GWT 有 <label> 小部件吗？

Question

我必须向 GWT 中实现的一小部分 AJAX 功能添加一个表单。在 HTML 术语中，我想

<label for="personName">Name:</label><input type="text" size="50" id="personName"/>

看起来 GWT 中的 Label 小部件只是呈现为 DIV。

理想情况下，我想单击标签文本来聚焦相关的输入。这是内置的浏览器功能，我不想在标签 div 上使用 ClickHandlers!

有没有人遇到过这个问题？是否作为内置小部件存在但被称为其他东西？

编辑:想出了以下内容。也许有更好的方法？

HTML label = new HTML();
label.setHTML("<label for='"+input.getElement().getId()+"'>"+labelText+"</label>");

Answer 1

应大众需求，我向您展示 InputLabel，一个 <label> + <input type="text">小工具:)

这是基于 CheckBox类(包装 <input type="checkbox"> 元素) - 它 没有 已经过彻底测试 - 我把它留给读者;)

import com.google.gwt.dom.client.Document;
import com.google.gwt.dom.client.InputElement;
import com.google.gwt.dom.client.LabelElement;
import com.google.gwt.event.dom.client.ChangeEvent;
import com.google.gwt.event.dom.client.ChangeHandler;
import com.google.gwt.event.dom.client.HasChangeHandlers;
import com.google.gwt.event.logical.shared.ValueChangeEvent;
import com.google.gwt.event.logical.shared.ValueChangeHandler;
import com.google.gwt.event.shared.HandlerRegistration;
import com.google.gwt.user.client.DOM;
import com.google.gwt.user.client.Element;
import com.google.gwt.user.client.Event;
import com.google.gwt.user.client.EventListener;
import com.google.gwt.user.client.ui.ButtonBase;
import com.google.gwt.user.client.ui.FormPanel;
import com.google.gwt.user.client.ui.HasName;
import com.google.gwt.user.client.ui.HasValue;
import com.google.gwt.user.client.ui.RadioButton;
import com.google.gwt.user.client.ui.UIObject;
import com.google.gwt.user.client.ui.Widget;

public class InputLabel extends ButtonBase implements HasName, HasValue<String>, HasChangeHandlers {
  InputElement inputElem;
  LabelElement labelElem;
  private boolean valueChangeHandlerInitialized;

  /**
   * Creates an input box with no label.
   */
  public InputLabel() {
    this(DOM.createInputText());
    //setStyleName("gwt-CheckBox"); //TODO: add a valid style name
  }

  /**
   * Creates an input box with the specified text label.
   * 
   * @param label the check box's label
   */
  public InputLabel(String label) {
    this();
    setText(label);
  }

  /**
   * Creates an input box with the specified text label.
   * 
   * @param label the input box's label
   * @param asHTML <code>true</code> to treat the specified label as html
   */
  public InputLabel(String label, boolean asHTML) {
    this();
    if (asHTML) {
      setHTML(label);
    } else {
      setText(label);
    }
  }

  protected InputLabel(Element elem) {
    super(DOM.createSpan());
    inputElem = InputElement.as(elem);
    labelElem = Document.get().createLabelElement();

    getElement().appendChild(labelElem);
    getElement().appendChild(inputElem);

    String uid = DOM.createUniqueId();
    inputElem.setPropertyString("id", uid);
    labelElem.setHtmlFor(uid);

    // Accessibility: setting tab index to be 0 by default, ensuring element
    // appears in tab sequence. FocusWidget's setElement method already
    // calls setTabIndex, which is overridden below. However, at the time
    // that this call is made, inputElem has not been created. So, we have
    // to call setTabIndex again, once inputElem has been created.
    setTabIndex(0);
  }

  public HandlerRegistration addValueChangeHandler(
      ValueChangeHandler<String> handler) {
    // Is this the first value change handler? If so, time to add handlers
    if (!valueChangeHandlerInitialized) {
      addChangeHandler(new ChangeHandler() {
        public void onChange(ChangeEvent event) {
          ValueChangeEvent.fire(InputLabel.this, getValue());
        }
      });
      valueChangeHandlerInitialized = true;
    }
    return addHandler(handler, ValueChangeEvent.getType());
  }

  /**
   * Returns the value property of the input element that backs this widget.
   * This is the value that will be associated with the InputLabel name and
   * submitted to the server if a {@link FormPanel} that holds it is submitted.
   * <p>
   * This will probably return the same thing as {@link #getValue}, left here for magic reasons.
   */
  public String getFormValue() {
    return inputElem.getValue();
  }

