如何修复 NullPointerException 并将数据放入 NatTable

Question

当我尝试使用这段代码时：

students.add(new Student("John","1", 3));
students.add(new Student("Chris","2", 2));
NatTable table = createTable(shell, students);
table.refresh();

出现 NullPointerException，可能是因为 Student class 中的 getter 有问题，或者生成 table。出现此问题时的消息之一也是 ReflectiveColumnPropertyAccessor.getDataValue。我还需要修复 NatTable 中的 ColumnGroup 以正确显示许多考试。

它给了我（我代码中的第 48 行是 Student Constructor）：

WARNING: java.lang.NullPointerException
java.lang.RuntimeException: java.lang.NullPointerException
    at net.sourceforge.nattable.data.ReflectiveColumnPropertyAccessor.getDataValue(ReflectiveColumnPropertyAccessor.java:48)
at net.sourceforge.nattable.data.ListDataProvider.getDataValue(ListDataProvider.java:36)
at net.sourceforge.nattable.layer.DataLayer.getDataValueByPosition(DataLayer.java:289)
at net.sourceforge.nattable.layer.AbstractLayerTransform.getDataValueByPosition(AbstractLayerTransform.java:319)
at net.sourceforge.nattable.layer.AbstractLayerTransform.getDataValueByPosition(AbstractLayerTransform.java:319)
at net.sourceforge.nattable.layer.AbstractLayerTransform.getDataValueByPosition(AbstractLayerTransform.java:319)
at net.sourceforge.nattable.layer.AbstractLayerTransform.getDataValueByPosition(AbstractLayerTransform.java:319)
at net.sourceforge.nattable.layer.AbstractLayerTransform.getDataValueByPosition(AbstractLayerTransform.java:319)
at net.sourceforge.nattable.layer.AbstractLayerTransform.getDataValueByPosition(AbstractLayerTransform.java:319)
at net.sourceforge.nattable.layer.AbstractLayerTransform.getDataValueByPosition(AbstractLayerTransform.java:319)
at net.sourceforge.nattable.layer.CompositeLayer.getDataValueByPosition(CompositeLayer.java:547)
at net.sourceforge.nattable.layer.cell.LayerCell.getDataValue(LayerCell.java:166)
at net.sourceforge.nattable.layer.cell.CellDisplayConversionUtils.convertDataType(CellDisplayConversionUtils.java:10)
at net.sourceforge.nattable.painter.cell.AbstractTextPainter.convertDataType(AbstractTextPainter.java:104)
at net.sourceforge.nattable.painter.cell.TextPainter.paintCell(TextPainter.java:96)
at net.sourceforge.nattable.painter.cell.CellPainterWrapper.paintCell(CellPainterWrapper.java:51)
at net.sourceforge.nattable.painter.cell.decorator.LineBorderDecorator.paintCell(LineBorderDecorator.java:64)
at net.sourceforge.nattable.painter.layer.CellLayerPainter.paintCell(CellLayerPainter.java:60)
at net.sourceforge.nattable.selection.SelectionLayerPainter.paintCell(SelectionLayerPainter.java:143)
at net.sourceforge.nattable.painter.layer.CellLayerPainter.paintLayer(CellLayerPainter.java:32)
at net.sourceforge.nattable.painter.layer.GridLineCellLayerPainter.paintLayer(GridLineCellLayerPainter.java:31)
at net.sourceforge.nattable.selection.SelectionLayerPainter.paintLayer(SelectionLayerPainter.java:34)
at net.sourceforge.nattable.layer.CompositeLayer$CompositeLayerPainter.paintLayer(CompositeLayer.java:898)
at net.sourceforge.nattable.painter.layer.NatLayerPainter.paintLayer(NatLayerPainter.java:26)
at net.sourceforge.nattable.NatTable.paintNatTable(NatTable.java:313)
at net.sourceforge.nattable.NatTable.paintControl(NatTable.java:309)
at org.eclipse.swt.widgets.TypedListener.handleEvent(Unknown Source)
at org.eclipse.swt.widgets.EventTable.sendEvent(Unknown Source)
at org.eclipse.swt.widgets.Display.sendEvent(Unknown Source)
at org.eclipse.swt.widgets.Widget.sendEvent(Unknown Source)
at org.eclipse.swt.widgets.Widget.sendEvent(Unknown Source)
at org.eclipse.swt.widgets.Widget.sendEvent(Unknown Source)
at org.eclipse.swt.widgets.Control.gtk_draw(Unknown Source)
at org.eclipse.swt.widgets.Composite.gtk_draw(Unknown Source)
at org.eclipse.swt.widgets.Canvas.gtk_draw(Unknown Source)
at org.eclipse.swt.widgets.Widget.windowProc(Unknown Source)
at org.eclipse.swt.widgets.Control.windowProc(Unknown Source)
at org.eclipse.swt.widgets.Display.windowProc(Unknown Source)
at org.eclipse.swt.internal.gtk.OS._gtk_main_do_event(Native Method)
at org.eclipse.swt.internal.gtk.OS.gtk_main_do_event(Unknown Source)
at org.eclipse.swt.widgets.Display.eventProc(Unknown Source)
at org.eclipse.swt.internal.gtk.OS._g_main_context_iteration(Native Method)
at org.eclipse.swt.internal.gtk.OS.g_main_context_iteration(Unknown Source)
at org.eclipse.swt.widgets.Display.readAndDispatch(Unknown Source)
at student.StudentMain.main(StudentMain.java:585)

