在 Kotlin 的私有 class 中调用 onBackPressed

Question

我正在尝试按照 Android 开发人员 website 上的指南创建手势检测器 class，但我被卡住了，因为我无法调用方法 onBackPressed( ) 在我创建的新私有 class 中。我该如何管理它？这是我的代码：

    class DetailActivity : AppCompatActivity() {

    private lateinit var mDetector: GestureDetectorCompat

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.detail_activity)

        mDetector = GestureDetectorCompat(this, MyGestureListener())
    }

    override fun onTouchEvent(event: MotionEvent): Boolean {
        mDetector.onTouchEvent(event)
        return super.onTouchEvent(event)
    }

    private class MyGestureListener : GestureDetector.SimpleOnGestureListener() {

        private val SWIPE_DISTANCE_THRESHOLD = 100
        private val SWIPE_VELOCITY_THRESHOLD = 100

        override fun onDown(event: MotionEvent): Boolean {
            //CALL onBackPressed
            return true
        }

        override fun onFling(
                event1: MotionEvent,
                event2: MotionEvent,
                velocityX: Float,
                velocityY: Float
        ): Boolean {
            //TODO
            var distanceX = event2.getX() - event1.getX()
            var distanceY = event2.getY() - event1.getY()
            if (Math.abs(distanceX) > Math.abs(distanceY) && Math.abs(distanceX) > SWIPE_DISTANCE_THRESHOLD && Math.abs(velocityX) > SWIPE_VELOCITY_THRESHOLD) {
                if (distanceX > 0)
                //CALL onBackPressed
            }
            return true
        }
    }
}

新代码：

    class DetailActivity : AppCompatActivity() {

    private lateinit var mDetector: GestureDetectorCompat

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.detail_activity)

        mDetector = GestureDetectorCompat(this, MyGestureListener())
    }

    override fun onTouchEvent(event: MotionEvent): Boolean {
        mDetector.onTouchEvent(event)
        return super.onTouchEvent(event)
    }

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

    inner class MyGestureListener : GestureDetector.SimpleOnGestureListener() {

        private val SWIPE_DISTANCE_THRESHOLD = 100
        private val SWIPE_VELOCITY_THRESHOLD = 100

        override fun onDown(event: MotionEvent): Boolean {
            System.out.println("LOGG")
            this@DetailActivity.onBackPressed()
            return true
        }

        override fun onFling(
                event1: MotionEvent,
                event2: MotionEvent,
                velocityX: Float,
                velocityY: Float
        ): Boolean {
            var distanceX = event2.getX() - event1.getX()
            var distanceY = event2.getY() - event1.getY()
            if (Math.abs(distanceX) > Math.abs(distanceY) && Math.abs(distanceX) > SWIPE_DISTANCE_THRESHOLD && Math.abs(velocityX) > SWIPE_VELOCITY_THRESHOLD) {
                if (distanceX > 0) {
                    System.out.println("LOGG")
                    this@DetailActivity.onBackPressed()
                }
            }
            return true
        }
    }
}

编辑：我添加了一个新方法 onBackPressed 并通过内部 class 调用它，但没有任何改变。我也没有在 Logcat.

中看到指纹

Answer 1

设为 private inner class.
在 Kotlin 中，嵌套的 classes 默认是静态的。要使其成为可以访问封闭 class 属性的内部 class，您必须使用 'inner' 关键字。

见Java inner class and static nested class

在 Kotlin 的私有 class 中调用 onBackPressed

Call onBackPressed inside a private class in Kotlin

android

class

gesture

kotlin