Android如何实现自定义倒计时

public class CountDownView extends View {
  //圆轮颜色
  private int mRingColor;
  //默认圆颜色
  private int mRingNormalColor ;
  //圆轮宽度
  private float mRingWidth;
  //圆轮进度值文本大小
  private int mRingProgessTextSize;
  //宽度
  private int mWidth;
  //高度
  private int mHeight;
  private Paint mPaint;
  private Paint paintNormal;
  //圆环的矩形区域
  private RectF mRectF;
  //
  private int mProgessTextColor;
  private int mCountdownTime;
  private float mCurrentProgress;
  private OnCountDownFinishListener mListener;
  private ValueAnimator valueAnimator ;
 
  public CountDownView(Context context) {
    this(context, null);
  }
 
  public CountDownView(Context context, AttributeSet attrs) {
    this(context, attrs, 0);
  }
 
  public CountDownView(Context context, AttributeSet attrs, int defStyleAttr) {
    super(context, attrs, defStyleAttr);
    TypedArray a = context.obtainStyledAttributes(attrs, R.styleable.CountDownView);
    mRingColor = a.getColor(R.styleable.CountDownView_ringColor, context.getResources().getColor(R.color.circle_progress));
    mRingWidth = a.getFloat(R.styleable.CountDownView_ringWidth, 8);
    mRingProgessTextSize = a.getDimensionPixelSize(R.styleable.CountDownView_progressTextSize, DisplayUtil.sp2px(context, 12));
    mProgessTextColor = a.getColor(R.styleable.CountDownView_progressTextColor, context.getResources().getColor(R.color.circle_progress));
    mCountdownTime = a.getInteger(R.styleable.CountDownView_countdownTime, 60);
    mRingNormalColor = a.getColor(R.styleable.CountDownView_ringColor, context.getResources().getColor(R.color._circle_progress));
    a.recycle();
    paintNormal = new Paint(Paint.ANTI_ALIAS_FLAG);
    paintNormal.setAntiAlias(true);
    mPaint = new Paint(Paint.ANTI_ALIAS_FLAG);
    mPaint.setAntiAlias(true);
    this.setWillNotDraw(false);
  }
 
  public void setCountdownTime(int mCountdownTime) {
    this.mCountdownTime = mCountdownTime;
  }
 
  @Override
  protected void onLayout(boolean changed, int left, int top, int right, int bottom) {
    super.onLayout(changed, left, top, right, bottom);
    mWidth = getMeasuredWidth();
    mHeight = getMeasuredHeight();
    mRectF = new RectF(0 + mRingWidth / 2, 0 + mRingWidth / 2,
        mWidth - mRingWidth / 2, mHeight - mRingWidth / 2);
  }
 
  @Override
  protected void onDraw(Canvas canvas) {
    super.onDraw(canvas);
    /**
     *圆环
     */
    //颜色
    mPaint.setColor(mRingColor);
    //空心
    mPaint.setStyle(Paint.Style.STROKE);
    //宽度
    mPaint.setStrokeWidth(mRingWidth);
    /**
     *默认圆环
     */
    //颜色
    paintNormal.setColor(mRingNormalColor);
    //空心
    paintNormal.setStyle(Paint.Style.STROKE);
    //宽度
    paintNormal.setStrokeWidth(mRingWidth);
    canvas.drawArc(mRectF, 360, 360, false, paintNormal);
    canvas.drawArc(mRectF, -90, mCurrentProgress - 360, false, mPaint);
    //绘制文本
    Paint textPaint = new Paint();
    textPaint.setAntiAlias(true);
    textPaint.setTextAlign(Paint.Align.CENTER);
    String text = mCountdownTime - (int) (mCurrentProgress / 360f * mCountdownTime) + "";
    textPaint.setTextSize(mRingProgessTextSize);
    textPaint.setColor(mProgessTextColor);
 
    //文字居中显示
    Paint.FontMetricsInt fontMetrics = textPaint.getFontMetricsInt();
    int baseline = (int) ((mRectF.bottom + mRectF.top - fontMetrics.bottom - fontMetrics.top) / 2);
    canvas.drawText(text, mRectF.centerX(), baseline, textPaint);
  }
 
  private ValueAnimator getValA(long countdownTime) {
    ValueAnimator valueAnimator = ValueAnimator.ofFloat(0, 100);
    valueAnimator.setDuration(countdownTime);
    valueAnimator.setInterpolator(new LinearInterpolator());
    valueAnimator.setRepeatCount(0);
    return valueAnimator;
  }
  /**
   * 开始倒计时
   */
  public void startCountDown() {
    setClickable(false);
    valueAnimator = getValA(mCountdownTime * 1000);
    valueAnimator.addUpdateListener(new ValueAnimator.AnimatorUpdateListener() {
      @Override
      public void onAnimationUpdate(ValueAnimator animation) {
        float i = Float.valueOf(String.valueOf(animation.getAnimatedValue()));
        mCurrentProgress = (int) (360 * (i / 100f));
        invalidate();
      }
    });
    valueAnimator.start();
    valueAnimator.addListener(new AnimatorListenerAdapter() {
      @Override
      public void onAnimationEnd(Animator animation) {
        super.onAnimationEnd(animation);
        //倒计时结束回调
        if (mListener != null) {
          mListener.countDownFinished();
        }
        setClickable(true);
      }
 
    });
  }
  public void setAddCountDownListener(OnCountDownFinishListener mListener) {
    this.mListener = mListener;
  }
  public interface OnCountDownFinishListener {
    void countDownFinished();
  }
  public void stopCountDown(){
    valueAnimator.end();
  }
 
}

losTime.setAddCountDownListener(new CountDownView.OnCountDownFinishListener() {
        @Override
        public void countDownFinished() {
          倒计时结束
        }
      });
losTime.setCountdownTime(60);
losTime.startCountDown();