在Swift中从userInfo获取键盘大小Getting keyboard size from userInfo in Swift

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}

or in one step:

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

Update for Swift 3.0.1 (Xpre 8.1):

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}

or in one step:

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