1.Constraints priority
将evInputView的高度约束的priority设为750,evInputView的inputTextView如果不设高度约束，那么高度就是defaultInputViewH,如果设了高度，那么就是这个高度.
evInputView.snp.remakeConstraints { (make) in
make.left.right.equalTo(0)
make.bottom.equalTo(bottom)
make.height.equalTo(defaultInputViewH).priority(750)
}
inputTextView.snp.remakeConstraints { (make) in
make.top.equalTo(textViewFrame.top)
make.bottom.equalTo(textViewFrame.bottom)
make.left.equalTo(textViewFrame.left)
make.right.equalTo(textViewFrame.right)
}
inputTextView.snp.remakeConstraints { (make) in
make.top.equalTo(textViewFrame.top)
make.bottom.equalTo(textViewFrame.bottom)
make.left.equalTo(textViewFrame.left)
make.right.equalTo(textViewFrame.right)
make.height.equalTo(height)
}
https://segmentfault.com/a/1190000004650551
https://github.com/February12/YLBaseChat/