Question

我知道这个问题问过很多次但是我找不到错误

我检查了所有事情我做错了什么但是我找不到我做错了什么。

我正在使用back4App作为后端。

我只是从中检索数据，只想在我的列表视图中显示。

我设置了日志以检查我正在检索的数据，因此它在doInbackground方法中显示完美的arraylist大小。但是当我将它返回到postexecute并且我也检查它的大小。但它在那里显示0。不知道我做了什么错误。

我的代码如下：

public class HomeActivity extends AppCompatActivity {
ProgressDialog mProgressDialog;
ArrayList<String> items;
ListView listView;

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


    listView = (ListView) findViewById(R.id.listview);
    items=new ArrayList<>();
    new GetServices().execute();


}




private class GetServices extends AsyncTask<Void, Void, ArrayList<String>> {

    @Override
    protected void onPreExecute() {
        super.onPreExecute();
        // Create a progressdialog
        mProgressDialog = new ProgressDialog(HomeActivity.this);
        // Set progressdialog title
        mProgressDialog.setTitle("Parse.com Simple ListView Tutorial");
        // Set progressdialog message
        mProgressDialog.setMessage("Loading...");
        mProgressDialog.setIndeterminate(false);
        // Show progressdialog
        mProgressDialog.show();

    }

    @Override
    protected ArrayList<String> doInBackground(Void... params) {
        // Locate the class table named "services" in Parse.com
        ParseQuery<ParseObject> query = new ParseQuery<ParseObject>("services");
        query.orderByAscending("updatedAt");


        query.findInBackground(new FindCallback<ParseObject>() {
            @Override
            public void done(List<ParseObject> objects, ParseException e) {
                if (e == null) {
                    items.clear();
                    Log.i("TAG", "datasize=>" + objects.size());
                    List<String> temp = new ArrayList<String>();

                    for (ParseObject services : objects) {
                        temp.clear();
                        items.add(services.getString("serviceTitle"));

                        temp = services.getList("serviceDetails");
                        items.add(Util.getHtmlText(temp));

                    }

                    Log.i("TAG", "itemsize=>" + items.size());

                } else {
                    e.printStackTrace();
                }
            }
        });



        return items;
    }

    @Override
    protected void onPostExecute(ArrayList<String> strings) {
        super.onPostExecute(strings);
        Log.i("TAG", "resultsize=>" + strings.size());

        for (int i = 0; i < strings.size(); i++) {
            Log.i("TAG", "==>" + strings.get(i));
        }
        // Pass the results into an ArrayAdapter
        CustomServiceListAdapter adapter = new CustomServiceListAdapter(HomeActivity.this, R.layout.custom_fragment_service_list_item, strings);


        // Binds the Adapter to the ListView
        listView.setAdapter(adapter);
        // Close the progressdialog
        mProgressDialog.dismiss();
        // Capture button clicks on ListView items
        listView.setOnItemClickListener(new AdapterView.OnItemClickListener() {
            @Override
            public void onItemClick(AdapterView<?> parent, View view,
                                    int position, long id) {
                // Send single item click data to SingleItemView Class
                Intent i = new Intent(HomeActivity.this,
                        DetailsActivity.class);
                // Pass data "name" followed by the position
                i.putExtra("data", items.get(position));
                // Open SingleItemView.java Activity
                startActivity(i);
            }
        });

    }
}}

我的Logcat显示如下：

05-20 13:10:28.661 19099-19099/com.example.apexweb I/TAG: resultsize=>0
05-20 13:10:29.409 19099-19099/com.example.apexweb I/TAG: datasize=>4
05-20 13:10:29.410 19099-19099/com.example.apexweb I/TAG: itemsize=>8

Answer 1

根据文档findInBackground从后台线程中的源检索满足此查询的ParseObject列表，并在回调中获取结果。 doInBackground不会等到调用带有结果的回调。这就是onPostExecute中大小仍为0的原因。由于doInBackground已经在另一个线程上运行，因此不需要第二级异步。您可以直接致电find()。或者，您可以摆脱AsyncTask并使用UI线程中的回调运行findInBackground

在onPostExecute（）中获取Arraylist大小为0，其中我在doInbackground（）方法中获取实际大小

1 个答案: