https://github.com/ldoublem/RingProgress

很棒的创意，我还以为是外国人写的呢，厉害。

分析下

旋转的部分，RotateDrawable 其实已经抽象了，或者 setStartAngle 也可以做到。

SweepAngle 的部分已经实现过了，就是个映射。

多了一个设置 StrokeWidth 的接口。

public class RingDrawable extends Drawable {

// =================== RingDrawable ===================

public RingDrawable() {
initPaints();
}

// =================== paints ===================

private final Paint ringPaint = new Paint(Paint.ANTI_ALIAS_FLAG);
private final Paint bgPaint = new Paint(Paint.ANTI_ALIAS_FLAG);
private final RectF innerBounds = new RectF();

// =================== fields ===================

private int mRingWidth = 20;
private int mStartAngle = 0;
private int mSweepAngle = 360;
private double mProgress = 0;
private int[] mRingColors;

// todo please ignore this
public int inset = 0;

// =================== initPaints ===================

private void initPaints() {
ringPaint.setStyle(Paint.Style.STROKE);
ringPaint.setStrokeWidth(mRingWidth);
bgPaint.setStyle(Paint.Style.STROKE);
bgPaint.setStrokeWidth(mRingWidth);
}

// =================== onBoundChange ===================

@Override
protected void onBoundsChange(Rect bounds) {
calcInnerBounds();
}

private void calcInnerBounds() {
final int delta = mRingWidth / 2 + inset;
innerBounds.set(delta, delta, Math.max(0, getBounds().width() - delta), Math.max(0, getBounds().height() - delta));
}

// =================== drawProgress & drawBg ===================

// drawPath 不会出现 drawArc 的问题
private void drawProgress(@NonNull Canvas canvas) {
setRingShader();
Path ringPath = new Path();
ringPath.addArc(innerBounds, mStartAngle, mSweepAngle * getPercent());
canvas.drawPath(ringPath, ringPaint);
}

private void setRingShader() {
if (mRingColors == null) {
return;
}
int cx = getBounds().width() / 2;
int cy = getBounds().height() / 2;
Matrix matrix = new Matrix();
matrix.setRotate(mStartAngle, cx, cy);
SweepGradient shader = new SweepGradient(cx, cy, mRingColors, getPositions());
shader.setLocalMatrix(matrix);
ringPaint.setShader(shader);
}

private float[] getPositions() {
int length = mRingColors.length;
float[] positions = new float[length];
float delta = getPercent() * mSweepAngle / 360 / (length - 1);
for (int i = 0; i != length; i++) {
positions[i] = delta * i;
}
return positions;
}

private float getPercent() {
return (float) mProgress / 100;
}

private void drawBg(@NonNull Canvas canvas) {
Path bgPath = new Path();
bgPath.addArc(innerBounds, mStartAngle, mSweepAngle);
canvas.drawPath(bgPath, bgPaint);
}

// =================== setter ===================

public void setProgress(@FloatRange(from = 0.0, to = 100.0) float progress) {
mProgress = progress;
invalidateSelf();
}

public void setRingWidth(int ringWidth) {
mRingWidth = ringWidth;
onRingWidthChange();
}

private void onRingWidthChange() {
bgPaint.setStrokeWidth(mRingWidth);
ringPaint.setStrokeWidth(mRingWidth);
calcInnerBounds();
invalidateSelf();
}

public void setStartAngle(int startAngle) {
mStartAngle = startAngle;
invalidateSelf();
}

public void setSweepAngle(int sweepAngle) {
mSweepAngle = sweepAngle;
invalidateSelf();
}

public void setRingColors(int[] ringColors) {
mRingColors = ringColors;
}

public void setBgColor(@ColorInt int bgColor) {
bgPaint.setColor(bgColor);
invalidateSelf();
}

// =================== draw ===================

@Override
public void draw(@NonNull Canvas canvas) {
drawBg(canvas);
drawProgress(canvas);
}

@Override
public void setAlpha(int alpha) {
}

@Override
public void setColorFilter(ColorFilter colorFilter) {
}

@Override
public int getOpacity() {
return PixelFormat.TRANSLUCENT;
}

}


其实最出彩的还是配色。