如何在 Vaadin 中实现延迟加载树？

Question

我在数据库中有一个相当大的树，加载所有项目并将它们添加到 HierarchicalContainer 在启动时表现不佳。
相反，我想在单击时加载树项的子项。
其实早一点，因为我不想 areChildrenAllowed() 或 hasChildren() 到 return 错误的值。

我希望在 JFace 中找到类似的东西 TreeViewer is used ITreeContentProvider。

是否有关于此主题的任何示例或最佳实践描述？

这是我目前得到的：

public class OutputNodeContainer extends HierarchicalContainer {

    /** the view service */
    private IViewService service = CommonPlugin.getService(IViewService.class);

    private List<Object> childrenRead = new ArrayList<>();

    @Override
    public boolean areChildrenAllowed(Object itemId) {
        if (!childrenRead.contains(itemId)) {
            OutputNode node = (OutputNode) itemId;
            List<OutputNode> children = service.getChildren(node.getNodeId(), false);
            for (OutputNode child : children) {
                addItem(child);
                setParent(child, itemId);
            }
            childrenRead.add(itemId);
            return !children.isEmpty();
        }
        return super.areChildrenAllowed(itemId);
    }
}

但是在 addItem(child); 我运行进入这个异常：

java.lang.IllegalStateException: A connector should not be marked as dirty while a response is being written.
        at com.vaadin.ui.ConnectorTracker.markDirty(ConnectorTracker.java:489)
        at com.vaadin.server.AbstractClientConnector.markAsDirty(AbstractClientConnector.java:143)
        at com.vaadin.ui.Tree.markAsDirty(Tree.java:348)
        at com.vaadin.ui.AbstractSelect.fireItemSetChange(AbstractSelect.java:1746)
        at com.vaadin.ui.AbstractSelect.containerItemSetChange(AbstractSelect.java:1713)
        at com.vaadin.ui.Tree.containerItemSetChange(Tree.java:992)
        at com.vaadin.data.util.AbstractContainer.fireItemSetChange(AbstractContainer.java:246)
        at com.vaadin.data.util.HierarchicalContainer.fireItemSetChange(HierarchicalContainer.java:436)
        at com.vaadin.data.util.IndexedContainer.fireItemSetChange(IndexedContainer.java:640)
        at com.vaadin.data.util.HierarchicalContainer.enableAndFireContentsChangeEvents(HierarchicalContainer.java:460)
        at com.vaadin.data.util.HierarchicalContainer.addItem(HierarchicalContainer.java:489)
        at ch.scodi.vaadin.viewer.OutputNodeContainer.areChildrenAllowed(OutputNodeContainer.java:78)
        at com.vaadin.ui.Tree.areChildrenAllowed(Tree.java:864)
        at com.vaadin.ui.Tree.paintContent(Tree.java:732)
        at com.vaadin.server.LegacyPaint.paint(LegacyPaint.java:65)
        at com.vaadin.server.communication.LegacyUidlWriter.write(LegacyUidlWriter.java:82)
        at com.vaadin.server.communication.UidlWriter.write(UidlWriter.java:143)
        at com.vaadin.server.communication.UIInitHandler.getInitialUidl(UIInitHandler.java:284)
        at com.vaadin.server.communication.UIInitHandler.synchronizedHandleRequest(UIInitHandler.java:80)
        at com.vaadin.server.SynchronizedRequestHandler.handleRequest(SynchronizedRequestHandler.java:41)
        at com.vaadin.server.VaadinService.handleRequest(VaadinService.java:1422)
        ... 63 common frames omitted

Answer 1

尽管在 Vaadin 文档中说 Tree 的延迟加载是 not supported，但我设法实现了以下 延迟加载 Hierarchical接口。

将所有元素存储在本地结构中非常重要（在我的例子中是 HashMap hierarchy），不要多次读取元素这是行不通的。我认为是因为 Vaadin 不使用 equals() 和 hashCode().

import java.util.Collection;
import java.util.Collections;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

import com.softmodeler.common.CommonPlugin;
import com.softmodeler.model.OutputNode;
import com.softmodeler.service.IViewService;
import com.vaadin.data.Container.Hierarchical;
import com.vaadin.data.Item;
import com.vaadin.data.Property;
import com.vaadin.data.util.BeanItem;

/**
 * @author Flavio Donzé
 * @version 1.0
 */
public class OutputNodeHierachical implements Hierarchical {
    private static final long serialVersionUID = 8289589835030184018L;

