NightRain.png

背景

原生的TextView是支持跑馬燈效果的局劲，但是在項(xiàng)目中實(shí)際用了之后飘痛，達(dá)不到需求，原因是內(nèi)容滾動(dòng)太慢容握，速度無法調(diào)節(jié)宣脉。因此，需要自定義一個(gè)可以調(diào)節(jié)速度的跑馬燈剔氏。

思路

目前實(shí)現(xiàn)的思路是對(duì)文本內(nèi)容不斷地重繪塑猖，同時(shí)改變每次重繪的坐標(biāo)，來在視覺上達(dá)到內(nèi)容在滾動(dòng)的效果谈跛。缺點(diǎn)是如果每次改變的坐標(biāo)差值太大羊苟，會(huì)有明顯的卡頓效果。經(jīng)過調(diào)試感憾，下面源碼中的速度感覺還可以接受蜡励，如果有特殊需求，自行在調(diào)試一下阻桅。

源碼

class CustomMarqueeView : AppCompatTextView {
    companion object {
        val SPEED_FAST = 9
        val SPEED_MEDIUM = 6
        val SPEED_SLOW = 3
    }

    //View寬度
    private var mViewWidth = 0
    private var mViewHeight = 0
    private var mScrollX = 0F
    private var mMarqueeMode = 3
    private val rect = Rect()

    constructor(context: Context) : this(context, null)
    constructor(context: Context, attrs: AttributeSet?) : this(context, attrs, 0)
    constructor(context: Context, attrs: AttributeSet?, defStyleAttr: Int) : super(
        context,
        attrs,
        defStyleAttr
    ) {
        includeFontPadding = false
        initAttrs(context, attrs)
    }

    fun setScrollSpeed(speed: Int) {
        if (speed == SPEED_FAST || speed == SPEED_MEDIUM || speed == SPEED_SLOW) {
            mMarqueeMode = speed
        }
    }


    override fun onDraw(canvas: Canvas?) {
        val textContentText = text.toString().trim()
        if (TextUtils.isEmpty(textContentText)) {
            return
        }
        val x = mViewWidth - mScrollX
        val y = mViewHeight / 2F + getTextContentHeight() / 2
        canvas?.drawText(textContentText, x, y, paint)
        mScrollX += mMarqueeMode
        if (mScrollX >= (mViewWidth + getTextContentWdith())) {
            mScrollX = 0F
        }
        invalidate()
    }

    override fun onMeasure(widthMeasureSpec: Int, heightMeasureSpec: Int) {
        super.onMeasure(widthMeasureSpec, heightMeasureSpec)
        mViewWidth = MeasureSpec.getSize(widthMeasureSpec)
        mViewHeight = MeasureSpec.getSize(heightMeasureSpec)
    }
    
    override fun setTextColor(color: Int) {
        super.setTextColor(color)
        paint.setColor(color)
    }

    private fun initAttrs(context: Context, attrs: AttributeSet?) {
        val typeArray = context.obtainStyledAttributes(attrs, R.styleable.CustomMarqueeView)
        mMarqueeMode =
            typeArray.getInt(R.styleable.CustomMarqueeView_customScrollSpeed, mMarqueeMode)
        typeArray.recycle()
    }

    /**
     * 測量文字寬度
     * @return 文字寬度
     */
    private fun getTextContentWdith(): Int {
        val textContent = text.toString().trim()
        if (!TextUtils.isEmpty(textContent)) {
            paint.getTextBounds(textContent, 0, textContent.length, rect)
            return rect.width()
        }
        return 0
    }

    /**
     * 測量文字高度
     * @return 文字高度
     */
    private fun getTextContentHeight(): Int {
        val textContent = text.toString().trim()
        if (!TextUtils.isEmpty(textContent)) {
            paint.getTextBounds(textContent, 0, textContent.length, rect)
            return rect.height()
        }
        return 0
    }
}

• 自定義屬性

    <declare-styleable name="CustomMarqueeView">
        <attr name="customScrollSpeed">
            <enum name="fast" value="9" />
            <enum name="medium" value="6" />
            <enum name="slow" value="3" />
        </attr>
    </declare-styleable>