Forward touch event to UITableView to produce inertia scroll - ios

Question

I have been trying to forward touch events from one view to a UITableView. But I have come across a problem.
In the figure is a prototype view to illustrate the problem. The white view in the bottom half is a normal UITableView. The yellow view is a UIView that forwards touches to the middle of the UITableView using hitTest:withEvent:. The red view is a UIButton.
The goal is to forward the up and down panning touches from the yellow view to the UITableView at the bottom. However, tapping the red UIButton should still work.
I have tried 2 main approaches both of which have problems.
The first approach is to add UIPanGestureRecognizer to the yellow view that can be used to set the contentOffset of the UITableView. The problem is that inertial scrolling of the table view does not work with this approach.
The second approach is to forward touches using hitTest:withEvent: in the yellow view.
-(UIView *)hitTest:(CGPoint)point withEvent:(UIEvent *)event {
if([self.button_red pointInside: [self convertPoint:point toView:self.button_red] withEvent:event]) {
return self.button_red;
} else {
return [self.view_table hitTest:CGPointMake(self.view_table.width/2.0,self.view_table.height/2.0) withEvent:event];
}
}
hitTest:withEvent: is only called when the touch starts in the yellow view. In other words, whenever a drag starts in the red view it won't forward the drag to the table view. Which is not good enough.
Is it possible to forward a pan gesture from the yellow view to the UITableView in a different way that keeps the red button working AND allows drags to work that start in the red button? Should I override the touch event methods in the yellow view to get this to work somehow? Is there way to do all this while keeping the inertial scrolling?

Answer 1

You need to add yellowView as a subview inside the UITableView.
You will also need to take care of the contentInset in order to
accommodate for yellowView height.
By default, cells will appear over this added yellowView, you need
to fix this by adjusting zPosition on the yellowView.
CGFloat height = CGRectGetHeight(yellowView.frame);
// fix yellowView's y position
yellowView.frame = CGRectMake(0, -height, CGRectGetWidth(yellowView.frame), height);
[tableView addSubview:yellowView];
yellowView.layer.zPosition = 10; // make it appear over cells
[tableView setContentInset:UIEdgeInsetsMake(height, 0, 0, 0)];
Hope this helps.