分层动态列表视图

Question

我正在尝试为学校作业安排撰写应用程序。主页面是用户在本学期学习的课程列表。用户可以根据自己的意愿添加任意数量的主题。当点击某个项目（课程）时，弹出菜单会显示与此课程相关的选项，如“截止日期”，“教师”，“网站链接”，“联系人”等。

我创建了一个Mainactivity类和另一个名为“Deadlines”的类，它处理“deadlines”选项。只要选择此选项，Mainactivity就会配置为指向此“deadlines”类。

然而，问题是我在截止日期列表中添加新项目后，单击返回主页面并返回，项目将消失。但这不会发生在主页上。

我想也许我可以创建Deadlines类的实例数组，并在主页上添加新项时添加新成员。但是，我不知道如何实现这一点。

我将在下面提供我的源代码： 这是我的MainActivity类：

package p.listviewexercise3;

import android.content.Intent;
import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.support.v7.widget.PopupMenu;
import android.view.MenuItem;
import android.view.View;
import android.widget.AdapterView;
import android.widget.ArrayAdapter;
import android.widget.Button;
import android.widget.EditText;
import android.widget.ListView;
import android.widget.Toast;

import java.util.ArrayList;

import static p.listviewexercise3.R.id.deadlines;

public class MainActivity extends AppCompatActivity {

    EditText editText;
    Button button;
    ArrayList list;
    ArrayAdapter<String> arrayAdapter;
    ListView listView;

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

        editText = (EditText) findViewById(R.id.editText);
        button = (Button) findViewById(R.id.button);
        button.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                String name = editText.getText().toString();
                if (name.isEmpty()){
                    Toast.makeText(getBaseContext(),"lol",Toast.LENGTH_SHORT).show();
                }
                else{
                    list.add(name);
                    arrayAdapter.notifyDataSetChanged();
                }
            }
        });
        list = new ArrayList();
        list.add("x");
        arrayAdapter = new ArrayAdapter<String>(this, android.R.layout.simple_list_item_1,list);
        listView = (ListView) findViewById(R.id.listView);
        listView.setAdapter(arrayAdapter);
        listView.setOnItemClickListener(new AdapterView.OnItemClickListener() {
            @Override
            public void onItemClick(AdapterView<?> adapterView, View view, final int position, long id) {
                PopupMenu popupMenu = new PopupMenu(MainActivity.this, listView);
                popupMenu.getMenuInflater().inflate(R.menu.menu, popupMenu.getMenu());
                popupMenu.setOnMenuItemClickListener(new PopupMenu.OnMenuItemClickListener(){
                    @Override
                    public boolean onMenuItemClick(MenuItem item){
                        switch(item.getItemId()){
                            case deadlines:
                                Intent intent = new Intent(getApplicationContext(), Deadlines.class);
                                intent.putExtra("ITEM_INDEX", position);
                                startActivity(intent);
                        }
                        return true;
                    }
                });
                popupMenu.show();
            }
        });
        listView.setOnItemLongClickListener(new AdapterView.OnItemLongClickListener() {
            @Override
            public boolean onItemLongClick(AdapterView<?> adapterView, View view, int position, long l) {
                list.remove(position);
                arrayAdapter.notifyDataSetChanged();
                return true;
            }
        });
    }


}

这是我的截止日期课程：

package p.listviewexercise3;

import android.content.Intent;
import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.view.View;
import android.widget.ArrayAdapter;
import android.widget.Button;
import android.widget.EditText;
import android.widget.ListView;

import java.util.ArrayList;

/**
 * Created by root on 9/28/17.
 */

public class Deadlines extends AppCompatActivity {
    Button button;
    EditText editText;
    ListView deadlines;
    ArrayList list;
    ArrayAdapter arrayAdapter;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.deadlines);
        Intent in = getIntent();
        int index = in.getIntExtra("p.ITEM_INDEX", -1);

        button = (Button) findViewById(R.id.button2);
        editText = (EditText) findViewById(R.id.editText2);
        deadlines = (ListView) findViewById(R.id.deadlines);
        list = new ArrayList();
        arrayAdapter = new ArrayAdapter(this, android.R.layout.simple_list_item_1, list);
        deadlines.setAdapter(arrayAdapter);

        button.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                String text = editText.getText().toString();
                list.add(text);
                arrayAdapter.notifyDataSetChanged();
            }
        });
    }
}