$this->content !== NULL ???

$this->content !== NULL ???

by Howard Miller -
Number of replies: 6
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This bit of code appears (uncommented... Grrr) at the start of the get_content() function of every/most blocks....



if($this->content !== NULL) {
return $this->content;
}

What, exactly, does it do? It looks like a caching thing but that leads me to wonder what the conditions for content being null (and, hence, the rest of the function being run).

The parent class has a method called refresh_content() which sets the content to null and calls get_content() but I don't see that this gets called from anyway... which seems strange.

Cheers smile
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In reply to Howard Miller

Re: $this->content !== NULL ???

by Hubert Chathi -
Yes, it is for caching. See http://docs.moodle.org/en/Development:Blocks#I_Just_Hear_Static

$this->content gets set to NULL initially, because the base class has "var $content = NULL;" (blocks/moodleblock.class.php:54)
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In reply to Hubert Chathi

Re: $this->content !== NULL ???

by Deleted user -
Could teh function calling get_content not check if there is a cached version available? This is a much more clean solution.

Ries
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In reply to Deleted user

Re: $this->content !== NULL ???

by Hubert Chathi -
It depends on what you mean by "clean". Object-oriented principles suggest that the caller should not need to know anything about the internal workings of get_content. It should just be able to call the function without worrying about how it produces the result.
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In reply to Hubert Chathi

Re: $this->content !== NULL ???

by sam marshall -
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Yes, but they also suggest that the various different implementations shouldn't all have to duplicate that code. A better approach would be:

public BlockContent getContent()
{
if(content == null)
{
content = innerGetContent();
}
return content;
}

protected abstract BlockContent innerGetContent();


Then you just override the 'inner' one in each block and you don't need to duplicate the cache logic. Caller uses outer getContent.

However, lazy-initialising is a good principle (definitely better than creating the content, which is usually the heaviest thing the block does, in constructor - what if it needs to refer to another block object or something...), so I don't think the current design is too bad really.

--sam

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In reply to Hubert Chathi

Re: $this->content !== NULL ???

by Howard Miller -
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Thanks.... I did read that documentation but it didn't make much sense to me. Having looked at the code again I see that get_content() can get called multiple times during the 'lifetime' of a block (e.g. a simple boolean check for the block having content at all) and this is merely to cache between those calls.
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