I have added some extra functionality to the standard GWT ListBox by extending it like so:
public class FeatureListBox extends ListBox
{
public FeatureListBox()
{
}
public FeatureListBox(boolean isMultipleSelect)
{
super(isMultipleSelect);
}
public FeatureListBox(Element element)
{
super(element);
}
}
Nothing fancy here. However, the Change event is not firing now, or at least the handler (attached per below) is not getting invoked.
FeatureListBox listBox = new FeatureListBox();
listBox.addChangeHandler(new ChangeHandler()
{
public void onChange(ChangeEvent event)
{
// Do something here...
}
});
Any ideas why?
Either remove the no-argument constructor from FeatureListBox or call super() inside it, otherwise the initialization in the superclasses won't happen, which would probably result in what you're seeing.
The problem was in the way I was using my custom list box. In my application I wrap GWT Widgets around existing DOM elements on the page using the static wrap() methods of their widget classes in which the widgets get marked as attached, making them fire events. I didn't do that with my custom list box class originally, so I ended up implementing a static wrap() method similar to the one of the regular ListBox widget and using it in my code. Everything works like a charm now.
Related
My problem is with how to stop firing unrelated event of event bus. as I got this solution for Dialog box.
but it does not work in case of where one instance already initialize and try to create new instance of same class.
Just example: A below scroll panel has handler initialized. it used for document preview.
class TestScroll extends ScrollPanel
{
public TestScroll(){
}
implemented onload()
{
// eventBus.addHandler code here.
//here some preview related code
}
unload() method
{
//eventBus remove handler code
}
}
This preview has some data which contains some links that open different preview but with same class and different data structure,
Now The problem is like onUnload ( which contains code of remove handler) event does not load , because other panel opened. that does not mean previous panel unload.
So in that case, twice event handler registered. when one event fired then other event also fired.
Due to that, Preview 1 data shows properly, but after that Preview2 opened and when I close it, I find Preview1=Preview2.
so how can I handle such situation?
As per no of instance created each event fired. but I have to check some unique document id with if condition in event itself.
is there any other ways to stop unrelated event firing?
Edit:
public class Gwteventbus implements EntryPoint {
int i=0;
#Override
public void onModuleLoad() {
TestApp panel=new TestApp();
Button button=new Button("Test Event");
button.addClickHandler(new ClickHandler() {
#Override
public void onClick(ClickEvent event) {
TestApp panel=new TestApp();
int j=i;
new AppUtils().EVENT_BUS.fireEventFromSource(new AuthenticationEvent(),""+(j));
i++;
}
});
panel.add(button);
RootPanel.get().add(panel);
}
}
public class AppUtils {
public static EventBus EVENT_BUS = GWT.create(SimpleEventBus.class);
}
public class TestApp extends VerticalPanel{
String testString="";
public TestApp( ) {
AppUtils.EVENT_BUS.addHandler(AuthenticationEvent.TYPE, new AuthenticationEventHandler() {
#Override
public void onAuthenticationChanged(AuthenticationEvent authenticationEvent) {
System.out.println("helloworld"+authenticationEvent.getSource());
}
});
}
}
These are wild guesses as it's difficult to really answer it without code and a clear description.
I'm guessing you have one eventbus for all the panels. So when you register a handler it is registered with that one eventbus. In case you fire an event from one of the panels to the eventbus all panels will receive the event.
To fix this you can either create a new eventbus per panel or check who fired the event with event.getSource().
If this doesn't make sense you probably are reusing a variable or use a static variable which actually should be a new instance or none static variable.
You can use the GwtEventService-Library to fire specific events over a unique domain and every receiver that is registered at this domain receives that events then. You can handle as many different events/domains as you want.
In order to remove a handler attached to the EventBus, you must first store a reference to the HandlerRegistration returned by the addHandler method:
HandlerRegistration hr = eventBus.addHandler(new ClickHandler(){...});
Then you can remove the handler with the removeHandler method:
hr.removeHandler();
A final note worth mentioning is that when using singleton views, like is typical with MVP and GWT Activities and Places, it is best practice to make use of a ResettableEventBus. The eventBus passed to an activity's start() is just such a bus. When the ActivityManager stops the activity, it automatically removes all handlers attached to the ResettableEventBus.
