I am trying to get forward and backwards pagination working for a query I have on my app.
I have started with the example at: https://developers.google.com/appengine/docs/python/ndb/queries#cursors
I would expect that example to do a typical forward/back pagination to create cursors that you can pass to your template in order to be used in a subsequent request for the page after/before the current one. But what it is doing is getting cursors for the same page, one from the beginning and the other from the end (if I have understood correctly).
What I want is a cursor to the beginning of the following page, and a cursor to the beginning of the previous page, to use in my UI.
I have managed to almost get that with the following code, based on the mentioned example:
curs = Cursor(urlsafe=self.request.get('cur'))
q = MyModel.query(MyModel.usett == usett_key)
q_forward = q.order(-MyModel.sugerida)
q_reverse = q.order(MyModel.sugerida)
ofus, next_curs, more = q_forward.fetch_page(num_items_page,
start_cursor=curs)
rev_cursor = curs.reversed()
ofus1, prev_curs, more1 = q_reverse.fetch_page(num_items_page,
start_cursor=rev_cursor)
context = {}
if more and next_curs:
context['next_curs'] = next_curs.urlsafe()
if more1 and prev_curs:
context['prev_curs'] = prev_curs.reversed().urlsafe()
The problem, and the point of this question, is that I use more and more1 to see if there is a next page. And that is not working in the backwards sense. For the first page, more1 is True, in the second page more1 is False, and subsequent pages give True.
I would need something that gives False for the first page and True for every other page. It seems like this more return value is the thing to use, but maybe I have a bad Query setup, or any other thing wrong.
Thanks everyone!
Edit: Since I didn't find a simple solution for this, I switched to using ndbpager.
There's no such thing.
You know thats theres (at least) one page before the current page if you started the query with a cursor (the first page usualy dosnt have a cursor).
A common trick to access the previous page is inverting the sort-order.
If you have a list, sorted by creationdate desc, you could take the creationdate of the first element of your current page, query for elements with creationdate < this creationdate using inverted sort order. This will return the oldest elements which are newer then the given creationdate. Flip the list of retrived elements (to bring them into the correct order again) and there you have the elements of the page before, without using a cursor.
Note: this requires the values of your sortorder beeing distinct.
In some cases, its also possible to use a prebuild index allowing random-access to different pages, see https://bitbucket.org/viur/server/src/98de79b91778bb9b16e520acb28e257b21091790/indexes.py for more.
I have a workaround and not the best solution. it is baiscally redirecting back to the previous page.
Previous
I think PagedQuery has the capability but still waiting for someone to post a more comprehensive tutorial about it.
Related
My initial logic of checking if an edge is present and creating an edge needs to query. Im trying to verify and create an edge in one instruction.
This query does not seem to work
ipdb> prop = self._graph.V('pppp').outE('friend').hasId('testEdge').as_('e').inV()
.hasId('dddd').select('e').
coalesce(__.property('testedder', 1111).fold().unfold(),
__.V('dddd'). as_('to_a').V('pppp').addE('friend').to('to_a')).
toList()
1) The first part of the coalesce - updating the property of Edges work fine
2) The second part of the coalesce is either not being called or not working. It is working as an independent query. Does 'as' not work in anonymous traversals?
PS: Im using AWS Neptune
You had the right idea but you needed some simplification. I'll try to do it in steps. First, whenever I see labelled steps, I try to see if there is a way to avoid using them. In this case, they can be factored out:
g.V('pppp').outE('friend').
filter(hasId('testEdge').inV().hasId('dddd')).
coalesce(__.property('testedder', 1111).fold().unfold(),
__.V('dddd'). as_('to_a').V('pppp').addE('friend').to('to_a'))
Readability of the traversal improves on those first two lines because the reader can immediately see that you want to find an edge given some criteria which was only implied by the step labeling approach. Next, I looked at coalesce(). As it stands, if filter() returns no edges then coalesce() will never get a chance to execute and that's why the second part of coalesce() never has an opportunity to work for you. So, let's clean that part up:
g.V(1).outE('knows').
