I do not want to the collectionView to Scroll but only want it to display as a list as its height.
But it seems there is no property to close the function.
Can anyone help?
The CollectionView is currently a preview, and lacks some of its planned functionality. In addition, the API may change as the implementation is completed.
So ,as Денис Чорный said, thought you just want it display just like a list.You can replace it with listview .
for more detail about collectview you can refer here
Related
I use the same DataTemplate to populate some of the views inside my CarouselView: a XAML file with a ContentView. I assign a custom class list to ItemsSource of the carouselview AND use bindings inside the template layout fields to fill them with the properties of my custom class. Everything is working fine. Here comes the wierd part: Let's say there's a button in the template and when you click it on the screen, a Label with "Well Done" text is added to the current Stacklayout of the shown carouselview. This is done by the codebehind of my template XAML. This is ok, too, but I expect this "Well Done" to disappear after I swipe back and forth enough. Because it's not part of the template. It does not disappear, instead I see it on other carousels once in every 4 swipes and it is replaced, I mean it appears on different carousels if I swipe back and forth. To make it disappear completely I have to swipe away from the views that share the same DataTemplate. I cannot understand the mechanics behind this behaviour. I can create another field inside the template to put the "Well Done" text there and show it when the time comes, I know. But I want to understand the mechanics. Thank you.
Asking the right question about a problem is the key to any solution..
After the realization that I've mentioned at the Update comment, I've searched for DataTemplate Caching and found this issue post on Xamarin.Forms Github: https://github.com/xamarin/Xamarin.Forms/issues/9200
There you can find an explanation to how CollectionView was designed and understand the mechanics behind the behaviour. No bug. It's by design.
I have a InfiniteListView which extend ListView from Xamarin Forms.
I know when you on the last item in the list but how can i figure out if the user scrolled to the top of the list ?
Unfortunately, the Xamarin Forms ListView does not expose a Scrolled event or Position property. So your only option is to use the ItemAppearing and ItemDisappearing events.
When you subscribe to these events, you can figure out if the first cell is appearing again, after it disappeared first. This does not actually give you a 100% correct outcome, since it can happen that only a part of the first cell is shown.
If you want a perfect check that you are at the absolute top, you will have to resort to a custom renderer:
On iOS you can make use of the tableView.contentOffset.y property on the UITableView.
On Android it's a little bit more involved, as there are multiple (but no straightforward) ways to achieve this. See this answer for one possibility. This approach is originally meant for saving and restoring scroll position, so adjust it to your needs.
Other platforms have similar ideas. Check which native control the Xamarin Forms renderer creates, and then search the internet for possible solutions for that specific platform.
This is driving me nuts. I have a custom menu class that, when set visible, shows a list of items located in a particular folder. When a hardware button is pressed, my application gets the latest list of items, populates the menu with them, and returns.
The menu displaying these items uses a QListWidget filled with custom widgets. Each of the widgets contains one or more QLabels in a horizontal layout, and is created at the time the menu is shown. In order to adjust the text displayed based on the menu width available, I need to get the size of the QLabel AFTER it has been resized according to the layout, but before the menu becomes visible to the user. The problem is, my layout does not get updated until all of the functions constructing my list return.
I have tried QApplication::ProcessEvents() and the layout update functions, but none of them have updated the values of my QLabels before returning. I can set a QTimer when the button is initially pressed, and have it show the menu, update the items, and stop itself, but that seems like a terrible solution.
Any help would really be appreciated! I've spent most of a day on this.
Marlon
I had this exact problem and could not find an answer anywhere on the Internet. Calling Layout.update(), Layout.activate(), or widget.adjustSize() (all suggested in various places) all did not work.
I had a widget with a vertical layout that I wanted to add a QLabel to and then immediately use the size of the QLabel.
The only thing that worked reliably was
layout->addWidget(myLabel);
myLabel->show();
size = myLabel->size();
It would seem that layouts will just not recalculate until you either return from a function and allow the Qt event loop to progress or manually call show() yourself.
How to update a QLayout and get the new dimensions before returning?
Don't. You're not meant to do that. It'll drive you "nuts" because you're doing it backwards. Layout updates are handled asynchronously from the event loop. Instead of getting layout dimensions right away, set yourself up to be part of the system. Some options are:
Implement a custom widget that will interact properly with the layout, growing to fill the available width of the layout. Perhaps all you need is a size policy and a way to elide text?
Make a custom layout that takes the special properties of your use case into account.
You want to call QWidget::adjustSize() on your parent widget. This will force the layout recalculations.
Have you tried using layout()->update(); ?
I've tried many but nothing works for me on Qt 5.15.
Only invented little patch - create timer and get size after 20 msec:
QTimer::singleShot(20, this, [this]
{
const auto height = myLayout->contentsRect().height();
// ...
});
I was hoping someone could give me some guidance on building an image gallery which loads images dynamically for a PlayBook application.I've uploaded a quick mockup of what I am trying to achieve, I want to dynamically load images into a QNX TileList or Flex equivalent and as the user scrolls through the list I want to call another 'page' of images dynamically. I have already produced an example which uses a custom cell renderer to dynamically load images but I am having problems when I attempt to identify when the user has reached the end of the list.
I have tried using the lastVisibleItem property of the list while the user is scrolling to identify if the last item visible in the list is also last in the DataProvider (so I know when I need to call for more images) but when I add images to the DataProvider it takes me back to the start of the list, can anyone tell me the reason for this?
Any advice on a different approach or how to modify the TileList would be greatly appreciated.
The scrollPosition automatically gets reset to 0 when you update the dataProvider. I've done workarounds that store the current scrollPosition before updating the dataProvider and then re-set it after the update to the dataProvider has completed. Let me know if you need some code sample and I'll see if I can dig something up.
Another option would be to use dataPaging. Here is a good example of how to do that:
http://www.jamesward.com/2010/10/11/data-paging-in-flex-4/
I have a List component from which I'd like to be able to remove items using drag & drop, but without having a specific target. If you use the mac, the behaviour I'm looking for is something like what the Dock uses; when you drag something out of the bounds of the control it should get an icon that indicates that it'll be deleted (OSX uses a cloud or something?) and then if you release it it will be removed from the list.
How can I do this?
(If I need to provide a more clear description, please comment; I'll fill in what I can)
In my experience with drag/drop in Flex, you cannot simply drag something out and handle that. There is no dragOut event (unfortunately), so that would leave you up to the task of writing dragOver and dragDrop listeners on all the containers surrounding your dragInitiator and handling the process accordingly.
It's more time consuming and can become complicated if any of these controls already have specific dragOver and dragDrop event handlers.
Hope this helps.
Having no Flex experience all I can offer is some psuedo code which resembles how I implemented a similar effect in JavaScript, but hopefully it will get you started.
Essentially what you'll want to do is during your drag event measure the current coordinates of the object you're dragging to see if they intersect the original container and when they fall outside of its bounds call the logic to update the icon in order to indicate it will be removed. Then, on the drop event, check the coordinates once more and delete the item if needed.