UIView background color affects touches in iOS 5

问题:

I had a custom view with subclassed touch responses that was working in iOS 4. On iOS 5, these touches would not respond at all when touched along the bottom edge of the view, if the view's background color was set to clearColor.

I have not been able to track this down, but does anyone know if iOS 5 changed the way views respond to touches depending on a transparent background?

I can make no changes to the code other than set the background color to any opaque color like orangeColor and the view fully responds.

Note the issue does not affect touches elsewhere in the view; only along the bottom edge, anywhere below the last subview added to the view; presumably a clear background is treated as if the view does not exist for the sake of touches when looking at an area of the view that has no content. Change the color, the view has "content" and the touches work!

回答1:

Instead of using [UIColor clearColor], try using this:

[view setBackgroundColor:[UIColor colorWithRed:0 green:0 blue:0 alpha:0.1]];

NOTE: A UIView does not respond to touch events when the alpha is anything below 0.1. [UIColor clearColor] sets an alpha to 0.0, so you won't get the touch events. Following the above method, you can receive the touch events on a transparent view.

回答2:

In case anyone else runs into this problem and wants a better solution than setting a partial opacity for the background, you can set the view's opaque property to NO and then add an empty drawRect: method. (Tested and working on iOS8, beta 4.)