filter(hasId(6).inV().hasId(2)).
fold().
coalesce(unfold().property('testedder', 1111),
V('dddd').as_('to_a').V('pppp').addE('friend').to('to_a'))
If it's not clear why the fold() and unfold() are where they are, you should check out my detailed explanation of the approach here. So, with fold() and unfold() where they should be, the coalesce() should now trigger both conditions depending on whether or not an edge passes the filter(). The first part of the coalesce() is fine, but the second could still use a bit of work as I'd again like to factor out the step labels if the aren't necessary:
g.V('pppp').outE('friend').
filter(hasId('testEdge').inV().hasId('dddd')).
fold().
coalesce(unfold().property('testedder', 1111),
addE('friend').from(V('pppp')).to(V('dddd')))
The above Gremlin assumes that you know "pppp" vertex exists. If you do not then you might try (as suggested by Daniel Kuppitz):
g.V('pppp').
not_(outE('friend').hasId('testEdge').
filter(inV().hasId('dddd')).
property('testedder', 1111)).as('p').
V('dddd').
addE('friend').from('p')
Actually i want to read emails one by one in junk folder of "outlook:live" and mark emails "Not spam".
emails = WebDriverWait(driver, 5).until(EC.element_to_be_clickable((By.XPATH,"//div[#class = 'xoCOIP8PzdTVy0T6q_uG6']")))
This xpath matches 400 instances. I want to make a loop to select one email at a time like select first email, click on the div and perform action and then 2nd email and so on. I'm trying this
emails = WebDriverWait(driver,
5).until(EC.element_to_be_clickable((By.XPATH,"//div[#class =
'xoCOIP8PzdTVy0T6q_uG6']")))
for count in range(0,len(emails)):
(emails)[count+1].click()
Please help me know where im doing wrong. Thanks in advance
It appears that the function you're using to return the clickable elements is only returning a single element, so you'll have to use a different function, make a change in your logic, etc.
For instance, you could use Selenium's find_elements_by_xpath("//div[#class = 'xoCOIP8PzdTVy0T6q_uG6']") which will return a list of WebElement object(s) if the element(s) are found, or an empty list if the element(s) is not found. This will, of course, not take into consideration the possibility of the elements not being completely loaded on the page. In my experience, just slapping a time.sleep(10) after you open the page is "'good enough".
I recommend making sure your elements can be discovered and interacted with first to make sure this isn't all in vain, if you haven't already.
Another option is to add another function, something like a elements_to_be_clickable() function, to the Expected Conditions source code.
From the Expected Condition documentation, I've done some research and it looks like the element_to_be_clickable() function only returns a single element. Moreover, from the source code, said function mainly makes use of the visibility_of_element_located() function. I believe you could follow similar logic to the element_to_be_clickable() function, but instead use the visibility_of_all_elements_located() function, in order to return multiple WebElements (since visibiilty_of_all_elements_located() returns a list of WebElements).
I have an array with a few items in it. Every x seconds, I receive a new array with the latest data. I check if the data has changed, and if it has, I replace the old one with the new one:
if (currentList != responseFromHttpCall) {
currentList = responseFromHttpCall;
}
This messes up the classes provided by ng-animate, as it acts like I replaced all of the items -- well, I do actually, but I don't know how to not.
These changes can occur in the list:
There's one (or more) new item(s) in the list - not necessaryly at the end of the list though.
One (or more) items in the list might be gone (deleted).
One (or more) items might be changed.
Two (or more) items might have been swapped.
Can anyone help me in getting ng-animate to understand what classes to show? I made a small "illustation" of my problem, found here: http://plnkr.co/edit/TS401ra58dgJS18ydsG1?p=preview
Thanks a lot!
