Xamarin.Forms - Force ListView layout to redraw

ios listview xamarin xamarin.forms redraw

14,470

Solution 1

The height of the cells aren't recalculated by default because it is an expensive process. If you want to force a re-size you need to call ForceUpdateSize() on the cell.

NOTE: This does not work on older versions of Xamarin Forms. It was added in 2.0.0.0, but try updating to at least 2.2.0.31

Solution 2

Set your CachingStrategy="RetainElement", it's expensive, but will force an update a lot more. If your list isn't too long, you won't notice.

I've noticed that if a cell is visible, even though bound to an obserablecollection, that cell doesn't update until I scroll up then down.

Solution 3

I've had terrible luck getting native controls to redraw. The one thing that has worked for me has been in a custom renderer: ((IVisualElementController)Element).NativeSizeChanged()

14,470

Author by

jbyrd

Updated on June 14, 2022

Comments

jbyrd almost 2 years

I have a ListView with HasUnevenRows = true, where the content of each cell is variant to begin with, but the content can also change on the fly (through clicking of a button in the cell). When the ListView initially loads, the system must perform a calculation in order to correctly determine and draw the heights of each cell based on their content.

But when I update the content after the initial load, this same calculation is apparently not done, because the height of the cell does not change -- until I've scrolled that item out of view and then back into view.

How can I force this same calculation and redraw manually, without completely refreshing the ListView??

I tried wrapping the ListView in a Frame and calling .ForceLayout() on the frame, but no luck.
jbyrd almost 8 years

I don't want to completely refresh the list, because I'm in a particular state of an item that I need to preserve.
jbyrd almost 8 years

I don't want to refresh the data, I only want to redraw the list in its current state.
Artem Zelinskiy almost 8 years

It will not refresh it. It will just recalculate row/list heights
Mr.Koçak almost 8 years

Do you use a DataTemplate for your listview?
jbyrd almost 8 years

Yes, I have a separate file for the DataTemplate.
jbyrd almost 8 years

I just tried it, but it has no effect. I added a "refresh" button with a .Clicked event that calls myListView.BeginRefresh() and myListView.EndRefresh(); No luck. In the clicked even, I even called a myListView.TranslateX = 100; to make sure it was affecting the list correctly, and it was - that worked. But BeginRefresh and EndRefresh didn't do anything.
Mr.Koçak almost 8 years

I know that when you delete something from your list and your itemsource is observableCollection it works, it upgrades the view.. but i don't know if it will work for you. And i also dont know if you can have different sizes per row in a listview.
Mr.Koçak almost 8 years

I think in your datatemplate you should have something like if(condition==true) layout.Add(newLabel) else layout.remove(newLabel) to get condition value of your object you have to use databinding
jbyrd almost 8 years

@MrKocak - what does that have to do with dynamically changing the height? Sorry, I'm not following.
jbyrd almost 8 years

Interesting - I just tried that, but my application crashed on calling that command. I created a button inside the cell with a .Clicked event calling ForceUpdateSize().
jbyrd almost 8 years

ForceUpdateSize(), haha - just that.
jbyrd almost 8 years

So.....turns out my Xamarin.Forms version was the problem. I was on 2.1.0.6526. Once I upgraded to 2.2.0.31, it worked!!
Scott Nimrod almost 5 years

I used CachingStrategy="RecycleElement" and it worked.