Android:当我启动一个新活动并按返回以返回它时，Listview会自我复制 [英] Android: Listview duplicates itself when I launch a new activity and press back to go back to it

问题描述

我有两个列表视图，它们是视图页面选项卡中的片段.当您单击列表视图中的项目时，它将启动一个新活动.但是，当我按下后退按钮返回到选项卡式列表视图时，列表视图已加倍，如果我打开活动并再次返回，则它将再次加倍，并且它将继续执行此操作.另外，我还有另一个带有五个选项卡的选项卡式列表视图，当我离开其中一个视图的两个选项卡时.当我回到它们时，该视图中的项目会加倍，所有其他选项卡都一样.这两个列表视图的代码是相同的.我尝试过list.clear()，它只清除所有列表项，并在视图持有者中使用"else"语句(由其他堆栈溢出答案推荐).但是每次列表视图仍然重复.另外，除非您尚未注意到，否则我是android的新手.

I have two list views that are fragments in view pager tabs. When you click on the items in the list view it launches a new activity. But when I press the back-button to get back to the tabbed list view, the list view has doubled and if I open the activity and go back again it doubles again and it will keep doing that. Also I have another tabbed list view with five tabs and when I go two tabs away from one of the views. The items in that view double when I come back to them and this is the same for all the other tabs. The code for the two listviews is identical. I have tried list.clear(), which just clears all of the list items and have played around with the "else" statement in the view holder (recommended by other stack overflow answers). But every time the list view still duplicates. Also unless you haven't noticed already I'm pretty new to android.

这是两个选项卡式活动中的列表视图片段(Due_Today_Fragment)的代码.

here is the code for the list view fragment (Due_Today_Fragment) that is in a two-tabbed activity.

      import java.util.ArrayList;
import java.util.List;

import android.content.Intent;
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.AdapterView;
import android.widget.ArrayAdapter;
import android.widget.ImageView;
import android.widget.ListView;
import android.widget.TextView;


public class Due_Today_Fragment extends Fragment  {
    private List<homeworkdue> myhomeworkdue;

    static class ViewHolder {
        public ImageView imageView;
        public TextView HomeworkDueText;
        public TextView DescriptionText;
        public TextView TeacherText;
      }


    public static final String KEY_HOMEWORK="homework";
    public static final String KEY_DESC="desc";

    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState){
        return inflater.inflate(R.layout.activity_main, container, false); }


    @Override
    public void onResume() {
        // TODO Auto-generated method stub
        super.onResume();
        myhomeworkdue = new ArrayList<homeworkdue>();
        populatehomeworkdueList();
        populateListView();
        registerClickCallback();
    }

    private void registerClickCallback() {
        ListView list = (ListView)getView().findViewById(R.id.listView1);
        list.setOnItemClickListener(new AdapterView.OnItemClickListener() {

            public void onItemClick(AdapterView<?> parent, View viewClicked, int position, long id) {

                homeworkdue clickedhomeworkdue = myhomeworkdue.get(position);

                Intent intent = new Intent(getActivity(), homeworkdueDetailsActivity.class);
                intent.putExtra(KEY_HOMEWORK, clickedhomeworkdue.getHomeworkdue());
                intent.putExtra(KEY_DESC, clickedhomeworkdue.getDesciption());

                startActivity(intent);
            }
        });
        }


    private void populatehomeworkdueList() {
        myhomeworkdue.add(new homeworkdue("History Homework", "Description 1", R.drawable.global_studies, "Anderson"));
        myhomeworkdue.add(new homeworkdue("Math Homework", "Description 2", R.drawable.mathematics, "Klein"));
        myhomeworkdue.add(new homeworkdue("English Homework", "Description 3", R.drawable.english, "Reed"));
        myhomeworkdue.add(new homeworkdue("Spanish Homework", "Description 4", R.drawable.spanish, "Joya"));
        myhomeworkdue.add(new homeworkdue("Science Homework", "Description 5", R.drawable.science, "Poole"));
    }

    private void populateListView() {
        ArrayAdapter<homeworkdue> adapter = new MyListAdapter();
        ListView list = (ListView)getView().findViewById(R.id.listView1);
        list.setAdapter(adapter);


