Question

如何在kotlin中编写等效代码，我需要使用定义的静态变量

public class ThisForThatApplication extends Application {

    static ThisForThatApplication appInstance;

    public static ThisForThatApplication getAppInstance() {
        if (appInstance == null) {
            appInstance = new ThisForThatApplication();
        }
        return appInstance;
    }
}

Answer 1

尝试这种方式

class ThisForThatApplication : Application() {

    companion object {

        @JvmField
        var appInstance: ThisForThatApplication? = null



        @JvmStatic fun getAppInstance(): ThisForThatApplication {
            return appInstance as ThisForThatApplication
        }
    }

    override fun onCreate() {
        super.onCreate()
        appInstance=this;
    }

}

有关更多信息，请阅读Static Fields和Static Methods

Answer 2

在Kotlin中没有static概念。但是，您可以使用companion objects实现相同的目的。请查看Kotlin object expression and declaration了解更多说明。

由于在您的示例中您只想创建一个Singleton，因此可以执行以下操作：

class ThisForThatApplication: Application() {
    companion object {
        val instance = ThisForThatApplication()
    }
}

但是，当您创建Android Application类时，就Android而言，以onCreate()方法初始化实例会更好：

class ThisForThatApplication : Application() {

    companion object {
        lateinit var instance: ThisForThatApplication
            private set
    }

    override fun onCreate() {
        super.onCreate()
        ThisForThatApplication.instance = this
    }
}

伴随对象底部的

private set仅允许ThisForThatApplication类设置该值。

Answer 3

Kotlin中的应用程序类和静态变量

class App : Application() {

init {
    instance = this
}

companion object {
    private var instance: App? = null

    fun applicationContext(): Context {
        return instance!!.applicationContext
    }
}

override fun onCreate() {
    super.onCreate()
}
}

如何在Kotlin中定义应用程序类和静态变量

3 个答案: