Android Scrollerの理解

Androidの原理を理解するには、ソースコードで分析するのが一番です.今度また来て、Scrollerがいったい何なのか見てみましょう.
Scrollerはスクロールの補助クラスで、Viewの位置と計算された位置だけを格納し、本当にViewを移動していません.嫌いなのはScrollerです.startScroll()は名前から人を誤導していて、最初はこの方法で移動したのかと思っていました.

public class Scroller  {
    private int mMode;

    private int mStartX;
    private int mStartY;
    private int mFinalX;
    private int mFinalY;

    private int mMinX;
    private int mMaxX;
    private int mMinY;
    private int mMaxY;

    private int mCurrX;
    private int mCurrY;
    private long mStartTime;
    private int mDuration;
    private float mDurationReciprocal;
    private float mDeltaX;
    private float mDeltaY;
    private boolean mFinished;
    private Interpolator mInterpolator;
    private boolean mFlywheel;

    private float mVelocity;
    private float mCurrVelocity;
    private int mDistance;

    private float mFlingFriction = ViewConfiguration.getScrollFriction();

    private static final int DEFAULT_DURATION = 250;
    private static final int SCROLL_MODE = 0;
    private static final int FLING_MODE = 1;

    private static float DECELERATION_RATE = (float) (Math.log(0.78) / Math.log(0.9));
    private static final float INFLEXION = 0.35f; // Tension lines cross at (INFLEXION, 1)
    private static final float START_TENSION = 0.5f;
    private static final float END_TENSION = 1.0f;
    private static final float P1 = START_TENSION * INFLEXION;
    private static final float P2 = 1.0f - END_TENSION * (1.0f - INFLEXION);

    private static final int NB_SAMPLES = 100;
    private static final float[] SPLINE_POSITION = new float[NB_SAMPLES + 1];
    private static final float[] SPLINE_TIME = new float[NB_SAMPLES + 1];

    private float mDeceleration;
    private final float mPpi;

    // A context-specific coefficient adjusted to physical values.
    private float mPhysicalCoeff;

Scrollerは最初は変数がたくさんあって、名前はいくつかの位置X、Yなどを見ることができて、スクロールの状態、速度の値があります.主な方法もgetXXXとsetXXXで、これが属性を得ることです.
重要な2つの方法は次のとおりです.

/**
     * Start scrolling by providing a starting point, the distance to travel,
     * and the duration of the scroll.
     * 
     * @param startX Starting horizontal scroll offset in pixels. Positive
     *        numbers will scroll the content to the left.
     * @param startY Starting vertical scroll offset in pixels. Positive numbers
     *        will scroll the content up.
     * @param dx Horizontal distance to travel. Positive numbers will scroll the
     *        content to the left.
     * @param dy Vertical distance to travel. Positive numbers will scroll the
     *        content up.
     * @param duration Duration of the scroll in milliseconds.
     */
    public void startScroll(int startX, int startY, int dx, int dy, int duration) {
        mMode = SCROLL_MODE;
        mFinished = false;
        mDuration = duration;
        mStartTime = AnimationUtils.currentAnimationTimeMillis();
        mStartX = startX;
        mStartY = startY;
        mFinalX = startX + dx;
        mFinalY = startY + dy;
        mDeltaX = dx;
        mDeltaY = dy;
        mDurationReciprocal = 1.0f / (float) mDuration;
    }

これは,与えられた開始と終了のxy値と時間により,対応する時間に対応すべき座標を算出する.いずれも付与された文であり,Viewの移動には触れていない.
もう1つは、

/**
     * Start scrolling based on a fling gesture. The distance travelled will
     * depend on the initial velocity of the fling.
     * 
     * @param startX Starting point of the scroll (X)
     * @param startY Starting point of the scroll (Y)
     * @param velocityX Initial velocity of the fling (X) measured in pixels per
     *        second.
     * @param velocityY Initial velocity of the fling (Y) measured in pixels per
     *        second
     * @param minX Minimum X value. The scroller will not scroll past this
     *        point.
     * @param maxX Maximum X value. The scroller will not scroll past this
     *        point.
     * @param minY Minimum Y value. The scroller will not scroll past this
     *        point.
     * @param maxY Maximum Y value. The scroller will not scroll past this
     *        point.
     */
    public void fling(int startX, int startY, int velocityX, int velocityY,
            int minX, int maxX, int minY, int maxY) {
        // Continue a scroll or fling in progress
        if (mFlywheel && !mFinished) {
            float oldVel = getCurrVelocity();

            float dx = (float) (mFinalX - mStartX);
            float dy = (float) (mFinalY - mStartY);
            float hyp = FloatMath.sqrt(dx * dx + dy * dy);

            float ndx = dx / hyp;
            float ndy = dy / hyp;

            float oldVelocityX = ndx * oldVel;
            float oldVelocityY = ndy * oldVel;
            if (Math.signum(velocityX) == Math.signum(oldVelocityX) &&
                    Math.signum(velocityY) == Math.signum(oldVelocityY)) {
                velocityX += oldVelocityX;
                velocityY += oldVelocityY;
            }
        }

        mMode = FLING_MODE;
        mFinished = false;

        float velocity = FloatMath.sqrt(velocityX * velocityX + velocityY * velocityY);
     
        mVelocity = velocity;
        mDuration = getSplineFlingDuration(velocity);
        mStartTime = AnimationUtils.currentAnimationTimeMillis();
        mStartX = startX;
        mStartY = startY;

        float coeffX = velocity == 0 ? 1.0f : velocityX / velocity;
        float coeffY = velocity == 0 ? 1.0f : velocityY / velocity;

        double totalDistance = getSplineFlingDistance(velocity);
        mDistance = (int) (totalDistance * Math.signum(velocity));
        
        mMinX = minX;
        mMaxX = maxX;
        mMinY = minY;
        mMaxY = maxY;

        mFinalX = startX + (int) Math.round(totalDistance * coeffX);
        // Pin to mMinX <= mFinalX <= mMaxX
        mFinalX = Math.min(mFinalX, mMaxX);
        mFinalX = Math.max(mFinalX, mMinX);
        
        mFinalY = startY + (int) Math.round(totalDistance * coeffY);
        // Pin to mMinY <= mFinalY <= mMaxY
        mFinalY = Math.min(mFinalY, mMaxY);
        mFinalY = Math.max(mFinalY, mMinY);
    }

fling、この恐ろしいやつがまた来たが、実は何でもない.指を離した瞬間、Viewの転がりはまだ速度があるので、速度によって次のViewの位置を計算したのだ.
では、このScrollerはVeiwを移動していませんが、何をしますか?これは補助移動で、私たちはいつでもgetCurrXとgetCurrYでViewの位置を得ることができて、それから..このVeiwをスクロールするにはScrollToを使用します.しかし注意しなければならないのは、ScrolToはViewの内容に対して、LinearLayoutであればScrollTo()、Linearlayoutの中のものはすべて移動します.それはTextViewです.ScrollTo()は、TextViewの中身が動いているだけなんですよね～、TextViewはそのまま動いていません.