5

谁能告诉我，为什么我要java.lang.StackOverflowError使用这个 Kotlin 类？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

4

2 回答 2

8

您正在instance递归地调用 getter 方法。更改您的吸气剂定义以改为使用field：

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

文档的相关摘录：

Kotlin 中的类不能有字段。但是，有时在使用自定义访问器时需要有一个支持字段。为此，Kotlin 提供了一个自动支持字段，可以使用字段标识符访问该字段：

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器中使用。

于 2016-04-11T17:19:17.150 回答
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。在声明你的类时，只需让它object像这样：

object TokenHelper {
    var token: String? = null
    var appId: String? = null
    var installationId: String? = null
    var userId: String? = null
}

然后按如下方式访问它：TokenHelper.token或从 Java TokenHelper.INSTANCE.getToken()。

于 2016-04-14T13:25:05.717 回答