To achieve what you want, you will need to modify existing list on controller (vm.list) on every action. I have one solution that may work for your particular example.
you would need to compare 2 lists (loop through first) similar to:
vm.list.forEach((val, index)=>{
// some code to check against array that's coming from ajax call
});
in case of adding you would need to loop against other list (in your case newList):
newList.forEach((val, index)=>{
// some code to check array on controller
});
I'm not saying this is the best solution but it works and will work in your case. Keep in mind - to properly test you will need to click reset after each action since you are looking at same global original list which will persist same data throughout the app cycle since we don't change it - if you want to change it just add before end of each function:
original = angular.copy(vm.list);
You could also make this more generic and put everything on one function, but for example, here's plnkr:
http://plnkr.co/edit/sr5CHji6DbiiknlgFdNm?p=preview
Hope it helps.
I'm using RSelenium to automatically scroll down a social media website and save posts. I want to find the last instance of a web element (specifically, the post dates), but it's taking unacceptably long using my current method (using findElements() to return all post dates then extracting the last one - see code below) if I've scrolled a long way down the page.
Can anyone recommend a fast way to find the last web element (specifically, the post date) on a web page? For example, is there a way you can use findElement() (which searches for the first match) such that it starts from the bottom of the page rather than the top? Any suggestions welcome.
Here's a trivial example of my code, but it takes an unacceptably long time if I've scrolled a long way down the page.
# Load webpage of interest
library(RSelenium)
library(rvest)
rD = rsDriver(browser = "firefox")
remDr = rD[["client"]]
url = paste0("https://stocktwits.com/symbol/NZDCHF")
remDr$navigate(url)
# Scroll down page three times, loading new content each time.
for (i in 1:3) { #Only scrolling 3 times for illustration
remDr$executeScript("window.scrollTo(0,document.body.scrollHeight);")
Sys.sleep(2) #delay by 3sec to give chance to load
}
# Get date of last post. WORKS BUT TAKES FOREVER IF I'VE SCROLLED MANY TIMES
e = remDr$findElements("css", ".message-date")
last_date = e[[length(e)]]$getElementText()
I found a messy workaround to solve the above. Specifically, I used the below to get the last message (which included the date), then wrote a regular expression to extract the last date.
last_child = remDriver$findElement(using = "css selector",
value = ".messageli:last-child")
last_child = unlist(last_child$getElementText())
My UIPageViewController was working fine in iOS 5. But when iOS 6 came along, I wanted to use the new scroll transition style (UIPageViewControllerTransitionStyleScroll) instead of the page curl style. This caused my UIPageViewController to break.
It works fine except right after I've called setViewControllers:direction:animated:completion:. After that, the next time the user scrolls manually by one page, we get the wrong page. What's wrong here?
My workaround of this bug was to create a block when finished that was setting the same viewcontroller but without animation
__weak YourSelfClass *blocksafeSelf = self;
[self.pageViewController setViewControllers:viewControllers direction:UIPageViewControllerNavigationDirectionForward animated:YES completion:^(BOOL finished){
if(finished)
{
dispatch_async(dispatch_get_main_queue(), ^{
[blocksafeSelf.pageViewController setViewControllers:viewControllers direction:UIPageViewControllerNavigationDirectionForward animated:NO completion:NULL];// bug fix for uipageview controller
});
}
}];
This is actually a bug in UIPageViewController. It occurs only with the scroll style (UIPageViewControllerTransitionStyleScroll) and only after calling setViewControllers:direction:animated:completion: with animated:YES. Thus there are two workarounds:
Don't use UIPageViewControllerTransitionStyleScroll.
Or, if you call setViewControllers:direction:animated:completion:, use only animated:NO.
To see the bug clearly, call setViewControllers:direction:animated:completion: and then, in the interface (as user), navigate left (back) to the preceding page manually. You will navigate back to the wrong page: not the preceding page at all, but the page you were on when setViewControllers:direction:animated:completion: was called.
The reason for the bug appears to be that, when using the scroll style, UIPageViewController does some sort of internal caching. Thus, after the call to setViewControllers:direction:animated:completion:, it fails to clear its internal cache. It thinks it knows what the preceding page is. Thus, when the user navigates leftward to the preceding page, UIPageViewController fails to call the dataSource method pageViewController:viewControllerBeforeViewController:, or calls it with the wrong current view controller.