    }


    public class MyListAdapter extends ArrayAdapter<homeworkdue>  {
        public MyListAdapter() {
            super(getActivity(), R.layout.item_view, myhomeworkdue);
        }

        @Override
        public View getView(int position, View convertView, ViewGroup parent) {
            ViewHolder holder;

            if(convertView==null){
            convertView = getActivity().getLayoutInflater().inflate(R.layout.item_view, parent, false);
             holder = new ViewHolder();

             holder.imageView = (ImageView)convertView.findViewById(R.id.item_iconclass);

            holder.HomeworkDueText = (TextView) convertView.findViewById(R.id.item_texthomeworkdue);

            holder.DescriptionText = (TextView) convertView.findViewById(R.id.item_textdescription);

            holder.TeacherText = (TextView) convertView.findViewById(R.id.item_textteacher);

            convertView.setTag(holder);


            }

        else {
            holder = (ViewHolder) convertView.getTag();
        }

        homeworkdue currenthomeworkdue = myhomeworkdue.get(position);

        holder.imageView.setImageResource(currenthomeworkdue.getIconID());


        holder.HomeworkDueText.setText(currenthomeworkdue.getHomeworkdue());


        holder.DescriptionText.setText(currenthomeworkdue.getDesciption());


        holder.TeacherText.setText(currenthomeworkdue.getTeacher());

        return convertView;

    }

        }


}

这是单击列表视图项时启动的活动的代码

Here is the code for the activity launched when a list view item is clicked

    import android.app.Activity;
import android.content.Intent;
import android.os.Bundle;
import android.view.Menu;
import android.widget.TextView;
import static com.bernard.beaconportal.Due_Today_Fragment.KEY_HOMEWORK;
import static com.bernard.beaconportal.Due_Today_Fragment.KEY_DESC;


public class homeworkdueDetailsActivity extends Activity {

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

        String homework = "";
        String desc = "";

        Intent intent = getIntent();
        if (null != intent) {
            homework = intent.getStringExtra(KEY_HOMEWORK);
            desc = intent.getStringExtra(KEY_DESC);
        }

        TextView headlineTxt = (TextView) findViewById(R.id.texthomeworkdue);
        headlineTxt.setText(homework);

        TextView pubdateTxt = (TextView) findViewById(R.id.textdescription);
        pubdateTxt.setText(desc);

    }


}

这是制表符片段的代码

import java.lang.reflect.Field;
import com.actionbarsherlock.app.SherlockFragment;
import com.astuetz.PagerSlidingTabStrip;

import android.os.Bundle;
import android.support.v4.app.Fragment;
import android.support.v4.view.ViewPager;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;

public class Fragments2 extends SherlockFragment {

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
            Bundle savedInstanceState) {
        View view = inflater.inflate(R.layout.viewpager_main, container, false);
        // Locate the ViewPager in viewpager_main.xml
        ViewPager pager = (ViewPager) view.findViewById(R.id.viewPager);
        // Set the ViewPagerAdapter into ViewPager
        pager.setAdapter(new ViewPagerAdapter(getChildFragmentManager()));
        PagerSlidingTabStrip tabs = (PagerSlidingTabStrip) view.findViewById(R.id.pagerTabStrip);
        tabs.setViewPager(pager);

        return view;
    }

    @Override
    public void onDetach() {
        super.onDetach();
        try {
            Field childFragmentManager = Fragment.class
                    .getDeclaredField("mChildFragmentManager");
            childFragmentManager.setAccessible(true);
            childFragmentManager.set(this, null);
        } catch (NoSuchFieldException e) {
            throw new RuntimeException(e);
        } catch (IllegalAccessException e) {
            throw new RuntimeException(e);
        }
    }
}

