protected void layoutChildren()

in android/widget/ListView.java [1624:1967]


    protected void layoutChildren() {
        final boolean blockLayoutRequests = mBlockLayoutRequests;
        if (blockLayoutRequests) {
            return;
        }

        mBlockLayoutRequests = true;

        try {
            super.layoutChildren();

            invalidate();

            if (mAdapter == null) {
                resetList();
                invokeOnItemScrollListener();
                return;
            }

            final int childrenTop = mListPadding.top;
            final int childrenBottom = mBottom - mTop - mListPadding.bottom;
            final int childCount = getChildCount();

            int index = 0;
            int delta = 0;

            View sel;
            View oldSel = null;
            View oldFirst = null;
            View newSel = null;

            // Remember stuff we will need down below
            switch (mLayoutMode) {
            case LAYOUT_SET_SELECTION:
                index = mNextSelectedPosition - mFirstPosition;
                if (index >= 0 && index < childCount) {
                    newSel = getChildAt(index);
                }
                break;
            case LAYOUT_FORCE_TOP:
            case LAYOUT_FORCE_BOTTOM:
            case LAYOUT_SPECIFIC:
            case LAYOUT_SYNC:
                break;
            case LAYOUT_MOVE_SELECTION:
            default:
                // Remember the previously selected view
                index = mSelectedPosition - mFirstPosition;
                if (index >= 0 && index < childCount) {
                    oldSel = getChildAt(index);
                }

                // Remember the previous first child
                oldFirst = getChildAt(0);

                if (mNextSelectedPosition >= 0) {
                    delta = mNextSelectedPosition - mSelectedPosition;
                }

                // Caution: newSel might be null
                newSel = getChildAt(index + delta);
            }


            boolean dataChanged = mDataChanged;
            if (dataChanged) {
                handleDataChanged();
            }

            // Handle the empty set by removing all views that are visible
            // and calling it a day
            if (mItemCount == 0) {
                resetList();
                invokeOnItemScrollListener();
                return;
            } else if (mItemCount != mAdapter.getCount()) {
                throw new IllegalStateException("The content of the adapter has changed but "
                        + "ListView did not receive a notification. Make sure the content of "
                        + "your adapter is not modified from a background thread, but only from "
                        + "the UI thread. Make sure your adapter calls notifyDataSetChanged() "
                        + "when its content changes. [in ListView(" + getId() + ", " + getClass()
                        + ") with Adapter(" + mAdapter.getClass() + ")]");
            }

            setSelectedPositionInt(mNextSelectedPosition);

            AccessibilityNodeInfo accessibilityFocusLayoutRestoreNode = null;
            View accessibilityFocusLayoutRestoreView = null;
            int accessibilityFocusPosition = INVALID_POSITION;

            // Remember which child, if any, had accessibility focus. This must
            // occur before recycling any views, since that will clear
            // accessibility focus.
            final ViewRootImpl viewRootImpl = getViewRootImpl();
            if (viewRootImpl != null) {
                final View focusHost = viewRootImpl.getAccessibilityFocusedHost();
                if (focusHost != null) {
                    final View focusChild = getAccessibilityFocusedChild(focusHost);
                    if (focusChild != null) {
                        if (!dataChanged || isDirectChildHeaderOrFooter(focusChild)
                                || (focusChild.hasTransientState() && mAdapterHasStableIds)) {
                            // The views won't be changing, so try to maintain
                            // focus on the current host and virtual view.
                            accessibilityFocusLayoutRestoreView = focusHost;
                            accessibilityFocusLayoutRestoreNode = viewRootImpl
                                    .getAccessibilityFocusedVirtualView();
                        }

                        // If all else fails, maintain focus at the same
                        // position.
                        accessibilityFocusPosition = getPositionForView(focusChild);
                    }
                }
            }

            View focusLayoutRestoreDirectChild = null;
            View focusLayoutRestoreView = null;

            // Take focus back to us temporarily to avoid the eventual call to
            // clear focus when removing the focused child below from messing
            // things up when ViewAncestor assigns focus back to someone else.
            final View focusedChild = getFocusedChild();
            if (focusedChild != null) {
                // TODO: in some cases focusedChild.getParent() == null

