android - 在 fragment 中显示graphview仅在应用程序重启后显示数据

Question

您好，我的代码遇到了障碍。我正在将一些数据保存到 sqlite，然后读取这些数据并将其显示在图表上。该图和保存一样工作正常。

我有 fragment 选项卡，可以轻松滑动。现在，当我保存数据时，我想在图表上检查它。然而，问题是当我向右滑动有图表的地方时，图表中没有数据。但是当我关闭应用程序并重新打开它时，数据就会出现。对此有什么好的解决方案？

图表代码:

public class overwiew extends Fragment {

        private LineGraphSeries<DataPoint> series1;
        private LineGraphSeries<DataPoint> series2;
        private LineGraphSeries<DataPoint> series3;
        private LineGraphSeries<DataPoint> series4;
        private LineGraphSeries<DataPoint> series5;
        private LineGraphSeries<DataPoint> series6;
        private LineGraphSeries<DataPoint> series7;
        Sqlite_DBHelper sqliteDbHelper_;
        SQLiteDatabase sqLiteDatabase;

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {
        View rootView = inflater.inflate(R.layout.owerview, container, false);


            sqliteDbHelper_ = new Sqlite_DBHelper(getActivity());
            sqLiteDatabase = sqliteDbHelper_.getWritableDatabase();

            GraphView graph = (GraphView) rootView.findViewById(R.id.graph);
            series1 = new LineGraphSeries<DataPoint>(getDataToday());
            series2 = new LineGraphSeries<DataPoint>(getDataToday_minus1());
            series3 = new LineGraphSeries<DataPoint>(getDataToday_minus2());
            series4 = new LineGraphSeries<DataPoint>(getDataToday_minus3());
            series5 = new LineGraphSeries<DataPoint>(getDataToday_minus4());
            series6 = new LineGraphSeries<DataPoint>(getDataToday_minus5());
            series7 = new LineGraphSeries<DataPoint>(getDataToday_minus6());


            series1.setColor(Color.parseColor("#D50000"));
            series2.setColor(Color.parseColor("#D500F9"));
            series3.setColor(Color.parseColor("#4527A0"));
            series4.setColor(Color.parseColor("#1565C0"));
            series5.setColor(Color.parseColor("#00838F"));
            series6.setColor(Color.parseColor("#1B5E20"));
            series7.setColor(Color.parseColor("#FF9800"));

            graph.addSeries(series1);
            graph.addSeries(series2);
            graph.addSeries(series3);
            graph.addSeries(series4);
            graph.addSeries(series5);
            graph.addSeries(series6);
            graph.addSeries(series7);

            graph.getViewport().setMinX(6);
            graph.getViewport().setMaxX(24);
            graph.getViewport().setMinY(0);
            graph.getViewport().setMaxY(10);
            graph.getViewport().setYAxisBoundsManual(true);
            graph.getViewport().setXAxisBoundsManual(true);

            graph.setTitle("Tedenski prikaz za zadnje 7 dni");

            series1.setTitle("danes");
            series2.setTitle("včeraj");
            series3.setTitle("x");
            series4.setTitle("x");
            series5.setTitle("x");
            series6.setTitle("x");
            series7.setTitle("x");

            graph.getLegendRenderer().setVisible(true);
            graph.getLegendRenderer().setAlign(LegendRenderer.LegendAlign.TOP);

        return rootView;

        }

        private DataPoint[] getDataToday() {

            String[] columns = {"hour_only","JAKOST"};

            GregorianCalendar gc = new GregorianCalendar();
            SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd");
            String today = sdf.format(gc.getTime());

            //  Cursor cursor = sqLiteDatabase.query("podatki", columns,null,null,null,null,null);
            Cursor cursor = sqLiteDatabase.query("podatki", columns,"date(timeStamp) = ?", new String[] {today},null,null,null);



            DataPoint[] dp = new DataPoint[cursor.getCount()];

            for (int i=0; i < cursor.getCount();i++){
                cursor.moveToNext();
                dp[i]=new DataPoint(cursor.getInt(0),cursor.getInt(1));
            }
            return dp;
        }


        private DataPoint[] getDataToday_minus1() {

            String[] columns = {"hour_only","JAKOST"};

            DateFormat dateFormat = new SimpleDateFormat("yyyy-MM-dd");
            Calendar cal = Calendar.getInstance();
            cal.add(Calendar.DATE, -1);
            String today_minus1 = dateFormat.format(cal.getTime());

            Cursor cursor = sqLiteDatabase.query("podatki", columns,"date(timeStamp) = ?", new String[] {today_minus1},null,null,null);



