Question

我想在Vaadin Grid组件上设置所选行（在Multiselect模式下）作为第一个显示的行，即按所选行的顺序。

有人知道这是否可能？

Answer 1

有可能。我在这里提出一个有四点需要注意的解决方案。可能会有更优雅的解决方案。

需要一个可以检查项目
比较者需要考虑排序顺序
排序是基于列的
无论如何都需要使用默认的排序方法/比较器对未选择的行进行排序，也可能选择其他所选行。

积分1＆amp;通过创建同时实现Comparator

的SortEvent.SortListener来满足2

@RequiredArgsConstructor
// above is a lombok annotation to generate constructor
// SelectedFirstComparator(grid, defaultComparator);
public class SelectedFirstComparator<T>
        implements SerializableComparator<T>, SortListener<GridSortOrder<T>> {
    private final Grid<T> grid; // used to dig selected rows
    // defaultComparator is used when selection status is not taken 
    // account to handle rest of sorting, related to point 4   
    private final SerializableComparator<T> defaultComparator; 
    // sortOrder is used to inverse the sorting order between
    // selected & not selected items
    // if not used selected items will change between first & last rows 
    // and we need them always first 
    private int sortOrder = 1; 
    @Override
    public int compare(T o1, T o2) {
        boolean o1Selected = grid.getSelectedItems().contains(o1);
        boolean o2Selected = grid.getSelectedItems().contains(o2);
        // if one is selected and one is not the selected one "wins"
        if(o1Selected && !o2Selected) return 1 * sortOrder;
        if(!o1Selected && o2Selected) return -1 * sortOrder;
        // if both are selected arrange amongst first rows
        // with default comparator
        // if both are not-selected arrange them to natural order
        // with default comparator
        return defaultComparator.compare(o1, o2);
    }

    // This method is listening the sort order change
    // and updating the sortOrder to keep selected rows as firts 
    @Override
    public void sort(SortEvent<GridSortOrder<T>> event) {
        switch(event.getSortOrder().get(0).getDirection()) {
        case ASCENDING:
            sortOrder = -1;
            break;
        case DESCENDING:
            sortOrder = 1;
            break;
        }
    }
}

第3点

您需要为每个可排序列添加SelectedFirstComparator的实例作为比较器，例如

col1.setComparator(col1Comparator);
col2.setComparator(col2Comparator);
...

对于每个colXcomparator，您需要在构造时提供相应的默认比较器处理列默认排序。如果col1的类型为String，则类似于

SelectedFirstComparator<GridEntity> col1Comparator = 
    new SelectedFirstComparator<GridEntity>( grid, (e11, e12) -> {
        return e11.getName().compareTo(e12.getName());
    }
);

第4点

要使比较器或监视器排序顺序和sort()方法更新sortOrder，您需要将所有比较器注册为网格SortListener

grid.addSortListener(col1Comparator);
grid.addSortListener(col2Comparator);
...

如何订购选择行的网格始终作为网格的第一行/最顶行？

1 个答案: