java - 为什么PageableListView没有模型或列表就没有构造函数

在我的应用程序中，我需要将pageableListView与propertyListView结合使用。我只是想知道为什么pageableListView没有模型或列表就没有构造函数。我只是创建一个新类，该类扩展了propertyListView，并具有带有pageableListView的主体和一个仅具有string = id和行数的附加构造函数。现在它看起来不错，并且也可以工作。我是否错过了某些有时不起作用的东西？

package org.toursys.web.components;

import java.util.List;

import org.apache.wicket.markup.html.list.ListView;
import org.apache.wicket.markup.html.list.PropertyListView;
import org.apache.wicket.model.IModel;

public abstract class PropertyPageableListView<T> extends PropertyListView<T> implements IPageableItems {
    private static final long serialVersionUID = 1L;

    /** The page to show. */
    private int currentPage;

    /** Number of rows per page of the list view. */
    private int itemsPerPage;

    /**
     * Constructor
     *
     * @param id
     *            See Component
     * @param model
     *            See Component
     * @param itemsPerPage
     *            Number of rows to show on a page
     */
    public PropertyPageableListView(final String id, int itemsPerPage) {
        super(id);
        this.itemsPerPage = itemsPerPage;
    }

    /**
     * Constructor
     *
     * @param id
     *            See Component
     * @param model
     *            See Component
     * @param itemsPerPage
     *            Number of rows to show on a page
     */
    public PropertyPageableListView(final String id, final IModel<? extends List<? extends T>> model, int itemsPerPage) {
        super(id, model);
        this.itemsPerPage = itemsPerPage;
    }

    /**
     * Creates a pageable list view having the given number of rows per page that uses the provided object as a simple
     * model.
     *
     * @param id
     *            See Component
     * @param list
     *            See Component
     * @param itemsPerPage
     *            Number of rows to show on a page
     * @see ListView#ListView(String, List)
     */
    public PropertyPageableListView(final String id, final List<? extends T> list, final int itemsPerPage) {
        super(id, list);
        this.itemsPerPage = itemsPerPage;
    }

    /**
     * Gets the index of the current page being displayed by this list view.
     *
     * @return Returns the currentPage.
     */
    public final int getCurrentPage() {
        // If first cell is out of range, bring page back into range
        while ((currentPage > 0) && ((currentPage * itemsPerPage) >= getItemCount())) {
            currentPage--;
        }

        return currentPage;
    }

    /**
     * Gets the number of pages in this list view.
     *
     * @return The number of pages in this list view
     */
    public final int getPageCount() {
        return ((getItemCount() + itemsPerPage) - 1) / itemsPerPage;
    }

    /**
     * Gets the maximum number of rows on each page.
     *
     * @return the maximum number of rows on each page.
     */
    public final int getItemsPerPage() {
        return itemsPerPage;
    }

    /**
     * Sets the maximum number of rows on each page.
     *
     * @param itemsPerPage
     *            the maximum number of rows on each page.
     */
    public final void setItemsPerPage(int itemsPerPage) {
        if (itemsPerPage < 0) {
            itemsPerPage = 0;
        }

        addStateChange();
        this.itemsPerPage = itemsPerPage;
    }

    /**
     * @return offset of first item
     */
    public int getFirstItemOffset() {
        return getCurrentPage() * getItemsPerPage();
    }

    /**
     * @see org.apache.wicket.markup.html.navigation.paging.IPageableItems#getItemCount()
     */
    public int getItemCount() {
        return getList().size();
    }

    /**
     * @see org.apache.wicket.markup.html.list.ListView#getViewSize()
     */
    @Override
    public int getViewSize() {
        if (getDefaultModelObject() != null) {
            super.setStartIndex(getFirstItemOffset());
            super.setViewSize(getItemsPerPage());
        }

        return super.getViewSize();
    }

    /**
     * Sets the current page that this list view should show.
     *
     * @param currentPage
     *            The currentPage to set.
     */
    public final void setCurrentPage(int currentPage) {
        if (currentPage < 0) {
            currentPage = 0;
        }

        int pageCount = getPageCount();
        if ((currentPage > 0) && (currentPage >= pageCount)) {
            currentPage = pageCount - 1;
        }

        addStateChange();
        this.currentPage = currentPage;
    }

    /**
     * Prevent users from accidentally using it.
     *
     * @see org.apache.wicket.markup.html.list.ListView#setStartIndex(int)
     * @throws UnsupportedOperationException
     *             always
     */
    @Override
    public ListView<T> setStartIndex(int startIndex) throws UnsupportedOperationException {
        throw new UnsupportedOperationException("You must not use setStartIndex() with PageableListView");
    }

    /**
     * Prevent users from accidentally using it.
     *
     * @param size
     *            the view size
     * @return This
     * @throws UnsupportedOperationException
     *             always
     * @see org.apache.wicket.markup.html.list.ListView#setStartIndex(int)
     */
    @Override
    public ListView<T> setViewSize(int size) throws UnsupportedOperationException {
        throw new UnsupportedOperationException("You must not use setViewSize() with PageableListView");
    }

}

最佳答案

扩展PageableListView并仅添加一种方法使其像PropertyListView那样工作会更容易：

/**
 * Wraps a ListItemModel in a CompoundPropertyModel.
 *
 * @param model
 * @param index
 * @return a CompoundPropertyModel wrapping a ListItemModel
 */
@Override
protected IModel<T> getListItemModel(final IModel<? extends List<T>> model, final int index)
{
    return new CompoundPropertyModel<T>(super.getListItemModel(model, index));
}

您也可以为其他构造函数提交RFE。