I have posted a movie that clearly demonstrates how to see the bug:
http://www.apeth.com/PageViewControllerBug.mov
EDIT This bug will probably be fixed in iOS 8.
EDIT For another interesting workaround for this bug, see this answer: https://stackoverflow.com/a/21624169/341994
Here is a "rough" gist I put together. It contains a UIPageViewController alternative that suffers from Alzheimer (ie: it doesn't have the internal caching of the Apple implementation).
This class isn't complete but it works in my situation (namely: horizontal scroll).
As of iOS 12 the problem described in the original question seems to be almost fixed. I came to this question because I experienced it in my particular setup, in which it does still happen, hence the word "almost" here.
The setup I experienced this issue was:
1) the app was opened via a deep link
2) based on the link the app had to switch to a particular tab and open a given item there via push
3) described issue happened only when the target tab was not previously selected by user (so that UIPageViewController was supposed to animate to that tab) and only when setViewControllers:direction:animated:completion: had animated = true
4) after the push returning back to the view controller containing the UIPageViewController, the latter was found to be a big mess - it was presenting completely wrong view controllers, even though debugging showed everything was fine on the logic level
I supposed that the root of the problem was that I was pushing view controller very quick after setViewControllers:direction:animated:completion: called, so that the UIPageViewController had no chance to finish something (maybe animation, or caching, or something else).
Simply giving UIPageViewController some spare time by delaying my programmatic navigation in UI via
DispatchQueue.main.asyncAfter(deadline: DispatchTime.now() + 1) { ... }
fixed the issue for me. And it also made the programmatic opening of the linked item more user friendly visually.
Hope this helps someone in similar situation.
Because pageviewVC call multi childVC when swipe it. But we just need last page that visible.
In my case, I need to change index for segmented control when change pageView.
Hope this help someone :)
extension ViewController: UIPageViewControllerDelegate {
func pageViewController(_ pageViewController: UIPageViewController, didFinishAnimating finished: Bool, previousViewControllers: [UIViewController], transitionCompleted completed: Bool) {
guard let pageView = pageViewController.viewControllers?.first as? ChildViewController else { return }
segmentedControl.set(pageView.index)
}
}
This bug still exists in iOS9. I am using the same workaround that George Tsifrikas posted above, but a Swift version:
pageViewController.setViewControllers([page], direction: direction, animated: true) { done in
if done {
dispatch_async(dispatch_get_main_queue()) {
self.pageViewController.setViewControllers([page], direction: direction, animated: false, completion: {done in })
}
}
}
Another simple workaround in Swift: Just reset the UIPageViewController's datasource. This apparently clears its cache and works around the bug. Here's a method to go directly to a page without breaking subsequent swipes. In the following, m_pages is an array of your view controllers. I show how to find currPage (the index of the current page) below.
func goToPage(_ index: Int, animated: Bool)
{
if m_pages.count > 0 && index >= 0 && index < m_pages.count && index != currPage
{
var dir: UIPageViewController.NavigationDirection
if index < currPage
{
dir = UIPageViewController.NavigationDirection.reverse
}
else
{
dir = UIPageViewController.NavigationDirection.forward
}
m_pageViewController.setViewControllers([m_pages[index]], direction: dir, animated: animated, completion: nil)
delegate?.tabDisplayed(sender: self, index: index)
m_pageViewController.dataSource = self;
}
}
How to find the current page:
var currPage: Int
{
get
{
if let currController = m_pageViewController.viewControllers?[0]
{
return m_pages.index(of: currController as! AtomViewController) ?? 0
}
return 0
}
}
STATEMENT:
It seems that Apple has spotted that developers are using UIPageViewController in very different applications that go way beyond the
originally intended ones Apple based their design-choices on in the first place. Rather than using it in a gesture driven linear fashion
PVC is often used to programmatically jump to random
positions within a structured environment. So they have enhanced their implementation of UIPageViewController and the class is now calling both DataSource
callbacks
- (UIViewController *)pageViewController:(UIPageViewController *)pageViewController viewControllerBeforeViewController:(UIViewController *)viewController
- (UIViewController *)pageViewController:(UIPageViewController *)pageViewController viewControllerAfterViewController:(UIViewController *)viewController
after setting a new contentViewController on UIPageViewController with
[self.pageViewController setViewControllers:viewControllers direction:UIPageViewControllerNavigationDirectionForward animated:YES completion:nil];
even if an animated turn of pages rather suggests a linear progress in an e.g. page hierarchy like a book or PDF with consecutive pages. Although - I doubt that Apple from a HIG standpoint
is very fond of seeing PVC being used this way, but - it doesn't break backwards compatibility, it was an easy fix, so - they eventually did it. Actually it is just one more call of one of the two DataSource methods that is absolutely unnecessary in a linear environment where pages (ViewControllers) have already been cashed for later use.
