Why there is a gap between Keyboard and the View when keyboard appears

Question

Structure:

UIView

BaseView

AutoLayout

1. Center X
2. Center Y
3. Equal Width to SafeView
4. Equal Height to SafeView

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UIView

InnerView (SubView of BaseView)

AutoLayout

1. Leading
2. Trailing
3. Top
4. Bottom (Create the IBOutLet named "bottomLayoutConstraint")

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    - (void)keyBoardWillShow:(NSNotification *)notification {

        NSDictionary *info  = notification.userInfo;
        NSValue      *value = info[UIKeyboardFrameEndUserInfoKey];
        CGRect rawFrame      = [value CGRectValue];
        CGRect keyboardFrame = [self.view convertRect:rawFrame fromView:nil];
        self.bottomLayoutConstraint.constant = CGRectGetHeight(keyboardFrame);
[self.view layoutIfNeeded];

    }

    - (void)keyBoardWillHide:(NSNotification *)notification {

        self.bottomLayoutConstraint.constant = 0.0;

    }

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Why there is a gap between Keyboard and the InnerView when keyboard appears?

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Edit:

After applying Aleksander Maj's solution the gap reduced to 5px

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Edit:

Here is my View hierarchy screenshot

Answer 1

CGRectGetHeight(keyboardFrame) returns the height of the keyboard counting from the bottom edge of the screen. Meanwhile your bottomLayoutConstraint is pinned to your BaseView's safe area's bottom edge (which is not the same as the bottom edge of the screen). The difference between those two horizontal guides is the height of your gap. You should calculate the constant of the bottomLayoutConstraint in the following way:

if (@available(iOS 11, *)) {
  self.bottomLayoutConstraint.constant = CGRectGetHeight(keyboardFrame) - self.view.safeAreaInsets.bottom
} else {
  self.bottomLayoutConstraint.constant = CGRectGetHeight(keyboardFrame)
}

At least that's what I suspect. I didn't reproduce your view hierarchy.

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EDIT:

Could you paste a screenshot of your view hierarchy (with all constraints expanded)? I think your issue with the 5pt gap may have something to do with incorrect constraint constant values.

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EDIT 2: