Android仿微信图片详情页面，可下拉关闭页面

public class DragViewPager extends ViewPager implements View.OnClickListener {    public static final int STATUS_NORMAL = 0;//正常浏览状态    public static final int STATUS_MOVING = 1;//滑动状态    public static final int STATUS_RESETTING = 2;//返回中状态    public static final String TAG = "DragViewPager";

    public static final float MIN_SCALE_SIZE = 0.3f;//最小缩放比例    public static final int BACK_DURATION = 300;//ms    public static final int DRAG_GAP_PX = 50;
    private int currentStatus = STATUS_NORMAL;    private int currentPageStatus;
    private float mDownX;    private float mDownY;    private float screenHeight;
    /**     * 要缩放的View     */    private View currentShowView;    /**     * 滑动速度检测类     */    private VelocityTracker mVelocityTracker;    private IAnimClose iAnimClose;
    public void setIAnimClose(IAnimClose iAnimClose) {        this.iAnimClose = iAnimClose;    }
    public DragViewPager(Context context) {        super(context);        init(context);    }
    public DragViewPager(Context context, AttributeSet attrs) {        super(context, attrs);        init(context);    }
    public void init(Context context) {        screenHeight = ScreenUtils.getScreenHeight(context);        setBackgroundColor(Color.BLACK);        addOnPageChangeListener(new OnPageChangeListener() {            @Override            public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) {            }
            @Override            public void onPageSelected(int position) {
            }
            @Override            public void onPageScrollStateChanged(int state) {                currentPageStatus = state;            }        });    }
    public void setCurrentShowView(View currentShowView) {        this.currentShowView = currentShowView;        if (this.currentShowView != null) {            this.currentShowView.setOnClickListener(this);        }    }
    //配合SubsamplingScaleImageView使用，根据需要拦截ACTION_MOVE    @Override    public boolean onInterceptTouchEvent(MotionEvent ev) {        if (getAdapter() instanceof ImagePagerAdapter) {            ImagePagerAdapter adapter = ((ImagePagerAdapter) getAdapter());            SubsamplingScaleImageView mImage = (SubsamplingScaleImageView) adapter.getItem(getCurrentItem()).getView().findViewById(R.id.image);            switch (ev.getAction()){                case MotionEvent.ACTION_DOWN:                    Log.e("jc","onInterceptTouchEvent:ACTION_DOWN");                    mDownX = ev.getRawX();                    mDownY = ev.getRawY();                    break;                case MotionEvent.ACTION_MOVE:                    Log.e("jc","onInterceptTouchEvent:ACTION_MOVE");                    if (mImage.getCenter() != null && mImage.getCenter().y <= mImage.getHeight() / mImage.getScale() / 2) {                        Log.e("jc","onInterceptTouchEvent:ACTION_MOVE");                        int deltaX = Math.abs((int) (ev.getRawX() - mDownX));                        int deltaY = (int) (ev.getRawY() - mDownY);                        if (deltaY > DRAG_GAP_PX && deltaX <= DRAG_GAP_PX) {//往下移动超过临界，左右移动不超过临界时，拦截滑动事件                            return true;                        }                    }                    break;                case MotionEvent.ACTION_UP:                    Log.e("jc","onInterceptTouchEvent:ACTION_UP");                    break;            }        }        return super.onInterceptTouchEvent(ev);    }
    @Override    public boolean onTouchEvent(MotionEvent ev) {        if (currentStatus == STATUS_RESETTING)            return false;        switch (ev.getActionMasked()) {            case MotionEvent.ACTION_DOWN:                mDownX = ev.getRawX();                mDownY = ev.getRawY();                addIntoVelocity(ev);                break;            case MotionEvent.ACTION_MOVE:                addIntoVelocity(ev);                int deltaY = (int) (ev.getRawY() - mDownY);                //手指往上滑动                if (deltaY <= DRAG_GAP_PX && currentStatus != STATUS_MOVING)                    return super.onTouchEvent(ev);                //viewpager不在切换中，并且手指往下滑动，开始缩放                if (currentPageStatus != SCROLL_STATE_DRAGGING && (deltaY > DRAG_GAP_PX || currentStatus == STATUS_MOVING)) {                    moveView(ev.getRawX(), ev.getRawY());                    return true;                }                break;            case MotionEvent.ACTION_UP:            case MotionEvent.ACTION_CANCEL:                if (currentStatus != STATUS_MOVING)                    return super.onTouchEvent(ev);                final float mUpX = ev.getRawX();                final float mUpY = ev.getRawY();
                float vY = computeYVelocity();//松开时必须释放VelocityTracker资源                if (vY >= 1200 || Math.abs(mUpY - mDownY) > screenHeight / 4) {                    //下滑速度快，或者下滑距离超过屏幕高度的一半，就关闭                    if (iAnimClose != null) {                        iAnimClose.onPictureRelease(currentShowView);                    }                } else {                    resetReviewState(mUpX, mUpY);                }                break;        }
        return super.onTouchEvent(ev);    }
    //返回浏览状态    private void resetReviewState(final float mUpX, final float mUpY) {        currentStatus = STATUS_RESETTING;        if (mUpY != mDownY) {            ValueAnimator valueAnimator = ValueAnimator.ofFloat(mUpY, mDownY);            valueAnimator.setDuration(BACK_DURATION);            valueAnimator.addUpdateListener(new ValueAnimator.AnimatorUpdateListener() {                @Override                public void onAnimationUpdate(ValueAnimator animation) {                    float mY = (float) animation.getAnimatedValue();                    float percent = (mY - mDownY) / (mUpY - mDownY);                    float mX = percent * (mUpX - mDownX) + mDownX;                    moveView(mX, mY);                    if (mY == mDownY) {                        mDownY = 0;                        mDownX = 0;                        currentStatus = STATUS_NORMAL;                    }                }            });            valueAnimator.start();        } else if (mUpX != mDownX) {            ValueAnimator valueAnimator = ValueAnimator.ofFloat(mUpX, mDownX);            valueAnimator.setDuration(BACK_DURATION);            valueAnimator.addUpdateListener(new ValueAnimator.AnimatorUpdateListener() {                @Override                public void onAnimationUpdate(ValueAnimator animation) {                    float mX = (float) animation.getAnimatedValue();                    float percent = (mX - mDownX) / (mUpX - mDownX);                    float mY = percent * (mUpY - mDownY) + mDownY;                    moveView(mX, mY);                    if (mX == mDownX) {                        mDownY = 0;                        mDownX = 0;                        currentStatus = STATUS_NORMAL;                    }                }            });            valueAnimator.start();        } else if (iAnimClose != null)            iAnimClose.onPictureClick();    }    //移动View    private void moveView(float movingX, float movingY) {        if (currentShowView == null)            return;        currentStatus = STATUS_MOVING;        float deltaX = movingX - mDownX;        float deltaY = movingY - mDownY;        float scale = 1f;        float alphaPercent = 1f;        if (deltaY > 0) {            scale = 1 - Math.abs(deltaY) / screenHeight;            alphaPercent = 1 - Math.abs(deltaY) / (screenHeight / 2);        }
        ViewHelper.setTranslationX(currentShowView, deltaX);        ViewHelper.setTranslationY(currentShowView, deltaY);        scaleView(scale);        setBackgroundColor(getBlackAlpha(alphaPercent));    }
    //缩放View    private void scaleView(float scale) {        scale = Math.min(Math.max(scale, MIN_SCALE_SIZE), 1);        ViewHelper.setScaleX(currentShowView, scale);        ViewHelper.setScaleY(currentShowView, scale);    }
    private int getBlackAlpha(float percent) {        percent = Math.min(1, Math.max(0, percent));        int intAlpha = (int) (percent * 255);        return Color.argb(intAlpha,0,0,0);    }
    private void addIntoVelocity(MotionEvent event) {        if (mVelocityTracker == null)            mVelocityTracker = VelocityTracker.obtain();        mVelocityTracker.addMovement(event);    }
    private float computeYVelocity() {        float result = 0;        if (mVelocityTracker != null) {            mVelocityTracker.computeCurrentVelocity(1000);            result = mVelocityTracker.getYVelocity();            releaseVelocity();        }        return result;    }
    private void releaseVelocity() {        if (mVelocityTracker != null) {            mVelocityTracker.clear();            mVelocityTracker.recycle();            mVelocityTracker = null;        }    }
    @Override    public void onClick(View v) {        if (iAnimClose != null) {            iAnimClose.onPictureClick();        }    }
    public interface IAnimClose {        void onPictureClick();
        void onPictureRelease(View view);    }}

public class ImagePagerAdapter extends FragmentStatePagerAdapter {    private DragViewPager mPager;    private ArrayList<Fragment> mFragmentList;
    public ImagePagerAdapter(FragmentManager fm, List<String> datas,DragViewPager pager) {        super(fm);        mPager=pager;        mPager.setAdapter(this);        updateData(datas);    }
    public void updateData(List<String> dataList) {        ArrayList<Fragment> fragments = new ArrayList<>();        for (int i = 0, size = dataList.size(); i < size; i++) {            final ImageDetailFragment fragment = ImageDetailFragment.newInstance(dataList.get(i));            fragment.setOnImageListener(new ImageDetailFragment.OnImageListener() {                @Override                public void onInit() {                    View view = fragment.getView();                    mPager.setCurrentShowView(view);                }            });            fragments.add(fragment);        }        setViewList(fragments);    }
    private void setViewList(ArrayList<Fragment> fragmentList) {        if (mFragmentList != null) {            mFragmentList.clear();        }        mFragmentList = fragmentList;        notifyDataSetChanged();    }
    @Override    public int getCount() {        return mFragmentList==null?0:mFragmentList.size();    }
    public int getItemPosition(Object object) {        return POSITION_NONE;    }
    @Override    public Fragment getItem(int position) {        return mFragmentList.get(position);    }}

<style name="translucent" parent="AppTheme">        <item name="windowActionBar">false</item>        <item name="windowNoTitle">true</item>        <item name="android:windowIsTranslucent">true</item>        <item name="android:windowBackground">@android:color/transparent</item></style>

<activity android:name=".ui.ImagePagerActivity"            android:theme="@style/translucent"/>

ImagePagerActivity.startImagePage(MainActivity.this,                        urls,pos,recyclerView.getLayoutManager().findViewByPosition(pos));

//设置转场动画的共享元素，因为跳转和返回时都会调用onMapSharedElements，需要判断bundle是否为空        setExitSharedElementCallback(new SharedElementCallback() {            @Override            public void onMapSharedElements(List<String> names, Map<String, View> sharedElements) {                if (bundle!=null){                    int index = bundle.getInt(ImagePagerActivity.STATE_POSITION,0);                    sharedElements.clear();                    sharedElements.put("img", recyclerView.getLayoutManager().findViewByPosition(index));                    bundle=null;                }            }        });

@Override    public void onActivityReenter(int resultCode, Intent data) {        super.onActivityReenter(resultCode, data);        bundle = data.getExtras();        int currentPosition = bundle.getInt(ImagePagerActivity.STATE_POSITION,0);        //做相应的滚动        recyclerView.scrollToPosition(currentPosition);        //暂时延迟 Transition 的使用，直到我们确定了共享元素的确切大小和位置才使用        //postponeEnterTransition后不要忘记调用startPostponedEnterTransition        ActivityCompat.postponeEnterTransition(this);        recyclerView.getViewTreeObserver().addOnPreDrawListener(new ViewTreeObserver.OnPreDrawListener() {            @Override            public boolean onPreDraw() {                recyclerView.getViewTreeObserver().removeOnPreDrawListener(this);                // TODO: figure out why it is necessary to request layout here in order to get a smooth transition.                recyclerView.requestLayout();                //共享元素准备好后调用startPostponedEnterTransition来恢复过渡效果                ActivityCompat.startPostponedEnterTransition(MainActivity.this);                return true;            }        });    }