在这里定义作业的字符串

here is where the strings are defined for homework due

public class homeworkdue {
    private String homework;
    private String desc;
    private int IconID;
    private String teacher;



    public homeworkdue(String homework, String desc, int IconID, String teacher) {



        super();
        this.homework = homework;
        this.desc = desc;
        this.IconID = IconID;
        this.teacher = teacher;
    }

    public String getHomeworkdue() {
        return homework;
    }
    public String getDesciption() {
        return desc;
    }   
    public int getIconID() {
        return IconID;
    }   
    public String getTeacher() {
        return teacher;
    }


    }

这是包含在五个选项卡中的片段的代码

here is the code for the fragment which is contained in five tabs

import java.util.ArrayList;
import java.util.List;

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.ArrayAdapter;
import android.widget.ListView;
import android.widget.TextView;


public class Thursday extends Fragment  {



    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState){
        return inflater.inflate(R.layout.schedule_list_view, container, false); }

    private List<schedule> myschedule = new ArrayList<schedule>();



    static class ViewHolder {

        public TextView HomeworkDueText;
      }

    public void onStart() {
        super.onStart();

        populatescheduleList();
        populateListView();

    }


    private void populatescheduleList() {
        myschedule.add(new schedule("E Band"));
        myschedule.add(new schedule("G Band"));
        myschedule.add(new schedule("F Band"));
        myschedule.add(new schedule("H Band"));
        myschedule.add(new schedule("A Band"));
        myschedule.add(new schedule("C Band"));
        myschedule.add(new schedule("D Band"));
    }

    private void populateListView() {
        ArrayAdapter<schedule> adapter = new MyListAdapter();
        ListView list = (ListView)getView().findViewById(R.id.listView2);
        list.setAdapter(adapter);

    }


     public class MyListAdapter extends ArrayAdapter<schedule>  {
            public MyListAdapter() {
                super(getActivity(), R.layout.item_view, myschedule);
            }

            @Override
            public View getView(int position, View convertView, ViewGroup parent) {
                ViewHolder holder;

                if(convertView==null){
                    convertView = getActivity().getLayoutInflater().inflate(R.layout.schedule_list_item, parent, false);
                 holder = new ViewHolder();

                 holder.HomeworkDueText = (TextView) convertView.findViewById(R.id.bandText);

                convertView.setTag(holder);
                }

            else {
                holder = (ViewHolder) convertView.getTag();
            }

                schedule currenthomeworkdue = myschedule.get(position);

                holder.HomeworkDueText.setText(currenthomeworkdue.Band());

            return convertView;


        }

        }

}

这是为计划定义字符串的地方

here is where the strings are defined for schedule

public class schedule {
    private String band;




    public schedule(String band) {



        super();
        this.band = band;

    }

    public String Band() {
        return band;


    }

}

如果您需要更多信息，请先询问并感谢您的帮助

If you need any more information just ask and thank you in advance for the help

我已经尝试修复此错误两天了，我处于机智状态.

I've been trying to fix this bug for two days and I'm at my wits end.

推荐答案

创建该片段后，我们会声明一次新列表的原因，因此当您返回到片段时，它不会声明一个新列表，而是它将使用旧的.因此，为了解决此问题，您需要将以下代码分成两部分:

the reason behind that we are declaring a new List once when the fragment is created, so when you get back to your fragment it wont declare a new one, instead it will use the old one. so in order to tackle this issue you need to split the following code into 2 parts:

private List<homeworkdue> myhomeworkdue = new ArrayList<homeworkdue>();

部分插入片段中的onResume中，您还需要将onStart以及onStart中的所有内容删除到onResume.但首先保留这样的声明:

part goes in onResume in your fragment you need also to remove onStart and everything within onStart to onResume. but first keep the declaration like this:

private List<homeworkdue> myhomeworkdue;

，然后将其余的移动到onResume.

and move the rest to onResume.

@Override
protected void onResume() {
    // TODO Auto-generated method stub
    super.onResume();
    myhomeworkdue = new ArrayList<homeworkdue>();
    populatehomeworkdueList();
    populateListView();
    registerClickCallback();
}

第二个ListView中存在相同的问题，因为它们是相同的.

same issue in your second ListView since they are identical.

希望这对您有用.如果有效，请给我反馈.

Hope this works for you. Please give me a feedback if it worked.

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