Shift Keyboard if Necessary (login view)

ShiftIfNecessary.m

- (void)shiftKeyboardIfNecessary {
    CGRect viewFrame = self.view.frame;
    CGRect activeTextFieldFrame = self.activeTextField.frame;
    CGFloat bottomPadding = 4;
    
    // The lowest point visible on the screen is the height of the screen minus the height of the keyboard, then adjusted by the current position
    // of the view. So, if the view has already been shifted upwards (negative origin), then more of the lower part of the screen is visible.
    CGFloat lowestPointCoveredByKeyboard = -viewFrame.origin.y + viewFrame.size.height - self.keyboardFrame.size.height;
    
    // The active text field's lowest point is its origin.y + its height (so, if it was at y=200, and is 21px tall, then the lowest point is 221.
    // We then check the lowest point covered by the keyboard, as described above, and check if we're below that (and if so, by how much). This
    // will be the amount (plus a little padding) that we further offset the view by.
    CGFloat distanceActiveTextFieldIsUnderFrame = activeTextFieldFrame.origin.y + activeTextFieldFrame.size.height - lowestPointCoveredByKeyboard;
    
    if (distanceActiveTextFieldIsUnderFrame > 0) {
        viewFrame.origin.y -= distanceActiveTextFieldIsUnderFrame + bottomPadding;
        
        self.view.frame = viewFrame;
    }
}