  @Override
  public String getHTML() {
    return labelElem.getInnerHTML();
  }

  public String getName() {
    return inputElem.getName();
  }

  @Override
  public int getTabIndex() {
    return inputElem.getTabIndex();
  }

  @Override
  public String getText() {
    return labelElem.getInnerText();
  }

  /**
   * Gets the text value of the input element. 
   * <p>
   * @return the value of the input box.
   * Will not return null
   */
  public String getValue() {
    if (isAttached()) {
      return inputElem.getValue();
    } else {
      return inputElem.getDefaultValue();
    }
  }

  @Override
  public boolean isEnabled() {
    return !inputElem.isDisabled();
  }

  @Override
  public void setAccessKey(char key) {
    inputElem.setAccessKey("" + key);
  }

  @Override
  public void setEnabled(boolean enabled) {
    inputElem.setDisabled(!enabled);
    if (enabled) {
      removeStyleDependentName("disabled");
    } else {
      addStyleDependentName("disabled");
    }
  }

  @Override
  public void setFocus(boolean focused) {
    if (focused) {
      inputElem.focus();
    } else {
      inputElem.blur();
    }
  }

  /**
   * Set the value property on the input element that backs this widget. This is
   * the value that will be associated with the InputLabel's name and submitted to
   * the server if a {@link FormPanel} that holds it is submitted.
   * <p>
   * Don't confuse this with {@link #setValue}.
   * 
   * @param value
   */
  public void setFormValue(String value) {
    inputElem.setAttribute("value", value);
  }

  @Override
  public void setHTML(String html) {
    labelElem.setInnerHTML(html);
  }

  public void setName(String name) {
    inputElem.setName(name);
  }

  @Override
  public void setTabIndex(int index) {
    // Need to guard against call to setTabIndex before inputElem is
    // initialized. This happens because FocusWidget's (a superclass of
    // InputLabel) setElement method calls setTabIndex before inputElem is
    // initialized. See InputLabel's protected constructor for more information.
    if (inputElem != null) {
      inputElem.setTabIndex(index);
    }
  }

  @Override
  public void setText(String text) {
    labelElem.setInnerText(text);
  }

  /**
   * Sets the text in the input box.
   * <p>
   * Note that this <em>does not</em> set the value property of the
   * input element wrapped by this widget. For access to that property, see
   * {@link #setFormValue(String)}
   * 
   * @param value the text to set; must not be null
   * @throws IllegalArgumentException if value is null
   */
  public void setValue(String value) {
    setValue(value, false);
  }

  /**
   * Sets the text in the input box, firing {@link ValueChangeEvent} if
   * appropriate.
   * <p>
   * Note that this <em>does not</em> set the value property of the
   * input element wrapped by this widget. For access to that property, see
   * {@link #setFormValue(String)}
   *
   * @param value true the text to set; must not be null
   * @param fireEvents If true, and value has changed, fire a
   *          {@link ValueChangeEvent}
   * @throws IllegalArgumentException if value is null
   */
  public void setValue(String value, boolean fireEvents) {
    if (value == null) {
      throw new IllegalArgumentException("value must not be null");
    }

    String oldValue = getValue();
    inputElem.setValue(value);
    inputElem.setDefaultValue(value);
    if (value.equals(oldValue)) {
      return;
    }
    if (fireEvents) {
      ValueChangeEvent.fire(this, value);
    }
  }

  // Unlike other widgets the InputLabel sinks on its inputElement, not
  // its wrapper
  @Override
  public void sinkEvents(int eventBitsToAdd) {
    if (isOrWasAttached()) {
      Event.sinkEvents(inputElem, 
          eventBitsToAdd | Event.getEventsSunk(inputElem));
    } else {
      super.sinkEvents(eventBitsToAdd);
    }
  }


  /**
   * <b>Affected Elements:</b>
   * <ul>
   * <li>-label = label next to the input box.</li>
   * </ul>
   * 
   * @see UIObject#onEnsureDebugId(String)
   */
  @Override
  protected void onEnsureDebugId(String baseID) {
    super.onEnsureDebugId(baseID);
    ensureDebugId(labelElem, baseID, "label");
    ensureDebugId(inputElem, baseID, "input");
    labelElem.setHtmlFor(inputElem.getId());
  }

  /**
   * This method is called when a widget is attached to the browser's document.
   * onAttach needs special handling for the InputLabel case. Must still call
   * {@link Widget#onAttach()} to preserve the <code>onAttach</code> contract.
   */
  @Override
  protected void onLoad() {
    setEventListener(inputElem, this);
  }

