elsie

var mystring = "hello wold, hello code";
var data : Data = mystring.data(using: .utf8)!;
if let range = mystring.range(of: "wold") {
    let startPos = mystring.distance(from: mystring.startIndex, to: range.lowerBound)
    data = data.subdata(in: Range(startPos..<data.endIndex));
    print(String(data:data, encoding:.ascii)!)
}

减去导航栏的高度就好了， 如果顶部有其他的也把其他元素给减掉。 self.tableView.frame.size.height设置为self.view.frame.size.height - 64，