android - Adapter, ListView, arraylist 항목추가, 삭제

package com.example.it.myapplication9_2;

import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
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 java.util.ArrayList;

public class MainActivity extends AppCompatActivity {

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

        final ArrayList<String> midList = new ArrayList<>();
        ListView list = (ListView) findViewById(R.id.listView1);

        final ArrayAdapter<String> adapter = new ArrayAdapter<>(this, android.R.layout.simple_list_item_1, midList);
        list.setAdapter(adapter);

        final EditText edtItem = (EditText) findViewById(R.id.editItem);
        Button btnAdd = (Button) findViewById(R.id.btnAdd);

        btnAdd.setOnClickListener(new View.OnClickListener() {
                                      @Override
                                      public void onClick(View v) {
                                          midList.add(edtItem.getText().toString());
                                          adapter.notifyDataSetChanged();
                                      }
                                  });

        list.setOnItemClickListener(new AdapterView.OnItemClickListener() {
            @Override
            public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
                midList.remove(position);
                adapter.notifyDataSetChanged();
            }
        });

    }
}

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    android:orientation="vertical" >

    <EditText
        android:id="@+id/editItem"
        android:layout_width="match_parent"
        android:layout_height="wrap_content" >
    </EditText>

    <Button
        android:id="@+id/btnAdd"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:background="#dddddd"
        android:text="항목 추가" />
    <ListView
        android:id="@+id/listView1"
        android:layout_width="match_parent"
        android:layout_height="wrap_content">
    </ListView>

</LinearLayout>