android - 滚动回到 listvview 的顶部

Question

我有一个从 parse.com 检索数据的 ListView 。我添加了 onscroll 监听器以在每 15 个项目之后加载列表项目。它工作正常，但是当加载整个列表并且当我们想要滚动回顶部时，滚动并不平滑，就像上下移动一样。为了更好地理解我的问题watch this video

我的代码

public class InterActivity extends Activity 
{


ListView listview;
List<ParseObject> ob;
ProgressDialog mProgressDialog;
FinalAdapter adapter;
 List<CodeList> codelist = null;
 SharedPreference shrdPreference;

 private int limit = 15;


View footerView;






@Override
public void onCreate(Bundle savedInstanceState)
{

    super.onCreate(savedInstanceState);
    setContentView(R.layout.inter_layout);
    shrdPreference = new SharedPreference();



    //Execute RemoteDataTask AsyncTask

    new RemoteDataTask().execute();
}

private class RemoteDataTask extends AsyncTask<Void, Void, Void> {
    @Override
    protected void onPreExecute() {
        super.onPreExecute();
        // Create a progressdialog
        mProgressDialog = new ProgressDialog(InterActivity.this);
        // Set progressdialog title
        mProgressDialog.setTitle("Loading");
        // Set progressdialog message
        mProgressDialog.setMessage("Please wait loading ...");
        mProgressDialog.setIndeterminate(false);
        mProgressDialog.setCancelable(false);
        // Show progressdialog
        mProgressDialog.show();
    }

    @Override
    protected Void doInBackground(Void... params) {
        // Create the array
        codelist = new ArrayList<CodeList>();
        try {
            // Locate the class table named "Country" in Parse.com
            ParseQuery<ParseObject> query = new ParseQuery<ParseObject>(
                "InterActivity");
            // Locate the column named "ranknum" in Parse.com and order list
            // by ascending
            query.orderByAscending("_created_at");
            query.setLimit(limit);
            ob = query.find();
            for (ParseObject inter : ob) {


                map.setIntroduction((String) inter.get("intro"));
                map.setFinalCodeText((String) inter.get("codetext"));


                codelist.add(map);
            }
        } catch (ParseException e) {
            Log.e("Error", e.getMessage());
            e.printStackTrace();
        }
        return null;
    }

    @Override
    protected void onPostExecute(Void result) {
        // Locate the listview in listview_main.xml
        listview = (ListView) findViewById(R.id.inter_layoutListView);
        // Pass the results into ListViewAdapter.java
        adapter = new FinalAdapter(InterActivity.this,
                                      codelist);

    //  AlphaInAnimationAdapter animationAdapter = new AlphaInAnimationAdapter(adapter);
    //  animationAdapter.setAbsListView(listview);



        // Binds the Adapter to the ListView
        listview.setAdapter(adapter);

        //listview.setOnItemClickListener(InterActivity.this);

        //listview.setOnItemLongClickListener(InterActivity.this); 
        // Close the progressdialog
        mProgressDialog.dismiss();

        listview.setOnScrollListener(new OnScrollListener() {

                @Override
                public void onScrollStateChanged(AbsListView view,
                                                 int scrollState) { // TODO Auto-generated method stub
                    int threshold = 1;
                    int count = listview.getCount();

                    if (scrollState == SCROLL_STATE_IDLE) {
                        if (listview.getLastVisiblePosition() >= count
                            - threshold) {
                            // Execute LoadMoreDataTask AsyncTask
                            new Loadmore().execute();
                        }
                    }
                }

                @Override
                public void onScroll(AbsListView view, int firstVisibleItem,
                                     int visibleItemCount, int totalItemCount) {
                    // TODO Auto-generated method stub

                }

            });




    }
}


private class Loadmore extends AsyncTask<Void, Void, Void> {
    @Override
    protected void onPreExecute() {
        super.onPreExecute();
        // Create a progressdialog
        mProgressDialog = new ProgressDialog(InterActivity.this);
        // Set progressdialog title
        mProgressDialog.setTitle("load More Tutorial");
        // Set progressdialog message
        mProgressDialog.setMessage("Loading more...");
        mProgressDialog.setIndeterminate(false);
        // Show progressdialog
        mProgressDialog.show();

    }

    @Override
    protected Void doInBackground(Void... params) {
        // Create the array
        codelist = new ArrayList<CodeList>();
        try {
            // Locate the class table named "Country" in Parse.com
            ParseQuery<ParseObject> query = new ParseQuery<ParseObject>(
                "InterActivity");
            // Locate the column named "ranknum" in Parse.com and order list
            // by ascending
            query.orderByAscending("_created_at");
            query.setLimit(limit += 15);
            ob = query.find();
            for (ParseObject inter : ob) {

                ParseFile listpic = (ParseFile) inter.get("alphabetimg");
                ParseFile levelpic = (ParseFile) inter.get("levelimg");
                ParseFile apipic = (ParseFile) inter.get("apiimg");
                ParseFile descpicone = (ParseFile) inter.get("descimgone");
                ParseFile descpictwo = (ParseFile) inter.get("descimgtwo");
                ParseFile videopic = (ParseFile) inter.get("videoimg");
                ParseFile hashtagpic = (ParseFile) inter.get("hashimg");
                ParseFile video = (ParseFile) inter.get("demovideo");

                //      ParseFile downloadfile = (ParseFile) inter.get("download");

                CodeList map = new CodeList();

                map.setIntroduction((String) inter.get("intro"));
                map.setFinalCodeText((String) inter.get("codetext"));



                codelist.add(map);
            }
        } catch (ParseException e) {
            Log.e("Error", e.getMessage());
            e.printStackTrace();
        }
        return null;
    }

    @Override
    protected void onPostExecute(Void result) {
        int position = listview.getLastVisiblePosition();
        adapter = new FinalAdapter(InterActivity.this,
                                   codelist);


        // Binds the Adapter to the ListView
        listview.setAdapter(adapter);

        listview.setSelectionFromTop(position, 0);
        mProgressDialog.dismiss();
    }
}

Answer 1

您不应在每次加载更多数据时重新创建列表和适配器。用这个替换 LoadMore 类:

private class Loadmore extends AsyncTask<Void, Void, Void> {
    @Override
    protected void onPreExecute() {
        super.onPreExecute();
        // Create a progressdialog
        mProgressDialog = new ProgressDialog(InterActivity.this);
        // Set progressdialog title
        mProgressDialog.setTitle("load More Tutorial");
        // Set progressdialog message
        mProgressDialog.setMessage("Loading more...");
        mProgressDialog.setIndeterminate(false);
        // Show progressdialog
        mProgressDialog.show();
    }

    @Override
    protected Void doInBackground(Void... params) {
        // Create the array
        codelist.clear();
        try {
            // Locate the class table named "Country" in Parse.com
            ParseQuery<ParseObject> query = new ParseQuery<ParseObject>(
                "InterActivity");
            // Locate the column named "ranknum" in Parse.com and order list
            // by ascending
            query.orderByAscending("_created_at");
            query.setLimit(limit += 15);
            ob = query.find();
            for (ParseObject inter : ob) {

                ParseFile listpic = (ParseFile) inter.get("alphabetimg");
                ParseFile levelpic = (ParseFile) inter.get("levelimg");
                ParseFile apipic = (ParseFile) inter.get("apiimg");
                ParseFile descpicone = (ParseFile) inter.get("descimgone");
                ParseFile descpictwo = (ParseFile) inter.get("descimgtwo");
                ParseFile videopic = (ParseFile) inter.get("videoimg");
                ParseFile hashtagpic = (ParseFile) inter.get("hashimg");
                ParseFile video = (ParseFile) inter.get("demovideo");

                //      ParseFile downloadfile = (ParseFile) inter.get("download");

                CodeList map = new CodeList();

                map.setIntroduction((String) inter.get("intro"));
                map.setFinalCodeText((String) inter.get("codetext"));

                codelist.add(map);
            }
        } catch (ParseException e) {
            Log.e("Error", e.getMessage());
            e.printStackTrace();
        }
        return null;
    }

    @Override
    protected void onPostExecute(Void result) {
        int position = listview.getLastVisiblePosition();
        adapter.notifyDataSetChanged();

        listview.setSelectionFromTop(position, 0);
        mProgressDialog.dismiss();
    }
}

告诉我:)