Android ListView在更新其数据时重置滚动状态

Question

我尝试根据listview滚动更新数据。数据正在更新。但在更新数据后，listview排在首位。我需要保持一致。我从stockoverflow尝试了很多。什么都没有帮助。我想我的代码错了。请帮我解决。

我的代码是：

public class ViewAll extends AppCompatActivity {

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

        new GetMessage().execute();

        FinalMessage = new ArrayList<HashMap<String, String>>();

        ProgressBar footer = new ProgressBar(this);
        ListView lv = (ListView) findViewById(listView);
        lv.addFooterView(footer);
    }

    private void getMessageFromUrl()
    {

        new GetMessage().execute();
    }

    private class GetMessage extends AsyncTask<Void, Void, Void> {
        @Override
        protected void onPreExecute() {
            super.onPreExecute();
            ......
        }

        @Override
        protected Void doInBackground(Void... arg0)
        {
            ServiceHandler sh = new ServiceHandler();
            nameValuePairs = new ArrayList<NameValuePair>(1);
            nameValuePairs.add(new BasicNameValuePair("page",String.valueOf(page)));
            String jsonStr = sh.makeServiceCall(url, ServiceHandler.POST, nameValuePairs);
            Log.d("Response: ", "> " + jsonStr);
            if (jsonStr != null) {
                try {
                        ......
                    }
                }
                catch (JSONException e)
                {
                    e.printStackTrace();
                }
            }
            else
            {
                Log.e("SericeHandler","Couldn't get any data from url");
            }
            return null;
        }

        @Override
        protected void onPostExecute(Void result) {
            super.onPostExecute(result);


            runOnUiThread(new Runnable() {
                public void run() {

                    if(dorefresh==1)
                    {
                        ListView lv = (ListView) findViewById(listView);
                        Customlistadapter adapter = new Customlistadapter(ViewAll.this, title1, msg1);
                        lv.setAdapter(adapter);
                        int index = lv.getFirstVisiblePosition();
                        View v = lv.getChildAt(0);
                        int top = (v == null) ? 0 : v.getTop();
                        lv.setSelectionFromTop(index, top);

                        page = page + 1;
                        lv.setOnScrollListener(new AbsListView.OnScrollListener() {
                            int currentVisibleItemCount;
                            int currentScrollState;
                            int currentFirstVisibleItem;
                            int totalItem;

                            @Override
                            public void onScrollStateChanged(AbsListView view, int scrollState) {
                                // TODO Auto-generated method stub
                                this.currentScrollState = scrollState;
                                this.isScrollCompleted();
                            }

                            @Override
                            public void onScroll(AbsListView view, int firstVisibleItem,
                                                 int visibleItemCount, int totalItemCount) {
                                // TODO Auto-generated method stub
                                this.currentFirstVisibleItem = firstVisibleItem;
                                this.currentVisibleItemCount = visibleItemCount;
                                this.totalItem = totalItemCount;
                            }

                            private void isScrollCompleted() {

                                if (totalItem - currentFirstVisibleItem == currentVisibleItemCount
                                        && this.currentScrollState == SCROLL_STATE_IDLE) {
                                    getMessageFromUrl();
                                }
                            }
                        });
                        Toast.makeText(ViewAll.this, "Updated", Toast.LENGTH_SHORT).show();
                    }
                    else
                    {
                        Toast.makeText(ViewAll.this, "No More Messages", Toast.LENGTH_SHORT).show();
                    }



                }

            });
        }

    }
}

CustomlistAdapter.java

public class Customlistadapter extends ArrayAdapter<String> {
    ArrayList<String> title;
    ArrayList<String> msg;
    Context context;
    public Customlistadapter(Activity context, ArrayList<String> text, ArrayList<String> msgView) {
        super(context, R.layout.list_row, text);
        // TODO Auto-generated constructor stub
        this.title = text;
        this.msg = msgView;
        this.context = context;
    }

    public View getView(final int position, View convertView, ViewGroup parent) {
        // TODO Auto-generated method stub
        LayoutInflater inflater = (LayoutInflater) context
                .getSystemService(Context.LAYOUT_INFLATER_SERVICE);
        View single_row = inflater.inflate(R.layout.list_row, null,
                true);
        TextView textView = (TextView) single_row.findViewById(R.id.title);
        TextView msgView = (TextView) single_row.findViewById(R.id.msgView);
        textView.setText(title.get(position));
        msgView.setText(msg.get(position));

        return single_row;
    }

}

Answer 1

您的问题是每次更新数据时都会创建一个新的Customlistadapter。如果希望ListView保持其滚动状态，则必须重用适配器。只需更改适配器中的数据并调用myAdapter.notifyDataSetChanged()。

E.g。如果您的适配器是ArrayAdapter，您可以这样做：

ArrayAdapter adapter = (ArrayAdapter)listView.getAdapter();
adapter.clear();
adapter.addAll(newData);
adapter.notifyDataSetChanged();