我正在尝试设置一个ListView,我可以使用一个简单的String []数组来完成它,你可以在代码中看到。
稍后,我注释掉了Array并使用了List
当我想使用List时,我的问题就出现了(因为我需要操作内容),并且无法动态更改简单的Array。 当我使用List时,我在创建ArrayAdapter时得到NullPointerException,我不知道为什么。
我在ArrayAdapter的文档中读到它有6个不同的构造函数重载,其中一个是
ArrayAdapter(Context context,int resource,List objects)
为什么我收到NullPointerException?
如何使其与List而不是数组一起使用?
提前致谢!
public class MainActivity extends Activity implements OnItemClickListener {
ListView l;
// String[] days = {"Sunday","Monday","Tuesday","Wednesday","Thursday","Friday","Saturday"};
List<String> days;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
days.add(0, "Sunday");
days.add(1, "Monday");
days.add(2, "Tuesday");
days.add(3, "Wednesday");
days.add(4, "Thursday");
days.add(5, "Friday");
days.add(6, "Saturday");
l = (ListView) findViewById(R.id.listView1);
ArrayAdapter<String> adapter = new ArrayAdapter<String>(this, android.R.layout.simple_list_item_1, days);
l.setAdapter(adapter);
l.setOnItemClickListener(this);
}
@Override
public void onItemClick(
AdapterView<?> adapterView, // ListView that was clicked
View view, // Reference to the row that was clicked (each row is a TextView)
int i, // position
long l) { // id of the TextView that was clicked
Toast.makeText(this, days.get(i) + " " + i, Toast.LENGTH_LONG).show();
}
}
答案 0 :(得分:2)
您忘记使用任何内容初始化days
字段,因此在调用add
方法时它仍为null。在days.add(0, "Sunday");
行之前,添加以下内容:
days = new ArrayList<String>();
另外,取出索引号。只需使用days.add("Sunday"); days.add("Monday");
,依此类推。
答案 1 :(得分:1)
您需要创建days
:
List<String> days = new ArrayList<String>();
例如。