致命异常：main KotlinNullPointerException

Question

 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()
    }

}

错误为：

11-17 06:23:34.603 354 0-3540/com.example.ruiru.salestracker E/AndroidRuntime：致命异常：主进程：com.example.ruiru.salestracker,pid：3540 java.lang.RuntimeException：无法启动activity ComponentInfo{com.example.ruiru.salestracker/com.example.ruiru.salestracker}：Kotlin.KotlinNullPointerException（位于Android.app.ActivityThread.PerformLaunchActivity（ActivityThread.java:2817)n在com.example.ruiru.salestracker.addsales.onCreate（addsales.kt:25)在android.app.activity.performCreate（activity.java:6975)在android.app.instrumentation.callactivityonCreate（instrumentation.java:1213)在android.app.activitythread.performLaunchActivity（activitythread.java:2770)在android.app.activitythread.handleLaunchActivity（activitythread.java:2892） 在android.app.activitythread.-wrap11（未知源：0） 在Android.app.ActivityThread$H.HandleMessage（ActivityThread.java:1593) 在android.os.handler.dispatchMessage(Handler.java:105) 在android.os.looper.loop(looper.java:164) 在android.app.activityThread.main（activityThread.java:6541) 在java.lang.Reflect.Method.Invoke（原生方法） 在com.android.internal.os.zygote$methodandargscaller.run(zygote.java:240) 在com.android.internal.os.zygoteinit.main（zygoteinit.java:767)

Answer 1

您似乎忘记初始化dateedittext。为什么不试试KotlinAndroid扩展插件。通过使用这个插件，您不需要初始化视图，而是可以直接使用它们的ID。对于您的情况：只需添加import

import kotlinx.android.synthetic.main.activity_add_sales.*

然后您现在可以删除：

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

您可以通过他们的ID访问他们。就像

date.setText("15-11-2017")