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.ui; import java.util.Collection; import java.util.Objects; import com.vaadin.data.HasDataProvider; import com.vaadin.data.provider.DataProvider; import com.vaadin.event.FieldEvents.BlurEvent; import com.vaadin.event.FieldEvents.BlurListener; import com.vaadin.event.FieldEvents.BlurNotifier; import com.vaadin.event.FieldEvents.FocusAndBlurServerRpcDecorator; import com.vaadin.event.FieldEvents.FocusEvent; import com.vaadin.event.FieldEvents.FocusListener; import com.vaadin.event.FieldEvents.FocusNotifier; import com.vaadin.shared.Registration; import com.vaadin.shared.data.DataCommunicatorConstants; import com.vaadin.shared.ui.nativeselect.NativeSelectState; /** * A simple drop-down select component. Represented on the client side by a * "native" HTML {@code <select>} element. Lacks advanced features such as lazy * loading, filtering, and adding new items. * * @author Vaadin Ltd. * * @param <T> * the data item type * * @see com.vaadin.ui.ComboBox */ public class NativeSelect<T> extends AbstractSingleSelect<T> implements FocusNotifier, BlurNotifier, HasDataProvider<T> { /** * Creates a new {@code NativeSelect} with an empty caption and no items. */ public NativeSelect() { registerRpc(new FocusAndBlurServerRpcDecorator(this, this::fireEvent)); addDataGenerator((item, json) -> { String caption = getItemCaptionGenerator().apply(item); if (caption == null) { caption = ""; } json.put(DataCommunicatorConstants.DATA, caption); }); setItemCaptionGenerator(String::valueOf); } /** * Creates a new {@code NativeSelect} with the given caption and no items. * * @param caption * the component caption to set, null for no caption */ public NativeSelect(String caption) { this(); setCaption(caption); } /** * Creates a new {@code NativeSelect} with the given caption, containing the * data items in the given collection. * * @param caption * the component caption to set, null for no caption * @param items * the data items to use, not null */ public NativeSelect(String caption, Collection<T> items) { this(caption); setItems(items); } /** * Creates a new {@code NativeSelect} with the given caption, using the * given {@code DataProvider} as the source of data items. * * @param caption * the component caption to set, null for no caption * @param dataProvider * the source of data items to use, not null */ public NativeSelect(String caption, DataProvider<T, ?> dataProvider) { this(caption); setDataProvider(dataProvider); } @Override public Registration addFocusListener(FocusListener listener) { return addListener(FocusEvent.EVENT_ID, FocusEvent.class, listener, FocusListener.focusMethod); } @Override public Registration addBlurListener(BlurListener listener) { return addListener(BlurEvent.EVENT_ID, BlurEvent.class, listener, BlurListener.blurMethod); } @Override protected NativeSelectState getState() { return getState(true); } @Override protected NativeSelectState getState(boolean markAsDirty) { return (NativeSelectState) super.getState(markAsDirty); } @Override public DataProvider<T, ?> getDataProvider() { return internalGetDataProvider(); } @Override public void setDataProvider(DataProvider<T, ?> dataProvider) { internalSetDataProvider(dataProvider); } @Override public void setItemCaptionGenerator(ItemCaptionGenerator<T> itemCaptionGenerator) { super.setItemCaptionGenerator(itemCaptionGenerator); } @Override public ItemCaptionGenerator<T> getItemCaptionGenerator() { return super.getItemCaptionGenerator(); } /** * Returns whether the user is allowed to select nothing in the combo box. * * @return true if empty selection is allowed, false otherwise * @since 8.0 */ public boolean isEmptySelectionAllowed() { return getState(false).emptySelectionAllowed; } /** * Sets whether the user is allowed to select nothing in the combo box. When * true, a special empty item is shown to the user. * * @param emptySelectionAllowed * true to allow not selecting anything, false to require * selection * @since 8.0 */ public void setEmptySelectionAllowed(boolean emptySelectionAllowed) { getState().emptySelectionAllowed = emptySelectionAllowed; } /** * Returns the empty selection caption. * <p> * The empty string {@code ""} is the default empty selection caption. * * @see #setEmptySelectionAllowed(boolean) * @see #isEmptySelectionAllowed() * @see #setEmptySelectionCaption(String) * @see #isSelected(Object) * * @return the empty selection caption, not {@code null} * @since 8.0 */ public String getEmptySelectionCaption() { return getState(false).emptySelectionCaption; } /** * Sets the empty selection caption. * <p> * The empty string {@code ""} is the default empty selection caption. * <p> * If empty selection is allowed via the * {@link #setEmptySelectionAllowed(boolean)} method (it is by default) then * the empty item will be shown with the given caption. * * @param caption * the caption to set, not {@code null} * @see #isSelected(Object) * @since 8.0 */ public void setEmptySelectionCaption(String caption) { Objects.nonNull(caption); getState().emptySelectionCaption = caption; } /** * Sets the number of items that are visible. If only one item is visible, * then the box will be displayed as a drop-down list (the default). * * @since 8.1 * @param visibleItemCount * the visible item count * @throws IllegalArgumentException * if the value is smaller than one */ public void setVisibleItemCount(int visibleItemCount) { if (visibleItemCount < 1) { throw new IllegalArgumentException("There must be at least one item visible"); } getState().visibleItemCount = visibleItemCount; } /** * Gets the number of items that are visible. If only one item is visible, * then the box will be displayed as a drop-down list. * * @since 8.1 * @return the visible item count */ public int getVisibleItemCount() { return getState(false).visibleItemCount; } }