Android自定义超级炫酷的ViewPage指示器

@RequiresApi(Build.VERSION_CODES.Q)
class CustomTextView : AppCompatTextView {
    /**
     * 未选中画笔
     */
    private var mUnSelectPaint: Paint? = null
    /**
     * 选中画笔
     */
    private var mSelectPaint: Paint? = null
    /**
     * 滑动进度百分比
     */
    var mScrollProcess = 0f
    /**
     * 是否左边滑动
     */
    var mScrollToLeft = true
    /**
     * 文字缩放比例
     */
    var mTextScale = 0.7f
    /**
     * 选中颜色以及未选中颜色
     */
    private var mSelectColor = Color.parseColor("#8966FF")
    private var mUnSelectColor = Color.parseColor("#DBC0FF")
    constructor(context: Context) : this(context, null)
    constructor(context: Context, attributeSet: AttributeSet?) : this(context, attributeSet, 0)
    constructor(context: Context, attributeSet: AttributeSet?, defStyleAttr: Int) : super(
        context,
        attributeSet,
        defStyleAttr
    ) {
        //初始化画笔
        mUnSelectPaint = Paint()
        mUnSelectPaint?.apply {
            color = mUnSelectColor
            textSize = this@CustomTextView.textSize
            isAntiAlias = true
            isDither = true
        }
        mSelectPaint = Paint()
        mSelectPaint?.apply {
            color = mSelectColor
            textSize = this@CustomTextView.textSize
            isAntiAlias = true
            isDither = true
        }
    }
    /**
     * 绘制内容
     */
    override fun onDraw(canvas: Canvas?) {
        val x = width * mScrollProcess
        if (mScrollToLeft) {
            drawText(canvas!!, mUnSelectPaint!!, x, width.toFloat())
            drawText(canvas!!, mSelectPaint!!, 0f, x)
        } else {
            drawText(canvas!!, mUnSelectPaint!!, 0f, width - x)
            drawText(canvas!!, mSelectPaint!!, width - x, width.toFloat())
        }
    }
    /**
     * 绘制文字
     */
    private fun drawText(canvas: Canvas, paint: Paint, startX: Float, endX: Float) {
        paint.textSize = textSize * mTextScale
        //保存画布，剪切画布（设置画布显示区域）
        canvas.save()
        canvas.clipRect(startX, 0f, endX, height.toFloat())
        //获取文字矩形区域
        var bounds = Rect()
        paint.getTextBounds(text, 0, text.length, bounds)
        //获取文字的度量指标
        val fontMetrics = paint.fontMetrics
        //计算基线到中心点位置
        val dy = (fontMetrics.bottom - fontMetrics.top) / 2 - fontMetrics.bottom
        //计算基线
        val baseLine = height / 2   dy
        //绘制文字
        canvas.drawText(
            text.toString(),
            (width / 2 - bounds.width() / 2).toFloat(),
            baseLine,
            paint
        )
        canvas.restore()
    }
    /**
     * 设置选中 未选中颜色
     */
    fun setColor(selectColor: Int, unSelectColor: Int) {
        mSelectColor = selectColor
        mUnSelectColor = unSelectColor
        mSelectPaint?.color = selectColor
        mUnSelectPaint?.color = unSelectColor
        invalidate()
    }
}

@RequiresApi(Build.VERSION_CODES.Q)
class MyIndicator : LinearLayout, ViewPager.OnPageChangeListener {
    var mTextScale = 0.7f
    constructor(context: Context) : this(context, null)
    constructor(context: Context, attributeSet: AttributeSet?) : this(context, attributeSet, 0)
    constructor(context: Context, attributeSet: AttributeSet?, defStyleAttr: Int) : super(
        context,
        attributeSet,
        defStyleAttr
    )
    /**
     * 添加多个tab
     */
    fun addTabs(texts: List<String>) {
        texts.forEach {
            addTab(it)
        }
        //选中第一个
        val customTextView = getChildAt(0) as CustomTextView
        customTextView.mScrollToLeft = false
        customTextView.mScrollProcess = 1f
        customTextView.mTextScale = 1f
        customTextView.invalidate()
    }
    /**
     * 添加tab
     */
    fun addTab(text: String) {
        val layoutParams = LayoutParams(LayoutParams.WRAP_CONTENT, LayoutParams.MATCH_PARENT)
        layoutParams.weight = 1f
        val customTextView = CustomTextView(context)
        customTextView.textSize = 21f
        customTextView.gravity = Gravity.CENTER
        customTextView.text = text
        customTextView.mScrollProcess = 0f
        customTextView.mTextScale = 0.7f
        customTextView.layoutParams = layoutParams
        addView(customTextView)
    }
    /**
     * 关联ViewPage
     */
    fun relationViewPage(viewPage: ViewPager) {
        viewPage.addOnPageChangeListener(this)
    }
    /**
     * 滑动回调
     */
    override fun onPageScrolled(position: Int, positionOffset: Float, positionOffsetPixels: Int) {
        if (positionOffset > 0) {
            val tabView = getChildAt(position) as CustomTextView
            tabView.mScrollToLeft = false
            tabView.mScrollProcess = 1 - positionOffset
            tabView.mTextScale = if ((1 - positionOffset) > mTextScale) 1 - positionOffset else mTextScale
            tabView.invalidate()
            val rightTabView = getChildAt(position   1) as CustomTextView
            rightTabView.mScrollToLeft = true
            rightTabView.mScrollProcess = positionOffset
            rightTabView.mTextScale = if (positionOffset > mTextScale) positionOffset else mTextScale
            rightTabView.invalidate()
        }
    }
    /**
     * 选中某个item回调
     */
    override fun onPageSelected(position: Int) {
    }
    /**
     * 滑动状态改变回调
     */
    override fun onPageScrollStateChanged(state: Int) {
    }
}