kotlin Android TextView显示部分文本，实现全文/展开和收起功能

可以使用以下代码实现TextView部分文本显示和展开/收起功能：

class ExpandableTextView(context: Context, attrs: AttributeSet?) : TextView(context, attrs) {

    private var isExpanded: Boolean = false
    private var collapsedMaxLines: Int = 2

    init {
        // 设置TextView默认的最大行数
        maxLines = collapsedMaxLines
        // 设置TextView默认的Ellipsize
        ellipsize = TextUtils.TruncateAt.END
        // 设置TextView点击事件
        setOnClickListener {
            toggle()
        }
    }

    /**
     * 设置TextView默认的最大行数
     */
    fun setCollapsedMaxLines(maxLines: Int) {
        this.collapsedMaxLines = maxLines
        this.maxLines = maxLines
    }

    /**
     * 切换TextView的展开/收起状态
     */
    private fun toggle() {
        isExpanded = !isExpanded
        setText(if (isExpanded) getFullText() else getCollapsedText())
        // 将TextView改为可聚焦状态，以便展开/收起时接收触摸事件
        isFocusable = true
        isFocusableInTouchMode = true
    }

    /**
     * 获取TextView展开状态下的完整文本
     */
    private fun getFullText(): CharSequence {
        val text = text
        movementMethod = LinkMovementMethod.getInstance()
        return text
    }

    /**
     * 获取TextView收起状态下的文本
     */
    private fun getCollapsedText(): CharSequence {
        val text = text
        val layout = layout ?: return text
        movementMethod = LinkMovementMethod.getInstance()
        val end = layout.getLineEnd(collapsedMaxLines - 1)
        val ellipsis = "..."
        val textTrimmed = text.subSequence(0, end)
        val lastSpace = textTrimmed.lastIndexOf(' ')
        val trimmedLength = textTrimmed.length
        return if (lastSpace == -1 || trimmedLength <= end - ellipsis.length) {
            "$textTrimmed$ellipsis"
        } else {
            val index = if (lastSpace + ellipsis.length > end) lastSpace else end - ellipsis.length
            "${textTrimmed.subSequence(0, index)}$ellipsis"
        }
    }

    /**
     * 保存TextView的状态
     */
    override fun onSaveInstanceState(): Parcelable? {
        val superState = super.onSaveInstanceState()
        return SavedState(superState).apply {
            isExpanded = this@ExpandableTextView.isExpanded
        }
    }

    /**
     * 恢复TextView的状态
     */
    override fun onRestoreInstanceState(state: Parcelable?) {
        var savedState = state
        if (savedState is SavedState) {
            isExpanded = savedState.isExpanded
            super.onRestoreInstanceState(savedState.superState)
            setText(if (isExpanded) getFullText() else getCollapsedText())
        } else {
            super.onRestoreInstanceState(savedState)
        }
    }

    private class SavedState : BaseSavedState {
        var isExpanded: Boolean = false

        constructor(superState: Parcelable?) : super(superState)

        constructor(source: Parcel) : super(source) {
            isExpanded = source.readInt() == 1
        }

        override fun writeToParcel(out: Parcel, flags: Int) {
            super.writeToParcel(out, flags)
            out.writeInt(if (isExpanded) 1 else 0)
        }

        companion object {
            @JvmField
            val CREATOR = object : Parcelable.Creator<SavedState> {
                override fun createFromParcel(source: Parcel): SavedState {
                    return SavedState(source)
                }

                override fun newArray(size: Int): Array<SavedState?> {
                    return arrayOfNulls(size)
                }
            }
        }
    }
}

使用方法：

在布局文件中使用该自定义TextView：

<com.example.ExpandableTextView
    android:id="@+id/tv_content"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:text="@string/lorem_ipsum" />

在代码中设置TextView的最大行数和展开/收起状态：

val tvContent = findViewById<ExpandableTextView>(R.id.tv_content)
tvContent.setCollapsedMaxLines(2) // 设置收起状态下的最大行数
tvContent.text = resources.getString(R.string.lorem_ipsum) // 设置TextView的文本

如果需要在RecyclerView中使用该自定义TextView，可以在Adapter中设置TextView的展开/收起状态：

override fun onBindViewHolder(holder: ViewHolder, position: Int) {
    val item = itemList[position]
    holder.itemView.apply {
        tvContent.setCollapsedMaxLines(2) // 设置收起状态下的最大行数
        tvContent.text = item.text // 设置TextView的文本
        tvContent.isExpanded = item.isExpanded // 设置TextView的展开/收起状态
    }
}