Câu hỏi phỏng vấn Android UI - Views

// View - single element
val textView = TextView(context).apply {
    text = "Hello, World!"
    textSize = 16f
}
 
// ViewGroup - container
val linearLayout = LinearLayout(context).apply {
    orientation = LinearLayout.VERTICAL
    addView(TextView(context).apply { text = "Child 1" })
    addView(TextView(context).apply { text = "Child 2" })
}

class CustomView @JvmOverloads constructor(
    context: Context,
    attrs: AttributeSet? = null
) : View(context, attrs) {
    
    override fun onAttachedToWindow() {
        super.onAttachedToWindow()
        // Start animations, register listeners
    }
    
    override fun onMeasure(widthMeasureSpec: Int, heightMeasureSpec: Int) {
        // Calculate desired size
        val width = calculateWidth(widthMeasureSpec)
        val height = calculateHeight(heightMeasureSpec)
        setMeasuredDimension(width, height)
    }
    
    override fun onDraw(canvas: Canvas) {
        // Draw content
        canvas.drawRect(...)
        canvas.drawText(...)
    }
    
    override fun onDetachedFromWindow() {
        super.onDetachedFromWindow()
        // Cleanup resources
    }
}

class UserAdapter : RecyclerView.Adapter<UserAdapter.ViewHolder>() {
    
    private var items = listOf<User>()
    
    class ViewHolder(view: View) : RecyclerView.ViewHolder(view) {
        private val binding = ItemUserBinding.bind(view)
        
        fun bind(user: User) {
            binding.nameText.text = user.name
            binding.avatar.load(user.avatarUrl)
        }
    }
    
    override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): ViewHolder {
        val view = ItemUserBinding.inflate(
            LayoutInflater.from(parent.context), parent, false
        )
        return ViewHolder(view.root)
    }
    
    override fun onBindViewHolder(holder: ViewHolder, position: Int) {
        holder.bind(items[position])
    }
    
    override fun getItemCount() = items.size
    
    fun submitList(newItems: List<User>) {
        items = newItems
        notifyDataSetChanged()  // Use DiffUtil for better performance
    }
}

// ❌ Without DiffUtil - redraws everything
adapter.submitList(newList)
adapter.notifyDataSetChanged()
 
// ✅ With DiffUtil - only updates changed items
class UserDiffCallback : DiffUtil.ItemCallback<User>() {
    override fun areItemsTheSame(oldItem: User, newItem: User): Boolean {
        return oldItem.id == newItem.id
    }
    
    override fun areContentsTheSame(oldItem: User, newItem: User): Boolean {
        return oldItem == newItem
    }
}
 
class UserAdapter : ListAdapter<User, UserAdapter.ViewHolder>(UserDiffCallback()) {
    
    override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): ViewHolder {
        // ...
    }
    
    override fun onBindViewHolder(holder: ViewHolder, position: Int) {
        holder.bind(getItem(position))
    }
}
 
// Usage
adapter.submitList(newList)  // DiffUtil handles updates automatically

// 1. Use setHasFixedSize for fixed-size items
recyclerView.setHasFixedSize(true)
 
// 2. Set item view cache size
recyclerView.setItemViewCacheSize(20)
 
// 3. Use RecycledViewPool for multiple RecyclerViews
val sharedPool = RecyclerView.RecycledViewPool()
recyclerView1.setRecycledViewPool(sharedPool)
recyclerView2.setRecycledViewPool(sharedPool)
 
// 4. Avoid nested RecyclerViews (use ConcatAdapter)
val concatAdapter = ConcatAdapter(headerAdapter, contentAdapter, footerAdapter)
recyclerView.adapter = concatAdapter
 
// 5. Use stable IDs
class MyAdapter : RecyclerView.Adapter<ViewHolder>() {
    init {
        setHasStableIds(true)
    }
    
    override fun getItemId(position: Int): Long = items[position].id
}
 
// 6. Prefetch for nested scrolling
(recyclerView.layoutManager as LinearLayoutManager)
    .initialPrefetchItemCount = 4

class UserInfoView @JvmOverloads constructor(
    context: Context,
    attrs: AttributeSet? = null
) : LinearLayout(context, attrs) {
    
    private val binding: ViewUserInfoBinding
    
    init {
        orientation = HORIZONTAL
        binding = ViewUserInfoBinding.inflate(
            LayoutInflater.from(context), this
        )
        
