SemiCircleProgressBar 实现代码 支持渐变色

以下是一个简单的实现 SemiCircleProgressBar 并支持渐变色的示例代码，使用了 Canvas 绘制。

public class SemiCircleProgressBar extends View {

    private static final int DEFAULT_START_COLOR = Color.parseColor("#FFC107");
    private static final int DEFAULT_END_COLOR = Color.parseColor("#FF5722");
    private static final int DEFAULT_ANIM_DURATION = 1000;

    private int startColor;
    private int endColor;
    private int animDuration;
    private float progress;
    private Paint paint;
    private RectF rectF;

    public SemiCircleProgressBar(Context context) {
        this(context, null);
    }

    public SemiCircleProgressBar(Context context, AttributeSet attrs) {
        super(context, attrs);
        TypedArray ta = context.obtainStyledAttributes(attrs, R.styleable.SemiCircleProgressBar);
        startColor = ta.getColor(R.styleable.SemiCircleProgressBar_startColor, DEFAULT_START_COLOR);
        endColor = ta.getColor(R.styleable.SemiCircleProgressBar_endColor, DEFAULT_END_COLOR);
        animDuration = ta.getInteger(R.styleable.SemiCircleProgressBar_animDuration, DEFAULT_ANIM_DURATION);
        ta.recycle();
        init();
    }

    private void init() {
        paint = new Paint();
        paint.setAntiAlias(true);
        paint.setStyle(Paint.Style.STROKE);
        paint.setStrokeWidth(10);

        rectF = new RectF();
    }

    public void setProgress(float progress) {
        this.progress = progress;
        invalidate();
    }

    @Override
    protected void onDraw(Canvas canvas) {
        super.onDraw(canvas);

        int width = getWidth();
        int height = getHeight();

        int centerX = width / 2;
        int centerY = height / 2;

        int radius = Math.min(centerX, centerY) - 20;

        rectF.set(centerX - radius, centerY - radius, centerX + radius, centerY + radius);

        LinearGradient gradient = new LinearGradient(0, 0, width, 0, startColor, endColor, Shader.TileMode.CLAMP);
        paint.setShader(gradient);

        canvas.drawArc(rectF, 180, 180 * progress, false, paint);
    }

    public void startAnim() {
        ValueAnimator animator = ValueAnimator.ofFloat(0, 1);
        animator.setDuration(animDuration);
        animator.addUpdateListener(new ValueAnimator.AnimatorUpdateListener() {
            @Override
            public void onAnimationUpdate(ValueAnimator animation) {
                setProgress((float) animation.getAnimatedValue());
            }
        });
        animator.start();
    }
}

在布局文件中使用：

<com.example.SemiCircleProgressBar
    android:layout_width="200dp"
    android:layout_height="200dp"
    app:startColor="#FFC107"
    app:endColor="#FF5722"
    app:animDuration="1000" />

其中，`startColor` 和 `endColor` 分别表示渐变色的起始颜色和结束颜色，`animDuration` 表示动画的时长。可以通过 `setProgress` 方法设置进度，通过 `startAnim` 方法开始动画。