XForms/Trailing Insert and Delete

Motivation

In some instances you only want to add to the end of a list or delete from the end of a list. This program demonstrates how you can use the last() function to do this.

Screen Image

When you insert a new row, it will always be inserted at the end of the list. When you delete a row, it will also be removed from the end of the list.

Link to XForms Application

Insert and delete from list

Sample Program

<html xmlns="http://www.w3.org/1999/xhtml" 
xmlns:xf="http://www.w3.org/2002/xforms" 
xmlns:ev="http://www.w3.org/2001/xml-events">
   <head>
      <title>Repeat Demo</title>
      <xf:model>
         <xf:instance xmlns="">
            <data xmlns="">
               <val>1</val>
               <val>2</val>
               <val>3</val>
            </data>
         </xf:instance>
      </xf:model>
   </head>
   <body>
         <xf:repeat nodeset="val">
            <div>
               <xf:output ref=".">
                  <xf:label>Value: </xf:label>
               </xf:output>
            </div>
         </xf:repeat>
         <xf:trigger>
            <xf:label>Insert new row</xf:label>
            <xf:action ev:event="DOMActivate">
               <xf:insert nodeset="val" position="after" at="last()" />
               <xf:setvalue ref="val[last()]" value="count(/data/val)" />
            </xf:action>
         </xf:trigger>
         <xf:trigger>
            <xf:label>Delete last row</xf:label>
            <xf:delete nodeset="val" at="last()" ev:event="DOMActivate" />
         </xf:trigger>
   </body>
</html>

Discussion

Notice that the xf:insert uses the xf:action element to trigger on the DOM activate and the xf:delete uses the ev:event attribute to trigger the delete. This is because we need to include the xf:setvalue in the insert.

So, as a general rule, if you just need to use a single element in a trigger, you can use the ev:event attribute. But if you need to include several elements that all must be triggered you should wrap them in an an xf:action element.

Potential problem: when you have deleted all the nodes, the insert trigger does not work anymore. This is because the nodeset selection on the insert element is empty in that situation. If the nodeset selector is empty, the insert trigger has no meaning (see the first rule in 'rules for insert processing')

References

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