1:想要從view的中心開始繪制可以如下
canvas.save(); canvas.translate(mWidth / 2, mHeight / 2); canvas.restore();2:數學相關的計算多用:Math類 —三角函數等等
3:想要在一組數據中查找value在這組數據中的位置,可以先排序,再用二分查找法(binarySearch)找出
int position = Arrays.binarySearch(endAngles, (float) touchDegree);4:在處理觸摸事件和繪制的時候,特別注意坐標問題,可以轉變坐標系,常用還可以用兩個變量來提升性能,不用一直繪制 lastTouchedPosition ,currentTouchedPosition
@Override public boolean onTouchEvent(MotionEvent event) { switch (event.getAction()) { case MotionEvent.ACTION_DOWN: case MotionEvent.ACTION_MOVE: float touchX = event.getX(); float touchY = event.getY(); //轉換坐標為圓中心點的坐標 touchX = touchX - mWidth / 2; touchY = touchY - mHeight / 2; //根據反正切值拿到角度 touchDegree = MathUtil.getTouchAngle(touchX, touchY); Log.e("degree", touchDegree + ""); //找出觸摸的是第幾塊區域 float touchRadius = (float) Math.sqrt(touchX * touchX + touchY * touchY); if (touchRadius < circleRadius) { int position = Arrays.binarySearch(startAngles, (float) touchDegree); if (position > 0) { currentTouchedPosition = position; } else { // -index - 1 = position currentTouchedPosition = -position - 1; } if (currentTouchedPosition != lastTouchedPosition) { lastTouchedPosition = currentTouchedPosition; Log.e("lastTouchedPosition",lastTouchedPosition +""); invalidate(); } } break; case MotionEvent.ACTION_UP: lastTouchedPosition = -1; invalidate(); break; } return true; }5:注意坐標系的象限和數學中不一樣
String percentText = String.format("%.2f", pieBean.getPercent() * 100) + "%"; if (startAngle % 360 > 90 && startAngle % 360 < 270) { mLinePaint.setTextAlign(Paint.Align.RIGHT); canvas.drawText(percentText, endX, endY, mLinePaint); mLinePaint.setTextAlign(Paint.Align.LEFT); } else { canvas.drawText(percentText, endX, endY, mLinePaint); }新聞熱點
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