swift 4.2实现工具栏

代码:

import UIKit

class ViewController: UIViewController {
    
    var label: UILabel!

    override func viewDidLoad() {
        super.viewDidLoad()
        // Do any additional setup after loading the view, typically from a nib.
        
        let screen = UIScreen.main.bounds
        
        let toolbarHeight: CGFloat = 44 //默认高度
        
        //1. 添加Toolbar
        let toolbar = UIToolbar(frame: CGRect(x: 0, y: screen.size.height - toolbarHeight, width: screen.size.width, height: toolbarHeight))
        
        //save是系统按钮,使用构造函数initWithBarButtonSystemItem:target:action:
        let saveButtonItem = UIBarButtonItem(barButtonSystemItem: UIBarButtonItem.SystemItem.save, target: self, action: #selector(ViewController.save(_:)))
        //open不是系统按钮,使用构造函数initWithTitle:Style:target:action:
        let openButtonItem = UIBarButtonItem(title: "Open", style: UIBarButtonItem.Style.plain, target: self, action: #selector(ViewController.open(_:)))
        
        //创建"可变空格",属于系统按钮,样式使用UIBarButtonSystemItem中的flexibleSpace成员("固定空格"则使用.fixedSpace成员)
        let flexibleButtonItem = UIBarButtonItem(barButtonSystemItem: UIBarButtonItem.SystemItem.flexibleSpace, target: nil, action: nil)
        
        //UIToolbar对象的items属性,用于设置工具栏中按钮的集合
        toolbar.items = [saveButtonItem,flexibleButtonItem,openButtonItem]
        self.view.addSubview(toolbar)
        
        //2. 添加标签
        let labelWidht: CGFloat = 84
        let labelHeigh: CGFloat = 21
        let labelTopView: CGFloat = 250
        self.label = UILabel(frame: CGRect(x: (screen.size.width - labelWidht)/2, y: labelTopView, width: labelWidht, height: labelHeigh))
        self.label.text = "Label"
        //字体左右居中
        self.label.textAlignment = .center
        self.view.addSubview(self.label)
        
    }
    
    @objc func save(_ sender:AnyObject){
        self.label.text = "点击Save"
    }
    
    @objc func open(_ sender:AnyObject){
        self.label.text = "点击Open"
    }


}

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关于"可变空格"和"固定空格":

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