                // We can remember the focused view to restore after re-layout
                // if the data hasn't changed, or if the focused position is a
                // header or footer.
                if (!dataChanged || isDirectChildHeaderOrFooter(focusedChild)
                        || focusedChild.hasTransientState() || mAdapterHasStableIds) {
                    focusLayoutRestoreDirectChild = focusedChild;
                    // Remember the specific view that had focus.
                    focusLayoutRestoreView = findFocus();
                    if (focusLayoutRestoreView != null) {
                        // Tell it we are going to mess with it.
                        focusLayoutRestoreView.dispatchStartTemporaryDetach();
                    }
                }
                requestFocus();
            }

            // Pull all children into the RecycleBin.
            // These views will be reused if possible
            final int firstPosition = mFirstPosition;
            final RecycleBin recycleBin = mRecycler;
            if (dataChanged) {
                for (int i = 0; i < childCount; i++) {
                    recycleBin.addScrapView(getChildAt(i), firstPosition+i);
                }
            } else {
                recycleBin.fillActiveViews(childCount, firstPosition);
            }

            // Clear out old views
            detachAllViewsFromParent();
            recycleBin.removeSkippedScrap();

            switch (mLayoutMode) {
            case LAYOUT_SET_SELECTION:
                if (newSel != null) {
                    sel = fillFromSelection(newSel.getTop(), childrenTop, childrenBottom);
                } else {
                    sel = fillFromMiddle(childrenTop, childrenBottom);
                }
                break;
            case LAYOUT_SYNC:
                sel = fillSpecific(mSyncPosition, mSpecificTop);
                break;
            case LAYOUT_FORCE_BOTTOM:
                sel = fillUp(mItemCount - 1, childrenBottom);
                adjustViewsUpOrDown();
                break;
            case LAYOUT_FORCE_TOP:
                mFirstPosition = 0;
                sel = fillFromTop(childrenTop);
                adjustViewsUpOrDown();
                break;
            case LAYOUT_SPECIFIC:
                final int selectedPosition = reconcileSelectedPosition();
                sel = fillSpecific(selectedPosition, mSpecificTop);
                /**
                 * When ListView is resized, FocusSelector requests an async selection for the
                 * previously focused item to make sure it is still visible. If the item is not
                 * selectable, it won't regain focus so instead we call FocusSelector
                 * to directly request focus on the view after it is visible.
                 */
                if (sel == null && mFocusSelector != null) {
                    final Runnable focusRunnable = mFocusSelector
                            .setupFocusIfValid(selectedPosition);
                    if (focusRunnable != null) {
                        post(focusRunnable);
                    }
                }
                break;
            case LAYOUT_MOVE_SELECTION:
                sel = moveSelection(oldSel, newSel, delta, childrenTop, childrenBottom);
                break;
            default:
                if (childCount == 0) {
                    if (!mStackFromBottom) {
                        final int position = lookForSelectablePosition(0, true);
                        setSelectedPositionInt(position);
                        sel = fillFromTop(childrenTop);
                    } else {
                        final int position = lookForSelectablePosition(mItemCount - 1, false);
                        setSelectedPositionInt(position);
                        sel = fillUp(mItemCount - 1, childrenBottom);
                    }
                } else {
                    if (mSelectedPosition >= 0 && mSelectedPosition < mItemCount) {
                        sel = fillSpecific(mSelectedPosition,
                                oldSel == null ? childrenTop : oldSel.getTop());
                    } else if (mFirstPosition < mItemCount) {
                        sel = fillSpecific(mFirstPosition,
                                oldFirst == null ? childrenTop : oldFirst.getTop());
                    } else {
                        sel = fillSpecific(0, childrenTop);
                    }
                }
                break;
            }

            // Flush any cached views that did not get reused above
            recycleBin.scrapActiveViews();

