環形ProgressBar的進度百分比顯示

要在環形ProgressBar上顯示進度百分比，可以通過設置ProgressBar的樣式和自定義繪制來實現。以下是一個示例代碼，演示如何在環形ProgressBar上顯示進度百分比：

public class CircleProgressBar extends View {

    private Paint mPaint;
    private RectF mRectF;
    private int mProgress;
    private int mMaxProgress;
    private String mProgressText;

    public CircleProgressBar(Context context) {
        super(context);
        init();
    }

    public CircleProgressBar(Context context, @Nullable AttributeSet attrs) {
        super(context, attrs);
        init();
    }

    public CircleProgressBar(Context context, @Nullable AttributeSet attrs, int defStyleAttr) {
        super(context, attrs, defStyleAttr);
        init();
    }

    private void init() {
        mPaint = new Paint();
        mPaint.setAntiAlias(true);
        mPaint.setStyle(Paint.Style.STROKE);
        mPaint.setStrokeWidth(10);
        mRectF = new RectF();
        mMaxProgress = 100;
    }

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

        int centerX = getWidth() / 2;
        int centerY = getHeight() / 2;
        int radius = Math.min(centerX, centerY) - 5;

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

        mPaint.setColor(Color.GRAY);
        canvas.drawCircle(centerX, centerY, radius, mPaint);

        mPaint.setColor(Color.BLUE);
        canvas.drawArc(mRectF, -90, 360 * mProgress / mMaxProgress, false, mPaint);

        mPaint.setTextSize(50);
        mProgressText = mProgress + "%";
        float textWidth = mPaint.measureText(mProgressText);
        canvas.drawText(mProgressText, centerX - textWidth / 2, centerY + mPaint.getTextSize() / 2, mPaint);
    }

    public void setProgress(int progress) {
        mProgress = progress;
        invalidate();
    }
}

在上面的代碼中，我們繼承了View類，并重寫了onDraw方法，通過繪制圓形和弧線來實現環形ProgressBar的效果。同時，在ProgressBar的中心繪制了進度百分比的文本。

要在Activity中使用這個自定義的CircleProgressBar，可以像下面這樣：

CircleProgressBar progressBar = findViewById(R.id.circleProgressBar);
progressBar.setProgress(50); // 設置進度為50%

通過調用setProgress方法，可以設置ProgressBar的進度，進度百分比將會顯示在環形ProgressBar的中心位置。