如何修复NullPointerException并将数据放入NatTable [英] How do I fix NullPointerException and putting data into NatTable
本文介绍了如何修复NullPointerException并将数据放入NatTable的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！
问题描述
当我尝试使用这段代码时:
When I try to use this piece of code:
students.add(new Student("John","1", 3));
students.add(new Student("Chris","2", 2));
NatTable table = createTable(shell, students);
table.refresh();
NullPointerException出现，可能是因为Student类中的getter出错或生成了表.出现此问题时，消息之一也是ReflectiveColumnPropertyAccessor.getDataValue.另外，我需要修复NatTable中的ColumnGroup才能正确显示许多检查.
NullPointerException appears, maybe it is because something is wrong with getters in Student class or maybe in generating the table. Also one of the messages when this problem appears is ReflectiveColumnPropertyAccessor.getDataValue. Also I need to fix ColumnGroup in NatTable to display many exams properly.
它给了我(我的代码中的第48行是学生构造函数):
It gives me (the line 48 in my code is the 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)
我的考试和学生的初始课程.
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的认识
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;
}
推荐答案
您的问题是您有嵌套对象，并且想通过反射访问它们.那是行不通的！
Your problem is that you have nested objects and you want to access them via reflection. That is not working!
如果您的Student仅进行一次考试，则需要将propertyNames更改为此:
If your Student would only have one exam, you would need to change the propertyNames to this:
String[] propertyNames = { "name", "groupNumber", "exam.name", "exam.mark" };
以及数据提供者的定义:
and the definition of the data provider to this:
IDataProvider bodyDataProvider =
new ListDataProvider<>(
students,
new ExtendedReflectiveColumnPropertyAccessor<Student>(propertyNames));
但是您的Student类具有一个Exam对象的数组.您想如何在表格中可视化这种树形结构? NatTable可以做到这一点，但随后您需要更多的东西，例如TreeLayer等.这又不适用于您的数据结构.
But your Student class has an array of Exam objects. How do you want to visualize such a tree structure in a table? NatTable is able to do this, but then you need some more things like the TreeLayer etc. And that in turn does not work with your data structure.
我建议先考虑一下要可视化的内容，然后检查哪个控件适合您的需求(它是表格还是树?)，然后检查一些确实存在的教程，例如 NatTable入门教程或 JFace Tree教程
I would suggest to first think about what you want to visualize, then check which control fits your needs (is it a table or a tree?), and then check for some tutorials that definitely exist, like the NatTable Getting Started Tutorial or the JFace Table tutorial or the JFace Tree tutorial
这篇关于如何修复NullPointerException并将数据放入NatTable的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！
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