（Swift）UITextView不显示文本

Question

我正在制作基于文本的iOS游戏，该游戏使用由UITextView（可滚动，不可编辑）和UITextField组成的单个视图。当我在编辑textField时按回车键时，键盘关闭，textField的文本被添加到textView中。但是，UITextView的文本根本没有出现。无论我如何尝试显示它，背景颜色仍然会出现，但没有其他颜色。我已经尝试过设置字体大小和颜色。

这是ViewController中处理两个UI组件的代码。

import UIKit

class ViewController: UIViewController, UITextFieldDelegate, UITextViewDelegate {
    // outlets / actions
    @IBOutlet weak var outputView: UITextView!
    @IBOutlet weak var inputField: UITextField!
    var uni: Universe? // a custom class that contains the game's data

    override func viewDidLoad() {
        //outputView.addObserver(self, forKeyPath: "contentSize", options: NSKeyValueObservingOptions.New, context: nil)
        inputField.delegate = self
        outputView.delegate = self
        inputField.text = "press return for help"
        outputView.text = ""
        outputView.textColor = UIColor.greenColor()
        outputView.frame = self.view.frame
        // The next 3 lines make a new Universe object.
        uni = Assembler.build(outputView)
        uni!.setUni()
        uni!.setParser()
        super.viewDidLoad()
        // Do any additional setup after loading the view, typically from a nib.
        uni!.player.viewLocation()
    }

    // delegate method; this should do 3 things:
    // 1. remove the keyboard
    // 2. call uni.parser.read(text)
    // 3. remove the text in the field

    func textFieldShouldReturn(textField: UITextField) -> Bool {
        textField.resignFirstResponder()
        outputView.text! += textField.text! + "\n"
        uni!.parser!.read(textField.text!) // This function interprets the text from textField and prints something appropriate in the textView.
        textField.text = ""
        return true
    }

    override func didReceiveMemoryWarning() {
        super.didReceiveMemoryWarning()
        // Dispose of any resources that can be recreated.
    }

    // The rest of the code makes the whole frame shift up/down when the keyboard appears/disappears to keep the UITextField visible.
}

任何帮助都将非常感谢。这个网站上的类似问题没有给我任何东西。