Android Launcher文件夹创建与拖拽操作解析

Folder相关

实时创建文件夹流程：
拖拽时会不断调用Workspace.java 中的onDragOver()方法：
    public void onDragOver(DragObject d) {
................
            setCurrentDropOverCell(mTargetCell[0], mTargetCell[1]);

            float targetCellDistance = mDragTargetLayout.getDistanceFromCell(
                    mDragViewVisualCenter[0], mDragViewVisualCenter[1], mTargetCell);

            final View dragOverView = mDragTargetLayout.getChildAt(mTargetCell[0],
                    mTargetCell[1]);

            manageFolderFeedback(info, mDragTargetLayout, mTargetCell,
                    targetCellDistance, dragOverView);//此句为重点

            boolean nearestDropOccupied = mDragTargetLayout.isNearestDropLocationOccupied((int)
                    mDragViewVisualCenter[0], (int) mDragViewVisualCenter[1], item.spanX,
                    item.spanY, child, mTargetCell);

            if (!nearestDropOccupied) {
                mDragTargetLayout.visualizeDropLocation(child, mDragOutline,
                        (int) mDragViewVisualCenter[0], (int) mDragViewVisualCenter[1],
                        mTargetCell[0], mTargetCell[1], item.spanX, item.spanY, false,
                        d.dragView.getDragVisualizeOffset(), d.dragView.getDragRegion());
            } else if ((mDragMode == DRAG_MODE_NONE || mDragMode == DRAG_MODE_REORDER)
                    && !mReorderAlarm.alarmPending() && (mLastReorderX != reorderX ||
                    mLastReorderY != reorderY)) {

                // Otherwise, if we aren't adding to or creating a folder and there's no pending
                // reorder, then we schedule a reorder
                ReorderAlarmListener listener = new ReorderAlarmListener(mDragViewVisualCenter,
                        minSpanX, minSpanY, item.spanX, item.spanY, d.dragView, child);
                mReorderAlarm.setOnAlarmListener(listener);
                mReorderAlarm.setAlarm(REORDER_TIMEOUT);
            }

            if (mDragMode == DRAG_MODE_CREATE_FOLDER || mDragMode == DRAG_MODE_ADD_TO_FOLDER ||
                    !nearestDropOccupied) {
                if (mDragTargetLayout != null) {
                    mDragTargetLayout.revertTempState();
                }
            }
        }
    }


   private void manageFolderFeedback(ItemInfo info, CellLayout targetLayout,
            int[] targetCell, float distance, View dragOverView) {
        boolean userFolderPending = willCreateUserFolder(info, targetLayout, targetCell, distance,
                false);

        if (mDragMode == DRAG_MODE_NONE && userFolderPending &&
                !mFolderCreationAlarm.alarmPending()) {
            mFolderCreationAlarm.setOnAlarmListener(new
                    FolderCreationAlarmListener(targetLayout, targetCell[0], targetCell[1]));
            mFolderCreationAlarm.setAlarm(FOLDER_CREATION_TIMEOUT);
            return;
        }