PullToRefresh源码阅读摘记

gistfile1.java

private boolean isFirstItemVisible() {
		final Adapter adapter = mRefreshableView.getAdapter();

		if (null == adapter || adapter.isEmpty()) {
			if (DEBUG) {
				Log.d(LOG_TAG, "isFirstItemVisible. Empty View.");
			}
			return true;

		} else {

			/**
			 * This check should really just be:
			 * mRefreshableView.getFirstVisiblePosition() == 0, but PtRListView
			 * internally use a HeaderView which messes the positions up. For
			 * now we'll just add one to account for it and rely on the inner
			 * condition which checks getTop().
			 */
			if (mRefreshableView.getFirstVisiblePosition() <= 1) {
				final View firstVisibleChild = mRefreshableView.getChildAt(0);
				if (firstVisibleChild != null) {
					return firstVisibleChild.getTop() >= mRefreshableView.getTop();
				}
			}
		}

		return false;
	}

	private boolean isLastItemVisible() {
		final Adapter adapter = mRefreshableView.getAdapter();

		if (null == adapter || adapter.isEmpty()) {
			if (DEBUG) {
				Log.d(LOG_TAG, "isLastItemVisible. Empty View.");
			}
			return true;
		} else {
			final int lastItemPosition = mRefreshableView.getCount() - 1;
			final int lastVisiblePosition = mRefreshableView.getLastVisiblePosition();

			if (DEBUG) {
				Log.d(LOG_TAG, "isLastItemVisible. Last Item Position: " + lastItemPosition + " Last Visible Pos: "
						+ lastVisiblePosition);
			}

			/**
			 * This check should really just be: lastVisiblePosition ==
			 * lastItemPosition, but PtRListView internally uses a FooterView
			 * which messes the positions up. For me we'll just subtract one to
			 * account for it and rely on the inner condition which checks
			 * getBottom().
			 */
			if (lastVisiblePosition >= lastItemPosition - 1) {
				final int childIndex = lastVisiblePosition - mRefreshableView.getFirstVisiblePosition();
				final View lastVisibleChild = mRefreshableView.getChildAt(childIndex);
				if (lastVisibleChild != null) {
					return lastVisibleChild.getBottom() <= mRefreshableView.getBottom();
				}
			}
		}

		return false;
	}

onInterceptTouchEvent()

@Override
	public final boolean onInterceptTouchEvent(MotionEvent event) {

		if (!isPullToRefreshEnabled()) {
			return false;
		}

		final int action = event.getAction();

		if (action == MotionEvent.ACTION_CANCEL || action == MotionEvent.ACTION_UP) {
			mIsBeingDragged = false;
			return false;
		}

		if (action != MotionEvent.ACTION_DOWN && mIsBeingDragged) {
			return true;
		}

		switch (action) {
			case MotionEvent.ACTION_MOVE: {
				// If we're refreshing, and the flag is set. Eat all MOVE events
				if (!mScrollingWhileRefreshingEnabled && isRefreshing()) {
					return true;
				}

				if (isReadyForPull()) {
					final float y = event.getY(), x = event.getX();
					final float diff, oppositeDiff, absDiff;

					// We need to use the correct values, based on scroll
					// direction
					switch (getPullToRefreshScrollDirection()) {
						case HORIZONTAL:
							diff = x - mLastMotionX;
							oppositeDiff = y - mLastMotionY;
							break;
						case VERTICAL:
						default:
							diff = y - mLastMotionY;
							oppositeDiff = x - mLastMotionX;
							break;
					}
					absDiff = Math.abs(diff);

					if (absDiff > mTouchSlop && (!mFilterTouchEvents || absDiff > Math.abs(oppositeDiff))) {
						if (mMode.showHeaderLoadingLayout() && diff >= 1f && isReadyForPullStart()) {
							mLastMotionY = y;
							mLastMotionX = x;
							mIsBeingDragged = true;
							if (mMode == Mode.BOTH) {
								mCurrentMode = Mode.PULL_FROM_START;
							}
						} else if (mMode.showFooterLoadingLayout() && diff <= -1f && isReadyForPullEnd()) {
							mLastMotionY = y;
							mLastMotionX = x;
							mIsBeingDragged = true;
							if (mMode == Mode.BOTH) {
								mCurrentMode = Mode.PULL_FROM_END;
							}
						}
					}
				}
				break;
			}
			case MotionEvent.ACTION_DOWN: {
				if (isReadyForPull()) {
					mLastMotionY = mInitialMotionY = event.getY();
					mLastMotionX = mInitialMotionX = event.getX();
					mIsBeingDragged = false;
				}
				break;
			}
		}

		return mIsBeingDragged;
	}