要實現在Android中繪制圓形的動畫效果，可以使用ValueAnimator類來實現圓形的大小和位置的變化。以下是一個簡單的示例代碼：

1. 創建一個自定義View類，并重寫其onDraw方法來繪制圓形：

public class CircleView extends View {
    private Paint mPaint;
    private float mRadius;
    private float mCenterX;
    private float mCenterY;

    public CircleView(Context context, AttributeSet attrs) {
        super(context, attrs);
        mPaint = new Paint();
        mPaint.setColor(Color.RED);
        mPaint.setStyle(Paint.Style.FILL);
    }

    @Override
    protected void onDraw(Canvas canvas) {
        canvas.drawCircle(mCenterX, mCenterY, mRadius, mPaint);
    }

    public void setCircleParams(float radius, float centerX, float centerY) {
        mRadius = radius;
        mCenterX = centerX;
        mCenterY = centerY;
        invalidate();
    }
}

2. 在Activity中使用該自定義View，并添加動畫效果：

public class MainActivity extends AppCompatActivity {

    private CircleView mCircleView;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        mCircleView = findViewById(R.id.circleView);

        ValueAnimator animator = ValueAnimator.ofFloat(0, 300);
        animator.setDuration(1000);
        animator.addUpdateListener(new ValueAnimator.AnimatorUpdateListener() {
            @Override
            public void onAnimationUpdate(ValueAnimator valueAnimator) {
                float value = (float) valueAnimator.getAnimatedValue();
                mCircleView.setCircleParams(value, 200, 200);
            }
        });

        animator.start();
    }
}

3. 在布局文件中添加自定義View：

<com.example.myapplication.CircleView
    android:id="@+id/circleView"
    android:layout_width="match_parent"
    android:layout_height="match_parent" />

通過以上步驟，可以實現一個簡單的在Android中繪制圓形的動畫效果。您可以根據實際需求調整動畫效果的參數和繪制內容。