Why TabBar images are not displayed

I started to use UITabBarController in ios. I encountered a problem when setting a custom image for the Tab Bar Item.

Configure as follows:

The result is:

Test24.png on supervisor should be:

After a long tangle, I used the images in the source code of the book.

It can be displayed, but the UI cannot be displayed. Fortunately, we woke up the dreamer by using the UI, saying that here we just took a shape and should have a color for it, so I asked my UI brother to add a layer color to the original image to see if it would be displayed.

New image:

Display result:

Sure enough, the Tab Bar Item only takes the shape of the image, and the other colors and things are processed by yourself.

Thank you for reminding me!