SinglePost> countries = new ArrayList<SinglePost>();
    public ListAdapter adapter;

    private OnListFragmentInteractionListener mListener;

    public BlankFragment() {
        // Required empty public constructor
    }


    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {
        // Inflate the layout for this fragment
        View rootView = inflater.inflate(R.layout.fragment_blank, container, false);

        if (rootView instanceof View) {
            list = (ListView) rootView.findViewById(R.id.list);
            adapter = new ListAdapter(this, this.countries, mListener);
            list.setAdapter(adapter);
            Download_data download_data = new Download_data((Download_data.download_complete) this);
            download_data.download_data_from_link("http://www.websitesdemo.net/Equity99_app_wp/wp-json/wp/v2/posts");
        }
        return rootView;
    }

    public void get_data(String data)
    {
        try {
            JSONArray data_array=new JSONArray(data);

            for (int i = 0 ; i < data_array.length() ; i++)
            {
                JSONObject obj=new JSONObject(data_array.get(i).toString());
                SinglePost add=new SinglePost();
                JSONObject titleObject = obj.getJSONObject("title");
                add.slug = titleObject.getString("rendered");
                add.id = obj.getString("id");

                countries.add(add);
            }

            adapter.notifyDataSetChanged();

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

    @Override
    public void onResume() {
        // TODO Auto-generated method stub
        super.onResume();
        //countries = new ArrayList<SinglePost>();

    }


    @Override
    public void onAttach(Context context) {
        super.onAttach(context);
        if (context instanceof OnListFragmentInteractionListener) {
            mListener = (OnListFragmentInteractionListener) context;
        } else {
            throw new RuntimeException(context.toString() + " must implement OnListFragmentInteractionListener");
        }
    }

    @Override
    public void onDetach() {
        super.onDetach();
        mListener = null;
    }

    public interface OnListFragmentInteractionListener {
        // TODO: Update argument type and name
        void onListFragmentInteraction(SinglePost item);
    }

}

这是我的DetailsFragment代码：

package com.equity99.equity99.learningrestjsonwithlistfragment;
import android.os.Bundle;
import android.support.v4.app.Fragment;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.TextView;


/**
 * A simple {@link Fragment} subclass.
 */
public class DetailsFragment extends Fragment {


    public DetailsFragment() {
        // Required empty public constructor
    }


    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {
        // Inflate the layout for this fragment
        View rootView = inflater.inflate(R.layout.fragment_details, container, false);
        TextView textView = (TextView) rootView.findViewById(R.id.full_item_detailss);

        Bundle bundle = this.getArguments();
        String itemDetails = bundle.getString("slug");
        textView.setText(itemDetails);

        return rootView;
    }

}

这是我的ListAdapter：

package com.equity99.equity99.learningrestjsonwithlistfragment;
import android.content.Context;
import android.support.v4.app.Fragment;
import android.util.Log;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.BaseAdapter;
import android.widget.TextView;

import java.util.ArrayList;

import com.equity99.equity99.learningrestjsonwithlistfragment.BlankFragment.OnListFragmentInteractionListener;

public class ListAdapter extends BaseAdapter {

    Fragment main;
    private ArrayList<SinglePost> countries = null;
    private final OnListFragmentInteractionListener mListener;
    ViewHolderItem holder = null;

    public ListAdapter(Fragment m, ArrayList<SinglePost> countriesRecieved, OnListFragmentInteractionListener listener)
    {
        main = m;
        countries = countriesRecieved;
        mListener = listener;
    }

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

    @Override
    public Object getItem(int position) {
        return null;
    }

    @Override
    public long getItemId(int position) {
        return 0;
    }

    public class ViewHolderItem {
        public TextView slug;
        public TextView id;
        public SinglePost singlePost;
    }

    @Override
    public View getView(int position, View convertView, ViewGroup parent){
        Log.d("bbbbbbbbbbbbb","bbbbbbbbbbbbb");

        if (convertView == null) {
            holder = new ViewHolderItem();
            holder.singlePost = countries.get(position);
            LayoutInflater inflater = (LayoutInflater) main.getActivity().getSystemService(Context.LAYOUT_INFLATER_SERVICE);
            convertView = inflater.inflate(R.layout.cell, null);

            convertView.setOnClickListener(new View.OnClickListener() {
                @Override
                public void onClick(View v) {
                    if (null != mListener) {
                        mListener.onListFragmentInteraction(holder.singlePost);
                    }
                }

