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## net.sf.saxon.trace
Interface TraceListener

All Superinterfaces:
  java.util.EventListener

All Known Implementing Classes:
  AbstractTraceListener, TimedTraceListener, TraceEventMulticaster

public interface TraceListener
extends java.util.EventListener

This interface defines methods that are called by Saxon during the execution of a stylesheet, if tracing is switched on. Tracing can be switched on by nominating an implementation of this class using the TRACE_LISTENER feature of the TransformerFactory, or using the addTraceListener() method of the Controller, which is Saxon's implementation of tyhe JAXP javax.xml.transform.Transformer interface.

Method Summary
`void` | `close()` Method called at the end of execution, that is, when the run-time execution ends
`void` | `endCurrentItem(Item currentItem)` Method that is called when an instruction has finished processing a new current item and is ready to select a new current item or revert to the previous current item.
`void` | `enter(InstructionInfo instruction, XPathContext context)` Method that is called when an instruction in the stylesheet gets processed.
`void` | `leave(InstructionInfo instruction)` Method that is called after processing an instruction of the stylesheet, that is, after any child instructions have been processed.
`void` | `open()` Method called at the start of execution, that is, when the run-time transformation starts
`void` | `startCurrentItem(Item currentItem)` Method that is called by an instruction that changes the current item in the source document: that is, xsl:for-each, xsl:apply-templates, xsl:for-each-group.

Method Detail

### open

    public void open()

  Method called at the start of execution, that is, when the run-time transformation starts

### close

    public void close()

  Method called at the end of execution, that is, when the run-time execution ends

### enter

    public void enter(InstructionInfo instruction,
                      XPathContext context)

  Method that is called when an instruction in the stylesheet gets processed.

  Parameters:
    `instruction` - gives information about the instruction being executed, and about the context in which it is executed. This object is mutable, so if information from the InstructionInfo is to be retained, it must be copied.

### leave

    public void leave(InstructionInfo instruction)

  Method that is called after processing an instruction of the stylesheet, that is, after any child instructions have been processed.

  Parameters:
    `instruction` - gives the same information that was supplied to the enter method, though it is not necessarily the same object. Note that the line number of the instruction is that of the start tag in the source stylesheet, not the line number of the end tag.

### startCurrentItem

    public void startCurrentItem(Item currentItem)

  Method that is called by an instruction that changes the current item in the source document: that is, xsl:for-each, xsl:apply-templates, xsl:for-each-group. The method is called after the enter method for the relevant instruction, and is called once for each item processed.

  Parameters:
    `currentItem` - the new current item. Item objects are not mutable; it is safe to retain a reference to the Item for later use.

### endCurrentItem

    public void endCurrentItem(Item currentItem)

  Method that is called when an instruction has finished processing a new current item and is ready to select a new current item or revert to the previous current item. The method will be called before the leave() method for the instruction that made this item current.

  Parameters:
    `currentItem` - the item that was current, whose processing is now complete. This will represent the same underlying item as the corresponding startCurrentItem() call, though it will not necessarily be the same actual object.

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