ListView特效2(列表拖拽)

即listView特效1,http://blog.youkuaiyun.com/pipisky2006/article/details/7393475，好久之后

列表的拖拽效果（参考Android源码下packages/apps/Music中的播放列表TouchInterceptor.java源码）

重写ListView中onInterceptTouchEvent(),onTouchEvent()方法来响应触控事件做相应的界面调整(选中，生成影像，拖动影像，数据更改后刷新界面)等等。

拖拽的动作实际上是WindowManager在最上层添加的ImageView随着手指移动被拖动。listView作为背景，数据随之变化。

下面是源码的分析

public class TouchInterceptor extends ListView {//继承自ListView

    public TouchInterceptor(Context context, AttributeSet attrs) {
        super(context, attrs);
        mTouchSlop = ViewConfiguration.get(context).getScaledTouchSlop();//检测滑动状态的阀值
        Resources res = getResources();
        mItemHeightNormal = res.getDimensionPixelSize(R.dimen.normal_height);
        mItemHeightHalf = mItemHeightNormal / 2;
        mItemHeightExpanded = res.getDimensionPixelSize(R.dimen.expanded_height);
    }
}

下面是用到的变量：

    private ImageView mDragView;//被拖拽的ImageView
    private WindowManager mWindowManager;
    private WindowManager.LayoutParams mWindowParams;
    private int mDragPos;      // which item is being dragged 被拖拽的View所在的当前的position
    private int mFirstDragPos; // where was the dragged item originally 被拖拽的View的最初的position
    private int mDragPoint;    // at what offset inside the item did the user grab it 在当前数据项中的位置
    private int mCoordOffset;  // the difference between screen coordinates and coordinates in this view 屏幕坐标和View坐标的差值，也就是getRawY和getY的差值
    private int mUpperBound; //拖动的时候，开始向上滚动的边界
    private int mLowerBound; //拖动的时候，开始向下滚动的边界
    private int mHeight;
    private Rect mTempRect = new Rect();
    private Bitmap mDragBitmap; 
    private final int mTouchSlop; //判断滑动的一个距离值
    private int mItemHeightNormal;
    private int mItemHeightExpanded;
    private int mItemHeightHalf;

捕捉down事件，在down事件中，判断是否需要拖动，如果是，我们做一些拖动的准备工作，准备影像。

    @Override
    public boolean onInterceptTouchEvent(MotionEvent ev) {
            switch (ev.getAction()) {
                case MotionEvent.ACTION_DOWN://down事件
                    int x = (int) ev.getX();
                    int y = (int) ev.getY();
                    int itemnum = pointToPosition(x, y);//选中的数据项位置，使用ListView自带的pointToPosition(x, y)方法
                    if (itemnum == AdapterView.INVALID_POSITION) {
                        break;
                    }
                    ViewGroup item = (ViewGroup) getChildAt(itemnum - getFirstVisiblePosition());//获取选中的View项
                    mDragPoint = y - item.getTop();//点击位置在点击View内的相对位置
                    mCoordOffset = ((int)ev.getRawY()) - y;
                    View dragger = item.findViewById(R.id.icon);//选中项中的拖动识别View
                    Rect r = mTempRect;
                    dragger.getDrawingRect(r);
                    // The dragger icon itself is quite small, so pretend the touch area is bigger
                    if (x < r.right * 2) {
                        item.setDrawingCacheEnabled(true);
                        // Create a copy of the drawing cache so that it does not get recycled
                        // by the framework when the list tries to clean up memory
                        Bitmap bitmap = Bitmap.createBitmap(item.getDrawingCache());//获取拖动影像
                        startDragging(bitmap, y);//准备拖动工作
                        mDragPos = itemnum;
                        mFirstDragPos = mDragPos;
                        mHeight = getHeight();
                        int touchSlop = mTouchSlop;
                        mUpperBound = Math.min(y - touchSlop, mHeight / 3);//当在屏幕的上部(上面1/3区域)或者更上的区域，执行拖动的边界，下同理定义
                        mLowerBound = Math.max(y + touchSlop, mHeight * 2 /3);
                        return false;
                    }
                    stopDragging();
                    break;
            }
        return super.onInterceptTouchEvent(ev);
    }