            // remove any header/footer that has been temp detached and not re-attached
            removeUnusedFixedViews(mHeaderViewInfos);
            removeUnusedFixedViews(mFooterViewInfos);

            if (sel != null) {
                // The current selected item should get focus if items are
                // focusable.
                if (mItemsCanFocus && hasFocus() && !sel.hasFocus()) {
                    final boolean focusWasTaken = (sel == focusLayoutRestoreDirectChild &&
                            focusLayoutRestoreView != null &&
                            focusLayoutRestoreView.requestFocus()) || sel.requestFocus();
                    if (!focusWasTaken) {
                        // Selected item didn't take focus, but we still want to
                        // make sure something else outside of the selected view
                        // has focus.
                        final View focused = getFocusedChild();
                        if (focused != null) {
                            focused.clearFocus();
                        }
                        positionSelector(INVALID_POSITION, sel);
                    } else {
                        sel.setSelected(false);
                        mSelectorRect.setEmpty();
                    }
                } else {
                    positionSelector(INVALID_POSITION, sel);
                }
                mSelectedTop = sel.getTop();
            } else {
                final boolean inTouchMode = mTouchMode == TOUCH_MODE_TAP
                        || mTouchMode == TOUCH_MODE_DONE_WAITING;
                if (inTouchMode) {
                    // If the user's finger is down, select the motion position.
                    final View child = getChildAt(mMotionPosition - mFirstPosition);
                    if (child != null) {
                        positionSelector(mMotionPosition, child);
                    }
                } else if (mSelectorPosition != INVALID_POSITION) {
                    // If we had previously positioned the selector somewhere,
                    // put it back there. It might not match up with the data,
                    // but it's transitioning out so it's not a big deal.
                    final View child = getChildAt(mSelectorPosition - mFirstPosition);
                    if (child != null) {
                        positionSelector(mSelectorPosition, child);
                    }
                } else {
                    // Otherwise, clear selection.
                    mSelectedTop = 0;
                    mSelectorRect.setEmpty();
                }

                // Even if there is not selected position, we may need to
                // restore focus (i.e. something focusable in touch mode).
                if (hasFocus() && focusLayoutRestoreView != null) {
                    focusLayoutRestoreView.requestFocus();
                }
            }

            // Attempt to restore accessibility focus, if necessary.
            if (viewRootImpl != null) {
                final View newAccessibilityFocusedView = viewRootImpl.getAccessibilityFocusedHost();
                if (newAccessibilityFocusedView == null) {
                    if (accessibilityFocusLayoutRestoreView != null
                            && accessibilityFocusLayoutRestoreView.isAttachedToWindow()) {
                        final AccessibilityNodeProvider provider =
                                accessibilityFocusLayoutRestoreView.getAccessibilityNodeProvider();
                        if (accessibilityFocusLayoutRestoreNode != null && provider != null) {
                            final int virtualViewId = AccessibilityNodeInfo.getVirtualDescendantId(
                                    accessibilityFocusLayoutRestoreNode.getSourceNodeId());
                            provider.performAction(virtualViewId,
                                    AccessibilityNodeInfo.ACTION_ACCESSIBILITY_FOCUS, null);
                        } else {
                            accessibilityFocusLayoutRestoreView.requestAccessibilityFocus();
                        }
                    } else if (accessibilityFocusPosition != INVALID_POSITION) {
                        // Bound the position within the visible children.
                        final int position = MathUtils.constrain(
                                accessibilityFocusPosition - mFirstPosition, 0,
                                getChildCount() - 1);
                        final View restoreView = getChildAt(position);
                        if (restoreView != null) {
                            restoreView.requestAccessibilityFocus();
                        }
                    }
                }
            }

            // Tell focus view we are done mucking with it, if it is still in
            // our view hierarchy.
            if (focusLayoutRestoreView != null
                    && focusLayoutRestoreView.getWindowToken() != null) {
                focusLayoutRestoreView.dispatchFinishTemporaryDetach();
            }

            mLayoutMode = LAYOUT_NORMAL;
            mDataChanged = false;
            if (mPositionScrollAfterLayout != null) {
                post(mPositionScrollAfterLayout);
                mPositionScrollAfterLayout = null;
            }
            mNeedSync = false;
            setNextSelectedPositionInt(mSelectedPosition);

            updateScrollIndicators();

            if (mItemCount > 0) {
                checkSelectionChanged();
            }

            invokeOnItemScrollListener();
        } finally {
            if (mFocusSelector != null) {
                mFocusSelector.onLayoutComplete();
            }
            if (!blockLayoutRequests) {
                mBlockLayoutRequests = false;
            }
        }
    }