However, even if this enhancement might come in very handy for certain use-cases the initial behavior of the class is NOT to be considered a bug. The fact that a lot of developers do - also in other
posts on SO that accuse UIPageViewController of misbehavior - rather emphasizes a widely spread misconception of its design, purpose and functionality.
Without trying to offend any of my fellow developers here in this great facility I nonetheless decided not to remove my initial 'disquisition' that clearly explains to the OP the mechanics of PVC and why his assumption is wrong that he has to deal with a bug here.
This might also be of use for any other fellow developer too who struggles with some intricacies in the implementation of UIPageViewController!
ORIGINAL ANSWER:
After having read all the answers over and over again - included the
accepted one - there is just one more thing left to say...
The design of UIPageViewController is absolutely FLAWLESS and all the
hacks you submit in order to circumvent an alleged bug is nothing but
remedies for your own faulty assumptions because you goofed it up in the
first place!!!
THERE IS NO BUG AT ALL! You are just fighting the framework. I'll explain why!
There is so much talk about page numbers and indices! These are concepts the
controller knows NOTHING about! The only thing it knows is - it is showing
some content (btw. provided by you as a dataViewController) and that it can
do something like a right/left animation in order to imitate a page turn.
CURL or SCROLL...!!!
In the pageViewController's world there only exists a current SPACE (let's call
it just this way to avoid confusion with pages and indices).
When you initially set a pageViewController it only minds about this very SPACE.
Only when you start panning its view it starts asking its DataSource what it
eventually should display in case a left/right flip should happen. When you start
panning to the left the PVC asks first for the BEFORE-SPACE and then for the
AFTER-SPACE, in case you start to the right it does it the other way round.
After the completed animation (a new SPACE is displayed by the PVC's view) the
PVC considers this SPACE as its new center of the universe and while it is at it, it
asks the DataSource about the one it still does not know anything about. In case of
a completed turn to the right it wants to know about the new AFTER space and in
case of a completed turn to the left it asks for a new BEFORE space.
The old BEFORE space (from before the animation) is in case of a completed turn to
the right completely obsolete and gets deallocated as soon as possible. The old center
is now the new BEFORE and the former AFTER is the new center. Everything just
shifted one step to the right.
So - no talk of 'which page' or 'whatever index' - just simply - is there a BEFORE or
an AFTER space. If you return NIL to one of the DataSource callbacks the PVC just
assumes it is at one extreme of your range of SPACES. If you return NIL to both
callbacks it assumes it is showing the one and only SPACE there is and will never
ever again call a DataSource callback anymore! The logic is up to you! You define
pages and indices in your code! Not the PVC!!!
For the user of the class there are two means of interacting with the PVC.
A pan-gesture that indicates whether a turn to the BEFORE/AFTER space is desired
A method - namely setViewControllers:direction:animated:completion:
This method does exactly the same than the pan gesture is doing. You are indicating the
direction (e.g. UIPageViewControllerNavigationDirectionBackward/Forward)
for the animation - if there is one intended - which in other words just means -> going to
BEFORE or AFTER...
Again - no mentioning of indices, page-numbers etc....!!!
It is just a programmatically way of achieving the same a gesture would!
