Change height of inputAccessoryView issue

After reading the answer above, which is a great find, I was concerned that relying on the constraint you need to change being [0] or firstObject is an implementation detail that's likely to change under us in the future.

After doing a bit of debugging, I found that the Apple-added constraints on the accessory input view seem to have a priority of 76. This is a crazy low value and not one of the listed enums in the documentation for priority.

Given this low priority value it seems like a cleaner solution to simply conditionally add/remove another constraint with a high priority level, say UILayoutPriorityDefaultHigh when you want to resize the view?

The first answer didn't totally solve my problem but gave me a huge hint. Apple did add a private constraint to the accessory view, but you cannot find it in the constraint list of the accessory view. You have to search for it from its superview. It killed my a few hours.

One way you can update the constraint mentioned in Yijun's answer when changing the height of the inputAccessoryView is by overwriting setFrame: on your inputAccessoryView. This doesn't rely on the height constraint being the first in the array.

- (void)setFrame:(CGRect)frame {
    [super setFrame:frame];

    for (NSLayoutConstraint *constraint in self.constraints) {
        if (constraint.firstAttribute == NSLayoutAttributeHeight) {
            constraint.constant = frame.size.height;
            break;
        }
    }
}

Finally, i found the answer. In ios8, apple add a NSContentSizeLayoutConstraints to inputAccessoryView and set a constant with 44. You can't remove this constaint, because ios8 use it to calculate the height of inputAccessoryView. So, the only solution is to change value of this constant.

Example

in ViewDidAppear

- (void)viewDidAppear:(BOOL)animated {
    if ([self.inputAccessoryView constraints].count > 0) {
        NSLayoutConstraint *constraint = [[self.inputAccessoryView constraints] objectAtIndex:0];
        constraint.constant = CommentInputViewBeginHeight;
    }
}

change inputAccessoryView height when the textview height changed

- (void)growingTextView:(HPGrowingTextView *)growingTextView willChangeHeight:(float)height {

    NSLayoutConstraint *constraint = [[self constraints] objectAtIndex:0];
    float new_height = height + _textView_vertical_gap*2;

    [UIView animateWithDuration:0.2 animations:^{
        constraint.constant = new_height;
    } completion:^(BOOL finished) {
        [self setHeight:new_height];
        [self reloadInputViews];
    }];
}

That is.