        // Read custom attributes
        context.obtainStyledAttributes(attrs, R.styleable.UserInfoView).use {
            binding.nameText.text = it.getString(R.styleable.UserInfoView_userName)
        }
    }
    
    fun setUser(user: User) {
        binding.nameText.text = user.name
        binding.avatar.load(user.avatarUrl)
    }
}

class CircleProgressView @JvmOverloads constructor(
    context: Context,
    attrs: AttributeSet? = null
) : View(context, attrs) {
    
    private val paint = Paint(Paint.ANTI_ALIAS_FLAG)
    var progress: Float = 0f
        set(value) {
            field = value.coerceIn(0f, 1f)
            invalidate()  // Request redraw
        }
    
    override fun onDraw(canvas: Canvas) {
        val centerX = width / 2f
        val centerY = height / 2f
        val radius = minOf(centerX, centerY) - paint.strokeWidth
        
        // Draw background circle
        paint.color = Color.LTGRAY
        canvas.drawCircle(centerX, centerY, radius, paint)
        
        // Draw progress arc
        paint.color = Color.BLUE
        canvas.drawArc(
            centerX - radius, centerY - radius,
            centerX + radius, centerY + radius,
            -90f, 360f * progress, false, paint
        )
    }
}

class SquareImageView @JvmOverloads constructor(
    context: Context,
    attrs: AttributeSet? = null
) : AppCompatImageView(context, attrs) {
    
    override fun onMeasure(widthMeasureSpec: Int, heightMeasureSpec: Int) {
        super.onMeasure(widthMeasureSpec, heightMeasureSpec)
        // Make it square
        val size = minOf(measuredWidth, measuredHeight)
        setMeasuredDimension(size, size)
    }
}

class CustomViewGroup : FrameLayout {
    
    override fun onInterceptTouchEvent(ev: MotionEvent): Boolean {
        // Return true to steal touch from children
        return when (ev.action) {
            MotionEvent.ACTION_MOVE -> {
                val dx = abs(ev.x - startX)
                dx > touchSlop  // Intercept if horizontal swipe
            }
            else -> false
        }
    }
    
    override fun onTouchEvent(event: MotionEvent): Boolean {
        when (event.action) {
            MotionEvent.ACTION_DOWN -> {
                startX = event.x
                return true
            }
            MotionEvent.ACTION_MOVE -> {
                // Handle drag
                return true
            }
            MotionEvent.ACTION_UP -> {
                // Handle release
                return true
            }
        }
        return super.onTouchEvent(event)
    }
}

<!-- ConstraintLayout - flat hierarchy -->
<androidx.constraintlayout.widget.ConstraintLayout>
    <ImageView
        android:id="@+id/avatar"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent"/>
    
    <TextView
        android:id="@+id/name"
        app:layout_constraintStart_toEndOf="@id/avatar"
        app:layout_constraintTop_toTopOf="@id/avatar"/>
    
    <TextView
        android:id="@+id/email"
        app:layout_constraintStart_toStartOf="@id/name"
        app:layout_constraintTop_toBottomOf="@id/name"/>
</androidx.constraintlayout.widget.ConstraintLayout>

override fun onMeasure(widthMeasureSpec: Int, heightMeasureSpec: Int) {
    val widthMode = MeasureSpec.getMode(widthMeasureSpec)
    val widthSize = MeasureSpec.getSize(widthMeasureSpec)
    
    val desiredWidth = 200.dpToPx()
    
    val width = when (widthMode) {
        MeasureSpec.EXACTLY -> widthSize
        MeasureSpec.AT_MOST -> minOf(desiredWidth, widthSize)
        else -> desiredWidth
    }
    
    setMeasuredDimension(width, calculatedHeight)
}

// ObjectAnimator
ObjectAnimator.ofFloat(view, "translationX", 0f, 100f).apply {
    duration = 300
    interpolator = AccelerateDecelerateInterpolator()
    start()
}
 
// ViewPropertyAnimator (simpler)
view.animate()
    .translationX(100f)
    .alpha(0.5f)
    .setDuration(300)
    .setInterpolator(AccelerateDecelerateInterpolator())
    .start()
 
// Transition
TransitionManager.beginDelayedTransition(container, Fade())
view.visibility = View.GONE  // Animates automatically
 
// MotionLayout
motionLayout.transitionToEnd()
motionLayout.setTransitionDuration(500)

// ❌ Bad - deep hierarchy
LinearLayout > LinearLayout > LinearLayout > TextView
 
// ✅ Good - flat with ConstraintLayout
ConstraintLayout > TextView, TextView, TextView