//根据操作处理滑动和放置操作。

    @Override
    public boolean onTouchEvent(MotionEvent ev) {
        if (mDragView != null) {
            int action = ev.getAction(); 
            switch (action) {
                case MotionEvent.ACTION_UP:
                case MotionEvent.ACTION_CANCEL:
                    Rect r = mTempRect;
                    mDragView.getDrawingRect(r);
                    stopDragging();//释放拖动影像
                    if (mDropListener != null && mDragPos >= 0 && mDragPos < getCount()) {
                        mDropListener.drop(mFirstDragPos, mDragPos);//放置工作的回调
                    }
                    unExpandViews(false);//放置后List内容的修正
                    break;
                    
                case MotionEvent.ACTION_DOWN:
                case MotionEvent.ACTION_MOVE:
                    int x = (int) ev.getX();
                    int y = (int) ev.getY();
                    mWindowParams.y = y - mDragPoint + mCoordOffset;//更新坐标位置
	            mWindowManager.updateViewLayout(mDragView, mWindowParams);//更新拖拽view的界面
                    int itemnum = getItemForPosition(y);//获取准确的position，考虑不可见view等情况，具体见其私有方法
                    if (itemnum >= 0) {
                        if (action == MotionEvent.ACTION_DOWN || itemnum != mDragPos) {
                            if (mDragListener != null) {
                                mDragListener.drag(mDragPos, itemnum);//拖动工作的回调
                            }
                            mDragPos = itemnum;
                            doExpansion();//
                        }
                        int speed = 0;
                        adjustScrollBounds(y);//调整滚动的阀值
                        if (y > mLowerBound) {//拖动位置偏下，内容向上滚动
                            // scroll the list up a bit
                            speed = y > (mHeight + mLowerBound) / 2 ? 16 : 4;
                        } else if (y < mUpperBound) {//拖动位置偏上，内容向下滚动
                            // scroll the list down a bit
                            speed = y < mUpperBound / 2 ? -16 : -4;
                        }
                        if (speed != 0) {
                            int ref = pointToPosition(0, mHeight / 2);
                            if (ref == AdapterView.INVALID_POSITION) {
                                //we hit a divider or an invisible view, check somewhere else
                                ref = pointToPosition(0, mHeight / 2 + getDividerHeight() + 64);
                            }
                            View v = getChildAt(ref - getFirstVisiblePosition());
                            if (v!= null) {
                                int pos = v.getTop();
                                setSelectionFromTop(ref, pos - speed);//列表滚动
                            }
                        }
                    }
                    break;
            }
            return true;
        }
        return super.onTouchEvent(ev);
    }

下面是具体的准备拖动影像和释放拖动影像的方法

    private void startDragging(Bitmap bm, int y) {
        stopDragging();

        mWindowParams = new WindowManager.LayoutParams();
        mWindowParams.gravity = Gravity.TOP;
        mWindowParams.x = 0;
        mWindowParams.y = y - mDragPoint + mCoordOffset;//计算拖动的起始位置

        mWindowParams.height = WindowManager.LayoutParams.WRAP_CONTENT;
        mWindowParams.width = WindowManager.LayoutParams.WRAP_CONTENT;
        mWindowParams.flags = WindowManager.LayoutParams.FLAG_NOT_FOCUSABLE
                | WindowManager.LayoutParams.FLAG_NOT_TOUCHABLE
                | WindowManager.LayoutParams.FLAG_KEEP_SCREEN_ON
                | WindowManager.LayoutParams.FLAG_LAYOUT_IN_SCREEN
                | WindowManager.LayoutParams.FLAG_LAYOUT_NO_LIMITS;
        mWindowParams.format = PixelFormat.TRANSLUCENT;
        mWindowParams.windowAnimations = 0;
        
        Context context = getContext();
        ImageView v = new ImageView(context);
        int backGroundColor = context.getResources().getColor(R.color.dragndrop_background);
        v.setBackgroundColor(backGroundColor);
        v.setImageBitmap(bm);
        mDragBitmap = bm;

        mWindowManager = (WindowManager)context.getSystemService("window");
        mWindowManager.addView(v, mWindowParams);//添加到窗口上
        mDragView = v;
    }
    //释放
    private void stopDragging() {
        if (mDragView != null) {
            WindowManager wm = (WindowManager)getContext().getSystemService("window");
            wm.removeView(mDragView);
            mDragView.setImageDrawable(null);//释放Imageview
            mDragView = null;
        }
        if (mDragBitmap != null) {//释放bitmap
            mDragBitmap.recycle();
            mDragBitmap = null;
        }
    }

