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This article mainly shows you the "sample analysis of Qt database and Chart historical data display in CAccord Craft +", which is easy to understand and well-organized. I hope it can help you solve your doubts. Here, let the editor lead you to study and study the "sample analysis of Qt database and Chart historical data display in CAccord +".

In the previous blog article specifically introduced how the QChart component draws a variety of general two-dimensional graphics, this chapter will continue to extend a new knowledge point, through the database to store the trend of node data for a certain period of time, when users submit query records through the edit box, the program automatically filters out all the data under the time node, and dynamically draws the data into the graphics component to achieve the function of dynamic query graphics.

First, create a Times table with the following code, which records the values under a certain time node of a host:

# include # include / / initialize the database / / https://www.cnblogs.com/lysharkvoid InitSql () {QSqlDatabase db = QSqlDatabase::addDatabase ("QSQLITE"); db.setDatabaseName ("lyshark.db"); if (! db.open ()) {std::cout setMinorTickCount (5); / / set the X axis scale QValueAxis * axisY = new QValueAxis / / Y axis axisY- > setRange (0100); / / Y axis range axisY- > setMinorTickCount (4); / / s set Y axis scale / / set X to Y axis data set chart- > setAxisX (axisX, series0); / / set axis chart- > setAxisY (axisY, series0) for sequence } / / generate data for sequence void MainWindow::SetData () {/ / get pointer QLineSeries * series0= (QLineSeries *) ui- > graphicsView- > chart ()-> series () .at (0); / / clear legend series0- > clear (); / / Link database QSqlDatabase db = QSqlDatabase::addDatabase ("QSQLITE"); db.setDatabaseName ("lyshark.db"); if (! db.open ()) {return } / / query the data QSqlQuery query ("SELECT * FROM Times;", db); QSqlRecord rec = query.record (); / / assign the data qreal tweets / / cycle through all records while (query.next ()) {/ / determine whether the current record is valid / / https://www.cnblogs.com/lyshark if (query.isValid ()) {QString address_value = query.value (rec.indexOf ("address"). ToString (); QString date_time = query.value (rec.indexOf ("datetime")). ToString () Int this_value = query.value (rec.indexOf ("value")) .toInt (); / / get the component string QString start_user_time = ui- > dateTimeEdit_Start- > text (); QString end_user_time = ui- > dateTimeEdit_End- > text () / / convert the time string to seconds and calculate the difference (in seconds) QDateTime start_timet = QDateTime::fromString (start_user_time, "yyyy-MM-dd hh:mm:ss"); QDateTime end_timet = QDateTime::fromString (end_user_time, "yyyy-MM-dd hh:mm:ss"); uint stime = start_timet.toTime_t () Uint etime = end_timet.toTime_t (); / / only records less than 180 seconds can be queried uint sub_time = etime-stime; if (sub_time = start_user_time.toStdString () & & date_time.toStdString () setDateTime (curDateTime); / / set time format ui- > dateTimeEdit_Start- > setDisplayFormat ("yyyy-MM-dd hh:mm:ss") Ui- > dateTimeEdit_End- > setDisplayFormat ("yyyy-MM-dd hh:mm:ss");} MainWindow::~MainWindow () {delete ui;} void MainWindow::on_pushButton_clicked () {SetData ();}

The query results are as follows:

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