com.google.gwt.user.client.ui.impl.FocusImplStandard Maven / Gradle / Ivy
/*
* Copyright 2010 Google Inc.
*
* 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.google.gwt.user.client.ui.impl;
import com.google.gwt.core.client.JavaScriptObject;
import com.google.gwt.dom.client.Element;
/**
* Implementation of {@link com.google.gwt.user.client.ui.impl.FocusImpl} that
* uses a hidden input element to serve as a 'proxy' for accesskeys, which are
* only supported on form elements in most browsers.
*/
public class FocusImplStandard extends FocusImpl {
/**
* Single focusHandler shared by all focusable.
*/
static JavaScriptObject focusHandler;
private static native Element createFocusable0(JavaScriptObject focusHandler) /*-{
// Divs are focusable in all browsers, but only IE supports the accessKey
// property on divs. We use the infamous 'hidden input' trick to add an
// accessKey to the focusable div. Note that the input is only used to
// capture focus when the accessKey is pressed. Focus is forwarded to the
// div immediately.
var div = $doc.createElement('div');
div.tabIndex = 0;
var input = $doc.createElement('input');
input.type = 'text';
input.tabIndex = -1;
input.setAttribute('role', 'presentation');
var style = input.style;
style.opacity = 0;
style.height = '1px';
style.width = '1px';
style.zIndex = -1;
style.overflow = 'hidden';
style.position = 'absolute';
// Note that we're using isolated lambda methods as the event listeners
// to avoid creating a memory leaks. (Lambdas here would create cycles
// involving the div and input). This also allows us to share a single
// set of handlers among every focusable item.
input.addEventListener('focus', focusHandler, false);
div.appendChild(input);
return div;
}-*/;
@Override
public Element createFocusable() {
return createFocusable0(ensureFocusHandler());
}
@Override
public native void setAccessKey(Element elem, char key) /*-{
elem.firstChild.accessKey = String.fromCharCode(key);
}-*/;
/**
* Use an isolated method call to create the handler to avoid creating memory
* leaks via handler-closures-element.
*/
private native JavaScriptObject createFocusHandler() /*-{
return function(evt) {
// This function is called directly as an event handler, so 'this' is
// set up by the browser to be the input on which the event is fired. We
// call focus() in a timeout or the element may be blurred when this event
// ends.
var div = this.parentNode;
if (div.onfocus) {
$wnd.setTimeout(function() {
div.focus();
}, 0);
}
};
}-*/;
private JavaScriptObject ensureFocusHandler() {
return focusHandler != null ? focusHandler : (focusHandler = createFocusHandler());
}
}