PullToRefreshListView学习分享

最新推荐文章于 2024-05-05 13:14:23 发布

原创最新推荐文章于 2024-05-05 13:14:23 发布 · 427 阅读

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#android #PullToRe

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本文详细解析了PullToRefreshListView的工作原理，重点介绍了其核心方法onInterceptTouchEvent和onTouchEvent的作用，通过分析源码，解释了如何通过触摸事件实现下拉刷新及上拉加载更多功能。

PullToRefreshListVeiw学习笔记

核心代码主要在

onInterceptTouchEvent(MotionEvent event)

onTouchEvent(MotionEvent event)

    @Override
    public final boolean onTouchEvent(MotionEvent event) {
        if (!isPullToRefreshEnabled()) {
            return false;
        }
        // If we're refreshing, and the flag is set. Eat the event
        if (!mScrollingWhileRefreshingEnabled && isRefreshing()) {
            return true;
        }
        if (event.getAction() == MotionEvent.ACTION_DOWN && event.getEdgeFlags() != 0) {
            return false;
        }
        switch (event.getAction()) {
            case MotionEvent.ACTION_MOVE: {
                if (mIsBeingDragged) {
                    mLastMotionY = event.getY();
                    mLastMotionX = event.getX();
                    pullEvent();
                    return true;
                }
                break;
            }
            case MotionEvent.ACTION_DOWN: {
                if (isReadyForPull()) {
                    mLastMotionY = mInitialMotionY = event.getY();
                    mLastMotionX = mInitialMotionX = event.getX();
                    return true;
                }
                break;
            }
            case MotionEvent.ACTION_CANCEL:
            case MotionEvent.ACTION_UP: {
                if (mIsBeingDragged) {
                    mIsBeingDragged = false;
                    if (mState == State.RELEASE_TO_REFRESH
                            && (null != mOnRefreshListener || null != mOnRefreshListener2)) {
                        setState(State.REFRESHING, true);
                        return true;
                    }
                    // If we're already refreshing, just scroll back to the top
                    if (isRefreshing()) {
                        smoothScrollTo(0);
                        return true;
                    }
                    // If we haven't returned by here, then we're not in a state
                    // to pull, so just reset
                    setState(State.RESET);
                    return true;
                }
                break;
            }
        }
        return false;
    }

onInterceptTouchEvent方法主要是判断是否将该事件传递到onTouchEvent中，然后在onTouchEvent事件中判断手指的移动，进而调用scrollTo方法来控制上面或者下面的Loading视图显示出来。

这里值得疑问的是为什么调用scrollTo方法就能将headerLoayout或footerLayout显示出来？

这里有一个方法值得注意：refreshLoadingViewsSize()。在这个方法中对headerLayout跟footerLayout的宽高做了设置，该操作是在初始化的时候做的。方法的底部调用了setPadding(int left, int top, int right, int bottom)方法。关键就在这里，因为将padding设置为负值就可以将headerLayout跟footerLayout隐藏起来了，然后再调用scrollTo(int x,int y)函数就可以将隐藏的布局逐渐的显示出来了。

    /**
     * Re-measure the Loading Views height, and adjust internal padding as
     * necessary
     */
    protected final void refreshLoadingViewsSize() {
        final int maximumPullScroll = (int) (getMaximumPullScroll() * 1.2f);

        int pLeft = getPaddingLeft();
        int pTop = getPaddingTop();
        int pRight = getPaddingRight();
        int pBottom = getPaddingBottom();

        switch (getPullToRefreshScrollDirection()) {
            case HORIZONTAL:
                if (mMode.showHeaderLoadingLayout()) {
                    mHeaderLayout.setWidth(maximumPullScroll);
                    pLeft = -maximumPullScroll;
                } else {
                    pLeft = 0;
                }

                if (mMode.showFooterLoadingLayout()) {
                    mFooterLayout.setWidth(maximumPullScroll);
                    pRight = -maximumPullScroll;
                } else {
                    pRight = 0;
                }
                break;

            case VERTICAL:
                if (mMode.showHeaderLoadingLayout()) {
                    mHeaderLayout.setHeight(maximumPullScroll);
                    pTop = -maximumPullScroll;
                } else {
                    pTop = 0;
                }

                if (mMode.showFooterLoadingLayout()) {
                    mFooterLayout.setHeight(maximumPullScroll);
                    pBottom = -maximumPullScroll;
                } else {
                    pBottom = 0;
                }
                break;
        }

        if (DEBUG) {
            Log.d(LOG_TAG, String.format("Setting Padding. L: %d, T: %d, R: %d, B: %d", pLeft, pTop, pRight, pBottom));
        }
        setPadding(pLeft, pTop, pRight, pBottom);
    }