android - 致命异常 : main KotlinNullPointerException

Question

这是我第一次构建 Android 应用程序。但是，当我在我的虚拟设备上运行该应用程序时，它停止工作并不断崩溃。该错误说明了一些关于空指针异常的信息。这是我第一次使用 Kotlin，我用 Java 编写代码并更改为 Kotlin。

 override fun onCreate(savedInstanceState: Bundle?) {
    super.onCreate(savedInstanceState)
    setContentView(R.layout.activity_add_sales)

    val date: EditText? = null
    val changeDate: CheckBox? = null
    val yes: RadioButton? = null
    val no: RadioButton? = null

    date!!.setText("15-11-2017")
    date.isEnabled = false

    val button2 = findViewById<View>(R.id.btnSubmit) as Button
    button2.setOnClickListener {
        var name = findViewById<View>(R.id.name) as EditText
        var cost = findViewById<View>(R.id.cost) as EditText
        val itemcost = Integer.parseInt(cost!!.text.toString())
        var price = findViewById<View>(R.id.price) as EditText
        val itemprice = Integer.parseInt(price!!.text.toString())
        var qty = findViewById<View>(R.id.quantity) as EditText
        var chgDate = false
        var discount = false
        val toast = Toast(applicationContext)
        if (itemprice < itemcost) {
            price!!.error = "Selling price cannot be lower than item price!"
        } else {
            if (changeDate!!.isChecked) {
                chgDate = true
                date.isEnabled = true
            }
            if (yes!!.isChecked) {
                discount = true
            }
        }
        Toast.makeText(this@AddSales, "Item Name: " + name!!.text + "\n" + "Cost: " + cost!!.text + "\n" + "Item Price: " + price!!.text + "\n" + "Quantity: " + qty!!.text + "Date: " + date + "Staff Discount: " + discount, Toast.LENGTH_SHORT).show()
    }

}

错误是:

11-17 06:23:34.603 3540-3540/com.example.ruiru.salestracker E/AndroidRuntime: FATAL EXCEPTION: main Process: com.example.ruiru.salestracker, PID: 3540 java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.ruiru.salestracker/com.example.ruiru.salestracker.AddSales}: kotlin.KotlinNullPointerException at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2817) at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2892) at android.app.ActivityThread.-wrap11(Unknown Source:0) at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1593) at android.os.Handler.dispatchMessage(Handler.java:105) at android.os.Looper.loop(Looper.java:164) at android.app.ActivityThread.main(ActivityThread.java:6541) at java.lang.reflect.Method.invoke(Native Method) at com.android.internal.os.Zygote$MethodAndArgsCaller.run(Zygote.java:240) at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:767) Caused by: kotlin.KotlinNullPointerException at com.example.ruiru.salestracker.AddSales.onCreate(AddSales.kt:25) at android.app.Activity.performCreate(Activity.java:6975) at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1213) at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2770) at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2892)  at android.app.ActivityThread.-wrap11(Unknown Source:0)  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1593)  at android.os.Handler.dispatchMessage(Handler.java:105)  at android.os.Looper.loop(Looper.java:164)  at android.app.ActivityThread.main(ActivityThread.java:6541)  at java.lang.reflect.Method.invoke(Native Method)  at com.android.internal.os.Zygote$MethodAndArgsCaller.run(Zygote.java:240)  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:767)

Answer 1

因为您的日期 EditText 为空。在使用 editText 之前像这样初始化 editText

var date = findViewById<View>(R.id.date) as? EditText

然后设置日期的值

date?.setText("15-11-2017")
date?.isEnabled = false