实现ConstraintLayout上下滑动显隐及val无法重新赋值问题求助

Hey there! Let's break down how to fix your immediate error and build the slide behavior you want.

1. Fixing the "val cannot be reassigned" Error #

You can't directly set scopeLayout.height because height is a read-only property for views. Instead, you need to modify the view's LayoutParams to adjust its height. Here's how to fix that part:

val scopeLayout = inflaterView.findViewById<ConstraintLayout>(R.id.scope_layout)
scopeLayout.setOnTouchListener { v, event ->
    when (event.action) {
        MotionEvent.ACTION_DOWN -> {
            Toast.makeText(context, "you just touch the screen :-)", Toast.LENGTH_SHORT).show()
            // Update height via LayoutParams
            val params = scopeLayout.layoutParams as ConstraintLayout.LayoutParams
            params.height = 215 // Tip: Convert dp to px with TypedValue.applyDimension() for device consistency!
            scopeLayout.layoutParams = params
        }
        // We'll add sliding logic actions here next
    }
    true
}

2. Implementing Slide-to-Reveal/Hide Behavior #

To make the layout slide down to reveal and slide up to hide, you'll need to track the user's touch movement, calculate slide distance, and adjust the layout's height (or position) accordingly. Here's a complete implementation with smooth animation:

val scopeLayout = inflaterView.findViewById<ConstraintLayout>(R.id.scope_layout)
var initialTouchY = 0f
val fullVisibleHeight = 800 // Your desired full visible height (in pixels)
val hiddenHeight = 100 // Height when the layout is hidden (in pixels)

scopeLayout.setOnTouchListener { v, event ->
    when (event.action) {
        MotionEvent.ACTION_DOWN -> {
            initialTouchY = event.rawY
            true
        }
        MotionEvent.ACTION_MOVE -> {
            val dragDelta = event.rawY - initialTouchY
            // Calculate new height, clamp it between hidden and full values
            var newHeight = scopeLayout.height + dragDelta.toInt()
            newHeight = newHeight.coerceIn(hiddenHeight, fullVisibleHeight)
            
            // Update layout height
            val params = scopeLayout.layoutParams as ConstraintLayout.LayoutParams
            params.height = newHeight
            scopeLayout.layoutParams = params
            
            // Reset initial touch position for smooth dragging
            initialTouchY = event.rawY
            true
        }
        MotionEvent.ACTION_UP -> {
            // Decide final state based on current height
            val targetHeight = if (scopeLayout.height > (fullVisibleHeight + hiddenHeight)/2) {
                fullVisibleHeight
            } else {
                hiddenHeight
            }
            // Animate to target state for polished finish
            ValueAnimator.ofInt(scopeLayout.height, targetHeight).apply {
                duration = 300
                addUpdateListener { animator ->
                    val params = scopeLayout.layoutParams as ConstraintLayout.LayoutParams
                    params.height = animator.animatedValue as Int
                    scopeLayout.layoutParams = params
                }
                start()
            }
            true
        }
        else -> false
    }
}

Key Details: #

• Track Initial Touch: We store the starting vertical position when the user first taps the layout.
• Drag to Adjust Height: As the user moves their finger, we adjust the layout's height based on drag distance, ensuring it never goes beyond your hidden/full limits.
• Smooth Release Animation: When the user lifts their finger, we animate the layout to either fully visible or hidden state based on its current position, making the interaction feel polished.

Extra Tips #

• If you prefer sliding the entire layout (instead of adjusting height), modify translationY instead of layout params height.
• For more complex touch interactions, consider using ViewDragHelper instead of a raw OnTouchListener for better gesture handling.

内容的提问来源于stack exchange，提问作者Kakashi