            });

            holder.slug = (TextView) convertView.findViewById(R.id.slug);
            holder.id = (TextView) convertView.findViewById(R.id.id);
            holder.singlePost = countries.get(position);

            convertView.setTag(holder);
        }
        else
        {
            holder = (ViewHolderItem) convertView.getTag();
        }

        holder.slug.setText(countries.get(position).slug);
        holder.id.setText(countries.get(position).id);
        holder.singlePost = countries.get(position);

        return convertView;
    }

}

MainActivity代码：

package com.equity99.equity99.learningrestjsonwithlistfragment;

import android.support.v4.app.FragmentTransaction;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.util.Log;

public class MainActivity extends AppCompatActivity implements BlankFragment.OnListFragmentInteractionListener{

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        BlankFragment updates = new BlankFragment();
        getSupportFragmentManager().beginTransaction()
                .add(R.id.main_container, updates).commit();

    }

    public void onListFragmentInteraction(SinglePost item) {

        DetailsFragment detailsFragment = new DetailsFragment();

        Bundle bundle = new Bundle();
        bundle.putString("itemDetails", item.slug);
        Log.d("Rakkkjjj", item.slug);
        detailsFragment.setArguments(bundle);

        FragmentTransaction fragmentTransaction = getSupportFragmentManager().beginTransaction();

        fragmentTransaction.replace(R.id.main_container, detailsFragment);
        fragmentTransaction.addToBackStack(null);
        fragmentTransaction.commit();
    }
}

Download_data class：

package com.equity99.equity99.learningrestjsonwithlistfragment;

import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.net.HttpURLConnection;
import java.net.URL;

import android.os.Bundle;
import android.os.Handler;
import android.os.Message;

public class Download_data implements Runnable  {

    public download_complete caller;

    public interface download_complete
    {
        public void get_data(String data);
    }

    Download_data(download_complete caller) {
        this.caller = caller;
    }

    private String link;
    public void download_data_from_link(String link)
    {
        this.link = link;
        Thread t = new Thread(this);
        t.start();
    }

    public void run() {
        //  caller.get_data(download(this.link));
        threadMsg(download(this.link));
    }

    private void threadMsg(String msg) {

        if (!msg.equals(null) && !msg.equals("")) {
            Message msgObj = handler.obtainMessage();
            Bundle b = new Bundle();
            b.putString("message", msg);
            msgObj.setData(b);
            handler.sendMessage(msgObj);
        }
    }


    private final Handler handler = new Handler() {
        public void handleMessage(Message msg) {
            String Response = msg.getData().getString("message");
            caller.get_data(Response);
        }
    };


    public static String download(String url) {
        URL website;
        StringBuilder response = null;
        try {
            website = new URL(url);

            HttpURLConnection connection = (HttpURLConnection) website.openConnection();
            connection.setRequestProperty("charset", "utf-8");

            BufferedReader in = new BufferedReader(
                    new InputStreamReader(connection.getInputStream()));

            response = new StringBuilder();
            String inputLine;

            while ((inputLine = in.readLine()) != null)
                response.append(inputLine);

            in.close();

        } catch (Exception  e) {
            return "";
        }

        return response.toString();
    }


}

最后是SinglePost类：

package com.equity99.equity99.learningrestjsonwithlistfragment;

public class SinglePost {
    String slug;
    String id;
}

请问我从昨天起就被困在这里，无法想到其他任何事情。试过很多解决方案但是因为我是新手，我无法让它发挥作用。谢谢你的帮助！

Answer 1

发布此问题后，我在一小时内找到了解决方案。问题出在file：BlankFragment上在这个方法里面：

public void get_data(String data)

我需要清除变量国家/地区以前的JSON数据。因此，当我恢复片段时，它以明确的数据开始。我试图通过添加以下内容来清除变量：

countries = null;

不知道我在想什么，它完全取消变量而不是清除变量，以清除我使用的数据

countries .clear();

它有效！

在ListFragment

1 个答案: