Swift 4 backgroundColor bug?

Question

I have a problem with transparency in my Views, especially with UITableView.

Just to make sure. I already have 3 years of experience with swift and this is the first time, I am getting this problem.

So in apple's docs it says the following: backgroundColor The view's background color.

Changes to this property can be animated. The default value is nil, which results in a transparent background color."

But when applying clear color to backgroundColor or tableView.backgroundColor = UIColor.clear, the background is still appearing white.

Is this a bug or a feature?

EDIT:

The tableView isn't the problem anymore. It is the cell within the tableView. Already tried solutions are clearing the background color of all subviews. Nothing changed.

EDIT 29.09.17

Ok, I debugged my application and got this:

UICachedDeviceWhiteColor and cachedColor.

A google searching also didn't help.

Edit 29.09.2017 Later that day ...

The problem occurs, when updating from swift 3 to swift 4. I made a new project with swift 4, but it actually works fine. Because it is a problem I have to solve. I will try some things and update this post from time to time.

Answer 1

In UITableViewCell and UICollectionViewCell there is a property view called contentView.

A common mistake is to manipulate the cell directly. Instead try to manipulate the cells content view:

Obj-c

UITableViewCell *cell = ....// get the cell

cell.backgroundColor = ... // BAD !

cell.contentView.backgroundColor = [UIColor redColor] // this is the correct way.

Swift

let cell = ...
cell.contentView.backgroundColor = UIColor.red // make sure its the contentView 

also a couple small nuances with colors and opacity:

If you want only the background to have opacity (i.e. less than 100%) , make sure you are not changing the view's opacity (i.e. view.alpha = 0.5 BAD) - change the color's opacity value instead:

i.e.

cell.contentView.backgroundColor = [UIColor colorWithRed:... green:... blue:... alpha:0.5];

Another useful trick is to pause the application and press the "visual debug" button.

Search for your view and check it's attributes in the inspector