我有一個方法，每次都必須傳入一個固定的對象 paint,因為這個函數會被頻繁調用，所以我不能在內聯函數中創建對象。inline fun Canvas.drawPoint(
point: PointF,
paint: Paint) {
drawPoint(point.x, point.y, paint)
}但是我很多地方都會調用這個方法。 //(Canvas.apply(..,..))
drawPoint(pointA, pointPaint)
drawPoint(pointB, pointPaint)
drawPoint(pointC, pointPaint)
drawPoint(pointD, pointPaint)可以看到每次都會傳入一個pointPaint對象。所以我在想有沒有類似這樣一個功能 //(Canvas.apply(..,..))
bind(pointPaint)
drawPoint(pointA)
drawPoint(pointB)
drawPoint(pointC)
drawPoint(pointD)
2 回答
蝴蝶刀刀
TA貢獻1801條經驗 獲得超8個贊
fun test() {
Canvas().bindPaintDrawPoints(Paint())(
arrayOf(PointF(1f, 2f),
PointF(2f, 2f),
PointF(3f, 2f),
PointF(4f, 2f))
)
}
fun Canvas.bindPaintDrawPoints(paint: Paint): (Array<PointF>) -> Unit {
return {
drawPoints(paint, it)
}
}
fun Canvas.drawPoints(paint: Paint, points: Array<PointF>) {
for (p in points) {
this.drawPoint(p.x, p.y, paint)
}
}
蕭十郎
TA貢獻1815條經驗 獲得超13個贊
完美符合你要求的方式肯定是沒有的，因為 bind 函數不可能改變另一個函數內部的局部變量。
折中的方式也有很多，比如定義一個包級屬性：
var drawPaint: Paint? = null
然后原來的函數改為：
inline fun Canvas.drawPoint(
point: PointF,
paint: Paint) {
paint?.let {
drawPoint(point.x, point.y, it)
}
}方便使用還可以再定義一個函數來確保 drawPaint 能被準確的賦值和釋放：
fun bindPaint(paint: Paint, action: () -> Unit) {
drawPaint = paint
action()
drawPaint = null}這樣使用時就是：
// Canvas().apply {bindPaint(somePaint) {
drawPoint(x, y)
}還有一種方式是定義一個包裝類，并在其中定義一個包含帶接收者 Lambda 表達式的參數的函數（接收者為 Canvas），然后將擴展函數定義到這個類中：
class PointPainter(private val paint: Paint) {
fun Canvas.drawPoint(rect: RectF) {
drawPoint(rect.x, rect.y, paint)
}
}然后定義含有接收者為這個包裝對象 Lambda 參數的函數：
fun bindPointPainter(paint: Paint, drawAction: PointPainter.() -> Unit) {
PointPainter(paint).drawAction()
}這樣用時更方便一些：
// in canvas.apply blockbindPointPainter(somePaint) {
drawPoint(rect1)
drawPoint(rect2) // ...}- 2 回答
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