GWT有<label>小部件吗？</label>

Question

我必须在GWT中实现的一小段AJAX功能中添加一个表单。在HTML术语中，我想

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

看来GWT中的Label小部件只是呈现为DIV。

理想情况下，我想点击标签文字以关注相关输入。这是内置的浏览器功能，我不想在标签div上乱七八糟地使用ClickHandlers！

有没有人遇到过这个问题？是作为内置窗口小部件存在，还是被称为其他东西？

编辑：提出以下内容。也许有更好的方法？

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

Answer 1

根据大众需求，我向您呈现InputLabel，<label> + <input type="text">小部件：）

这是基于CheckBox类（包含<input type="checkbox">元素） - 未经彻底测试 - 我将其留给读者;）< / p>

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());
  }
}

---

以下答案留给那些喜欢使用“标准”GWT小部件和/或更喜欢以其他方式执行此操作的人：）

您可以使用<label>轻松创建DOM.createLabel()元素：

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

但我坚持使用GWT提供的Widgets - 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，如果你放置Image内联，它将被包装在一个表中，iirc - 因为通过display:inline设置内联将无法在所有浏览器中使用：咳嗽：IE：咳嗽：）

tl; dr：除非你有非常具体的需求（比如创建自己的低级元素），坚持使用提供的Widgets（或通过Composite创建自己的） - 你会受益更多。

PS：如果你担心网络标准，可访问性等等 - 请不要，例如，大多数标准GWT小部件support ARIA - 你必须自己做的事情，如果你自己构建了组件。

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{ {1}}将被设置为iframe - 多亏了这一点，页面将不必重新加载 - 这将超过AJAX的目的:)）：

target

请注意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); 行 - 这是您在提交此表单时设置将用于box.setName("name");的值的名称。那么，Widgets会TextBox支持哪些内容？实现FormPanel接口的那些：

• 文本框
• 密码框
• 单选按钮
• SimpleRadioButton
• 复选框
• SimpleCheckBox
• 的TextArea
• 列表框
• 文件上传
• 隐藏

（当然，您可以添加任何Widget，但只会发送上述值）

最后一件事：除非你真的必须使用表格（比如发送文件或类似的东西），RequestBuilder可能值得尝试 - 它正在使用com.google.gwt.user.client.ui.HasName惊天动地 - 母亲/ AJAX的父亲;）

Answer 2

使用UIbinder，您只需使用 ui：field 属性在模板中创建标准html标签。

<label ui:field="myLabel">Some Text</label>

在视图中，您可以使用注释引用此元素：

@UiField LabelElement myLabel;

请注意，您用于GWT小部件的一些方法不可用。

e.g。而不是：

myLabel.setVisible(false);

你必须使用

myLabel.setAttribute("style", "display:none");

Answer 3

作为Bayard为每个标签创建@UiField元素的方法的替代方法，您还可以对标签和文本框组合执行以下操作：

<label for="{myTextBox.getElement.getId}">Some field:</label>
<g:TextBox ui:field="myTextBox"/>

您不能在同一元素上设置ui：field和id属性，因此您必须在Java代码中为TextBox指定一个id：

...

@UiField(provided=true) TextBox myTextBox = new TextBox();

public MyFormView() {
    myTextBox.getElement().setId(DOM.createUniqueId());
    uiBinder.createAndBindUi(this);
}

...

这是指向正确方向的Ray Ryan's comment on UiBinder id generation。他确实提到了运行时ID生成，这将消除对java片段的需求，但据我所知，它被废弃了。

Answer 4

我有同样的需求，最终创建了自己的Widget

public class Label extends Widget implements HasText {

public Label() {
  setElement(DOM.createLabel());
}

@Override
public void add(Widget w) {
  super.add(w, getElement());
}

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

@Override
public void setText(String text) {
  getElement().setInnerText((text == null) ? "" : text);
}

public void setFor(String forWho) {
  getElement().setAttribute("for", forWho);
}

}

Answer 5

我在UiBinder中编写了一个名为InputLabel的简单Widget（源代码如下）。 它使用HTML标签，但ui：字段用于引用输入小部件。我希望两全其美。

InputLabel小部件可以在UiBinder中使用，如下所示：

xmlns:tmp='urn:import:{REPLACE_WITH_JAVA_PACKAGE_PATH_TO_INPUTLABEL}'

    <tmp:InputLabel for="{fieldRef}">Label text</tmp:InputLabel>
    <g:FlowPanel ui:field="fieldRef">
        <g:TextBox/>
    </g:FlowPanel>

或者像这样：

    <g:FlowPanel>
        <g:CheckBox ui:field="fieldRef" />
    </g:FlowPanel>
    <tmp:InputLabel for="{fieldRef}">Label text</tmp:InputLabel>

Java源代码是：

import com.google.gwt.dom.client.*;
import com.google.gwt.i18n.client.HasDirection;
import com.google.gwt.i18n.shared.DirectionEstimator;
import com.google.gwt.i18n.shared.HasDirectionEstimator;
import com.google.gwt.user.client.DOM;
import com.google.gwt.user.client.ui.DirectionalTextHelper;
import com.google.gwt.user.client.ui.HasDirectionalText;
import com.google.gwt.user.client.ui.IsWidget;
import com.google.gwt.user.client.ui.Widget;

public class InputLabel extends Widget implements HasDirectionalText, HasDirectionEstimator {

    final DirectionalTextHelper directionalTextHelper;
    private boolean init = false;

    public InputLabel() {
        this(Document.get().createLabelElement());
    }

    public InputLabel(Element element) {
        assert (LabelElement.TAG.equalsIgnoreCase(element.getTagName()));

        this.setElement(element);
        this.directionalTextHelper = new DirectionalTextHelper(this.getElement(), true);
    }

    public DirectionEstimator getDirectionEstimator() {
        return this.directionalTextHelper.getDirectionEstimator();
    }

    public void setDirectionEstimator(DirectionEstimator directionEstimator) {
        this.directionalTextHelper.setDirectionEstimator(directionEstimator);
    }

    public void setDirectionEstimator(boolean enabled) {
        this.directionalTextHelper.setDirectionEstimator(enabled);
    }

    private InputElement getInputElement(Widget widget) {
        if (widget.getElement().hasTagName(InputElement.TAG)) return InputElement.as(widget.getElement());
        NodeList<Element> l = widget.getElement().getElementsByTagName(InputElement.TAG);
        if (l.getLength() > 0) {
            return InputElement.as(l.getItem(0));
        }

        return null;
    }

    public void setFor(IsWidget target) {
        if (init) return;
        init = true;
        //

        final InputElement input = getInputElement(target.asWidget());
        if (input != null) {
            if (!input.hasAttribute("id")) input.setId(DOM.createUniqueId());
            getElement().setAttribute("for", input.getId());
        }
    }

    public void setForm(String form) {
        getElement().setAttribute("form", form);
    }

    public String getText() {
        return this.directionalTextHelper.getTextOrHtml(false);
    }

    public void setText(String text) {
        this.directionalTextHelper.setTextOrHtml(text, false);
    }

    public HasDirection.Direction getTextDirection() {
        return this.directionalTextHelper.getTextDirection();
    }

    public void setText(String text, HasDirection.Direction dir) {
        this.directionalTextHelper.setTextOrHtml(text, dir, false);
    }
}