iOS 7 AutoLayout sticky button to bottom screen

Question

I have read lot of documents and tutorials about autolayout and constraints but I don't know what I'm doing wrong but in my case the examples doesn't work...I know that this is a repeated question but I don't know what I can do...

I'm trying to fix a button to my bottom screen. Bottom with 0 distance. In 4 hinches screen all is ok but when I'm changig to 3,5" the button dissapear. This is what I'm doing:

1. Normal button
2. Select button and add the bottom space constraint
3. Button look likes fine
4. When screen size changes, the button dissapears

Thanks a lot!

Answer 1

You can complete the following steps to achieve that:

1. Add bottom constraint, width and height:

2. Add horizontal centre constraint:

3. Now you can test on your storyboard by clicking the Apply from factor button:

Answer 2

Select the button, and select "Update Frames"

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Suggestion: you should add constraints to the button for left, right and height.