如何检查Listview是否为空

Question

我的活动查询我的解析数据库,然后根据查询重新设置数据.数据以列表视图中的名称存储.但我无法弄清楚如何检查列表视图是否为空.我希望它发布一个警告,说明列表视图在事件发生时是空的.这是我的活动

public class OfferPage extends Activity {
    String obj;
    ProgressDialog mProgressDialog;

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

        Intent i = getIntent();
        obj = i.getStringExtra("RestName");
        populateList(obj, "Restraunt");

    }

    private void populateList(final String Value, final String Key) {
        ParseQueryAdapter.QueryFactory<ParseObject> factory = new ParseQueryAdapter.QueryFactory<ParseObject>() {

            @Override
            @SuppressWarnings({ "unchecked", "rawtypes" })
            public ParseQuery create() {
                ParseQuery query = new ParseQuery("Offers");
                query.whereEqualTo(Key, Value);
                return query;
            }
        };
        ParseQueryAdapter<ParseObject> adapter = new ParseQueryAdapter<ParseObject>(
                this, factory);
        adapter.setTextKey("Offer");
        adapter.addOnQueryLoadListener(new OnQueryLoadListener<ParseObject>() {

            @Override
            public void onLoading() {
                mProgressDialog = new ProgressDialog(OfferPage.this);
                mProgressDialog.setTitle("Searching for Offers");
                mProgressDialog.setMessage("Loading...");
                mProgressDialog.setIndeterminate(false);
                mProgressDialog.show();
            }

            @Override
            public void onLoaded(List<ParseObject> objects, Exception e) {
                mProgressDialog.dismiss();
            }
        });

        final ListView listView = (ListView) findViewById(R.id.offerList);
        listView.setAdapter(adapter);
    }

我的主要问题似乎无法确定如果列表为空,检查的位置.有什么建议？

Answer 1

您必须控制适配器是否为空,而不是列表视图,因为适配器保存值.

      if (adapter== null) {
            adapter= new  ParseQueryAdapter(this,getElements());
            eList.setAdapter(adapter);
        } else {
            adapter.addAll(getElements());
        }