Java，Vaadin 8，延迟加载网格

问题描述

我正在尝试在Vaadin 8中使用Grid进行延迟加载.但是它仅显示一个空表.我做错了什么?另外，如何将要加载(限制)的项目数设置为例如20个项目(默认为40个项目)?

I am trying to implement lazy loading with Grid in Vaadin 8. But it only shows an empty table. What do I do wrong? Also, how do I set the number of items to load (limit) to for example 20 items (the default is 40 items)?

private Grid<Image> makeLazyTable()
{
  Grid<Image> grid = new Grid<Image>();
  DataProvider<Image, Void> dataProvider = DataProvider.fromCallbacks(
    query -> {
      int offset = query.getOffset();
      int limit = query.getLimit();
      OffsetRequest request = new OffsetRequest();
      request.setLimit(limit);
      request.setOffset(offset);
      List<QuerySortOrder> sort = query.getSortOrders();
      return ImagesRepository.findAll(request, sort);
    },
    query -> ImagesRepository.getImageCount()
  );
  grid.setDataProvider(dataProvider);
  return grid;
}

推荐答案

我没有添加任何列.这就是表格为空的原因.这样工作:

I did not add any columns. That was the reason why the table was empty.This way it works:

Column<Image, String> filenameColumn = grid.addColumn(Image::getFilename);
Column<Image, String> orientationColumn = grid.addColumn(Image::getOrientation);
Column<Image, String> latitudeColumn = grid.addColumn(Image::getLatitude);
Column<Image, String> longitudeColumn = grid.addColumn(Image::getLongitude);

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