在GWT VerticalPanel上注册KeyDownHandler [英] Register KeyDownHandler on GWT VerticalPanel

问题描述

我有一个gwt的VerticalPanel类，我需要处理KeyDown事件。
我用于在我的类中实现键盘处理程序的方法是：
i add：

  this.sinkEvents （Event.ONKEYDOWN）; 
  

构造函数
然后我覆盖方法onBrowserEvent（）来处理key down事件。

  @Override 
 public void onBrowserEvent（Event event）{
 // TODO自动生成的方法存根
 super.onBrowserEvent（event）; 
 int type = DOM.eventGetType（event）; 
 switch（type）{
 case Event.ONKEYDOWN：
 //调用方法来处理这个keydown事件
 onKeyDownEvent（event）; 
 break; 
默认值：
 return; 
 
} 
} 
  

然而，这种方法不起作用对于这个VerticalPanel类。当我按一个键时，KeyDown事件被触发！

有特定的gwt小部件支持KeyDownHandler，如Button等.VerticalPanel不是其中之一..我们需要一个工作，在一个扩展VerticalPanel的类上注册一个KeyDownHandler。
你可以提出一个想法或提示吗？

谢谢

解决方案

您可以创建一个复合，其中包含 FocusPanel 和 VerticalPanel 。通过这种方式，您可以捕获所有关键事件，前提是 FocusPanel 被重点关注。只需将所需的方法委托给面板：

  public void onModuleLoad（）{
 ExtendedVerticalPanel panel = new ExtendedVerticalPanel（） ; 
 panel.add（new Label（some content））; 
 panel.addKeyDownHandler（new KeyDownHandler（）{
 
 @Override 
 public void onKeyDown（KeyDownEvent event）{
 if（event.getNativeKeyCode（）== KeyCodes。 KEY_ENTER）{
 Window.alert（enter hit）; 
} 
} 
}）; 
 RootPanel.get（）。add（panel）; 
} 
 
 private class ExtendedVerticalPanel extends Composite实现HasWidgets，HasAllKeyHandlers {
 
 private VerticalPanel fVerticalPanel; 
私人FocusPanel fFocusPanel; 
 
 public ExtendedVerticalPanel（）{
 fVerticalPanel = new VerticalPanel（）; 
 fFocusPanel = new FocusPanel（）; 
 fFocusPanel.setWidget（fVerticalPanel）; 
 initWidget（fFocusPanel）; 
} 
 
 @Override 
 public void add（Widget w）{
 fVerticalPanel.add（w）; 
} 
 
 @Override 
 public void clear（）{
 fVerticalPanel.clear（）; 
} 
 
 @Override 
 public Iterator< Widget> iterator（）{
 return fVerticalPanel.iterator（）; 
} 
 
 @Override 
 public boolean remove（Widget w）{
 return fVerticalPanel.remove（w）; 
} 
 
 @Override 
 public HandlerRegistration addKeyUpHandler（KeyUpHandler handler）{
 return fFocusPanel.addKeyUpHandler（handler）; 
} 
 
 @Override 
 public HandlerRegistration addKeyDownHandler（KeyDownHandler handler）{
 return fFocusPanel.addKeyDownHandler（handler）; 
} 
 
 @Override 
 public HandlerRegistration addKeyPressHandler（KeyPressHandler handler）{
 return fFocusPanel.addKeyPressHandler（handler）; 
} 
} 
  

更新

您的问题是如何在按下箭头键时阻止浏览器滚动。这里有一个适用于我的小例子：

  public void onModuleLoad（）{
 ExtendedVerticalPanel panel = new ExtendedVerticalPanel ; 
 // make panel reeeeaally big 
 panel.setHeight（3000px）; 
 panel.add（new TextBox（））; 
 panel.addKeyDownHandler（new KeyDownHandler（）{
 
 @Override 
 public void onKeyDown（KeyDownEvent event）{
 if（event.getNativeKeyCode（）== KeyCodes。 KEY_DOWN）{
 Window.alert（down hit）; 
 event.preventDefault（）; 
} 
} 
}）; 
 RootPanel.get（）。add（panel）; 
} 
  

添加您需要的处理程序，并调用 preventDefault（） 浏览器不能照顾的事件。

I have a gwt VerticalPanel class that i need to handel KeyDown events for it. the method i used to implement keyboard handler in my class is: i add :

this.sinkEvents(Event.ONKEYDOWN);

to constructor then i override method onBrowserEvent() to handle key down event.