  /**
   * This method is called when a widget is detached from the browser's
   * document. Overridden because of IE bug that throws away checked state and
   * in order to clear the event listener off of the <code>inputElem</code>.
   */
  @Override
  protected void onUnload() {
    // Clear out the inputElem's event listener (breaking the circular
    // reference between it and the widget).
    setEventListener(asOld(inputElem), null);
    setValue(getValue());
  }

  /**
   * Replace the current input element with a new one. Preserves
   * all state except for the name property, for nasty reasons
   * related to radio button grouping. (See implementation of 
   * {@link RadioButton#setName}.)
   * 
   * @param elem the new input element
   */
  protected void replaceInputElement(Element elem) {
    InputElement newInputElem = InputElement.as(elem);
    // Collect information we need to set
    int tabIndex = getTabIndex();
    String checked = getValue();
    boolean enabled = isEnabled();
    String formValue = getFormValue();
    String uid = inputElem.getId();
    String accessKey = inputElem.getAccessKey();
    int sunkEvents = Event.getEventsSunk(inputElem);   

    // Clear out the old input element
    setEventListener(asOld(inputElem), null);

    getElement().replaceChild(newInputElem, inputElem);

    // Sink events on the new element
    Event.sinkEvents(elem, Event.getEventsSunk(inputElem));
    Event.sinkEvents(inputElem, 0);
    inputElem = newInputElem;

    // Setup the new element
    Event.sinkEvents(inputElem, sunkEvents);
    inputElem.setId(uid);
    if (!accessKey.equals("")) {
      inputElem.setAccessKey(accessKey);
    }
    setTabIndex(tabIndex);
    setValue(checked);
    setEnabled(enabled);
    setFormValue(formValue);

    // Set the event listener
    if (isAttached()) {
      setEventListener(asOld(inputElem), this);
    }
  }

  private Element asOld(com.google.gwt.dom.client.Element elem) {
    Element oldSchool = elem.cast();
    return oldSchool;
  }

  private void setEventListener(com.google.gwt.dom.client.Element e,
      EventListener listener) {
    DOM.setEventListener(asOld(e), listener);
  }

  @Override
  public HandlerRegistration addChangeHandler(ChangeHandler handler) {
      return addDomHandler(handler, ChangeEvent.getType());
  }
}

下面的答案留给那些喜欢使用“标准”GWT 小部件和/或喜欢以其他方式使用的人:)

您可以轻松创建 <label>带有 DOM.createLabel() 的元素:

LabelElement label = DOM.createLabel().cast();
label.setHtmlFor("inputId");

但是我会坚持使用 GWT 提供的小部件 - 它们是由 GWT 构建和选择的，因此它们在所有支持的浏览器中的外观和行为都完全相同。他们选择的方法(例如，如果您放置一个 Image 内联，它将被包裹在一个表中，iirc - 因为通过 display:inline 将其设置为内联将不适用于所有浏览器:咳嗽:IE:咳嗽:)。

tl;dr:除非您有非常特殊的需求(例如创建自己的低级元素)，否则请坚持使用提供的 Widgets (或通过 Composite 创建自己的) - 你会受益更多。

PS:如果您担心 Web 标准、可访问性等 - 例如，不要担心大多数标准 GWT 小部件 support ARIA - 如果您构建了自己的组件，则必须自己做一些事情。

编辑:回答 AlexJReid 的评论:

您可以使用 FormPanel 通过表单发送数据(值得注意的是，这种方式将适用于所有浏览器，因为与其他浏览器不同，IE6 会触发与其他浏览器不同的事件；此外，表单的 target 将设置为 iframe - 多亏了这一点，页面不必重新加载 - 这会违背 AJAX 的目的 :)):

final FormPanel form = new FormPanel();
form.setAction("page.php");

TextBox box = new TextBox();
box.setName("name");
box.setText("fasdf");

Button button = new Button("Send", new ClickHandler() {
    @Override
    public void onClick(ClickEvent event) {
        form.submit();
    }
});

form.add(box);
form.add(button);

请注意 box.setName("name");行 - 这是您设置将用于该值的名称 TextBox当您提交此表格时。那么，Widgets 做了什么FormPanel支持？那些实现 com.google.gwt.user.client.ui.HasName界面:

文本框

密码文本框

单选按钮

SimpleRadioButton

复选框

简单复选框

文本区域

列表框

文件上传

隐藏

(当然，您可以添加任何 Widget，但只会发送上述那些的值)

最后一件事:除非你真的必须使用表单(比如发送文件或类似的东西)，否则 RequestBuilder可能值得一试 - 它使用的是 XmlHttpRequest隐藏在引擎盖之下 - AJAX 的母亲/父亲 ;)