I would strongly recommend reading the GWT Project's documentation on:
Activities and Places
Large scale application development and MVP
I'm trying to do the following:
I want to add a specific handler for some links, denoted by a class.
$("a.link_list").live("click", new ListLinkHandler());
I need .live() instead of .bind() because new such links will be generated. (I know jQuery's .live() is deprecated in favor of .on(), but gwt-query doesn't have a .on() yet.)
I defined the handler like this (just as the gwtquery example does):
public class ListLinkHandler extends Function {
#Override
public boolean f(Event e) { [...] }
}
However, the handler method is never called when I click the links.
I can see the event listener in Chrome Dev Tools: http://screencloud.net/v/bV5V. I think it's on the body because it's a .live().
I tried using .bind() and it worked fine. The body event listener changed in a a.link_list and the handler does what it's supposed to do, but (as documented, I didn't test) not for newly created links.
I filed a bug for the .live() method, but maybe I'm doing something wrong.
Also, I have no idea how to do it without gwtquery, GWT doesn't seem to have a method for selecting elements by class, neither to continually add the listener to new elements.
It seems you are doing something wrong, but I need more code to be sure. Could you send the complete onModuleLoad code which demonstrates this wrong behavior?
I have written a quick example using live, and it works either when adding new gwt widgets or dom elements with gquery, in both Chrome and FF
public void onModuleLoad() {
$("a.link_list").live("click", new ListLinkHandler());
// Add a new link via gquery
$("<a class='link_list' href=javascript:alert('href') onClick=alert('onClick')>Click </a>").appendTo(document);
// Add a new link via gwt widgets
Anchor a = new Anchor("click");
a.setStyleName("link_list");
a.addClickHandler(new ClickHandler() {
public void onClick(ClickEvent event) {
Window.alert("clickHandler");
}
});
RootPanel.get().add(a);
}
public class ListLinkHandler extends Function {
#Override
public boolean f(Event e) {
Window.alert("live");
return true;
}
}
I'm trying to use a custom widget: gwtupload with it's custom handlers. The handlers are defined as interfaces, as in, Interface.OnCustomEventHandler and the method, according to the API, that I want to use is like this code, but I'm not sure how to implement this with uiBinder.:
void onCustomEvent (Interface interface)
Normally for uiBinder I use this code for the regular gwt widgets:
#Widget widget;
#UiHandler("widget")
void onClick(ClickEvent event){
//Handle the event processing here.
}
Presently, when I try this,
#UiHandler("widget")
void onCustomEvent(ICustomInterface customInterface){
...
I get this null pointer exception:
[ERROR] Generator 'com.google.gwt.uibinder.rebind.UiBinderGenerator' threw an exception while rebinding '...ViewImpl.ViewImplUiBinder'
java.lang.NullPointerException
Here is the new code I tried:
public class MUpld extends Composite {
private static MUpldUiBinder uiBinder = GWT.create(MUpldUiBinder.class);
interface MUpldUiBinder extends UiBinder<Widget, MUpld> {
}
#UiField MultiUploader uploader;
public MUpld() {
final IUploader.OnFinishUploaderHandler onFinishUploaderHandler = new IUploader.OnFinishUploaderHandler() {
#Override
public void onFinish(IUploader iUploader) {
if (uploader.getStatus() == Status.SUCCESS){
System.out.println("In the onFinish method!");
}
}
};
initWidget(uiBinder.createAndBindUi(this));
uploader.addOnFinishUploadHandler(onFinishUploaderHandler);
}
}
In the debugger, I saw the handler get attached to the uploader widget I defined, but then the current uploader became a different one once the code moved out of this class. I tried using the final modifier, as that is the only way I know to get a variable into an inner class, but gwt would complain with:
[ERROR] com.cdg.complexityCalculator.client.view.MUpld has no default (zero args) constructor.
To fix this, you can define a #UiFactory method on the UiBinder's owner, or annotate a constructor of MUpld with #UiConstructor.
I wasn't able to get either of those options to work, but I realized I had the last two lines of code switched, so I changed it to what I have now and the handler loaded up with the correct object.
Any ideas as to how to get this to work? Everything else is in place, I just need a way to capture this event after my servlet has finished processing.
