This tag is always the child of some other tag which is used to call action from apex controller. The tags which support apex:param as a child element are:

• <apex:actionFunction>
• <apex:actionSupport>
• <apex:commandLink>
• <apex:outputLink>
• <apex:outputText>
• <flow:interview>

For apex:param the value attribute must always be specified, and with it, either the assignedto or name attribute is also required. What is the meaning of these attributes and how are they used, that I am going to explain in the next part with an example.

public class paramtest {
    public string value { get; set;}
    
    public void testdirect(){
        system.debug(value);
    }
    public void testinput(){
        value = apexpages.currentPage().getParameters().get('inpval');
        system.debug(value);
    }
}

This apex class does not have much use and the only important piece of code in it is the first line of the function of testinput(). The getParameters() gets all the parameters and make a map out of them with the key being the name of the parameter. This name is the same name used in the apex:param attribute.

<apex:page controller="paramtest" docType="html-5.0">
<apex:form>

<apex:commandbutton action="{!testdirect}" reRender="test" value="Static value">
<apex:param assignTo="{!value}" value="The static value that was set from vf page"/>
</apex:commandbutton><br/>
<input type="text" id="testinput"/>
<input type="button" onclick="testinputJS()" value="Dynamic Value" class="btn"/>
<apex:outputPanel id="test">
<apex:outputText value="{!value}"/>
</apex:outputPanel>
<apex:actionFunction action="{!testinput}" name="passToController" rerender="test">
<apex:param value="" name="inpval"/>
</apex:actionFunction>
</apex:form>
<script>
function testinputJS(){
var str = document.getElementById('testinput').value;
if(str.length >4){
str= str.substring(0,4);
}
passToController(str);
}
</script>
</apex:page>

In the VF page we have used param at two places, one in the commandbutton and the other in actionfunction. The param which is in the command button has a value specified to it and also assigned to a variable in controller. This value will be passed to the variable in the controller if the button is clicked. This type of parameter passing is helpful when you are using it in a table over iterated values.

The other is with actionfunction where the name of the value is specified, however the value is not specified, and it is just left blank. Here we will have to manually get the data and store it in a variable like I had done earlier in the VF page.

The output of both action will be like:

That’s all about using apex:param, for any further queries feel free to contact us:

https://wedgecommerce.com/contact-us/

Or let us know your views on how to make this code better, in comments section below.