 @Override 
public void onBrowserEvent(Event event) {
// TODO Auto-generated method stub
  super.onBrowserEvent(event);
  int type = DOM.eventGetType(event);
  switch (type) {
  case Event.ONKEYDOWN:
                        //call method to handle this keydown event
   onKeyDownEvent(event);
   break;
  default:
   return;

  }
 }

however this method doesn’t work for this VerticalPanel class.no KeyDown Event is fired when i press a key!

there are specific gwt widgets that support KeyDownHandler like Button etc..VerticalPanel is not one of them..so we need a work around to register a KeyDownHandler on a class extending VerticalPanel. can you suggest an idea or hint?

thanks

解决方案

You could create a Composite that wrappes a FocusPanel and a VerticalPanel. This way you can catch all key events provided the FocusPanel is focused. Simply delegate the needed methods to the panels:

public void onModuleLoad() {
    ExtendedVerticalPanel panel = new ExtendedVerticalPanel();
    panel.add(new Label("some content"));
    panel.addKeyDownHandler(new KeyDownHandler() {

        @Override
        public void onKeyDown(KeyDownEvent event) {
            if (event.getNativeKeyCode() == KeyCodes.KEY_ENTER) {
                Window.alert("enter hit");
            }
        }
    });
    RootPanel.get().add(panel);
}

private class ExtendedVerticalPanel extends Composite implements HasWidgets, HasAllKeyHandlers {

    private VerticalPanel fVerticalPanel;
    private FocusPanel fFocusPanel;

    public ExtendedVerticalPanel() {
        fVerticalPanel = new VerticalPanel();
        fFocusPanel = new FocusPanel();
        fFocusPanel.setWidget(fVerticalPanel);
        initWidget(fFocusPanel);
    }

    @Override
    public void add(Widget w) {
        fVerticalPanel.add(w);
    }

    @Override
    public void clear() {
        fVerticalPanel.clear();
    }

    @Override
    public Iterator<Widget> iterator() {
        return fVerticalPanel.iterator();
    }

    @Override
    public boolean remove(Widget w) {
        return fVerticalPanel.remove(w);
    }

    @Override
    public HandlerRegistration addKeyUpHandler(KeyUpHandler handler) {
        return fFocusPanel.addKeyUpHandler(handler);
    }

    @Override
    public HandlerRegistration addKeyDownHandler(KeyDownHandler handler) {
        return fFocusPanel.addKeyDownHandler(handler);
    }

    @Override
    public HandlerRegistration addKeyPressHandler(KeyPressHandler handler) {
        return fFocusPanel.addKeyPressHandler(handler);
    }
}

UPDATE

Your question on how to prevent the browser from scrolling when the arrow keys are pressed. Here a small example that works for me:

public void onModuleLoad() {
    ExtendedVerticalPanel panel = new ExtendedVerticalPanel();
    // make panel reeeeaally big
    panel.setHeight("3000px");
    panel.add(new TextBox());
    panel.addKeyDownHandler(new KeyDownHandler() {

        @Override
        public void onKeyDown(KeyDownEvent event) {
            if (event.getNativeKeyCode() == KeyCodes.KEY_DOWN) {
                Window.alert("down hit");
                event.preventDefault();
            }
        }
    });
    RootPanel.get().add(panel);
}

Add the handlers you need and call preventDefault() on the events the browser must not take care of.

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