How does apply-templates work?

2020-07-07 03:27发布

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I have just started learning XSL(T) and I wonder how apply-templates work? I do not understand the recursively applies templates part of it as it is written in my book.

I understand the XPath-part of XSL(T) and so on but not what apply-templates is doing and why I write it multiple times.

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放我归山
2楼-- · 2020-07-07 03:28

You use <xsl:apply-templates> to invoke the <xsl:template>:s you have defined.

<xsl:apply-templates> calls a matching template for each node in the set.

You can control processing order by specifying a select attribute on apply-templates.

See this example from w3schools:

<?xml version="1.0" encoding="ISO-8859-1"?>
<xsl:stylesheet version="1.0"
xmlns:xsl="http://www.w3.org/1999/XSL/Transform">

<xsl:template match="/">
  <html>
  <body>
  <h2>My CD Collection</h2>
  <xsl:apply-templates/>
  </body>
  </html>
</xsl:template>

<xsl:template match="cd">
  <p>
  <xsl:apply-templates select="title"/>
  <xsl:apply-templates select="artist"/>
  </p>
</xsl:template>

<xsl:template match="title">
  Title: <span style="color:#ff0000">
  <xsl:value-of select="."/></span>
  <br />
</xsl:template>

<xsl:template match="artist">
  Artist: <span style="color:#00ff00">
  <xsl:value-of select="."/></span>
  <br />
</xsl:template>

</xsl:stylesheet>

  • The first apply-templates calls the cd template each time an element named "cd" is encountered.

  • The cd template, in turn calls the title and artist templates to process the children elements of <cd>.

  • title is processed before artist. Note, that the order of artist and title elements in the source XML makes no difference.

You could think of apply-templates as analoguous to a subroutine call in procedural languages.

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混吃等死
3楼-- · 2020-07-07 03:42

If you've read about apply-templates in a book but haven't understood it, then it's not clear that a few words here will help. Perhaps you need a different book: different tutorial styles appeal to different people. Or perhaps an online tutorial such as http://vimeo.com/15234803 will get the ideas across.

The essence of the template mechanism is that there are two parties involved. The xsl:apply-templates instruction selects some nodes for processing, and the template rules (between them) decide what that processing should be. This gives very loose coupling and great separation of concerns; it's rather like object-oriented message/method despatch, but much more flexible.

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时光不老，我们不散
4楼-- · 2020-07-07 03:47

If you understand template rules you are done! Even if it's not that easy, they always give surprise. Read the specs.

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