public class MainActivity extends AppCompatActivity {
    private RecyclerView recyclerView;
    private MainAdapter mainAdapter;
    //图片集合    private ArrayList<String> urls;
    //存放返回时当前页码    private Bundle bundle;
    @Override    protected void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.activity_main);        urls=new ArrayList<>();        //为了显示效果，重复添加了三次        urls.add("https://timgsa.baidu.com/timg?image&quality=80&size=b9999_10000&sec=1524477979306&di=3eb07e9302606048abe13d7b6a2bc601&imgtype=0&src=http%3A%2F%2Fimg4.duitang.com%2Fuploads%2Fitem%2F201406%2F12%2F20140612211118_YYXAC.jpeg");        urls.add("https://timgsa.baidu.com/timg?image&quality=80&size=b9999_10000&sec=1524133463580&di=1315bc4db30999f00b89ef79c3bb06e5&imgtype=0&src=http%3A%2F%2Fpic36.photophoto.cn%2F20150710%2F0005018721870517_b.jpg");        urls.add("https://timgsa.baidu.com/timg?image&quality=80&size=b9999_10000&sec=1524133463575&di=6221f21bcb761675c5d161ebc53d5948&imgtype=0&src=http%3A%2F%2Fimg5.duitang.com%2Fuploads%2Fitem%2F201410%2F03%2F20141003112442_AkkuH.thumb.700_0.jpeg");
        urls.add("https://timgsa.baidu.com/timg?image&quality=80&size=b9999_10000&sec=1524477979306&di=3eb07e9302606048abe13d7b6a2bc601&imgtype=0&src=http%3A%2F%2Fimg4.duitang.com%2Fuploads%2Fitem%2F201406%2F12%2F20140612211118_YYXAC.jpeg");        urls.add("https://timgsa.baidu.com/timg?image&quality=80&size=b9999_10000&sec=1524133463580&di=1315bc4db30999f00b89ef79c3bb06e5&imgtype=0&src=http%3A%2F%2Fpic36.photophoto.cn%2F20150710%2F0005018721870517_b.jpg");        urls.add("https://timgsa.baidu.com/timg?image&quality=80&size=b9999_10000&sec=1524133463575&di=6221f21bcb761675c5d161ebc53d5948&imgtype=0&src=http%3A%2F%2Fimg5.duitang.com%2Fuploads%2Fitem%2F201410%2F03%2F20141003112442_AkkuH.thumb.700_0.jpeg");
        urls.add("https://timgsa.baidu.com/timg?image&quality=80&size=b9999_10000&sec=1524477979306&di=3eb07e9302606048abe13d7b6a2bc601&imgtype=0&src=http%3A%2F%2Fimg4.duitang.com%2Fuploads%2Fitem%2F201406%2F12%2F20140612211118_YYXAC.jpeg");        urls.add("https://timgsa.baidu.com/timg?image&quality=80&size=b9999_10000&sec=1524133463580&di=1315bc4db30999f00b89ef79c3bb06e5&imgtype=0&src=http%3A%2F%2Fpic36.photophoto.cn%2F20150710%2F0005018721870517_b.jpg");        urls.add("https://timgsa.baidu.com/timg?image&quality=80&size=b9999_10000&sec=1524133463575&di=6221f21bcb761675c5d161ebc53d5948&imgtype=0&src=http%3A%2F%2Fimg5.duitang.com%2Fuploads%2Fitem%2F201410%2F03%2F20141003112442_AkkuH.thumb.700_0.jpeg");        initView();    }
    private void initView() {        recyclerView = (RecyclerView) findViewById(R.id.recycler);        recyclerView.setLayoutManager(new GridLayoutManager(this, 2));        mainAdapter = new MainAdapter(urls);        mainAdapter.setOnItemClickListener(new MainAdapter.OnItemClickListener() {            @Override            public void onItemClick(int pos) {                ImagePagerActivity.startImagePage(MainActivity.this,                        urls,pos,recyclerView.getLayoutManager().findViewByPosition(pos));            }        });        recyclerView.setAdapter(mainAdapter);
        //设置转场动画的共享元素，因为跳转和返回都会调用，需要判断bundle是否为空        setExitSharedElementCallback(new SharedElementCallback() {            @Override            public void onMapSharedElements(List<String> names, Map<String, View> sharedElements) {                if (bundle!=null){                    int index = bundle.getInt(ImagePagerActivity.STATE_POSITION,0);                    sharedElements.clear();                    sharedElements.put("img", recyclerView.getLayoutManager().findViewByPosition(index));                    bundle=null;                }            }        });    }
    //返回的时候获取数据    @Override    public void onActivityReenter(int resultCode, Intent data) {        super.onActivityReenter(resultCode, data);        bundle = data.getExtras();        int currentPosition = bundle.getInt(ImagePagerActivity.STATE_POSITION,0);        //做相应的滚动        recyclerView.scrollToPosition(currentPosition);        //暂时延迟 Transition 的使用，直到我们确定了共享元素的确切大小和位置才使用        //postponeEnterTransition后不要忘记调用startPostponedEnterTransition        ActivityCompat.postponeEnterTransition(this);        recyclerView.getViewTreeObserver().addOnPreDrawListener(new ViewTreeObserver.OnPreDrawListener() {            @Override            public boolean onPreDraw() {                recyclerView.getViewTreeObserver().removeOnPreDrawListener(this);                // TODO: figure out why it is necessary to request layout here in order to get a smooth transition.                recyclerView.requestLayout();                //共享元素准备好后调用startPostponedEnterTransition来恢复过渡效果                ActivityCompat.startPostponedEnterTransition(MainActivity.this);                return true;            }        });    }}