VelocityTracker简介

VelocityTracker：

android.view.VelocityTracker主要用跟踪触摸屏事件（flinging事件和其他gestures手势事件）的速率。用addMovement(MotionEvent)函数将Motion event加入到VelocityTracker类实例中.你可以使用getXVelocity() 或getXVelocity()获得横向和竖向的速率到速率时，但是使用它们之前请先调用computeCurrentVelocity(int)来初始化速率的单位 。

 

示例： 

    private VelocityTracker mVelocityTracker;//生命变量 

    //在onTouchEvent(MotionEvent ev)中 

    if (mVelocityTracker == null) { 

            mVelocityTracker = VelocityTracker.obtain();//获得VelocityTracker类实例 

    } 

    mVelocityTracker.addMovement(ev);//将事件加入到VelocityTracker类实例中 

    //判断当ev事件是MotionEvent.ACTION_UP时：计算速率 

    // 1000 provides pixels per second 

    velocityTracker.computeCurrentVelocity(1, (float)0.01); //设置maxVelocity值为0.1时，速率大于0.01时，显示的速率都是0.01,速率小于0.01时，显示正常 

    Log.i("test","velocityTraker"+velocityTracker.getXVelocity());                     

    velocityTracker.computeCurrentVelocity(1000); //设置units的值为1000，意思为一秒时间内运动了多少个像素 

    Log.i("test","velocityTraker"+velocityTracker.getXVelocity()); 

大体的使用是这样的：

当你需要跟踪触摸屏事件的速度的时候,使用obtain()方法来获得VelocityTracker类的一个实例对象

在onTouchEvent回调函数中，使用addMovement(MotionEvent)函数将当前的移动事件传递给VelocityTracker对象

使用computeCurrentVelocity  (int units)函数来计算当前的速度，使用 getXVelocity  ()、 getYVelocity  ()函数来获得当前的速度

类：

package android.view;import android.view.MotionEvent;public final class VelocityTracker {    VelocityTracker() {        throw new RuntimeException("Stub!");    }    public static VelocityTracker obtain() {        throw new RuntimeException("Stub!");    }    public void recycle() {        throw new RuntimeException("Stub!");    }    protected void finalize() throws Throwable {        throw new RuntimeException("Stub!");    }    public void clear() {        throw new RuntimeException("Stub!");    }    public void addMovement(MotionEvent event) {        throw new RuntimeException("Stub!");    }    public void computeCurrentVelocity(int units) {        throw new RuntimeException("Stub!");    }    public void computeCurrentVelocity(int units, float maxVelocity) {        throw new RuntimeException("Stub!");    }    public float getXVelocity() {        throw new RuntimeException("Stub!");    }    public float getYVelocity() {        throw new RuntimeException("Stub!");    }    public float getXVelocity(int id) {        throw new RuntimeException("Stub!");    }    public float getYVelocity(int id) {        throw new RuntimeException("Stub!");    }}

使用例子介绍：

package com.hitomi.aslibrary;import android.animation.Animator;import android.animation.AnimatorListenerAdapter;import android.animation.AnimatorSet;import android.animation.ObjectAnimator;import android.animation.ValueAnimator;import android.content.Context;import android.support.annotation.NonNull;import android.util.AttributeSet;import android.util.Log;import android.view.MotionEvent;import android.view.VelocityTracker;import android.view.View;import android.view.ViewGroup;import android.view.animation.DecelerateInterpolator;import android.widget.FrameLayout;/** * 排列、展示、拖动 Activity 容器类 <br/> * * email : [e-mail] <br/> * * github : https://github.com/Hitomis <br/> * * Created by hitomi on 2016/10/11. */class ActivityControllerLayout extends FrameLayout implements View.OnClickListener{    public static final String TAG = "ActivitySwitcher";    public static final int FLAG_DISPLAYING = 100;    public static final int FLAG_DISPLAYED = 200;    public static final int FLAG_CLOSING = -100;    public static final int FLAG_CLOSED = -200;    public static final int FLAG_SLIDING = 0;    private static final int STYLE_SINGLE = 1;    private static final int STYLE_DOUBLE = 1 << 1;    private static final int STYLE_MULTIPLE = 1 << 2;    private static final float CENTER_SCALE_RATE = .65f;    private static final float OFFSET_SCALE_RATE = .02f;    private static final int MIN_OFFSET_SIZE = 80;    private static final int MAX_OFFSET_SIZE = 180;    private int maxVelocity = 2500;    private int touchSlop = 8;    private int flag;    private int width;    private float pageOffsetSize;    private float preY, diffY;    private float controlViewBottom = 0.f;    private float[] originalContainerX;    private float[] originalContainerScale;    private boolean resetBackground;    private VelocityTracker velocityTracker;    private OnControlCallback onControlCallback;    private ActivityContainer controlView;    public ActivityControllerLayout(Context context) {        this(context, null);    }    public ActivityControllerLayout(Context context, AttributeSet attrs) {        this(context, attrs, 0);    }    public ActivityControllerLayout(Context context, AttributeSet attrs, int defStyleAttr) {        super(context, attrs, defStyleAttr);        flag = FLAG_CLOSED;        width = getResources().getDisplayMetrics().widthPixels;    }    @Override    public void addView(View child) {        child.setOnClickListener(this);        super.addView(child);    }    @Override    public boolean dispatchTouchEvent(MotionEvent ev) {        if (flag == FLAG_DISPLAYED || flag == FLAG_SLIDING)        switch (ev.getAction()) {            case MotionEvent.ACTION_DOWN:                if (null == velocityTracker) {                    velocityTracker = VelocityTracker.obtain();                } else {                    velocityTracker.clear();                }                velocityTracker.addMovement(ev);                if (findControlView(ev) == null || flag == FLAG_SLIDING) return false;                cacheOrginalContainerParamter(controlView = findControlView(ev));                preY = ev.getY();                break;            case MotionEvent.ACTION_MOVE:                velocityTracker.addMovement(ev);                diffY = ev.getY() - preY;                float newDiffY = diffY;                if (controlView.getY() <= 0) { // 在中线之上                    moveToLastContainerPos();                } else if (controlView.getY() > 0 && diffY > 0) { // 在中线之下                    float slopRate = 1.f - 1.65f * controlView.getY() / (controlView.getIntrinsicHeight());                    newDiffY *= slopRate;                }                controlView.setY(controlView.getY() + newDiffY);                preY = ev.getY();                break;            case MotionEvent.ACTION_UP:                velocityTracker.addMovement(ev);                velocityTracker.computeCurrentVelocity(1000);                float velocityY = velocityTracker.getYVelocity();                boolean over = Math.abs(controlView.getY()) >= controlView.getIntrinsicHeight() * .618;                if (diffY < touchSlop * .4f && controlView.getY() < 0 && (over || Math.abs(velocityY) >= maxVelocity)) {                    // 上移且超出阈值 或者 上移速度超过阈值 -> 移除到窗外                    slideOutAnimation();                } else if (flag != FLAG_CLOSING && Math.abs(controlView.getY()) >= touchSlop) {                    // 下移或者上移没有超出阈值- > 回落到原始位置                    slideOrignalPosAnimation();                }                diffY = 0;                if (null != velocityTracker) {                    velocityTracker.recycle();                    velocityTracker = null;                }                break;            case MotionEvent.ACTION_CANCEL:                if (null != velocityTracker) {                    velocityTracker.recycle();                    velocityTracker = null;                }                break;        }        return super.dispatchTouchEvent(ev);    }    @Override    public void onClick(final View view) {        if (flag == FLAG_DISPLAYED                && Math.abs(diffY) < touchSlop                && Math.abs(view.getY()) < touchSlop) {            closure(false);        }    }    private void cacheOrginalContainerParamter(ActivityContainer controlContainer) {        controlViewBottom = controlContainer.getBounds().bottom;        int controlIndex = indexOfChild(controlContainer);        if (getChildCount() != 3) {            originalContainerX = new float[getChildCount()];            originalContainerScale = new float[getChildCount()];            View child;            for (int i = 0; i < getChildCount(); i++) {                child = getChildAt(i);                originalContainerX[i] = child.getX();                originalContainerScale[i] = child.getScaleX();            }        } else {            originalContainerX = new float[2];            originalContainerScale = new float[2];            if (controlIndex == 0) {                originalContainerX[0] = getChildAt(1).getX();                originalContainerX[1] = getChildAt(2).getX();                originalContainerScale[0] = getChildAt(1).getScaleX();                originalContainerScale[1] = getChildAt(2).getScaleX();            } else if (controlIndex == 1) {                originalContainerX[0] = getChildAt(0).getX();                originalContainerX[1] = getChildAt(2).getX();                originalContainerScale[0] = getChildAt(0).getScaleX();                originalContainerScale[1] = getChildAt(2).getScaleX();            } else {                originalContainerX[0] = getChildAt(0).getX();                originalContainerX[1] = getChildAt(1).getX();                originalContainerScale[0] = getChildAt(0).getScaleX();                originalContainerScale[1] = getChildAt(1).getScaleX();            }        }    }    private void slideOrignalPosAnimation() {        ObjectAnimator tranYAnima = ObjectAnimator.ofFloat(controlView, "Y", controlView.getY(), 0);        tranYAnima.setDuration(350);        tranYAnima.setInterpolator(new DecelerateInterpolator());        tranYAnima.addUpdateListener(new ValueAnimator.AnimatorUpdateListener() {            @Override            public void onAnimationUpdate(ValueAnimator valueAnimator) {                if (controlView.getY() < 0)                    moveToLastContainerPos();            }        });        tranYAnima.start();    }    private void slideOutAnimation() {        flag = FLAG_SLIDING;        float endTranY = controlView.getY() - controlView.getBounds().bottom;        ObjectAnimator tranYAnima = ObjectAnimator.ofFloat(controlView, "Y", controlView.getY(), endTranY);        tranYAnima.setDuration(150);        tranYAnima.addUpdateListener(new ValueAnimator.AnimatorUpdateListener() {            @Override            public void onAnimationUpdate(ValueAnimator valueAnimator) {                moveToLastContainerPos();            }        });        tranYAnima.addListener(new AnimatorListenerAdapter() {            @Override            public void onAnimationEnd(Animator animation) {                if (onControlCallback != null) {                    onControlCallback.onFling(controlView);                }                flag = FLAG_DISPLAYED;            }        });        tranYAnima.start();    }    private void moveToLastContainerPos() {        int controlIndex = indexOfChild(controlView);        if (getChildCount() == 3) {            View belowChild, aboveChild;            float totalOffset, currOffset;            if (controlIndex == 0) {                belowChild = getChildAt(1);                aboveChild = getChildAt(2);            } else if (controlIndex == 1) {                belowChild = getChildAt(0);                aboveChild = getChildAt(2);            } else {                belowChild = getChildAt(0);                aboveChild = getChildAt(1);            }            totalOffset = originalContainerX[0];            currOffset = calcOffsetSize(totalOffset);            belowChild.setX(originalContainerX[0] + currOffset);            totalOffset = CENTER_SCALE_RATE - originalContainerScale[0];            currOffset = calcOffsetSize(totalOffset);            belowChild.setScaleX(originalContainerScale[0] - currOffset);            belowChild.setScaleY(originalContainerScale[0] - currOffset);            totalOffset = width * (CENTER_SCALE_RATE + OFFSET_SCALE_RATE) / 2 - originalContainerX[1];            currOffset = calcOffsetSize(totalOffset);            aboveChild.setX(originalContainerX[1] - currOffset);            totalOffset = CENTER_SCALE_RATE + OFFSET_SCALE_RATE - originalContainerScale[1];            currOffset = calcOffsetSize(totalOffset);            aboveChild.setScaleX(originalContainerScale[1] - currOffset);            aboveChild.setScaleY(originalContainerScale[1] - currOffset);        } else if (getChildCount() != 1 && getChildCount() != controlIndex + 1) {            float currOffsetX, currScaleSize;            float totalOffsetX = originalContainerX[controlIndex + 1] - originalContainerX[controlIndex];            float totalScaleSize = getLayoutStyle() == STYLE_DOUBLE                    ? OFFSET_SCALE_RATE : 3 * OFFSET_SCALE_RATE;            View child;            for (int i = controlIndex + 1; i < getChildCount(); i++) {                if (controlViewBottom == 0.f) continue;                child = getChildAt(i);                currOffsetX = calcOffsetSize(totalOffsetX);                child.setX(originalContainerX[i] + currOffsetX);                currScaleSize = calcOffsetSize(totalScaleSize);                child.setScaleX(originalContainerScale[i] + currScaleSize);                child.setScaleY(originalContainerScale[i] + currScaleSize);            }        }    }    private float calcOffsetSize(float totalSize) {        return controlView.getY() * totalSize / controlViewBottom;    }    private ActivityContainer findControlView(MotionEvent ev) {        int childCount = getChildCount();        ActivityContainer controlView = null;        ActivityContainer container;        for (int i = childCount - 1; i >= 0; i--) {            container = (ActivityContainer) getChildAt(i);            if (container.getBounds().contains(ev.getX(), ev.getY())) {                controlView = container;                break;            }        }        return controlView;    }    @NonNull    private ObjectAnimator getCheckedScaleXAnima(View view) {        ObjectAnimator chooseScaleXAnima = ObjectAnimator.ofFloat(view, "scaleX", view.getScaleX(), 1.0f);        chooseScaleXAnima.setDuration(200);        return chooseScaleXAnima;    }    @NonNull    private ObjectAnimator getCheckedScaleYAnima(View view) {        ObjectAnimator chooseScaleYAnima = ObjectAnimator.ofFloat(view, "scaleY", view.getScaleY(), 1.0f);        chooseScaleYAnima.setDuration(200);        chooseScaleYAnima.addUpdateListener(new ValueAnimator.AnimatorUpdateListener() {            @Override            public void onAnimationUpdate(ValueAnimator valueAnimator) {                removeShadow(valueAnimator);            }        });        return chooseScaleYAnima;    }    @NonNull    private AnimatorSet singleStyleAnimator(View view) {        AnimatorSet animatorSet = new AnimatorSet();        animatorSet.play(getCheckedScaleXAnima(view))                .with(getCheckedScaleYAnima(view));        return animatorSet;    }    private AnimatorSet doubleStyleAnimator(View view) {        ObjectAnimator preObjAnima;        if (indexOfChild(view) == 0) {            float afterEndTranX = width * .5f;            View afterChild = getChildAt(1);            preObjAnima = ObjectAnimator.ofFloat(afterChild, "X",                    afterChild.getX(), afterChild.getX() + afterEndTranX);            preObjAnima.setDuration(300);        } else {            preObjAnima = ObjectAnimator.ofFloat(view, "X", view.getX(), 0);            preObjAnima.setDuration(200);        }        AnimatorSet animatorSet = new AnimatorSet();        animatorSet.play(preObjAnima)                .before(getCheckedScaleXAnima(view))                .before(getCheckedScaleYAnima(view));        return animatorSet;    }    private AnimatorSet multipleStyleAnimator(final View view) {        final int chooseIndex = indexOfChild(view);        ValueAnimator afterTranXAnima = null;        if (chooseIndex < getChildCount() - 1) {            float afterEndTranX = width - (chooseIndex + 2) * pageOffsetSize;            final float[] currX = new float[getChildCount() - chooseIndex -1];            for (int i = chooseIndex + 1; i < getChildCount(); i++) {                currX[i - chooseIndex - 1] = getChildAt(i).getX();            }            afterTranXAnima = ValueAnimator.ofFloat(0, afterEndTranX);            afterTranXAnima.setDuration(300);            afterTranXAnima.addUpdateListener(new ValueAnimator.AnimatorUpdateListener() {                @Override                public void onAnimationUpdate(ValueAnimator valueAnimator) {                    float valueX = Float.parseFloat(valueAnimator.getAnimatedValue().toString());                    View afterChild;                    for (int i = chooseIndex + 1; i < getChildCount(); i++) {                        afterChild = getChildAt(i);                        afterChild.setX(currX[i - chooseIndex - 1] + valueX);                    }                }            });        }        ObjectAnimator chooseTranXAnima = ObjectAnimator.ofFloat(view, "X", view.getX(), 0);        chooseTranXAnima.setDuration(200);        AnimatorSet animatorSet = new AnimatorSet();        AnimatorSet.Builder animaBuilder = animatorSet                .play(chooseTranXAnima)                .before(getCheckedScaleXAnima(view))                .before(getCheckedScaleYAnima(view));        if (afterTranXAnima != null) {            animaBuilder.after(afterTranXAnima);        }        return animatorSet;    }    private Animator displayBySingleStyle() {        final View singleChild = getChildAt(0);        ValueAnimator scaleAnima = ValueAnimator.ofFloat(1, 100);        scaleAnima.setDuration(200);        scaleAnima.setInterpolator(new DecelerateInterpolator());        scaleAnima.addUpdateListener(new ValueAnimator.AnimatorUpdateListener() {            @Override            public void onAnimationUpdate(ValueAnimator valueAnimator) {                float fraction = valueAnimator.getAnimatedFraction();                float scaleValue = 1 - (1 - CENTER_SCALE_RATE) * fraction;                singleChild.setScaleX(scaleValue);                singleChild.setScaleY(scaleValue);            }        });        return scaleAnima;    }    private Animator displayByDoubleStyle() {        final View belowChild = getChildAt(0);        final View aboveChild = getChildAt(1);        ValueAnimator scaleAnima = ValueAnimator.ofFloat(1, 100);        scaleAnima.addUpdateListener(new ValueAnimator.AnimatorUpdateListener() {            @Override            public void onAnimationUpdate(ValueAnimator valueAnimator) {                float fraction = valueAnimator.getAnimatedFraction();                float scaleValue = 1 - (1 - CENTER_SCALE_RATE) * fraction;                belowChild.setScaleX(scaleValue);                belowChild.setScaleY(scaleValue);                scaleValue = 1 - (1 - (CENTER_SCALE_RATE + OFFSET_SCALE_RATE)) * fraction;                aboveChild.setScaleX(scaleValue);                aboveChild.setScaleY(scaleValue);            }        });        float endTranX = width * (CENTER_SCALE_RATE + OFFSET_SCALE_RATE) / 2;        ObjectAnimator tranXAnima = ObjectAnimator.ofFloat(aboveChild, "X", aboveChild.getX(), endTranX);        AnimatorSet animatorSet = new AnimatorSet();        animatorSet.setDuration(200);        animatorSet.setInterpolator(new DecelerateInterpolator());        animatorSet.play(scaleAnima).with(tranXAnima);        return animatorSet;    }    private Animator displayByMultipleStyle() {        ValueAnimator scaleAnima = ValueAnimator.ofFloat(1, 100);        scaleAnima.addUpdateListener(new ValueAnimator.AnimatorUpdateListener() {            @Override            public void onAnimationUpdate(ValueAnimator valueAnimator) {                float fraction = valueAnimator.getAnimatedFraction();                float scaleValue;                int childCount = getChildCount();                View child;                for (int i = 0; i <  childCount; i++) {                    child = getChildAt(i);                    scaleValue = CENTER_SCALE_RATE + 3 * OFFSET_SCALE_RATE * (i - 1);                    scaleValue = 1 - (1 - scaleValue) * fraction;                    child.setScaleX(scaleValue);                    child.setScaleY(scaleValue);                }            }        });        ValueAnimator tranXAnima = ValueAnimator.ofFloat(1, 100);        tranXAnima.addUpdateListener(new ValueAnimator.AnimatorUpdateListener() {            @Override            public void onAnimationUpdate(ValueAnimator valueAnimator) {                float fraction = valueAnimator.getAnimatedFraction();                int childCount = getChildCount();                float tranX;                View child;                float initTranX;                for (int i = 0; i < childCount; i++) {                    child = getChildAt(i);                    initTranX = (width - width * (CENTER_SCALE_RATE + 3 * OFFSET_SCALE_RATE * (i - 1))) * .5f;                    tranX = pageOffsetSize * i;                    tranX = fraction * tranX - initTranX + pageOffsetSize;                    child.setX(tranX);                }            }        });        AnimatorSet animatorSet = new AnimatorSet();        animatorSet.setDuration(200);        animatorSet.setInterpolator(new DecelerateInterpolator());        animatorSet.play(scaleAnima).with(tranXAnima);        return animatorSet;    }    private void removeShadow(ValueAnimator valueAnimator) {        ViewGroup vgChild;        RoundRectDrawableWithShadow drawable;        if (valueAnimator.getAnimatedFraction() > .3f && !resetBackground) {            for (int i = 0; i < getChildCount(); i++) {                vgChild = (ViewGroup) getChildAt(i);                if (vgChild.getBackground() instanceof RoundRectDrawableWithShadow) {                    drawable = (RoundRectDrawableWithShadow) vgChild.getBackground();                    vgChild.setBackgroundColor(drawable.getBackgroundColor());                }            }            resetBackground = true;        }    }    private int getLayoutStyle() {        int style = 0;        int childCount = getChildCount();        if (childCount == 1) {            style = STYLE_SINGLE;        } else if (childCount == 2) {            style = STYLE_DOUBLE;        } else if (childCount >=3) {            style = STYLE_MULTIPLE;        }        return style;    }    private void updateContainerIntercept(boolean interceptEvent) {        ActivityContainer container;        for (int i = 0; i < getChildCount(); i++) {            container = (ActivityContainer) getChildAt(i);            container.setIntercept(interceptEvent);        }    }    public void display(@NonNull OnControlCallback callback) {        onControlCallback = callback;        flag = FLAG_DISPLAYING;        Animator animator;        int childCount = getChildCount();        if (childCount <=0) return ;        if (childCount == 1) {            animator = displayBySingleStyle();        } else if (childCount == 2) {            animator = displayByDoubleStyle();        } else {            pageOffsetSize = width * 1.f / (childCount + 1);            pageOffsetSize = pageOffsetSize < MIN_OFFSET_SIZE ? MIN_OFFSET_SIZE : pageOffsetSize;            pageOffsetSize = pageOffsetSize > MAX_OFFSET_SIZE ? MAX_OFFSET_SIZE : pageOffsetSize;            animator = displayByMultipleStyle();        }        animator.addListener(new AnimatorListenerAdapter() {            @Override            public void onAnimationStart(Animator animation) {                updateContainerIntercept(true);            }            @Override            public void onAnimationEnd(Animator animation) {                flag = FLAG_DISPLAYED;                if (onControlCallback != null)                    onControlCallback.onDisplayed();            }        });        animator.start();    }    public void closure(boolean back) {        controlView = controlView == null || indexOfChild(controlView) == -1 || back                ? (ActivityContainer) getChildAt(getChildCount() - 1)                : controlView;        flag = FLAG_CLOSING;        AnimatorSet animatorSet = null;        resetBackground = false;        switch (getLayoutStyle()) {            case STYLE_SINGLE:                animatorSet = singleStyleAnimator(controlView);                break;            case STYLE_DOUBLE:                animatorSet = doubleStyleAnimator(controlView);                break;            case STYLE_MULTIPLE:                animatorSet = multipleStyleAnimator(controlView);                break;        }        if (animatorSet == null) return ;        animatorSet.addListener(new AnimatorListenerAdapter() {            @Override            public void onAnimationEnd(Animator animation) {                if (onControlCallback != null)                    onControlCallback.onSelected(controlView);                updateContainerIntercept(false);                controlView.setOnClickListener(null);                controlView = null;                flag = FLAG_CLOSED;            }        });        animatorSet.start();    }    public int getFlag() {        return flag;    }    public void log(String text) {        Log.d(TAG, text);    }    public interface OnControlCallback {        void onDisplayed();        void onSelected(ActivityContainer selectedContainer);        void onFling(ActivityContainer flingContainer);    }}

本文参考来自：

http://www.cnblogs.com/0616--ataozhijia/p/3684988.html