Kotlin Swipe Listener

当用户通过向左或向右滑动屏幕来触发事件时，我们需要在Kotlin应用中捕获“Swipe”动作。要实现这一点，我们可以为视图添加Swipe Listener，以便在用户执行手势时执行所需的操作。

添加Swipe Listener

要为Kotlin视图添加Swipe Listener，请按照以下步骤操作：

1. 创建一个扩展函数，并将其绑定到视图

fun View.setOnSwipeListener(onSwipe: (Direction) -> Unit) {
    val swipeGestureDetector = GestureDetectorCompat(context, object : GestureDetector.SimpleOnGestureListener() {
        override fun onFling(event1: MotionEvent, event2: MotionEvent, velocityX: Float, velocityY: Float): Boolean {
            try {
                val diffY = event2.y - event1.y
                val diffX = event2.x - event1.x
                if (abs(diffX) > abs(diffY) && abs(diffX) > SWIPE_THRESHOLD && abs(velocityX) > SWIPE_VELOCITY_THRESHOLD) {
                    onSwipe(if (diffX > 0) Direction.RIGHT else Direction.LEFT)
                    return true
                }
            } catch (exception: Exception) {
                exception.printStackTrace()
            }

            return false
        }
    })

    setOnTouchListener { _, event -> swipeGestureDetector.onTouchEvent(event) }
}

enum class Direction {
    LEFT, RIGHT
}

private const val SWIPE_THRESHOLD = 100
private const val SWIPE_VELOCITY_THRESHOLD = 100

2. 现在，您可以为任何视图设置Swipe Listener。例如，如果您想要为TextView设置Swipe Listener，则可以在Activity中完成如下操作：

textView.setOnSwipeListener { direction ->
    when(direction) {
        Direction.LEFT -> { Toast.makeText(this, "Swiped left", Toast.LENGTH_SHORT).show() }
        Direction.RIGHT -> { Toast.makeText(this, "Swiped right", Toast.LENGTH_SHORT).show() }
    }
}

这样就可以在TextView上设置Swipe Listener，并在用户左右滑动时触发Toast消息。

代码片段

以下是包含Swipe Listener实现的完整代码片段：

fun View.setOnSwipeListener(onSwipe: (Direction) -> Unit) {
    val swipeGestureDetector = GestureDetectorCompat(context, object : GestureDetector.SimpleOnGestureListener() {
        override fun onFling(event1: MotionEvent, event2: MotionEvent, velocityX: Float, velocityY: Float): Boolean {
            try {
                val diffY = event2.y - event1.y
                val diffX = event2.x - event1.x
                if (abs(diffX) > abs(diffY) && abs(diffX) > SWIPE_THRESHOLD && abs(velocityX) > SWIPE_VELOCITY_THRESHOLD) {
                    onSwipe(if (diffX > 0) Direction.RIGHT else Direction.LEFT)
                    return true
                }
            } catch (exception: Exception) {
                exception.printStackTrace()
            }

            return false
        }
    })

    setOnTouchListener { _, event -> swipeGestureDetector.onTouchEvent(event) }
}

enum class Direction {
    LEFT, RIGHT
}

private const val SWIPE_THRESHOLD = 100
private const val SWIPE_VELOCITY_THRESHOLD = 100

// Example usage:
textView.setOnSwipeListener { direction ->
    when(direction) {
        Direction.LEFT -> { Toast.makeText(this, "Swiped left", Toast.LENGTH_SHORT).show() }
        Direction.RIGHT -> { Toast.makeText(this, "Swiped right", Toast.LENGTH_SHORT).show() }
    }
}