While building the Pleroma client (https://www.b4x.com/android/forum/threads/b4x-b4xpages-pleroma-mastodon-client-step-1.119426/), I've encountered several cases where the touch events had some unwanted behavior.
The reason for this, is that there are multiple stacked views that listen for the touch events: B4XDrawer, xCustomListView (= ScrollView) and panels that hold the modified BBCodeViews.
Two things that help improve the touch events behavior:
1. Removing the built-in click event of CLV.
2. Adding a special action value to cancelled touch gestures.
By default, touch events start with ACTION_DOWN, followed by zero or more ACTION_MOVE events and end with ACTION_UP event.
There are some cases where the ACTION_UP event happens because the touch gesture was cancelled.
It can happen, for example, when the user touches a panel inside a ScrollView and starts moving the finger slowly. At some point the ScrollView starts treating it as a "scrolling" gesture and the panel will receive an ACTION_UP event although the user didn't really lift the finger.
We can change this behavior by adding this code to the main module:
It will cause the touch event to be raised with action = 4 and will allow us to treat this differently.
The reason for this, is that there are multiple stacked views that listen for the touch events: B4XDrawer, xCustomListView (= ScrollView) and panels that hold the modified BBCodeViews.
Two things that help improve the touch events behavior:
1. Removing the built-in click event of CLV.
B4X:
CLV.Add(pnl, Value)
#if B4i
RemoveClickRecognizer(pnl)
#End If
#if B4i
Private Sub RemoveClickRecognizer (pnl As B4XView)
Dim no As NativeObject = pnl.Parent
Dim recs As List = no.GetField("gestureRecognizers")
For Each rec As Object In recs
no.RunMethod("removeGestureRecognizer:", Array(rec))
Next
End Sub
#End If2. Adding a special action value to cancelled touch gestures.
By default, touch events start with ACTION_DOWN, followed by zero or more ACTION_MOVE events and end with ACTION_UP event.
There are some cases where the ACTION_UP event happens because the touch gesture was cancelled.
It can happen, for example, when the user touches a panel inside a ScrollView and starts moving the finger slowly. At some point the ScrollView starts treating it as a "scrolling" gesture and the panel will receive an ACTION_UP event although the user didn't really lift the finger.
We can change this behavior by adding this code to the main module:
B4X:
#if OBJC
@end
@interface B4IPanelView (touchcancelled)
@end
@implementation B4IPanelView (touchcancelled)
- (void)touchesCancelled:(NSSet *)touches withEvent:(UIEvent *)event {
B4I* bi = [self valueForKey:@"bi"];
NSString* eventName = [self valueForKey:@"eventName"];
for (UITouch *u in touches) {
CGPoint p = [u locationInView:self];
[bi raiseEvent:self event:eventName params:@[@4, @(p.x), @(p.y)]];
}
}
#End IfIt will cause the touch event to be raised with action = 4 and will allow us to treat this differently.
