开发Kotlin猜数字游戏时，无输入点击按钮程序崩溃求助

问题根源 #

• 崩溃原因：当用户未输入任何内容就点击按钮时，userAnsText是空字符串，直接调用toInt()会抛出NumberFormatException，直接导致程序崩溃。
• 初始if条件失效：userAnsInt是通过toInt()生成的非空Int类型，永远不可能等于null，所以if(userAnsInt == null)这个判断逻辑永远不会触发。

修复方案 #

使用toIntOrNull()进行安全类型转换——当输入为空或不是有效数字时，这个方法会返回null，同时调整条件判断的顺序：

class MainActivity : AppCompatActivity() {
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)
        val button = findViewById<Button>(R.id.guessBtn)
        button.setOnClickListener {
            buttonPressed()
        }
    }

    private fun buttonPressed() {
        val result = findViewById<TextView>(R.id.result)
        val userAnsEditText = findViewById<EditText>(R.id.answer)
        val userAnsText = userAnsEditText.text.toString().trim() // 去除首尾空白字符，避免空格触发空提示
        val userAnsInt = userAnsText.toIntOrNull() // 安全转换，失败返回null

        val answerCorrect = "Congrats, you have correctly guessed the number"
        val answerWrong = "Sorry,you have guessed the wrong number"
        val answerEmpty = "Please enter a number"

        val randomValues = Random.nextInt(1, 11)

        // 优先判断输入是否有效
        if(userAnsInt == null) {
            result.text = answerEmpty
        }
        else if(userAnsInt == randomValues) {
            result.text = answerCorrect
        }
        else {
            result.text = answerWrong
        }
    }
}

额外优化点 #

把视图查找逻辑移到onCreate中，避免每次点击按钮都重复查找视图，提升性能：

class MainActivity : AppCompatActivity() {
    // 提前声明视图变量
    private lateinit var resultTextView: TextView
    private lateinit var userAnsEditText: EditText
    private lateinit var guessButton: Button

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)
        
        // 仅初始化时查找一次视图
        resultTextView = findViewById(R.id.result)
        userAnsEditText = findViewById(R.id.answer)
        guessButton = findViewById(R.id.guessBtn)
        
        guessButton.setOnClickListener {
            buttonPressed()
        }
    }

    private fun buttonPressed() {
        val userAnsText = userAnsEditText.text.toString().trim()
        val userAnsInt = userAnsText.toIntOrNull()

        val answerCorrect = "Congrats, you have correctly guessed the number"
        val answerWrong = "Sorry,you have guessed the wrong number"
        val answerEmpty = "Please enter a number"

        val randomValues = Random.nextInt(1, 11)

        if(userAnsInt == null) {
            resultTextView.text = answerEmpty
        }
        else if(userAnsInt == randomValues) {
            resultTextView.text = answerCorrect
        }
        else {
            resultTextView.text = answerWrong
        }
    }
}

内容的提问来源于stack exchange，提问作者Blinky