ValueChangeEvents being fired only after other components are clicked

问题

I'm trying to use an InputFile within JSF (1.1.7) and Apache Trinidad (1.0.11). I define a change event for it but the event is not being fired when I change the file selection but when I click on another component of the form.

Here is the jsp code:

    <trh:body>
        <tr:panelPage>
            <tr:form usesUpload="true" id="myForm"> 
                <tr:inputFile columns="80" id="archivo" 
                    valueChangeListener="#{myBean.changeInputFile}" 
                    immediate="true">
                </tr:inputFile>
                <tr:commandButton text="Begin"/>
            </tr:form>
        </tr:panelPage>
    </trh:body>

Here is the relevant part of the bean:

public void changeInputFile(ValueChangeEvent event) {
    UploadedFile f = (UploadedFile)event.getNewValue();
}

The code only enters into the myBean.changeInputFile method when I click the Begin button (having changed the file selection previously). I would like it to enter into myBean.changeInputFile when I change the selected file in the inputFile component.

Any idea why could be this happening?

回答1:

Your expextation is wrong. The valuechangelistener is a server-side action that will fire when something is submitted to the server and effectively has a different value than it did before. It is NOT telling the component to behave like modern ajax (jsf 1.1.7 and its valuechangelistener predate the ajax era). The form value is only submitted to the server when you, well, in 'old' html terms use form submission like pressing a submit button (or use some javascript to trigger that like you would in the old plain html days). And since without pressing a button or the added javascript, nothing is submitted to the server the valuechangelistener will not spontaneously do something.

So the behaviour you see is exactly as it should be.

来源：https://stackoverflow.com/questions/55003188/valuechangeevents-being-fired-only-after-other-components-are-clicked