navigate prev and next

[bwakad]

For mobile layout I want to make use of the functions provided by PW: prev and next. So I have this, but it will not display both. Can someone point me in the right direction?

<ul class="inline-list">
<?php
     $browse = $pages->find("parent=/browse/");
     if($page->prev($browse) == null) {
        echo "<li><a href='{$page->url}'>{$page->name}</a></li>";                            
     } else {
     echo "<li><a href='{$page->prev($browse)->url}'>{$page->prev($browse)->name}</a></li>";
     }                            
                            
     if($page->next($browse) == null) {
        echo "<li><a href='{$page->url}'>{$page->name}</a></li>";
     } else {
        echo "<li><a href='{$page->next($browse)->url}'>{$page->next($browse)->name}</a></li>";
     }                            
?>
</ul>

[bwakad]

- edit -

I could only get it to work if testing for empty string:

if($page->prev($browse) == '') {

[renobird]

find() returns a pageArray, so null will not work.

[renobird]

what about:

if ($page->parent->next->id){
    // next
}

if ($page->parent->prev->id){
    //prev
}

[LostKobrakai]

Just for the record, if you've looked into the cheatsheet.

NullPage != null

[bwakad]

find() returns a pageArray, so null will not work.

but in the docs:

http://processwire.com/api/variables/page/

$page->next($pageArray)

Given a PageArray which includes the current page (among others), return the next page after the current.† Returns a NullPage if it is the last page in the provided PageArray. If called without a PageArray, it assumes the current page's siblings (same as $page->next).

Then why should null not work

ps: NullPage != null .... were in cheatsheat ?

[teppo]

NullPage is an object, kind of a placeholder for non-existing page, and that is very different from NULL (PHP's way of saying that a variable has no value at all). They're not the same thing, so NullPage == null is not true. It's that simple, really.

[bwakad]

Ohw. That's were I was off track, lol. Thanks, I understand now. The link to NullPage in docs helped! Apparantly I have to check for ->id

if(!$page->prev($browse)->id ) {

so if there is no ->id, NullPage is true.

[Martijn Geerts]

so if there is no ->id, NullPage is true.

a NullPage returns an id of 0, so evaluating to false.

[bwakad]

a NullPage returns an id of 0, so evaluating to false.

thats what I said: if NOT id then NullPage = true

lol. if false = true then false = false, but if true = true then true = true.

[Martijn Geerts]

There is an ID, but the id is 0, is different then "if NOT id"

[bwakad]

Maybe I do not get what you say, but from what I do understand from the pageArray (limited amount of pages) >>> $browse = $pages->find("parent=/browse/") -

the next code would produce a NullPage if there is no previous, there would be none (no id), because I used === "0" == "0" and = "0" ... and it did not work.

if(!$page->prev($browse)->id ) {

[LostKobrakai]

var_dump($pages->find("template=notAvailable")->id); // output: NULL

So yeah, it's not 0 but NULL.

[Martijn Geerts]

@LostKobrakai, a WireArray has no id, thus resulting in NULL
 

$nullpage = new NullPage;

var_dump($nullpage->id); // (int) 0

if ($nullpage->id == false) {
    // is true
}

if ($nullpage->id === false) {
    // is not true
}

Edited September 19, 2014 by Martijn Geerts
Always fun those strict comparisons :-)

[bwakad]

you all want to confuse me

Lostkobrakai - is right when he say is not 0 but NULL. But checking for that did not solve it.

Martijn - is right when $nullpage = new NullPage, hence id = 0

Teppo is right when he say NullPage is not Null.

but NOW I don't know anymore!!!

[LostKobrakai]

Damned confused myself. "get()" was the one which either returns a NullPage or null, depending on where you call it, not "find()".

[Martijn Geerts]

@bwaked:

You have Loose comparisons, and you have strict comparisons.

loose are written with two operators like ==

strict is written with three operators like ===

Strict will look next to value also to the type.

I will write it here in text rather then in values:

if (string === integer) {

    // a string is never an integer, thus evaluate to false

}

[bwakad]

So, if I want to evaluate if there is none - which one is the best to use... I prefer your example of == false, but is this always accurate with regards to a NullPage ?

if($page->prev($browse)->id == false ) {
// display somthing else
}

or

if(!$page->prev($browse)->id === true ) { // which is rather confusing
// display somthing else
}

or

if(!$page->prev($browse)->id ) {
// display somthing else
}

[LostKobrakai]

@bwakad

Essentially, if you work with pages, there are two options. Either you expect one page or a failure or secondly one or more pages or failure.

$single_page = $pages->get("something");

if($single_page->id) echo "Page found";

$multiple = $pages->find("something");

if(count($multiple)) echo "at least one page found";

The first check works, because get() returns a NullPage on failure, which has an id of 0. 

The second one counts the found PageArray elements. If there are none it's also 0. 

The difficulty is not to confuse those (as I did), as NullPage is something completely different as a PageArray / WireArray. 

[Martijn Geerts]

Here's some reading about types bwaked: http://php.net/manual/en/language.types.php

I hope that clarifies a bit. It will take some time to fully understand what is going on, but take your time, we all did.

[bwakad]

well, thanks all, for helping on this one - I will set my mind to 0 Null or blanc page (NullPage) and try to read from the link...

[diogo]

the next code would produce a NullPage if there is no previous, there would be none (no id), because I used === "0" == "0" and = "0" ... and it did not work.

Just don't forget that "0" != 0 and "0" != FALSE because it's a string. A string is always TRUE

[LostKobrakai]

A string is always TRUE

, if it has chars in it! An empty string equals false. 

[Martijn Geerts]

Good advise Bwaked: I will also set my set my mind to 0, with a new beer.

[bwakad]

Just don't forget that "0" != 0 and "0" != FALSE because it's a string. A string is always TRUE

I just see on PHP that checking on ->id is integer (martijn said that to) while I used =>id =, == and === "0". I now understand why it did not work...

This one tumbled me:

// the easiest way…if(!$page->id) {    // $page is a NullPage} 

I used it so I could display something else, but I forgot the ->id... which makes it an object, and I did not know how to check an object.

So my best bet is either

if(!$page->prev($browse)->id) { OR if($page->prev($browse)->id == false ) {