    /** the view service */
    private IViewService service = CommonPlugin.getService(IViewService.class);

    /** collection of all root nodes */
    private List<OutputNode> rootNodes = null;
    /** parent=>children mapping */
    private Map<OutputNode, List<OutputNode>> hierarchy = new HashMap<>();

    /**
     * constructor
     *
     * @param rootNodes collection of all root nodes
     */
    public OutputNodeHierachical(List<OutputNode> rootNodes) {
        this.rootNodes = Collections.unmodifiableList(rootNodes);

        addToHierarchy(rootNodes);
    }

    @Override
    public Collection<?> getChildren(Object itemId) {
        try {
            List<OutputNode> children = hierarchy.get(itemId);
            if (children == null) {
                OutputNode node = (OutputNode) itemId;
                children = service.getChildren(node.getNodeId(), false);

                hierarchy.put(node, children);

                // add children to hierarchy, their children will be added on click
                addToHierarchy(children);
            }
            return children;
        } catch (Exception e) {
            VaadinUtil.handleException(e);
        }
        return null;
    }

    /**
     * add each element to the hierarchy without their children hierarchy(child=>null)
     *
     * @param children elements to add
     */
    private void addToHierarchy(List<OutputNode> children) {
        for (OutputNode child : children) {
            hierarchy.put(child, null);
        }
    }

    @Override
    public boolean areChildrenAllowed(Object itemId) {
        return !((OutputNode) itemId).getChilds().isEmpty();
    }

    @Override
    public boolean hasChildren(Object itemId) {
        return !((OutputNode) itemId).getChilds().isEmpty();
    }

    @Override
    public Object getParent(Object itemId) {
        String parentId = ((OutputNode) itemId).getParentId();
        for (OutputNode node : hierarchy.keySet()) {
            if (node.getNodeId().equals(parentId)) {
                return node;
            }
        }
        return null;
    }

    @Override
    public Collection<?> rootItemIds() {
        return rootNodes;
    }

    @Override
    public boolean isRoot(Object itemId) {
        return rootNodes.contains(itemId);
    }

    @Override
    public Item getItem(Object itemId) {
        return new BeanItem<OutputNode>((OutputNode) itemId);
    }

    @Override
    public boolean containsId(Object itemId) {
        return hierarchy.containsKey(itemId);
    }

    @Override
    public Collection<?> getItemIds() {
        return hierarchy.keySet();
    }

    @Override
    public int size() {
        return hierarchy.size();
    }

    @Override
    public boolean setParent(Object itemId, Object newParentId) throws UnsupportedOperationException {
        throw new UnsupportedOperationException();
    }

    @Override
    public boolean setChildrenAllowed(Object itemId, boolean areChildrenAllowed) throws UnsupportedOperationException {
        throw new UnsupportedOperationException();
    }

    @Override
    public Item addItem(Object itemId) throws UnsupportedOperationException {
        throw new UnsupportedOperationException();
    }

    @Override
    public Object addItem() throws UnsupportedOperationException {
        throw new UnsupportedOperationException();
    }

    @Override
    public boolean removeItem(Object itemId) throws UnsupportedOperationException {
        throw new UnsupportedOperationException();
    }

    @Override
    public boolean removeAllItems() throws UnsupportedOperationException {
        throw new UnsupportedOperationException();
    }

    @Override
    public Class<?> getType(Object propertyId) {
        throw new UnsupportedOperationException();
    }

    @Override
    public Collection<?> getContainerPropertyIds() {
        throw new UnsupportedOperationException();
    }

    @Override
    public Property<?> getContainerProperty(Object itemId, Object propertyId) {
        throw new UnsupportedOperationException();
    }

    @Override
    public boolean addContainerProperty(Object propertyId, Class<?> type, Object defaultValue) throws UnsupportedOperationException {
        throw new UnsupportedOperationException();
    }

    @Override
    public boolean removeContainerProperty(Object propertyId) throws UnsupportedOperationException {
        throw new UnsupportedOperationException();
    }

}

像这样将容器添加到 Tree：

OutputNodeHierachical dataSource = new OutputNodeHierachical(rootNodes);

Tree mainTree = new Tree();
mainTree.setSizeFull();
mainTree.setContainerDataSource(dataSource);
mainTree.addItemClickListener(new ItemClickListener() {
    private static final long serialVersionUID = -413371711541672605L;

    @Override
    public void itemClick(ItemClickEvent event) {
        OutputNode node = (OutputNode) event.getItemId();
        openObject(node.getObjectId());
    }
});

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