記錄使用Scroller實(shí)現(xiàn)平滑滾動(dòng)，效果圖如下：

一、自定義View中實(shí)現(xiàn)View的平滑滾動(dòng)

public class ScrollerView extends View { private Scroller mScroller; private Paint mPaint; /** * 屏幕拖動(dòng)最小像素 */ private int mTouchSlop; /** * View寬度 */ private int width; /** * View高度 */ private int height; /** * MotionEvent.getX() */ private int mEventX; /** * MotionEvent.getY() */ private int mEventY; private Bitmap mBitmap; /** * View到屏幕左邊距離 */ private int mStartX; /** * View到屏幕頂部距離 */ private int mStartY; /** * View默認(rèn)大小 */ private static int DEFAULT_SIZE = 200; public ScrollerView(Context context) { this(context, null); } public ScrollerView(Context context, @Nullable AttributeSet attrs) { super(context, attrs); mPaint = new Paint(); mScroller = new Scroller(context); ViewConfiguration configuration = ViewConfiguration.get(context); mTouchSlop = ViewConfigurationCompat.getScaledHoverSlop(configuration); mBitmap = BitmapFactory.decodeResource(getResources(), R.drawable.ic_launcher); } @Override protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) { super.onMeasure(widthMeasureSpec, heightMeasureSpec); int widthMode = MeasureSpec.getMode(widthMeasureSpec); int heightMode = MeasureSpec.getMode(heightMeasureSpec); if (widthMode == MeasureSpec.EXACTLY) { width = MeasureSpec.getSize(widthMeasureSpec); } else { if (heightMode == MeasureSpec.EXACTLY) { width = MeasureSpec.getSize(heightMeasureSpec); } else { width = DEFAULT_SIZE; } } if (heightMode == MeasureSpec.EXACTLY) { height = MeasureSpec.getSize(heightMeasureSpec); } else { height = width; } setMeasuredDimension(width, height); } @Override protected void onDraw(Canvas canvas) { super.onDraw(canvas); if (null != mBitmap) { Rect src = new Rect(0, 0, mBitmap.getWidth(), mBitmap.getHeight()); Rect dst = new Rect(0, 0, width, height); canvas.drawBitmap(mBitmap, src, dst, mPaint); } else { Log.e('zzy', 'Bitmap is null'); } } @Override public boolean onTouchEvent(MotionEvent event) { int action = event.getAction(); switch (action) { case MotionEvent.ACTION_DOWN: mEventX = (int) event.getX(); mEventY = (int) event.getY(); break; case MotionEvent.ACTION_MOVE: mStartX = (int) event.getRawX() - mEventX; mStartY = (int) event.getRawY() - mEventY; layout(mStartX,mStartY,mStartX+width,mStartY+height); break; case MotionEvent.ACTION_UP: startScroller(); break; } return true; } @Override public void computeScroll() { if (mScroller.computeScrollOffset()){ int l = mScroller.getCurrX(); layout(l,mStartY,l+width,mStartY+height); invalidate(); } } /** * 開始Scroller動(dòng)畫 */ private void startScroller(){ mScroller.forceFinished(true); mScroller.startScroll(mStartX, mStartY,-mStartX,0); int screenWidth = getScreenWidth(); // Scroller動(dòng)畫默認(rèn)250ms，超過(guò)屏幕一半時(shí)設(shè)置為500ms if (mStartX > screenWidth / 2){ mScroller.extendDuration(500); } invalidate(); } private int getScreenWidth(){ return getResources().getDisplayMetrics().widthPixels; }}

Scroller其實(shí)是個(gè)輔助類，本身并不能完成動(dòng)畫的執(zhí)行。而是幫我們計(jì)算隨著時(shí)間的流逝，動(dòng)畫應(yīng)該執(zhí)行的位置值，我們需要獲得當(dāng)前時(shí)間的位置，然后調(diào)用View位置移動(dòng)方法，將View移動(dòng)到該位置，完成動(dòng)畫。

所以，在自定義View中。我們需要調(diào)用invalidate()觸發(fā)View的重繪，并覆寫重繪會(huì)執(zhí)行的方法computeScroll()。

在computeScroll()方法中調(diào)用Scroller的computeScrollOffset()計(jì)算當(dāng)前時(shí)間動(dòng)畫應(yīng)該移動(dòng)的位置，返回值是動(dòng)畫是否在執(zhí)行。

通過(guò)mScroller.getCurrX()和mScroller.getCurrY()獲得當(dāng)前時(shí)間的位置。手動(dòng)調(diào)用View位置移動(dòng)的方法將View的位置移動(dòng)到當(dāng)前時(shí)間的位置，實(shí)現(xiàn)View的滾動(dòng)。

然后再次調(diào)用invalidate()觸發(fā)刷新。直到computeScrollOffset()返回false，動(dòng)畫執(zhí)行完成，滾動(dòng)完成。

二、直接使用Scroller實(shí)現(xiàn)View的平滑滾動(dòng)

我們知道，Scroller會(huì)幫我們計(jì)算當(dāng)前時(shí)間，插值器返回的值。

而如果直接使用Scroller實(shí)現(xiàn)平滑滾動(dòng)的話，也需要借助帶時(shí)間的監(jiān)聽器。

這里借助ValueAnimator來(lái)實(shí)現(xiàn)Scroller平滑滾動(dòng)

private Scroller mScroller; private ImageView mImage; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_main); mImage = findViewById(R.id.image); mScroller =new Scroller(this); } public void btnStart(View view){ start(); } private void start(){ mScroller.forceFinished(false); mScroller.extendDuration(500); mScroller.startScroll(0,0,400,400); ValueAnimator valueAnimator = ValueAnimator.ofFloat(0,1); valueAnimator.setDuration(500); valueAnimator.addUpdateListener(new ValueAnimator.AnimatorUpdateListener() { @Override public void onAnimationUpdate(ValueAnimator animation) { if (mScroller.computeScrollOffset()){ ViewGroup.MarginLayoutParams params = (ViewGroup.MarginLayoutParams) mImage.getLayoutParams(); params.leftMargin = mScroller.getCurrX(); params.topMargin = mScroller.getCurrY(); mImage.setLayoutParams(params); } } }); valueAnimator.start(); }

在ValueAnimator的addUpdateListener中刷新Scroller當(dāng)前值。并移動(dòng)位置。效果如下：

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