WPF RepeatButton fires only once on TouchUp when hosted in ListBox #8223
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singhashish-wpf
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lindexi
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Jan 30, 2024
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@cmjthomas Sorry for delay. From the call stack, it’s evident that touch behavior is influenced by Manipulation. Due to the complexity of handling Manipulation logic for touch, unlike a mouse, WPF can only intercept touch in the ManipulationDevice to prevent touch from escalating to mouse and affecting normal logic. In the demo, the RepeatButton is placed inside a ListBox, and the default style of ListBox includes a ScrollViewer object. This ScrollViewer object sets the IsManipulationEnabled property to true. This results in the touch received by the RepeatButton inside the ListBox being consumed by Manipulation, preventing the continuous triggering of Click events. How to prove this? Try setting the IsManipulationEnabled property of the ListBox’s ScrollViewer to false, and you will find that the RepeatButton can continuously trigger Click events under touch. The specific implementation code can be found in my demo application. Additionally, I have read the source code of WPF and found that this issue may be difficult to fix. I apologize that I can only tell you the cause of this issue, and I may not be able to help you fix it. If there is anything you don’t understand, feel free to discuss. |
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And you will find that after setting the IsManipulationEnabled property of RepeatButton to true, no matter where the RepeatButton is placed, it can reproduce the behavior you mentioned of placing the RepeatButton inside a ListBox. <RepeatButton IsManipulationEnabled="True" Height="100" Click="StackPanelRepeatButtonClick" Content="Long touch 'repeat' works on this RepeatButton"/> |
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Description
Using a touchscreen, the RepeatButton fails to raise repeated Click events when the button is hosted inside a ListBox or ListView.
Similarly, the grip of a Slider (when hosted in a ListBox) cannot be grabbed by touching the screen.
Both Slider and RepeatButton work as expected when interacted with a mouse.
Reproduction Steps
ListBoxRepeatButtonBug.zip
Expected behavior
RepeatButton raises repeated click events when touched/depressed.
Should be able to grab/slide a Slider control
Actual behavior
RepeatButton raises a Click event only once on TouchUp.
Cannot slide a Slider
Regression?
No. Repro'd on other .NET versions
Known Workarounds
None known
Impact
Affects any WPF application where the user interacts with a ListBox using a touchscreen
Configuration
Other information
The attached repro was inspired by a similar bug report #4512
That particular bug was observed in Core 3.1 but is no longer a problem on NET6.
I have tested that and can confirm that I also see that as fixed since NET6.
During my investigation for this new bug, I tried disabling the Touch API using two methods:
This makes the touchscreen behave instead like a mouse touchpad.
The repeat Click event of the RepeatButton will be raised as expected in this scenario, but to initiate the ButtonDown/depressed state the user must double-tap the screen so this is not a viable solution.
On further investigation, I started monitoring the TouchDown/Up/Move/Enter/Leave events of the RepeatButton.
When the button works I see the following event sequence:
Then when I release
When the RepeatButton doesn't work (ie is inside a ListBox), I see the following sequence:
When I release
There is a spurious TouchLeave event while the button is depressed which seems to inhibit any further Click events.
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