Question

我用列创建数据库和表（类别）（_id，title，...）我想从db中读取类别并将类别列表显示为列表视图。

这是y代码：

   public class MainActivity extends listActivity{

    private ArrayAdapter arrayAdapter;
    ArrayList results = new ArrayList();
    ListView catlist;
    Cursor cur;

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

        catlist = getListView();

        int parentid = getIntent().getIntExtra("catid", 0);
        openAndQueryDatabase(parentid);

        displayCatListView();




    }

    private void displayCatListView() {

        setListAdapter(new ArrayAdapter<String>(this,
                android.R.layout.simple_list_item_1, results));


        catlist.setOnItemClickListener(new OnItemClickListener() {

               @Override
               public void onItemClick(AdapterView<?> parent, View v,
                 final int position, long id) {


                Toast.makeText(MainActivity.this,
                  "List View Clicked:" + position, Toast.LENGTH_LONG)
                  .show();
               }
              });     

    }

    private void openAndQueryDatabase(int parentid) {
        DataBaseHelper db = new DataBaseHelper(this);

        SQLiteDatabase dbr = db.getReadableDatabase();
        cur = dbr.rawQuery(
                "SELECT _id, title, has_sub FROM categories where parent_id=?",
                new String[] { String.valueOf(parentid) });


        if (cur != null) {
            while (cur.moveToNext()) {

                int cat_id = cur.getInt(cur.getColumnIndex("_id"));
                String cattitle = cur.getString(cur.getColumnIndex("title"));
                int has_sub = cur.getInt(cur.getColumnIndex("has_sub"));
                results.add(cat_id + cattitle + has_sub);
            }
            cur.close();
        }

        db.close();

    }
}

1）我可以获得onItemClick的位置。但是我希望获得类别_id onItemClick。请帮忙

2）我是新人。我的代码有什么错误吗？

非常感谢

Answer 1

使用CursorAdapter（http://developer.android.com/reference/android/widget/CursorAdapter.html）代替，当您使用ArrayAdapter时，它会超出内存分配，如果db发生更改，您也不会收到通知。

此外，如果使用CursorAdapter，您将拥有

public void onItemClick(AdapterView<?> parent, View v, final int position, long id)

“id”参数将与表的_id字段

一致

让整行完成

adapter.getItem(int position)

Answer 2

而不是

int cat_id = cur.getInt(cur.getColumnIndex("_id"));
String cattitle = cur.getString(cur.getColumnIndex("title"));
int has_sub = cur.getInt(cur.getColumnIndex("has_sub"));
results.add(cat_id + cattitle + has_sub);

创建一个Category类来包含这些值，并使用参数化的ArrayList。像

这样的东西

class Category {
    public int cat_id;
    public String cattitle;
    public int has_sub;

    public Category(int cat_id, ...) {
        // constructor logic here
    }
}

和

results.add(new Category(cat_id, cattitle, has_sub));

有了这个，你可以这样设置onItemClickListener：

        catlist.setOnItemClickListener(new OnItemClickListener() {

           @Override
           public void onItemClick(AdapterView<?> parent, View v,
             final int position, long id) {
                 Category clickedCategory = results.get(position);
                 int id = clickedCategory.cat_id;

                 // do something with id
           }
          });

您的ArrayList是ArrayAdapter的数据源，position对应于其中单击的类别的索引。

android：listview：获取项目点击的光标值

2 个答案: