在Kotlin中使用Singleton的StackOverflowError

时间：2016-04-11 17:15:24

标签： android kotlin jetbrains-ide kotlin-android-extensions

任何人都可以说，为什么我使用这个Kotlin课程获得java.lang.StackOverflowError？第41行是if (instance == null) { 

class TokenHelper protected constructor() {
    var token: String? = null
    var appId: String? = null
    var installationId: String? = null
    var userId: String? = null

    companion object {
        var instance: TokenHelper? = null
            get() {
                if (instance == null) {
                    instance = TokenHelper()
                }
                return instance
            }
    }
}

堆栈跟踪：

04-11 19:07:42.188 16142-16142/com.foo.bar.debug E/AndroidRuntime: FATAL EXCEPTION: main
  Process: com.foo.bar.debug, PID: 16142
  java.lang.StackOverflowError: stack size 8MB
      at com.foo.bar.helper.TokenHelper$Companion.getInstance(TokenHelper.kt:0)
      at com.foo.bar.helper.TokenHelper$Companion.getInstance(TokenHelper.kt:41)
      at com.foo.bar.helper.TokenHelper$Companion.getInstance(TokenHelper.kt:41)
      at com.foo.bar.helper.TokenHelper$Companion.getInstance(TokenHelper.kt:41)
      at com.foo.bar.helper.TokenHelper$Companion.getInstance(TokenHelper.kt:41)
      at com.foo.bar.helper.TokenHelper$Companion.getInstance(TokenHelper.kt:41)
      at com.foo.bar.helper.TokenHelper$Companion.getInstance(TokenHelper.kt:41)
      at com.foo.bar.helper.TokenHelper$Companion.getInstance(TokenHelper.kt:41)
      at com.foo.bar.helper.TokenHelper$Companion.getInstance(TokenHelper.kt:41)
      at com.foo.bar.helper.TokenHelper$Companion.getInstance(TokenHelper.kt:41)
      at com.foo.bar.helper.TokenHelper$Companion.getInstance(TokenHelper.kt:41)
      at com.foo.bar.helper.TokenHelper$Companion.getInstance(TokenHelper.kt:41)
      at com.foo.bar.helper.TokenHelper$Companion.getInstance(TokenHelper.kt:41)
      at com.foo.bar.helper.TokenHelper$Companion.getInstance(TokenHelper.kt:41)
      at com.foo.bar.helper.TokenHelper$Companion.getInstance(TokenHelper.kt:41)
      at com.foo.bar.helper.TokenHelper$Companion.getInstance(TokenHelper.kt:41)
      at com.foo.bar.helper.TokenHelper$Companion.getInstance(TokenHelper.kt:41)
      at com.foo.bar.helper.TokenHelper$Companion.getInstance(TokenHelper.kt:41)
      at com.foo.bar.helper.TokenHelper$Companion.getInstance(TokenHelper.kt:41)
      at com.foo.bar.helper.TokenHelper$Companion.getInstance(TokenHelper.kt:41)
      at com.foo.bar.helper.TokenHelper$Companion.getInstance(TokenHelper.kt:41)
      at com.foo.bar.helper.TokenHelper$Companion.getInstance(TokenHelper.kt:41)
      at com.foo.bar.helper.TokenHelper$Companion.getInstance(TokenHelper.kt:41)
      at com.foo.bar.helper.TokenHelper$Companion.getInstance(TokenHelper.kt:41)
      at com.foo.bar.helper.TokenHelper$Companion.getInstance(TokenHelper.kt:41)
      at com.foo.bar.helper.TokenHelper$Companion.getInstance(TokenHelper.kt:41)
      at com.foo.bar.helper.TokenHelper$Companion.getInstance(TokenHelper.kt:41)
      at com.foo.bar.helper.TokenHelper$Companion.getInstance(TokenHelper.kt:41)
      at com.foo.bar.helper.TokenHelper$Companion.getInstance(TokenHelper.kt:41)
      at com.foo.bar.helper.TokenHelper$Companion.getInstance(TokenHelper.kt:41)
      at com.foo.bar.helper.TokenHelper$Companion.getInstance(TokenHelper.kt:41)
      at com.foo.bar.helper.TokenHelper$Companion.getInstance(TokenHelper.kt:41)
      at com.foo.bar.helper.TokenHelper$Companion.getInstance(TokenHelper.kt:41)
      at com.foo.bar.helper.TokenHelper$Companion.getInstance(TokenHelper.kt:41)
      at com.foo.bar.helper.TokenHelper$Companion.getInstance(TokenHelper.kt:41)
      at com.foo.bar.helper.TokenHelper$Companion.getInstance(TokenHelper.kt:41)
      at com.foo.bar.helper.TokenHelper$Companion.getInstance(TokenHelper.kt:41)
      at com.foo.bar.helper.TokenHelper$Companion.getInstance(TokenHelper.kt:41)
      at com.foo.bar.helper.TokenHelper$Companion.getInstance(TokenHelper.kt:41)
      at com.foo.bar.helper.TokenHelper$Companion.getInstance(TokenHelper.kt:41)
      at com.foo.bar.helper.TokenHelper$Companion.getInstance(TokenHelper.kt:41)
      at com.foo.bar.helper.TokenHelper$Companion.getInstance(TokenHelper.kt:41)
      at com.foo.bar.helper.TokenHelper$Companion.getInstance(TokenHelper.kt:41)
      at com.foo.bar.helper.TokenHelper$Companion.getInstance(TokenHelper.kt:41)
      at com.foo.bar.helper.TokenHelper$Companion.getInstance(TokenHelper.kt:41)
      at com.foo.bar.helper.TokenHelper$Companion.getInstance(TokenHelper.kt:41)
    at com.foo.bar.helper.TokenHelper$Companion.getInstance(TokenHelper.kt:41
04-11 19:07:42.271 16142-16142/com.foo.bar.debug D/Error: ERR: exClass=java.lang.StackOverflowError
04-11 19:07:42.271 16142-16142/com.foo.bar.debug D/Error: ERR: exMsg=stack size 8MB
04-11 19:07:42.271 16142-16142/com.foo.bar.debug D/Error: ERR: file=TokenHelper.kt
04-11 19:07:42.271 16142-16142/com.foo.bar.debug D/Error: ERR: class=com.foo.bar.helper.TokenHelper$Companion
04-11 19:07:42.271 16142-16142/com.foo.bar.debug D/Error: ERR: method=getInstance line=0
04-11 19:07:42.282 16142-16142/com.foo.bar.debug D/Error: ERR: stack=java.lang.StackOverflowError: stack size 8MB
  at com.foo.bar.helper.TokenHelper$Companion.getInstance(TokenHelper.kt:0)
  at com.foo.bar.helper.TokenHelper$Companion.getInstance(TokenHelper.kt:41)
  at com.foo.bar.helper.TokenHelper$Companion.getInstance(TokenHelper.kt:41)
  at com.foo.bar.helper.TokenHelper$Companion.getInstance(TokenHelper.kt:41)
  at com.foo.bar.helper.TokenHelper$Companion.getInstance(TokenHelper.kt:41)
  at com.foo.bar.helper.TokenHelper$Companion.getInstance(TokenHelper.kt:41)
  at com.foo.bar.helper.TokenHelper$Companion.getInstance(TokenHelper.kt:41)
  at com.foo.bar.helper.TokenHelper$Companion.getInstance(TokenHelper.kt:41)
  at com.foo.bar.helper.TokenHelper$Companion.getInstance(TokenHelper.kt:41)
  at com.foo.bar.helper.TokenHelper$Companion.getInstance(TokenHelper.kt:41)
  at com.foo.bar.helper.TokenHelper$Companion.getInstance(TokenHelper.kt:41)
  at com.foo.bar.helper.TokenHelper$Companion.getInstance(TokenHelper.kt:41)
  at com.foo.bar.helper.TokenHelper$Companion.getInstance(TokenHelper.kt:41)
  at com.foo.bar.helper.TokenHelper$Companion.getInstance(TokenHelper.kt:41)
  at com.foo.bar.helper.TokenHelper$Companion.getInstance(TokenHelper.kt:41)
  at com.foo.bar.helper.TokenHelper$Companion.getInstance(TokenHelper.kt:41)
  at com.foo.bar.helper.TokenHelper$Companion.getInstance(TokenHelper.kt:41)
  at com.foo.bar.helper.TokenHelper$Companion.getInstance(TokenHelper.kt:41)
  at com.foo.bar.helper.TokenHelper$Companion.getInstance(TokenHelper.kt:41)
  at com.foo.bar.helper.TokenHelper$Companion.getInstance(TokenHelper.kt:41)
