GWT：我如何从RootPanel获取对按钮的引用？

问题描述

我正在使用GWT 2.4。在我的onModuleLoad方法中，如果给定一个字符串ID，我如何从RootPanel对象获取页面上现有按钮的引用？我想这个

  public void onModuleLoad（）{
 ... 
 final Button submitButton = （Button）RootPanel.get（submit）; 
  

但是出现编译错误，无法从RootPanel转换到按钮。

编辑：

我认为使用迭代器会治愈痛苦，但不会骰子。这里是默认的HTML加载（注意id =submit的按钮）...

$ p $ < div>

< form name =f>

文件名：< input type =textsize =25id =filenamename =filename

value =/> < input type =buttonid =submitname =submit

value =Submit/> < input type =hiddenname =curIdid =curId

value =/>

< / form>

< / div>

< div id =content>< / div>


但onModuleLoad中的这段代码会导致NullPointerException（因为找不到submitButton id）.. 。

  public void onModuleLoad（）{
 
 final Button submitButton =（Button）getWidgetById（submit ）; 
 submitButton.addStyleName（submitButton）; 
 ... 
 
 private Widget getWidgetById（final String id）{
 Widget eltToFind = null; 
 final Iterator< Widget> iter = RootPanel.get（）。iterator（）; 
 while（iter.hasNext（））{
 final Widget widget = iter.next（）; 
 final Element elt = widget.getElement（）; 
 if（elt.getId（）！= null&& elt.getId（）。equals（id））{
 eltToFind = widget; 
休息; 
} // if 
} // while 
 return eltToFind; 
 
  

谢谢， - Dave

Document.get（）。getElementById（submit）。< InputElement> cast（）获取您的输入元素。 $ c>，但你将无法获得 Button 小部件。

如果你更改您的代码以读取< / code>而不是< code>< button type =buttonid =submitname =submitvalue =Submit >< input> （类型=按钮部分在技术上是不需要的，但是如果你不这样做，某些浏览器会像type = submit一样），那么你可以使用 Button.wrap（）：

  Button button = Button。包裹（Document.get（）的getElementById（ 提交））; 
  




I'm using GWT 2.4. In my onModuleLoad method, given a string id, how do I get a reference to an existing button on the page from the RootPanel object? I'm trying this

public void onModuleLoad() {
    ...
    final Button submitButton = (Button) RootPanel.get("submit");

but getting the compile error, "Cannot cast from RootPanel to Button".

Edit:

I thought using an iterator would heal the pain, but no dice. Here is the default HTML loaded (notice the button with id="submit") ...

<div>

    <form name="f">

        File name: <input type="text" size="25" id="filename" name="filename"

            value="" /> <input type="button" id="submit" name="submit"

            value="Submit" /> <input type="hidden" name="curId" id="curId"

            value="" />

    </form>

</div>

<div id="content"></div>

but this code in onModuleLoad causes a NullPointerException (because the submitButton id can't be found) ...

public void onModuleLoad() {

    final Button submitButton = (Button) getWidgetById("submit");
    submitButton.addStyleName("submitButton");
    ...

private Widget getWidgetById(final String id) {
    Widget eltToFind = null;
    final Iterator<Widget> iter = RootPanel.get().iterator();
    while (iter.hasNext()) {
        final Widget widget = iter.next();
        final Element elt = widget.getElement();
        if (elt.getId() != null && elt.getId().equals(id)) {
            eltToFind = widget;
            break;
        } // if
    } // while
    return eltToFind;
}

Thanks, - Dave

解决方案

You can get your input element using Document.get().getElementById("submit").<InputElement>cast(), but you won't be able to get a Button widget out of it.

If you change your code to read <button type="button" id="submit" name="submit" value="Submit"> instead of <input> (the type=button part is technically not needed, but some browsers will treat it like a type=submit if you don't), then you can use Button.wrap():

Button button = Button.wrap(Document.get().getElementById("submit"));

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