在打开一个可选值swift时,意外地发现了nil

Question

我收到一条错误消息" 从Swift nil解包时意外发现Optional",下面是类.该行发生错误:

(cell.contentView.viewWithTag(1) as UILabel).text = object["firstName"] as? String

我有一个自定义单元类,其中2个UILabels标记为1和2,插座已设置

    import UIKit
    import Foundation

    class dictionaryTableViewController: UIViewController,       UITableViewDelegate, UITableViewDataSource{

    var objects = NSMutableArray()
    var dataArray = [["firstName":"Debasis","lastName":"Das","email":"debasis_das@knowstack.com"],["firstName":"John","lastName":"Doe","email":"jdoe@knowstack.com"],["firstName":"Jane","lastName":"Doe","email":"janedoe@knowstack.com"],["firstName":"Mary","lastName":"Jane","email":"mjane@knowstack.com"]]

    @IBOutlet
    var tableView: UITableView!

    var items: [String] = ["We", "Heart", "Swift"]

    override func viewDidLoad() {
        super.viewDidLoad()
        self.tableView.registerClass(UITableViewCell.self, forCellReuseIdentifier: "MyCell")
    }

    override func didReceiveMemoryWarning() {
        super.didReceiveMemoryWarning()
    }


    func tableView(tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
        return dataArray.count;//self.items.count;
    }

    func tableView(tableView: UITableView, cellForRowAtIndexPath indexPath: NSIndexPath) -> UITableViewCell {
        //var cell:UITableViewCell = self.tableView.dequeueReusableCellWithIdentifier("cell") as UITableViewCell
        //cell.textLabel?.text = self.items[indexPath.row]
        //return cell
        let cell = tableView.dequeueReusableCellWithIdentifier("MyCell", forIndexPath: indexPath) as UITableViewCell
        let object = dataArray[indexPath.row] as NSDictionary
        (cell.contentView.viewWithTag(1) as UILabel).text = object["firstName"] as? String
        (cell.contentView.viewWithTag(2) as UILabel).text = object["lastName"] as? String
        return cell
    }

    func tableView(tableView: UITableView, didSelectRowAtIndexPath indexPath: NSIndexPath) {

        println("You selected cell #\(indexPath.row)!")

    }

}

Answer 1

如果你想使用自定义单元格布局,我建议

1. 子类UITableViewCell:

   //  CustomTableViewCell.swift
   
   import UIKit
   
   class CustomTableViewCell: UITableViewCell {
   
       @IBOutlet weak var firstNameLabel: UILabel!
       @IBOutlet weak var lastNameLabel: UILabel!
   
   }
   

2. 在故事板中创建表视图.将单元格原型添加到storyboard中的tableview.设计细胞原型(添加你想要的任何标签).

3. 将单元格原型的故事板标识符指定为您想要的任何内容(MyCell在您的示例中).

   

4. 在此示例中,指定单元原型的基类CustomTableViewCell:

   

5. IBOutlet连接单元原型和UITableViewCell子类之间的引用.

   

   请注意IBOutlet引用左侧的实心项目符号.这表明插座正确连接.

6. cellForRowAtIndexPath在您的数据源中实现,例如在Swift 3中:

   func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
       let cell = tableView.dequeueReusableCell(withIdentifier: "MyCell", for: indexPath) as! CustomTableViewCell
   
       let person = dataArray[indexPath.row]
   
       cell.firstNameLabel.text = person["firstName"]
       cell.lastNameLabel.text = person["lastName"]
   
       return cell
   }
   

   或者在Swift 2中:

   override func tableView(tableView: UITableView, cellForRowAtIndexPath indexPath: NSIndexPath) -> UITableViewCell {
       let cell = tableView.dequeueReusableCellWithIdentifier("MyCell", forIndexPath: indexPath) as! CustomTableViewCell
   
       let person = dataArray[indexPath.row]
   
       cell.firstNameLabel.text = person["firstName"]
       cell.lastNameLabel.text = person["lastName"]
   
       return cell
   }
   

7. 请注意,如果使用电池的原型,你就不会想打电话给registerClass在viewDidLoad.故事板将自动为您重新注册您的自定义类(因为您在步骤3和4中已完成的操作).