接下来响应操作是拖拽影像，影像动了后背后的列表内容也要配合变化，主要就是添加了个空内容格

 /** Adjust visibility and size to make it appear as though
     * an item is being dragged around and other items are making
     * room for it: 调整可见性和大小来表现的像一个内容项被拖动，其他在给他让位置。
     * If dropping the item would result in it still being in the
     * same place, then make the dragged listitem's size normal,
     * but make the item invisible.
     * Otherwise, if the dragged listitem is still on screen, make
     * it as small as possible and expand the item below the insert
     * point.
     * If the dragged item is not on screen, only expand the item
     * below the current insertpoint.
     */
    private void doExpansion() {
        int childnum = mDragPos - getFirstVisiblePosition();
        if (mDragPos > mFirstDragPos) {
            childnum++;
        }

        View first = getChildAt(mFirstDragPos - getFirstVisiblePosition());

        for (int i = 0;; i++) {
            View vv = getChildAt(i);
            if (vv == null) {
                break;
            }
            int height = mItemHeightNormal;
            int visibility = View.VISIBLE;
            if (vv.equals(first)) {
                // processing the item that is being dragged
                if (mDragPos == mFirstDragPos) {
                    // hovering over the original location
                    visibility = View.INVISIBLE;
                } else {
                    // not hovering over it
                    height = 1;
                }
            } else if (i == childnum) {
                if (mDragPos < getCount() - 1) {
                    height = mItemHeightExpanded;
                }
            }
            ViewGroup.LayoutParams params = vv.getLayoutParams();
            params.height = height;
            vv.setLayoutParams(params);
            vv.setVisibility(visibility);
        }
    }

放置后的操作

/**
     * Restore size and visibility for all listitems
     */
    private void unExpandViews(boolean deletion) {
        for (int i = 0;; i++) {
            View v = getChildAt(i);
            if (v == null) {
                if (deletion) {
                    // HACK force update of mItemCount
                    int position = getFirstVisiblePosition();
                    int y = getChildAt(0).getTop();
                    setAdapter(getAdapter());
                    setSelectionFromTop(position, y);
                    // end hack
                }
                layoutChildren(); // force children to be recreated where needed
                v = getChildAt(i);
                if (v == null) {
                    break;
                }
            }
            ViewGroup.LayoutParams params = v.getLayoutParams();
            params.height = mItemHeightNormal;
            v.setLayoutParams(params);
            v.setVisibility(View.VISIBLE);
        }
    }

剩下的几个私有方法

    /**
     * pointToPosition() doesn't consider invisible views, but we
     * need to, so implement a slightly different version.
     */
    private int myPointToPosition(int x, int y) {

        if (y < 0) {
            // when dragging off the top of the screen, calculate position
            // by going back from a visible item
            int pos = myPointToPosition(x, y + mItemHeightNormal);
            if (pos > 0) {
                return pos - 1;
            }
        }

        Rect frame = mTempRect;
        final int count = getChildCount();
        for (int i = count - 1; i >= 0; i--) {
            final View child = getChildAt(i);
            child.getHitRect(frame);
            if (frame.contains(x, y)) {
                return getFirstVisiblePosition() + i;
            }
        }
        return INVALID_POSITION;
    }
    
    private int getItemForPosition(int y) {
        int adjustedy = y - mDragPoint - mItemHeightHalf;
        int pos = myPointToPosition(0, adjustedy);
        if (pos >= 0) {
            if (pos <= mFirstDragPos) {
                pos += 1;
            }
        } else if (adjustedy < 0) {
            // this shouldn't happen anymore now that myPointToPosition deals
            // with this situation
            pos = 0;
        }
        return pos;
    }
    
    private void adjustScrollBounds(int y) {
        if (y >= mHeight / 3) {
            mUpperBound = mHeight / 3;
        }
        if (y <= mHeight * 2 / 3) {
            mLowerBound = mHeight * 2 / 3;
        }
    }

参考：  http://www.cnblogs.com/qianxudetianxia/archive/2011/06/12/2068761.html

http://www.cnblogs.com/qianxudetianxia/archive/2011/06/13/2079253.html

http://www.oschina.net/code/explore/android-2.2-froyo/com/android/music/TouchInterceptor.java