ExpandableTextViewDelegate

README.md

Simple type to help implement expand and collapse behaviour for a textview.

ExpandableTextViewDelegate.kt

package myapp

import android.text.Layout
import android.util.Log
import android.widget.TextView
import myapp.ExpandableTextViewDelegate.State.*
import kotlin.properties.Delegates

private const val TAG = "ExpandableTextViewDel"

//https://stackoverflow.com/questions/31668697/android-expandable-text-view-with-view-more-button-displaying-at-center-after
/**
 * Type responsible for handling a [TextView] that can be expanded and collapsed.
 * Asserting the state and behaviour can be delegated to this type.
 * This pattern is know as "Read More" to show all text.
 * @param textView [TextView] that implements read more behaviour.
 * @param collapsedStateMaxLines threshold for the collapsed,
 * after this a read more action button should be displayed so user can trigger expand.
 * @param onStateChanged callback when the state of the textview behaviour
 */
class ExpandableTextViewDelegate(
        private val textView: TextView,
        private val collapsedStateMaxLines: Int = textView.maxLines,
        private val onStateChanged: (State) -> Unit
) {

    private val expandedStateMaxLine = Int.MAX_VALUE

    var state: State by Delegates.observable(AWAITING_LAYOUT_PASS) { _, _, newState ->
        Log.v(TAG,"state=$state")
        onStateChanged(newState)
    }

    fun setText(value: CharSequence) {
        textView.text = value
        awaitLayoutPassAndUpdateState()
    }

    fun toggle() {
        when (state) {
            AWAITING_LAYOUT_PASS -> { }
            WRAPPED -> { }
            COLLAPSED -> { expand() }
            EXPANDED -> { collapse() }
        }
    }

    @Suppress("MemberVisibilityCanBePrivate")
    fun expand() {
        textView.maxLines = expandedStateMaxLine
        awaitLayoutPassAndUpdateState()
    }

    fun collapse() {
        textView.maxLines = collapsedStateMaxLines
        awaitLayoutPassAndUpdateState()
    }

    private fun awaitLayoutPassAndUpdateState() {
        onStateChanged(AWAITING_LAYOUT_PASS)
        textView.post {
            state = getTextViewState()
        }
    }

    private fun getTextViewState(): State = with(textView) {
        val layout = textView.layout ?: return AWAITING_LAYOUT_PASS
        val lines = layout.lineCount
        Log.d(TAG,"lines=$lines")

        return when {
            lines > collapsedStateMaxLines -> EXPANDED
            lines < collapsedStateMaxLines -> WRAPPED
            layout.isEllipsized() -> COLLAPSED
            else -> WRAPPED
        }
    }

    // https://stackoverflow.com/questions/4005933/how-do-i-tell-if-my-textview-has-been-ellipsized
    // https://stackoverflow.com/questions/15567235/check-if-textview-is-ellipsized-in-android?noredirect=1&lq=1
    private fun Layout.isEllipsized() = getEllipsisCount(lineCount - 1) > 0

    /**
     * State of the [TextView] regarding expand and collapse behaviour.
     */
    enum class State {
        /**
         * Awaiting a new Layout Pass for the [TextView] before asserting the next state.
         * This state is triggered when text is changed.
         */
        AWAITING_LAYOUT_PASS,

        /**
         * Text is completely wrapped by the [TextView].
         * Don't need to show Expand Action.
         */
        WRAPPED,

        /**
         * Text is truncated/ellipsized.
         * Need to show Expand Action.
         */
        COLLAPSED,

        /**
         * Text is expanded an completely visible.
         * Need to show Collapse Action.
         */
        EXPANDED
    }
}

ViewHolderUsage.kt

inner class ViewHolder(
        override val containerView: View
    ) : RecyclerView.ViewHolder(containerView), LayoutContainer {

        private val readMoreDelegate = ExpandableTextViewDelegate(
                textView = tv_review_body,
                onStateChanged = ::onReadMoreStateChanged
        )

        init {
            tv_read_toggle.setOnClickListener {
                readMoreDelegate.toggle()
            }
        }


        fun bind(model: Model) {
            readMoreDelegate.collapse()
            readMoreDelegate.setText(model.text)
        }

        private fun onReadMoreStateChanged(state: ExpandableTextViewDelegate.State) {
            when (state) {
                ExpandableTextViewDelegate.State.AWAITING_LAYOUT_PASS -> {
                    tv_read_toggle.isGone = true
                }
                ExpandableTextViewDelegate.State.WRAPPED -> {
                    tv_read_toggle.isGone = true
                }
                ExpandableTextViewDelegate.State.COLLAPSED -> {
                    tv_read_toggle.text = "Read More"
                    tv_read_toggle.isVisible = true
                }
                ExpandableTextViewDelegate.State.EXPANDED -> {
                    tv_read_toggle.text = "Read Less"
                    tv_read_toggle.isVisible = true
                }
            }
        }
    }