            DataPoint[] dp = new DataPoint[cursor.getCount()];

            for (int i=0; i < cursor.getCount();i++){
                cursor.moveToNext();
                dp[i]=new DataPoint(cursor.getInt(0),cursor.getInt(1));
            }
            return dp;
        }
        private DataPoint[] getDataToday_minus2() {

            String[] columns = {"hour_only","JAKOST"};

            DateFormat dateFormat = new SimpleDateFormat("yyyy-MM-dd");
            Calendar cal = Calendar.getInstance();
            cal.add(Calendar.DATE, -2);
            String today_minus2 = dateFormat.format(cal.getTime());

            Cursor cursor = sqLiteDatabase.query("podatki", columns,"date(timeStamp) = ?", new String[] {today_minus2},null,null,null);



            DataPoint[] dp = new DataPoint[cursor.getCount()];

            for (int i=0; i < cursor.getCount();i++){
                cursor.moveToNext();
                dp[i]=new DataPoint(cursor.getInt(0),cursor.getInt(1));
            }
            return dp;
        }

        private DataPoint[] getDataToday_minus3() {

            String[] columns = {"hour_only","JAKOST"};

            DateFormat dateFormat = new SimpleDateFormat("yyyy-MM-dd");
            Calendar cal = Calendar.getInstance();
            cal.add(Calendar.DATE, -3);
            String today_minus3 = dateFormat.format(cal.getTime());

            Cursor cursor = sqLiteDatabase.query("podatki", columns,"date(timeStamp) = ?", new String[] {today_minus3},null,null,null);



            DataPoint[] dp = new DataPoint[cursor.getCount()];

            for (int i=0; i < cursor.getCount();i++){
                cursor.moveToNext();
                dp[i]=new DataPoint(cursor.getInt(0),cursor.getInt(1));
            }
            return dp;
        }

        private DataPoint[] getDataToday_minus4() {

            String[] columns = {"hour_only","JAKOST"};

            DateFormat dateFormat = new SimpleDateFormat("yyyy-MM-dd");
            Calendar cal = Calendar.getInstance();
            cal.add(Calendar.DATE, -4);
            String today_minus4 = dateFormat.format(cal.getTime());

            Cursor cursor = sqLiteDatabase.query("podatki", columns,"date(timeStamp) = ?", new String[] {today_minus4},null,null,null);



            DataPoint[] dp = new DataPoint[cursor.getCount()];

            for (int i=0; i < cursor.getCount();i++){
                cursor.moveToNext();
                dp[i]=new DataPoint(cursor.getInt(0),cursor.getInt(1));
            }
            return dp;
        }

        private DataPoint[] getDataToday_minus5() {

            String[] columns = {"hour_only","JAKOST"};

            DateFormat dateFormat = new SimpleDateFormat("yyyy-MM-dd");
            Calendar cal = Calendar.getInstance();
            cal.add(Calendar.DATE, -5);
            String today_minus5 = dateFormat.format(cal.getTime());

            Cursor cursor = sqLiteDatabase.query("podatki", columns,"date(timeStamp) = ?", new String[] {today_minus5},null,null,null);



            DataPoint[] dp = new DataPoint[cursor.getCount()];

            for (int i=0; i < cursor.getCount();i++){
                cursor.moveToNext();
                dp[i]=new DataPoint(cursor.getInt(0),cursor.getInt(1));
            }
            return dp;
        }

        private DataPoint[] getDataToday_minus6() {

            String[] columns = {"hour_only","JAKOST"};

            DateFormat dateFormat = new SimpleDateFormat("yyyy-MM-dd");
            Calendar cal = Calendar.getInstance();
            cal.add(Calendar.DATE, -6);
            String today_minus6 = dateFormat.format(cal.getTime());

            Cursor cursor = sqLiteDatabase.query("podatki", columns,"date(timeStamp) = ?", new String[] {today_minus6},null,null,null);



            DataPoint[] dp = new DataPoint[cursor.getCount()];

            for (int i=0; i < cursor.getCount();i++){
                cursor.moveToNext();
                dp[i]=new DataPoint(cursor.getInt(0),cursor.getInt(1));
            }
            return dp;
        }


    }

Answer 1

您正在使用 View 寻呼机来显示您的 fragment ，对吧？

View Pager 保留 View 的缓存，默认是当前 View 的缓存，左 View 和右 View 。

如果您从当前 View 滚动两个 View 并返回，您的 View 将更新，因为 fragment 将被重新创建。

您可以使用 setOffscreenPageLimit 禁用 View 寻呼机缓存(0);

或者你可以实现一个特殊的行为来知道 fragment 何时可​​见，你可以检查这个问题的例子:How to determine when Fragment becomes visible in ViewPager

我建议采用特殊行为，禁用屏幕外的查看寻呼机会对性能产生影响。