  at com.foo.bar.helper.TokenHelper$Companion.getInstance(TokenHelper.kt:41)
  at com.foo.bar.helper.TokenHelper$Companion.getInstance(TokenHelper.kt:41)
  at com.foo.bar.helper.TokenHelper$Companion.getInstance(TokenHelper.kt:41)
  at com.foo.bar.helper.TokenHelper$Companion.getInstance(TokenHelper.kt:41)
  at com.foo.bar.helper.TokenHelper$Companion.getInstance(TokenHelper.kt:41)
  at com.foo.bar.helper.TokenHelper$Companion.getInstance(TokenHelper.kt:41)
  at com.foo.bar.helper.TokenHelper$Companion.getInstance(TokenHelper.kt:41)
  at com.foo.bar.helper.TokenHelper$Companion.getInstance(TokenHelper.kt:41)
  at com.foo.bar.helper.TokenHelper$Companion.getInstance(TokenHelper.kt:41)
  at com.foo.bar.helper.TokenHelper$Companion.getInstance(TokenHelper.kt:41)
  at com.foo.bar.helper.TokenHelper$Companion.getInstance(TokenHelper.kt:41)
  at com.foo.bar.helper.TokenHelper$Companion.getInstance(TokenHelper.kt:41)
  at com.foo.bar.helper.TokenHelper$Companion.getInstance(TokenHelper.kt:41)
  at com.foo.bar.helper.TokenHelper$Companion.getInstance(TokenHelper.kt:41)
  at com.foo.bar.helper.TokenHelper$Companion.getInstance(TokenHelper.kt:41)
  at com.foo.bar.helper.TokenHelper$Companion.getInstance(TokenHelper.kt:41)
  at com.foo.bar.helper.TokenHelper$Companion.getInstance(TokenHelper.kt:41)
  at com.foo.bar.helper.TokenHelper$Companion.getInstance(TokenHelper.kt:41)
  at com.foo.bar.helper.TokenHelper$Companion.getInstance(TokenHelper.kt:41)
  at com.foo.bar.helper.TokenHelper$Companion.getInstance(TokenHelper.kt:41)
  at com.foo.bar.helper.TokenHelper$Companion.getInstance(TokenHelper.kt:41)
  at com.foo.bar.helper.TokenHelper$Companion.getInstance(TokenHelper.kt:41)
  at com.foo.bar.helper.TokenHelper$Companion.getInstance(TokenHelper.kt:41)
  at com.foo.bar.helper.TokenHelper$Companion.getInstance(TokenHelper.kt:41)
  at com.foo.bar.helper.TokenHelper$Companion.getInstance(TokenHelper.kt:41)
  at com.foo.bar.helper.TokenHelper$Companion.getInstance(TokenHelper.kt:41)
  at com.foo.bar.helper.TokenHelper$Companion.getInstance(TokenHelper.kt:41)
    at com.foo.bar.helper.TokenHelper$Companion.getInstance(
04-11 19:07:42.283 16142-16142/com.foo.bar.debug D/Error: ERR: TOTAL BYTES WRITTEN: 880768
04-11 19:07:45.527 16142-16142/com.foo.bar.debug D/Process: killProcess, pid=16142
04-11 19:07:45.528 16142-16142/com.foo.bar.debug D/Process: com.android.internal.os.RuntimeInit$UncaughtHandler.uncaughtException:113 java.lang.ThreadGroup.uncaughtException:693 java.lang.ThreadGroup.uncaughtException:690

Android Studio 2.0，Kotlin 1.0.1-2

2 个答案:

答案 0 :(得分：8)

您以递归方式调用instance getter方法。将您的getter定义更改为使用field代替：

var instance: TokenHelper? = null
    get() {
        if (field == null) {
            field = TokenHelper()
        }
        return field
    }

文件中的相关摘录：

  

Kotlin中的类不能有字段。但是，有时它是   使用自定义访问器时必须具有支持字段。对于   为了这些目的，Kotlin提供了一个可以自动支持的领域   使用字段标识符访问：

var counter = 0 // the initializer value is written directly to the backing field
  set(value) {
    if (value >= 0)
      field = value
  }
     

字段标识符只能在属性的访问者中使用。

答案 1 :(得分：1)

改编自对原始答案的评论：

在Kotlin中，您不需要所有样板来声明单例。在宣布您的课程时，只需将其设为object TokenHelper { var token: String? = null var appId: String? = null var installationId: String? = null var userId: String? = null } 即可：

TokenHelper.token

然后按如下方式访问它：TokenHelper.INSTANCE.getToken()或来自Java {{1}}。

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