@Override
protected void onDraw(Canvas canvas) {
if (adapter == null) {
return;
}
// 可见的item数组
Object visibles[] = new Object[itemsVisible];
// 更加滚动的Y值高度除去每行Item的高度，得到滚动了多少个item，即change数
change = (int) (totalScrollY / (lineSpacingMultiplier * maxTextHeight));
try {
// 滚动中实际的预选中的item(即经过了中间位置的item) ＝ 滑动前的位置 ＋ 滑动相对位置
preCurrentIndex = initPosition + change % adapter.getItemsCount();
} catch (ArithmeticException e) {
System.out.println("出错了！adapter.getItemsCount() == 0，联动数据不匹配");
}
if (!isLoop) { // 不循环的情况
if (preCurrentIndex < 0) {
preCurrentIndex = 0;
}
if (preCurrentIndex > adapter.getItemsCount() - 1) {
preCurrentIndex = adapter.getItemsCount() - 1;
}
} else { // 循环
if (preCurrentIndex
< 0) { // 举个例子：如果总数是5，preCurrentIndex ＝ －1，那么preCurrentIndex按循环来说，其实是0的上面，也就是4的位置
preCurrentIndex = adapter.getItemsCount() + preCurrentIndex;
}
if (preCurrentIndex > adapter.getItemsCount() - 1) { // 同理上面,自己脑补一下
preCurrentIndex = preCurrentIndex - adapter.getItemsCount();
}
}
// 跟滚动流畅度有关，总滑动距离与每个item高度取余，即并不是一格格的滚动，每个item不一定滚到对应Rect里的，这个item对应格子的偏移值
int itemHeightOffset = (int) (totalScrollY % (lineSpacingMultiplier * maxTextHeight));
// 设置数组中每个元素的值
int counter = 0;
while (counter < itemsVisible) {
int index =
preCurrentIndex
- (itemsVisible / 2 - counter); // 索引值，即当前在控件中间的item看作数据源的中间，计算出相对源数据源的index值
// 判断是否循环，如果是循环数据源也使用相对循环的position获取对应的item值，如果不是循环则超出数据源范围使用""空白字符串填充，在界面上形成空白无数据的item项
if (isLoop) {
if (index < 0) {
index = index + adapter.getItemsCount();
if (index < 0) {
index = 0;
}
}
if (index > adapter.getItemsCount() - 1) {
index = index - adapter.getItemsCount();
if (index > adapter.getItemsCount() - 1) {
index = adapter.getItemsCount() - 1;
}
}
visibles[counter] = adapter.getItem(index);
} else if (index < 0) {
visibles[counter] = "";
} else if (index > adapter.getItemsCount() - 1) {
visibles[counter] = "";
} else {
visibles[counter] = adapter.getItem(index);
}
counter++;
}
// 中间两条横线
canvas.drawLine(0.0F, firstLineY, measuredWidth, firstLineY, paintIndicator);
canvas.drawLine(0.0F, secondLineY, measuredWidth, secondLineY, paintIndicator);
// 单位的Label
if (label != null) {
int drawRightContentStart = measuredWidth - getTextWidth(paintCenterText, label);
// 靠右并留出空隙
canvas.drawText(label, drawRightContentStart - CENTERCONTENTOFFSET, centerY, paintCenterText);
}
counter = 0;
while (counter < itemsVisible) {
canvas.save();
// L(弧长)=α（弧度）* r(半径) （弧度制）
// 求弧度--> (L * π ) / (π * r) (弧长X派/半圆周长)
float itemHeight = maxTextHeight * lineSpacingMultiplier;
double radian = ((itemHeight * counter - itemHeightOffset) * Math.PI) / halfCircumference;
// 弧度转换成角度(把半圆以Y轴为轴心向右转90度，使其处于第一象限及第四象限
float angle = (float) (90D - (radian / Math.PI) * 180D);
if (angle >= 90F || angle <= -90F) {
canvas.restore();
} else {
String contentText = getContentText(visibles[counter]);
// 计算开始绘制的位置
measuredCenterContentStart(contentText);
measuredOutContentStart(contentText);
int translateY =
(int) (radius - Math.cos(radian) * radius - (Math.sin(radian) * maxTextHeight) / 2D);
// 根据Math.sin(radian)来更改canvas坐标系原点，然后缩放画布，使得文字高度进行缩放，形成弧形3d视觉差
canvas.translate(0.0F, translateY);
canvas.scale(1.0F, (float) Math.sin(radian));
if (translateY <= firstLineY && maxTextHeight + translateY >= firstLineY) {
// 条目经过第一条线
canvas.save();
canvas.clipRect(0, 0, measuredWidth, firstLineY - translateY);
canvas.scale(1.0F, (float) Math.sin(radian) * SCALECONTENT);
canvas.drawText(contentText, drawOutContentStart, maxTextHeight, paintOuterText);
canvas.restore();
canvas.save();
canvas.clipRect(0, firstLineY - translateY, measuredWidth, (int) (itemHeight));
canvas.scale(1.0F, (float) Math.sin(radian) * 1F);
canvas.drawText(
contentText,
drawCenterContentStart,
maxTextHeight - CENTERCONTENTOFFSET,
paintCenterText);
canvas.restore();
} else if (translateY <= secondLineY && maxTextHeight + translateY >= secondLineY) {
// 条目经过第二条线
canvas.save();
canvas.clipRect(0, 0, measuredWidth, secondLineY - translateY);
canvas.scale(1.0F, (float) Math.sin(radian) * 1.0F);
canvas.drawText(
contentText,
drawCenterContentStart,
maxTextHeight - CENTERCONTENTOFFSET,
paintCenterText);
canvas.restore();
canvas.save();
canvas.clipRect(0, secondLineY - translateY, measuredWidth, (int) (itemHeight));
canvas.scale(1.0F, (float) Math.sin(radian) * SCALECONTENT);
canvas.drawText(contentText, drawOutContentStart, maxTextHeight, paintOuterText);
canvas.restore();
} else if (translateY >= firstLineY && maxTextHeight + translateY <= secondLineY) {
// 中间条目
canvas.clipRect(0, 0, measuredWidth, (int) (itemHeight));
canvas.drawText(
contentText,
drawCenterContentStart,
maxTextHeight - CENTERCONTENTOFFSET,
paintCenterText);
int preSelectedItem = adapter.indexOf(visibles[counter]);
if (preSelectedItem != -1) {
selectedItem = preSelectedItem;
}
} else {
// 其他条目
canvas.save();
canvas.clipRect(0, 0, measuredWidth, (int) (itemHeight));
canvas.scale(1.0F, (float) Math.sin(radian) * SCALECONTENT);
canvas.drawText(contentText, drawOutContentStart, maxTextHeight, paintOuterText);
canvas.restore();
}
canvas.restore();
}
counter++;
}
}
