Swift NSLayoutConstraint

        voiceButton.translatesAutoresizingMaskIntoConstraints = false
        
        // 宽度约束
        let width: NSLayoutConstraint = NSLayoutConstraint(item: voiceButton, attribute: .width, relatedBy:.equal, toItem:nil, attribute: .notAnAttribute, multiplier:0.0, constant:width)

        voiceButton.addConstraint(width)

        // 高度约束
        let height: NSLayoutConstraint = NSLayoutConstraint(item: voiceButton, attribute: .height, relatedBy:.equal, toItem:nil, attribute: .notAnAttribute, multiplier:0.0, constant:height)

        voiceButton.addConstraint(height)

        // 居中约束
        let centerX: NSLayoutConstraint = NSLayoutConstraint(item: voiceButton, attribute: .centerX, relatedBy:.equal, toItem:viewController?.view, attribute:.centerX, multiplier:1.0, constant: 0)

        voiceButton.superview!.addConstraint(centerX)

        // 下边约束
        let bottom: NSLayoutConstraint = NSLayoutConstraint(item: voiceButton, attribute: .bottom, relatedBy:.equal, toItem:viewController?.view, attribute:.bottomMargin, multiplier:1.0, constant: -bottom)


        voiceButton.superview!.addConstraint(bottom)

let margins = viewController?.view.layoutMarginsGuide
        voiceButton.translatesAutoresizingMaskIntoConstraints = false
        NSLayoutConstraint.activate([
            voiceButton.bottomAnchor.constraint(equalTo: margins!.bottomAnchor, constant: -30),
            voiceButton.centerXAnchor.constraint(equalTo: margins!.centerXAnchor, constant: 0),
            voiceButton.heightAnchor.constraint(equalToConstant: wb_voice_button_width),
            voiceButton.widthAnchor.constraint(equalToConstant: wb_voice_button_width),
        ])