RatingBar
效果分析：
star_normal.png
star_select.png
准备两张星星图，一张默认，一张选中。初始的时候绘制默认的 5 颗星星，然后根据手势绘制选中的星星。
自定义属性
代码语言：javascript复制<declare-styleable name="KRatingbar">
//要绘制的个数
<attr name="starNum" format="integer"/>
//星星之间的间距
<attr name="starPadding" format="integer" />
//默认星星的 resId
<attr name="starNormal" format="reference" />
//选中星星的 resId
<attr name="starSelect" format="reference" />
</declare-styleable>具体实现
代码语言：javascript复制class KRatingbar @JvmOverloads constructor(
context: Context,
attributes: AttributeSet?,
defStyle: Int = 0
) : View(context, attributes, defStyle) {
private var mCount = 5
private var mNormalBitmap: Bitmap
private var mSelectBitmap: Bitmap
private var mStarPadding = dp2Px(5, resources)
private var mCurSelect = -1
init {
val ta = context.obtainStyledAttributes(attributes, R.styleable.KRatingbar)
mCount = ta.getInt(R.styleable.KRatingbar_starNum, 5)
mStarPadding = ta.getInt(R.styleable.KRatingbar_starPadding, dp2Px(5, resources))
val normalId = ta.getResourceId(R.styleable.KRatingbar_starNormal, -1)
if (normalId == 1.unaryMinus()) throw RuntimeException("starNormal can't be empty")
mNormalBitmap = BitmapFactory.decodeResource(resources, normalId)
val selectId = ta.getResourceId(R.styleable.KRatingbar_starSelect, -1)
if (selectId == 1.unaryMinus()) throw RuntimeException("starSelect can't be empty")
mSelectBitmap = BitmapFactory.decodeResource(resources, selectId)
ta.recycle()
}
override fun onMeasure(widthMeasureSpec: Int, heightMeasureSpec: Int) {
super.onMeasure(widthMeasureSpec, heightMeasureSpec)
//图片宽度*绘制的个数 星星间的间隙 paddingLeft paddingRight
val width =
mNormalBitmap.width * mCount mStarPadding * (mCount - 1) paddingLeft paddingRight
//图片的高度 paddingTop paddingBottom
val height = mNormalBitmap.height paddingTop paddingBottom
setMeasuredDimension(width, height)
}
override fun onDraw(canvas: Canvas) {
super.onDraw(canvas)
for (i in 0 until mCount) {
var x = i * mNormalBitmap.width
if (i != 0) {
//平移画布，其实就是在绘制间隙
canvas.translate(mStarPadding.toFloat(), 0f)
}
if (i < mCurSelect) {
//绘制选中的星星
canvas.drawBitmap(mSelectBitmap, x.toFloat(), 0f, null)
} else {
//绘制默认星星
canvas.drawBitmap(mNormalBitmap, x.toFloat(), 0f, null)
}
}
}
override fun onTouchEvent(event: MotionEvent): Boolean {
when (event.action) {
MotionEvent.ACTION_DOWN, MotionEvent.ACTION_MOVE, MotionEvent.ACTION_UP -> {
//根据手指按下的 x 坐标去计算按压的是第几个星星
//这里要 1，因为 index 是从 0 开始的
val count = event.x.toInt() / (mNormalBitmap.width mStarPadding) 1
//当前选中的和之前一样不再重复绘制，count !=1 是为了处理，按压第一个时，无法滑动选中的 bug
if (mCurSelect == count && count != 1) {
return false
}
//越界时为 0
if (count < 0) {
mCurSelect = 0
}
//越界时默认为最大的绘制个数
if (count > mCount) {
mCurSelect = mCount
}
//当前选中了第几个
mCurSelect = count
//重绘
invalidate()
}
}
//这里要返回 true 才会处理 onTouchEvent 事件
return true
}
}