Answer 2

编辑2:这个解决方案可能更适合您的目的.通过这个,您可以为自己的UITableViewCell创建自己的类,并将其用于重用模式.评论在代码中:

    class dictionaryTableViewController: UIViewController, UITableViewDelegate, UITableViewDataSource{

    // The data
    var dataArray = [["firstName":"Debasis","lastName":"Das","email":"debasis_das@knowstack.com"],["firstName":"John","lastName":"Doe","email":"jdoe@knowstack.com"],["firstName":"Jane","lastName":"Doe","email":"janedoe@knowstack.com"],["firstName":"Mary","lastName":"Jane","email":"mjane@knowstack.com"]]

    // The outlet to your tableview in the ViewController in storyboard
    @IBOutlet var tableView: UITableView!

    override func viewDidLoad() {
        super.viewDidLoad()

        // Create a nib for reusing
        let nib = UINib(nibName: "MyCell", bundle: nil)
        // Register the nib for reusing within the tableview with your reuseidentifier
        tableView.registerNib(nib, forCellReuseIdentifier: "MyCell")

        // Set delegate and datasource to self (you can do that in interface builder as well
        tableView.delegate = self
        tableView.dataSource = self
    }

    func tableView(tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
        return dataArray.count; // return the number of datasets
    }

    func tableView(tableView: UITableView, cellForRowAtIndexPath indexPath: NSIndexPath) -> UITableViewCell {

        // create a reusable cell with the reuse identifier you registered in viewDidLoad and cast it to MyCell
        let cell = tableView.dequeueReusableCellWithIdentifier("MyCell") as MyCell
        let object = dataArray[indexPath.row] as NSDictionary

        // set the strings matching your array
        cell.label1.text = object["firstName"] as? String
        cell.label2.text = object["lastName"] as? String

        // return the cell
        return cell

    }

    // some example for the delegate
    func tableView(tableView: UITableView, didSelectRowAtIndexPath indexPath: NSIndexPath) {
        println("You selected cell #\(indexPath.row)!")
    }


}


// class for you own UITableViewCell
// has own xib file
class MyCell: UITableViewCell {

    // two outlets representing two labels in the xib file
    @IBOutlet private weak var label1: UILabel!
    @IBOutlet private weak var label2: UILabel!
}

为此,您必须使用正确的名称创建一个xib文件(在本例中为MyCell).它应该类似于:

设置自定义视图和插座的类非常重要.

-------------------------------------其他解决方案----------- ---------------------------

编辑:我认为你没有初始化你自己的类'MyCell',而是使用reuseIdentifier'MyCell'来初始化Apple的'UITableViewCell'类.这就是使用UITableViewCell的解决方案:

该行(cell.contentView.viewWithTag(1) as UILabel)不仅是对特定类的强制转换,它还展开了Optional(UIView).你在其他情况下用'!'来做到这一点.所以问题是:你正在创建一个UITableViewCell实例,这是Apple创建的一个类.您希望使用特定标记获取该视图内的子视图.你怎么知道苹果给了他们这些标签？你真正想要的是创建一个具有特殊样式的UITableViewCell实例,并设置textLabels的值,如下所示:

override func tableView(tableView: UITableView, cellForRowAtIndexPath indexPath: NSIndexPath) -> UITableViewCell {
        // Create an instance of UITableViewCell. Style is .Subtitle but could be others as well
        var cell = tableView.dequeueReusableCellWithIdentifier("MyCell") as? UITableViewCell
    let object = dataArray[indexPath.row] as NSDictionary

    // set the strings matching your array
    cell?.textLabel?.text = object["firstName"] as? String
    cell?.detailTextLabel?.text = object["lastName"] as? String

    // return the cell
    return cell!
    }