Android - 在Kotlin中声明和使用视图

Question

我正在尝试使用kotlin for android并试图像这样声明Linearlayout:

internal var linlay_SuccessfulPayment : LinearLayout = null!!
internal var linlay_failPayment : LinearLayout

linlay_SuccessfulPayment = findViewById(R.id.linlay_SuccessfulPayment) as LinearLayout
linlay_failPayment = findViewById(R.id.linlay_failPayment) as LinearLayout

但是在日志中我得到了这个:

Caused by: kotlin.KotlinNullPointerException
                                                                         at com.example.activities.PaymentResult.<init>(Result.kt:14)
                                                                         at java.lang.Class.newInstance(Native Method)
                                                                         at android.app.Instrumentation.newActivity(Instrumentation.java:1096)
                                                                         at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3122)
                                                                         at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3415) 
                                                                         at android.app.ActivityThread.access$1100(ActivityThread.java:229) 
                                                                         at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1821) 
                                                                         at android.os.Handler.dispatchMessage(Handler.java:102) 
                                                                         at android.os.Looper.loop(Looper.java:148) 
                                                                         at android.app.ActivityThread.main(ActivityThread.java:7329) 
                                                                         at java.lang.reflect.Method.invoke(Native Method) 
                                                                         at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1230) 
                                                                         at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1120) 

请帮帮我.

Answer 1

你的问题是可空性,这将是一个使用lateinit关键字(文档)的好地方:

private lateinit var linlay_SuccessfulPayment: LinearLayout
private lateinit var linlay_failPayment: LinearLayout

这样,您可以定义一个不可为空的var,但会延迟初始化,您可以在onCreate()中执行此操作.
你必须在访问它之前初始化它,否则你会得到一个PropertyNotInitialisedException.

第二种选择是使用属性委派进行延迟初始化:

private var linlay_SuccessfulPayment: LinearLayout by Delegates.lazy { findViewById(R.id.linlay_SuccessfulPayment) as LinearLayout }

这样,视图仅在第一次使用时初始化,并且您将所有内容放在一个位置.

Answer 2

初始化如下

internal var linlay_SuccessfulPayment : LinearLayout ?= null
internal var linlay_failPayment : LinearLayout ?= null

并像下面一样使用它

linlay_SuccessfulPayment = findViewById<LinearLayout>(R.id.linlay_SuccessfulPayment)
linlay_failPayment = findViewById<LinearLayout>(R.id.linlay_failPayment)