And the PVC is doing right by showing the old content again when moving back
to the left after having moved to the right in the first place. Remember
- it is just showing content (that you provide) in a structured way - which is a 'single page turn' by design!!!
That is the concept of a page turn - or BOOK, if you like that term better!
Just because you goof it up by submitting PAGE 8 after PAGE 1 doesn't mean the PVC
cares at all about your twisted opinion of how a book should work. And the user of your
apps neither. Flipping to the right and back to the left should definitely result in reaching
the original page - IF done with an animation. And it is up to YOU to correct the goof by
finding a solution for the disaster. Don't blame it on the UIPageViewController. It is doing
its job perfectly!
Just ask yourself - would you do the same thing with a PAGE-CURL animation? NO ?
Well, neither should you with a SCROLL animation!!! An animated page turn is a page turn and only a page turn!
In either mode!
And if you decide to tear out PAGE 2 to PAGE 7 of your BOOK that's perfectly fine!
But just don't expect UIPageViewController to invent a non-existing PAGE 7 when turning back to the recent page unless YOU tell it that things have changed...
If you really want to achieve an uncoordinated jump to elsewhere, well - do it without an
animation! In most cases this will not be very elegant but - it's possible... -
And the PVC even plays nicely along! When jumping to a new SPACE without animation
it will ask you further down the road for both - the BEFORE and AFTER controller. So your application-logic can keep up with the PVC...
But with an animation you are always conveying - move to the previous/next space (BEFORE -
AFTER). So logically there is no need at all for the PVC to ask again about a space it already
knows about when animating page turns!!!
If you wanna see PAGE 7 when flipping back to the left after having animated from PAGE 1
to the right - well, I would say - that's definitely your very own problem!
And just in case you are looking for a better solution than the 'completion-block' hack from
the accepted answer (because with it you are doing work beforehand for something that might
possibly not even get used further down the road) use the gesture recognizer delegate:
- (BOOL)gestureRecognizerShouldBegin:(UIGestureRecognizer *)gestureRecognizer
Set your PVC's DataViewController here (without animation) if you really intend to go back
left to PAGE 7 and the DataSource will be asked for BEFORE and AFTER and you can submit
whatever page you like! With a flag or ivar that you should have stashed away when doing your uncontrolled
jump from PAGE 1 to 8 this should be no problem...
And when people keep on complaining about a bug in the PVC - doing 2 page turns when it is
supposed to do 1 turn only - point them to this article.
Same problem - triggering an un-animated setViewControllers: method within the transition gesture
will cause exactly the same havoc. You think you set the new center - the DataSource is asked
for the new BEFORE - AFTER dataController - you reset your index count... - Well, that seems OK...
But - after all that business the PVC ends its transition/animation and wants to know about the
next (still unknown to it) dataViewController (BEFORE or AFTER) and also triggers the DataSource. That's totally justified ! It needs to know where in its small BEFORE - CENTER - AFTER
world it is and be prepared for the next turn.
But your program-logic adds another index++ count to its logic and suddenly got 2 page turns !!!
And that is one off from where you think you are.
And YOU have to account for that! Not UIPageViewController !!!
That is exactly the point of the DataSourceProtocol only having two methods! It wants to be as generic as possible - leaving you the space and freedom to define your own logic and not being stuck with somebody else's special ideas and use-cases! The logic is completely up to you. And only because you find functions like
- (DataViewController *)viewControllerAtIndex:(NSUInteger)index storyboard:(UIStoryboard *)storyboard position:(GSPositionOfDataViewController)position;
- (NSUInteger)indexOfViewController:(DataViewController *)viewController;
in all the copy/pasted sample applications in the cloud doesn't necessarily mean that you have to eat that pre-cook food! Extend them any way you like! Just look above - in my signature you will find a 'position:' argument! I extended this to know later on if a completed page turn was a right or a left turn. Because the delegate unfortunately just tells you whether your turn completed or not! It doesn't tell you about the direction! But this sometimes matters for index-counting, depending on your application's need...
Go crazy - they are your's...
HAPPY CODING !!!