如何使用ObservableList在Javafx中创建折线图的BarChart

Posted 2021-03-28

我正在尝试使用Java从sql数据库中保存的数据生成统计图表（条形图和折线图）。数据预计会不时变化。

我尝试过使用ObservableLists但收到错误消息。

以下是我到目前为止所尝试的内容;注意：它驻留在DatabaseHandler类中

public ObservableList<BarChart.Data> getItemGraphStatistics(){
        ObservableList<BarChart.Data> data = FXCollections.observableArrayList();

        String sql = "SELECT itemID, COUNT(*) FROM (SELECT itemID FROM SALES UNION ALL SELECT itemID FROM STOCK) t GROUP BY itemID";
        System.out.println(sql );
        ResultSet rs = handler.execQuery(sql);
        try{

            while(rs.next()){
                String item= rs.getString("itemID");
                int count = rs.getInt(2);

                data.add(new BarChart.Data(item+ "(" + count + ")", count));

            }
        } catch (SQLException ex) {
            Logger.getLogger(DatabaseHandler.class.getName()).log(Level.SEVERE, null, ex);
        }
        return data;

    }

在运行上面的我得到

java.lang.ClassCastException: javafx.scene.chart.XYChart$Data cannot be cast to javafx.scene.chart.XYChart$Series

当我尝试将BarChart.Data更改为BarChart.Series时，我无法将int转换为observableList错误消息。

以下是上述试验的一个例子;

import com.jfoenix.controls.JFXButton;
import com.jfoenix.controls.JFXRadioButton;
import com.jfoenix.controls.JFXTextField;
import java.net.URL;
import java.util.Calendar;
import java.util.Dictionary;
import java.util.Hashtable;
import java.util.ResourceBundle;
import java.util.concurrent.TimeUnit;
import javafx.event.ActionEvent;
import javafx.event.Event;
import javafx.fxml.FXML;
import javafx.fxml.Initializable;
import javafx.scene.chart.BarChart;
import javafx.scene.chart.CategoryAxis;
import javafx.scene.chart.LineChart;
import javafx.scene.chart.NumberAxis;
import javafx.scene.chart.PieChart;
import javafx.scene.control.ChoiceBox;
import javafx.scene.control.DatePicker;
import javafx.scene.control.ToggleGroup;
import javafx.scene.input.MouseEvent;
import javafx.scene.layout.AnchorPane;
import javafx.scene.layout.HBox;
import sales.manager.database.DatabaseHandler;

/**
 * FXML Controller class
 *
 * @author Garande
 */
public class PerformanceAnalyzerController implements Initializable {

    @FXML
    private AnchorPane analysisHandler;
    @FXML
    private AnchorPane graphHandler;
    @FXML
    private PieChart piechart;
    @FXML
    private BarChart<?, ?> barchart;
    @FXML
    private LineChart<?, ?> linechart;

    @FXML
    private NumberAxis yBarGraph;
    @FXML
    private CategoryAxis xBarGraph;
    @FXML
    private NumberAxis yLineGraph;
    @FXML
    private CategoryAxis xLineGraph;

    DatabaseHandler handler = DatabaseHandler.getInstance();

    /**
     * Initializes the controller class.
     */
    @Override
    public void initialize(URL url, ResourceBundle rb) {


    }    

    @FXML
    private void performAnalysisOperation(ActionEvent event) {
        //Performing analysis operation

        barchart.setData(handler.getItemGraphStatistics());
        graphHandler.getChildren().add(barchart);
    }
}

答案

data的XYChart属性持有ObservableList<XYChart.Series>。每个XYChart.Series也有data属性，但它持有ObservableList<XYChart.Data>。问题是你的方法返回一个ObservableList<XYChart.Data>然后你尝试在XYChart.data上设置 - 类型不匹配。我不确定你是如何获得ClassCastException的，因为你的代码甚至不应该编译。

您需要将数据列表包装在一个系列中，然后将该系列添加到图表中。你也应该avoid using raw types。 Series和Data都有类型参数，但您没有指定它们。根据您构建Data的方式，您的代码应该类似于（为简洁起见，省略了一些代码）：

public class PerformanceAnalyzerController {

    @FXML private BarChart<String, Number> barChart;

    @FXML
    private void performAnalysisOperation(ActionEvent event) {
        //Performing analysis operation

        ObservableList<XYChart.Data<String, Number>> data = handler.getItemsGraphicsStatisitics();
        XYChart.Series<String, Number> series = new XYChart.Series<>("Series Name", data);

        barchart.getData().setAll(series);
        graphHandler.getChildren().add(barchart);
    }

}

和：

// Use generic types
public ObservableList<XYChart.Data<String, Number>> getItemGraphStatistics(){
    ObservableList<XYChart.Data<String, Number>> data = FXCollections.observableArrayList();

    String sql = "SELECT itemID, COUNT(*) FROM (SELECT itemID FROM SALES UNION ALL SELECT itemID FROM STOCK) t GROUP BY itemID";
    System.out.println(sql );
    ResultSet rs = handler.execQuery(sql);
    try{

        while(rs.next()){
            String item= rs.getString("itemID");
            int count = rs.getInt(2);

            // add diamond operator "<>"
            data.add(new XYChart.Data<>(item+ "(" + count + ")", count));

        }
    } catch (SQLException ex) {
        Logger.getLogger(DatabaseHandler.class.getName()).log(Level.SEVERE, null, ex);
    }
    return data;

}

注意：我用BarChart.Data替换了XYChart.Data的用法，但在这种情况下我不认为这很重要。