如何修复android程序？

Question

我刚开始在eclipse上使用java编写android，我一直在youtube上做教程。我最近从其中一个教程中复制了以下代码，但是当我运行它时，它说＆＃34;不幸的是（我的应用程序）已停止＆＃34;我不明白为什么......

package com.example.trythisout;

import java.util.ArrayList;

import android.app.ListActivity;
import android.content.DialogInterface;
import android.content.DialogInterface.OnClickListener;
import android.os.Bundle;
import android.util.SparseBooleanArray;
import android.view.Menu;
import android.widget.ArrayAdapter;
import android.widget.Button;
import android.widget.EditText;
import android.widget.Toast;

public class Trying extends ListActivity {

    ArrayList list = new ArrayList();

    ArrayAdapter adapter;

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

        Button add = (Button) findViewById(R.id.btnAdd);

        Button del = (Button) findViewById(R.id.btnDelete);

        adapter = new ArrayAdapter(this, R.layout.simple_list_item_multiple_choice,list);

        OnClickListener listener = new OnClickListener() {

            @Override
            public void onClick(DialogInterface dialog, int which) {
                // TODO Auto-generated method stub

                EditText edit = (EditText)findViewById(R.id.items);

                if(edit.getText().toString().equals(""))
                {
                    list.add(edit.getText().toString());
                    edit.setText("");
                    adapter.notifyDataSetChanged();
                }
                else
                {
                    Toast.makeText(getApplicationContext(),"Please enter data", Toast.LENGTH_LONG).show();
                }
            }
        };

        OnClickListener listener2 = new OnClickListener() {

            @Override
            public void onClick(DialogInterface dialog, int which) {
                // TODO Auto-generated method stub

                SparseBooleanArray checkedItemsPosition = getListView().getCheckedItemPositions();

                int count = getListView().getCount();

                for(int i = count; i>=0; i--)
                {
                    if(checkedItemsPosition.get(i))
                    {
                        adapter.remove(list.get(i));
                    }
                }
                adapter.notifyDataSetChanged();
            }
        };

        add.setOnClickListener((android.view.View.OnClickListener) listener);
        del.setOnClickListener((android.view.View.OnClickListener) listener2);

        del.setOnClickListener((android.view.View.OnClickListener) listener2);
        setListAdapter(adapter);
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.trying, menu);
        return true;
    }

}