用于 valueChangeListener 的 Ajax

Ajax for valueChangeListener

提问by Danubian Sailor

I'm using the p:ajaxlistener to handle value change events (because valueChangeListeneris launched on form submit):

我正在使用p:ajax侦听器来处理值更改事件（因为valueChangeListener在表单提交时启动）：

<p:ajax event="change" listener="#{bean.onNameChanged}"/>

Handle method:

处理方法：

public void onNameChanged(final AjaxBehaviorEvent event)

The problem is, I can't find in AjaxBehaviorEventnor its class hierarchy the place to read the old valueof the input. Neither could I find hint in google, how to get the old value...

问题是，我在AjaxBehaviorEvent它的类层次结构中也找不到读取输入旧值的地方。我也无法在谷歌中找到提示，如何获得旧值...

How to access the old value in the p:ajax onChangeevent?

如何访问p:ajax onChange事件中的旧值？

回答by BalusC

The problem is, I can't find in AjaxBehaviorEvent nor its class hierarchy the place to read the old value of the input. Neither could I find hint in google, how to get the old value...

问题是，我在 AjaxBehaviorEvent 及其类层次结构中都找不到读取输入旧值的地方。我也无法在谷歌中找到提示，如何获得旧值...

Use a valueChangeListener.

使用一个valueChangeListener.

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Unfortunatelly, valueChangeListener is invoked before p:ajax, so I don't have actual data from forms in that method, so in theory I could use valueChangeListener to remember the old value and then wait for p:ajax to process...

不幸的是，valueChangeListener 在 p:ajax 之前被调用，所以我在该方法中没有来自表单的实际数据，所以理论上我可以使用 valueChangeListener 来记住旧值，然后等待 p:ajax 处理......

Queue the value change event to the invoke application phase.

将值更改事件排队到调用应用程序阶段。

public void valueChangeListenerMethod(ValueChangeEvent event) {
    if (event.getPhaseId() != PhaseId.INVOKE_APPLICATION) {
        event.setPhaseId(PhaseId.INVOKE_APPLICATION);
        event.queue();
        return;
    }

    // Do your original job here. 
    // It will only be invoked when current phase ID is INVOKE_APPLICATION.
}

回答by Matt Handy

The ValueChangeListener should work this way:

ValueChangeListener 应该这样工作：

The view:

风景：

<h:form>
  <h:inputText value="#{sessionBean.hello}" 
               valueChangeListener="#{sessionBean.valueChangeListener}">
    <p:ajax/>
  </h:inputText>
</h:form>

The bean:

豆：

public void valueChangeListener(ValueChangeEvent e) {
  System.out.println("valueChangeListener invoked:" 
                      + " OLD: " + e.getOldValue() 
                      + " NEW: " + e.getNewValue());
}

The above code will print if I change the text field from "hello" to "world":

如果我将文本字段从“hello”更改为“world”，则会打印上面的代码：

valueChangeListener invoked: OLD: hello NEW: world

valueChangeListener 调用：旧：你好新：世界

回答by kolossus

You could try the following:

您可以尝试以下操作：

1. Implement the value change event in your bean

    public void processValueChange(ValueChangeEvent e){
    //foo the bar
    }
   

2. Define a valueChangeListeneron your selection component

    <p:selectOneMenu value="#{yourBean.value}" onchange="submit()" valueChangeListener="{#yourBean.processValueChange}">
   

   The key piece there is the submit()bit that processes the enclosing form on change of the value. You can then getNewValue()and getOldValue()as necessary.

1. 在 bean 中实现值更改事件

    public void processValueChange(ValueChangeEvent e){
    //foo the bar
    }
   

2. valueChangeListener在您的选择组件上定义 a

    <p:selectOneMenu value="#{yourBean.value}" onchange="submit()" valueChangeListener="{#yourBean.processValueChange}">
   

   关键是submit()在值改变时处理封装形式的位。然后getNewValue()，您可以getOldValue()根据需要。

EDIT: Now that I think about it, I see no reason why you cannot leave your setup as-is and simply define the valueChangeListener. It should still be processed during the changeevent in the <p:ajax/>, in fact, it will be processed before the listener for the ajax event itself.

编辑：现在我考虑了一下，我看不出为什么您不能按原样保留设置并简单地定义valueChangeListener. 应该还是在change事件期间处理的<p:ajax/>，实际上它会在ajax事件本身的监听器之前处理。

回答by Abed Kanbar

you can use this:

你可以使用这个：

public void onNameChanged(AjaxBehaviorEvent event)
 {
    String myVal = (String) ((UIOutput) event.getSource()).getValue();
    System.out.println("myVal: " + myVal);
 }