我最初的 class 考试和学生。

public static class Student {
    private String name;
    private String groupNumber;
    private Exam[] exams;
    public Student() { }
    public Student(String name, String groupNumber, int numbOfExams) {
        this.name = name;
        this.groupNumber = groupNumber;
        this.exams = new Exam[numbOfExams];
        for(int i=0;i<numbOfExams;i++) {
            exams[i]= new Exam();
            this.exams[i].setName("");
            this.exams[i].setMark(0);
        }           
    }
    public String getName() {
        return name;
    }
    public String getGroupNumber() {
        return groupNumber;
    }
    public void setName(String name) {
        this.name = name;
    }
    public void setGroupNumber(String groupNumber) {
        this.groupNumber = groupNumber;
    }
    public void setExam(Exam[] exams) {
        this.exams = exams;
    }
    public Exam[] getExam() {
        return exams;
    }       
}
public static class Exam {
    private String name;
    private int mark;
    public Exam() { }
    public Exam(String name, int mark) {
        this.name = name;
        this.mark = mark;
    }
    public String getName() {
        return name;
    }
    public int getMark() {
        return mark;
    }    
    public void setName(String name) {
        this.name = name;
    }
    public void setMark(int mark) {
        this.mark = mark;
    }
}

我对NatTable的实现

public static NatTable createTable(final Shell shell, ArrayList<Student> students) {
    final ColumnGroupModel columnGroupModel = new ColumnGroupModel();
    ColumnHeaderLayer columnHeaderLayer;

    String[] propertyNames = { "name", "groupNumber", "examName", "examMark" };
    Map<String, String> propertyToLabelMap = new HashMap<String, String>();
    propertyToLabelMap.put("name", "Full Name");
    propertyToLabelMap.put("groupNumber", "Group");
    propertyToLabelMap.put("examName", "Name");
    propertyToLabelMap.put("examMark", "Mark");
    DefaultBodyDataProvider<Student> bodyDataProvider = new DefaultBodyDataProvider<Student>(students, propertyNames);
    ColumnGroupBodyLayerStack bodyLayer = new ColumnGroupBodyLayerStack(new DataLayer(bodyDataProvider), columnGroupModel);

    DefaultColumnHeaderDataProvider defaultColumnHeaderDataProvider = new DefaultColumnHeaderDataProvider(propertyNames, propertyToLabelMap);
    DefaultColumnHeaderDataLayer columnHeaderDataLayer = new DefaultColumnHeaderDataLayer(defaultColumnHeaderDataProvider);
    columnHeaderLayer = new ColumnHeaderLayer(columnHeaderDataLayer, bodyLayer, bodyLayer.getSelectionLayer());
    ColumnGroupHeaderLayer columnGroupHeaderLayer = new ColumnGroupHeaderLayer(columnHeaderLayer, bodyLayer.getSelectionLayer(), columnGroupModel);

    columnGroupHeaderLayer.addColumnsIndexesToGroup("Exams", 2, 3);
    columnGroupHeaderLayer.setGroupUnbreakable(2);

    final DefaultRowHeaderDataProvider rowHeaderDataProvider = new DefaultRowHeaderDataProvider(bodyDataProvider);
    DefaultRowHeaderDataLayer rowHeaderDataLayer = new DefaultRowHeaderDataLayer(rowHeaderDataProvider);
    ILayer rowHeaderLayer = new RowHeaderLayer(rowHeaderDataLayer, bodyLayer, bodyLayer.getSelectionLayer());

    final DefaultCornerDataProvider cornerDataProvider = new DefaultCornerDataProvider(defaultColumnHeaderDataProvider, rowHeaderDataProvider);
    DataLayer cornerDataLayer = new DataLayer(cornerDataProvider);
    ILayer cornerLayer = new CornerLayer(cornerDataLayer, rowHeaderLayer, columnGroupHeaderLayer);

    GridLayer gridLayer = new GridLayer(
            bodyLayer,
            columnGroupHeaderLayer,
            rowHeaderLayer,
            cornerLayer);

    NatTable table = new NatTable(shell, gridLayer, true);
    return table;
}

Answer 1

你的问题是你有嵌套的对象，你想通过反射来访问它们。那是行不通的！

如果您的 Student 只参加一次考试，您需要将 propertyNames 更改为：

String[] propertyNames = { "name", "groupNumber", "exam.name", "exam.mark" };

以及数据提供者的定义为：

IDataProvider bodyDataProvider =
            new ListDataProvider<>(
                    students,
                    new ExtendedReflectiveColumnPropertyAccessor<Student>(propertyNames));

但是您的 Student class 有一个 Exam 对象数组。你想如何在 table 中可视化这样的树结构？ NatTable 能够做到这一点，但是你需要更多的东西，比如 TreeLayer 等。而这反过来不适用于你的数据结构。

我建议先想想你想可视化什么，然后检查哪个控件适合你的需要（是 table 还是树？），然后检查一些确实存在的教程，喜欢 NatTable Getting Started Tutorial or the JFace Table tutorial or the JFace Tree tutorial

如何修复 NullPointerException 并将数据放入 NatTable

How do I fix NullPointerException and putting data into NatTable

java

nullpointerexception

swt

nattable