Java tutorial
/* * Copyright 2000-2018 Vaadin Ltd. * * Licensed under the Apache License, Version 2.0 (the "License"); you may not * use this file except in compliance with the License. You may obtain a copy of * the License at * * http://www.apache.org/licenses/LICENSE-2.0 * * Unless required by applicable law or agreed to in writing, software * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the * License for the specific language governing permissions and limitations under * the License. */ package com.vaadin.client.renderers; import com.google.gwt.dom.client.TableCellElement; import com.google.gwt.user.client.ui.Widget; import com.vaadin.client.WidgetUtil; import com.vaadin.client.widget.grid.RendererCellReference; /** * A renderer for rendering widgets into cells. * * @since 7.4 * @author Vaadin Ltd * @param <T> * the row data type * @param <W> * the Widget type */ public abstract class WidgetRenderer<T, W extends Widget> extends ComplexRenderer<T> { @Override public void init(RendererCellReference cell) { // Implement if needed } /** * Creates a widget to attach to a cell. The widgets will be attached to the * cell after the cell element has been attached to DOM. * * @return widget to attach to a cell. All returned instances should be new * widget instances without a parent. */ public abstract W createWidget(); @Override public void render(RendererCellReference cell, T data) { W w = getWidget(cell.getElement()); assert w != null : "Widget not found in cell (" + cell.getColumn() + "," + cell.getRow() + ")"; render(cell, data, w); } /** * Renders a cell with a widget. This provides a way to update any * information in the widget that is cell specific. Do not detach the Widget * here, it will be done automatically by the Grid when the widget is no * longer needed. * <p> * For optimal performance, work done in this method should be kept to a * minimum since it will be called continuously while the user is scrolling. * The renderer can use {@link Widget#setLayoutData(Object)} to store cell * data that might be needed in e.g. event listeners. * * @param cell * The cell to render. Note that the cell is a flyweight and * should not be stored and used outside of this method as its * contents will change. * @param data * the data of the cell * @param widget * the widget embedded in the cell */ public abstract void render(RendererCellReference cell, T data, W widget); /** * Returns the widget contained inside the given cell element. Cannot be * called for cells that do not contain a widget. * * @param e * the element inside which to find a widget * @return the widget inside the element */ protected W getWidget(TableCellElement e) { W w = getWidget(e, null); assert w != null : "Widget not found inside cell"; return w; } /** * Returns the widget contained inside the given cell element, or null if it * is not an instance of the given class. Cannot be called for cells that do * not contain a widget. * * @param e * the element inside to find a widget * @param klass * the type of the widget to find * @return the widget inside the element, or null if its type does not match */ protected static <W extends Widget> W getWidget(TableCellElement e, Class<W> klass) { W w = WidgetUtil.findWidget(e.getFirstChildElement(), klass); assert w == null || w.getElement() == e.getFirstChildElement() : "Widget not found inside cell"; return w; } }