Android自定義View實現隨機數驗證碼

<?xml version="1.0" encoding="utf-8"?>
<resources>

    <attr name="randomText" format="string"/>
    <attr name="randomTextColor" format="color"/>
    <attr name="randomTextSize" format="dimension"/>

    <declare-styleable name="RandomTextView" >
        <attr name="randomText"/>
        <attr name="randomTextColor"/>
        <attr name="randomTextSize"/>
    </declare-styleable>

</resources>

 <com.yechaoa.customviews.randomtext.RandomTextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:padding="20dp"
        app:randomText="1234"
        app:randomTextColor="@color/colorAccent"
        app:randomTextSize="50sp" />

xmlns:app="http://schemas.android.com/apk/res-auto"

class RandomTextView : View {

    //文本
    private var mRandomText: String

    //文本顏色
    private var mRandomTextColor: Int = 0

    //文本字體大小
    private var mRandomTextSize: Int = 0

    private var paint = Paint()
    private var bounds = Rect()

    //調用兩個參數的構造
    constructor(context: Context) : this(context, null)

    //xml默認調用兩個參數的構造，再調用三個參數的構造，在三個參數構造裡獲取自定義屬性
    constructor(context: Context, attributeSet: AttributeSet?) : this(context, attributeSet, 0)

    constructor(context: Context, attributeSet: AttributeSet?, defStyle: Int) : super(context, attributeSet, defStyle) {
        ...
    }
    ...
}

  constructor(context: Context, attributeSet: AttributeSet?, defStyle: Int) : super(context, attributeSet, defStyle) {
        //獲取自定義屬性
        val typedArray = context.theme.obtainStyledAttributes(
            attributeSet,
            R.styleable.RandomTextView,
            defStyle,
            0
        )

        mRandomText = typedArray.getString(R.styleable.RandomTextView_randomText).toString()
        mRandomTextColor = typedArray.getColor(R.styleable.RandomTextView_randomTextColor, Color.BLACK)//默認黑色
        mRandomTextSize = typedArray.getDimensionPixelSize(
            R.styleable.RandomTextView_randomTextSize,
            TypedValue.applyDimension( TypedValue.COMPLEX_UNIT_SP, 16F, resources.displayMetrics ).toInt()
        )

        //獲取完回收
        typedArray.recycle()

        paint.textSize = mRandomTextSize.toFloat()

        //返回文本邊界，即包含文本的最小矩形，沒有所謂“留白”，返回比measureText()更精確的text寬高，數據保存在bounds裡
        paint.getTextBounds(mRandomText, 0, mRandomText.length, bounds)
    }

paint.getTextBounds(mRandomText, 0, mRandomText.length, bounds)

 @SuppressLint("DrawAllocation")
    override fun onDraw(canvas: Canvas?) {
        super.onDraw(canvas)

        /**
         * 自定義View時，需要我們自己在onDraw中處理padding，否則是不生效的
         * 自定義ViewGroup時，子view的padding放在onMeasure中處理
         */

        /**
         * 矩形背景
         */
        paint.color = Color.YELLOW
        //計算坐標，因為原點是在文字的左下角，左邊要是延伸出去就還要往左邊去，所以是減，右邊和下邊是正，所以是加
        canvas?.drawRect(
            (0 - paddingLeft).toFloat(),
            (0 - paddingTop).toFloat(),
            (measuredWidth + paddingRight).toFloat(),
            (measuredHeight + paddingBottom).toFloat(),
            paint
        )

        /**
         * 文本
         */
        paint.color = mRandomTextColor
        //註意這裡的坐標xy不是左上角，而是左下角，所以高度是相加的，在自定義view中，坐標軸右下為正
        //getWidth 等於 measuredWidth
        canvas?.drawText(
            mRandomText,
            (width / 2 - bounds.width() / 2).toFloat(),
            (height / 2 + bounds.height() / 2).toFloat(),
            paint
        )
    }

  override fun onMeasure(widthMeasureSpec: Int, heightMeasureSpec: Int) {
        super.onMeasure(widthMeasureSpec, heightMeasureSpec)

        /**
         * EXACTLY：一般是設置瞭明確的值或者是MATCH_PARENT
         * AT_MOST：表示子佈局限制在一個最大值內，一般為WARP_CONTENT
         * UNSPECIFIED：表示子佈局想要多大就多大，很少使用
         */
        val widthMode = MeasureSpec.getMode(widthMeasureSpec)
        val widthSize = MeasureSpec.getSize(widthMeasureSpec)

        val heightMode = MeasureSpec.getMode(heightMeasureSpec)
        val heightSize = MeasureSpec.getSize(heightMeasureSpec)

        var width = 0
        var height = 0

        //如果指定瞭寬度，或不限制寬度，用可用寬度即可，如果是WARP_CONTENT，則用文本寬度，再加上左右padding
        when (widthMode) {
            MeasureSpec.UNSPECIFIED,
            MeasureSpec.EXACTLY -> {
                width = widthSize + paddingLeft + paddingRight
            }
            MeasureSpec.AT_MOST -> {
                width = bounds.width() + paddingLeft + paddingRight
            }
        }

        //如果指定瞭高度，或不限制高度，用可用高度即可，如果是WARP_CONTENT，則用文本高度，再加上上下padding
        when (heightMode) {
            MeasureSpec.UNSPECIFIED,
            MeasureSpec.EXACTLY -> {
                height = heightSize + paddingTop + paddingBottom
            }
            MeasureSpec.AT_MOST -> {
                height = bounds.height() + paddingTop + paddingBottom
            }
        }

        //保存測量的寬高
        setMeasuredDimension(width, height)
    }

constructor(context: Context, attributeSet: AttributeSet?, defStyle: Int) : super(context, attributeSet, defStyle) {
        ...
        /**
         * 添加點擊事件
         */
        this.setOnClickListener {
            mRandomText = randomText()
            //更新
            postInvalidate()
        }
    }

 /**
     * 根據文本長度 隨意數字
     */
    private fun randomText(): String {
        val list = mutableListOf<Int>()
        for (index in mRandomText.indices) {
            list.add(Random.nextInt(10))
        }
        val stringBuffer = StringBuffer()
        for (i in list) {
            stringBuffer.append("" + i)
        }
        return stringBuffer.toString()
    }