这行代码为什么会出现空指针

Question

public class MainActivitytwo extends ActionBarActivity implements

OnItemClickListener {

private ListView listView1;

// private ArrayAdapter<String> arr_adapter;

SimpleAdapter adapter;

List<Map<String, Object>> list;

// ArrayList<Map<String, Object>> data = new ArrayList<Map<String,

// Object>>();

@Override

protected void onCreate(Bundle savedInstanceState) {

super.onCreate(savedInstanceState);

setContentView(R.layout.activity_main_activitytwo);

listView1 = (ListView) findViewById(R.id.listView1);

// 绑定listView1；

list=new ArrayList<Map<String, Object>>();

getData();   //这里出现的空指针

adapter = new SimpleAdapter(this,list,

// 上下文，当前lisiView加载的每一个列表所对应的的布局文件；

R.layout.item,

// 调用系统的数据源

new String[] { "book", "author", "image" },

// from

new int[] { R.id.bookn, R.id.anthor,R.id.image});

// too

listView1.setAdapter(adapter);

// 调用一个simpleAdapter

listView1.setOnItemClickListener(this);

// 监听item

}

public void addList(View v) {

Intent intent = new Intent();

intent.setClass(this, AddMainActivity.class);

startActivity(intent);

}

public void getData() {

Bundle bundle = this.getIntent().getExtras();

Map<String, Object> map;

if(bundle!=null){

String book = bundle.getString("KEY_BOOK");

String author = bundle.getString("KEY_AUTHOR");

// 创建一个返回值为List的getData方法；

// new 一个ArrayList

map = new HashMap<String, Object>();

map.put("book", book);

map.put("author", author);

map.put("image",R.drawable.ic_launcher );

list.add(map);

adapter.notifyDataSetChanged();// 这里也出现了空指针

}

}

@Override

public void onItemClick(AdapterView<?> arg0, View arg1, final int arg2,

long arg3) {

Builder builder = new AlertDialog.Builder(this);

builder.setTitle(R.string.mgn);

builder.setItems(R.array.mg, new OnClickListener() {

@Override

public void onClick(DialogInterface arg0, int arg1) {

switch (arg1) {

case 0:

break;

case 1:

list.remove(arg2);

adapter.notifyDataSetChanged();

break;

}

}

});

builder.create().show();

}

}

//注释：其他的文件都完整

Answer 1

adapter没实例化就调用方法当然会报错了