When I changed the last two lines of code, the handler got loaded properly. Now the objects are being created with the handler binding to the correct object.
initWidget(uiBinder.createAndBindUi(this));
uploader.addOnFinishUploadHandler(onFinishUploaderHandler);
I had to wait until the uiBinder created the instance of the uploader widget, then I was able to add the handler to it.
One of the tricks I've learned is to add a handler in the constructor for a composite widget you create, that way it's more of an encapsulated component. It handles it's own events.
I'm optimizing a GWT application that previously used a variety of nested panels to work with DIVs and Spans. I generate the entire table as a single SafeHtml object and then assigning it into a single SafeHtml widget.
I now want to be able to track mouseover/mouseout events at the level of the specific 'cell' spans rather than the entire table, but I'm not sure how to do this.
If I add a handler to the HTML widget itself, I'll get events sourced at various elements.
Since 2.0 there is quite a simple way to do it.
For example if you HTML code is contained in some kind of widget (HTMLPanel or HTML), you can calladdDomHandler(<handler>,<eventtyoe>) on that widget, so you will receive events from inner html.
For example if you have a bunch of anchors inside HTMLPanel and you want to know which one was clicked you can do something like this:
panel.addDomHandler(new ClickHandler() {
#Override
public void onClick(ClickEvent event) {
Element element= event.getNativeEvent().getEventTarget().cast();
if(element.getTagName().equals("A")) {
AnchorElement anchor = element.cast();
Window.alert("Anchor with href " + anchor.getHref() + " was clicked");
}
}
}, ClickEvent.getType());
Since you want to track mouseover/out events you will have to use 2 different dom handlers, find out cell you need when event is fired and then change its state.
The way to approach this is:
Find the element you need with one of the DOM methods, like DOM.getElementById(..) or any other means. View Widget.getElement() etc.
Call DOOM.sinkEvents(element,eventBits) or DOM.sinkBitlessEvent(element,eventName) and pass the required events you want to sink in form of a bitmask, like Event.MOUSEEVENTS or using a named event like click or touchstart if using the second method.
set and EventListener on the element, by calling DOM.setEventListerner(element,eventListener) like so:
DOM.setEventListener( element, new EventListener()
{
#Override
public void onBrowserEvent( Event event )
{
if ("click".event.getType()) {
// ..do stuff..
}
}
} );
Only events you've specified in step 2 will be fired to your EventListener, so you need to only handle those.
lets say i have a custom widget which has a ClickHandler. Here's the example:
public class TestWidget extends Composite {
private static TestWidgetUiBinder uiBinder = GWT
.create(TestWidgetUiBinder.class);
interface TestWidgetUiBinder extends UiBinder<Widget, TestWidget> {
}
#UiField
Button button;
public TestWidget(String firstName) {
initWidget(uiBinder.createAndBindUi(this));
button.setText(firstName);
}
#UiHandler("button")
void onClick(ClickEvent e) {
Window.alert("Hello!");
}
}
When i try to add this Widget like this:
TestWidget testWidget = new TestWidget("myTestWidget");
RootPanel.get().add(testWidget);
everything is fine. If i click on my button i get the message i expect.
However if i add it like this:
TestWidget testWidget = new TestWidget("myTestWidget");
RootPanel.getBodyElement().appendChild(testWidget.getElement());
my click event is not being fired. I'm struggeling to understand why.
It would be nice if someone could explain this to me or link me to an resource where i can read this up. Finally i would like to know if it is possible to add the clickhandler afterwards i appended the child event and if that way is recommended. Thanks it advance for help.
kuku
When you call add(), Widget.onAttach() is called on the widget that is being added to the panel. onAttach does some work to register the widget to receive events. appendChild() simply attaches one DOM element to another and does nothing else. You should be able to get events working in the second case by doing this:
Element element = testWidget.getElement();
RootPanel.getBodyElement().appendChild(element);
DOM.sinkEvents(element,
Event.getTypeInt(ClickEvent.getType().getName())
| DOM.getEventsSunk(element);
However, I haven't tested this and I wouldn't recommend that you use it in a real application. Using add() is definitely preferred, using appendChild() in this way has no advantages and may lead to unexpected behaviour.