在Swift中从userInfo获取键盘大小

您的生产线存在一些问题

var keyboardSize = notification.userInfo(valueForKey(UIKeyboardframeBeginUserInfoKey))

• notification.userInfo

  返回一个 可选的 dictionary

  [NSObject : AnyObject]?

  ，因此在访问它的值之前必须先将其拆开。
• Objective-C

  NSDictionary

  映射到Swift本机字典，因此您必须使用字典下标语法（

  dict[key]

  ）来访问值。
• 该值必须强制转换为

  NSValue

  以便可以调用

  CGRectValue

  它。

所有这些都可以通过可选分配，可选链接和可选强制转换的组合来实现：

if let userInfo = notification.userInfo {   if let keyboardSize = (userInfo[UIKeyboardframeBeginUserInfoKey] as? NSValue)?.CGRectValue() {    let contentInsets = UIEdgeInsets(top: 0, left: 0, bottom: keyboardSize.height, right: 0)       // ...   } else {       // no UIKeyboardframeBeginUserInfoKey entry in userInfo   }} else {   // no userInfo dictionary in notification}

或一步：

if let keyboardSize = (notification.userInfo?[UIKeyboardframeBeginUserInfoKey] as? NSValue)?.CGRectValue() {    let contentInsets = UIEdgeInsets(top: 0, left: 0, bottom: keyboardSize.height, right: 0)    // ...}

Swift 3.0.1（Xpre 8.1）更新：

if let userInfo = notification.userInfo {    if let keyboardSize = userInfo[UIKeyboardframeBeginUserInfoKey] as? CGRect {        let contentInsets = UIEdgeInsets(top: 0, left: 0, bottom: keyboardSize.height, right: 0)        // ...    } else {        // no UIKeyboardframeBeginUserInfoKey entry in userInfo    }} else {    // no userInfo dictionary in notification}

或一步：

if let keyboardSize = notification.userInfo?[UIKeyboardframeBeginUserInfoKey] as? CGRect {    let contentInsets = UIEdgeInsets(top: 0, left: 0, bottom: keyboardSize.height, right: 0)    // ...}