MJRefreshComponent
一、主要功能
1、给子类留下准备工作的钩子方法，并设置基本属性
- (instancetype)initWithFrame:(CGRect)frame
{
if (self = [super initWithFrame:frame]) {
// 准备工作
[self prepare];
// 默认是普通状态
self.state = MJRefreshStateIdle;
}
return self;
}
- (void)prepare
{
// 基本属性
self.autoresizingMask = UIViewAutoresizingFlexibleWidth;
self.backgroundColor = [UIColor clearColor];
}
- (void)layoutSubviews
{
[self placeSubviews];
[super layoutSubviews];
}
- (void)placeSubviews{}
2、在属性的View节将加入到UIScrollView上时，
2.1设置UIScrollView可滚动的弹簧属性
2.2保存要添加上的scrollView为自己的成员变量，并且保存最开始的contentInset
3.3 删除旧的监听、重新添加新的监听，主要用来监听滚动的距离
- (void)willMoveToSuperview:(UIView *)newSuperview
{
[super willMoveToSuperview:newSuperview];
// 如果不是UIScrollView，不做任何事情
if (newSuperview && ![newSuperview isKindOfClass:[UIScrollView class]]) return;
// 旧的父控件移除监听
[self removeObservers];
if (newSuperview) { // 新的父控件
// 设置宽度
self.mj_w = newSuperview.mj_w;
// 设置位置
self.mj_x = 0;
// 记录UIScrollView
_scrollView = (UIScrollView *)newSuperview;
// 设置永远支持垂直弹簧效果
_scrollView.alwaysBounceVertical = YES;
// 记录UIScrollView最开始的contentInset
_scrollViewOriginalInset = _scrollView.contentInset;
// 添加监听
[self addObservers];
}
}
- (void)drawRect:(CGRect)rect
{
[super drawRect:rect];
if (self.state == MJRefreshStateWillRefresh) {
// 预防view还没显示出来就调用了beginRefreshing
self.state = MJRefreshStateRefreshing;
}
}
3.3 删除旧的监听、重新添加新的监听，主要用来监听滚动的距离contentOffset、可滚动区域的变化contentSize以及添加在uiscrollview上的滑动手势的的状态监听state
#pragma mark - KVO监听
- (void)addObservers
{
NSKeyValueObservingOptions options = NSKeyValueObservingOptionNew | NSKeyValueObservingOptionOld;
[self.scrollView addObserver:self forKeyPath:MJRefreshKeyPathContentOffset options:options context:nil];
[self.scrollView addObserver:self forKeyPath:MJRefreshKeyPathContentSize options:options context:nil];
self.pan = self.scrollView.panGestureRecognizer;
[self.pan addObserver:self forKeyPath:MJRefreshKeyPathPanState options:options context:nil];
}
- (void)removeObservers
{
[self.superview removeObserver:self forKeyPath:MJRefreshKeyPathContentOffset];
[self.superview removeObserver:self forKeyPath:MJRefreshKeyPathContentSize];;
[self.pan removeObserver:self forKeyPath:MJRefreshKeyPathPanState];
self.pan = nil;
}
- (void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary *)change context:(void *)context
{
// 遇到这些情况就直接返回
if (!self.userInteractionEnabled) return;
// 这个就算看不见也需要处理
if ([keyPath isEqualToString:MJRefreshKeyPathContentSize]) {
[self scrollViewContentSizeDidChange:change];
}
// 看不见
if (self.hidden) return;
if ([keyPath isEqualToString:MJRefreshKeyPathContentOffset]) {
[self scrollViewContentOffsetDidChange:change];
} else if ([keyPath isEqualToString:MJRefreshKeyPathPanState]) {
[self scrollViewPanStateDidChange:change];
}
}
// 在子类进行具体的实现操作
- (void)scrollViewContentOffsetDidChange:(NSDictionary *)change{}
- (void)scrollViewContentSizeDidChange:(NSDictionary *)change{}
- (void)scrollViewPanStateDidChange:(NSDictionary *)change{}
总结：所用知识点，
1、View的生命周期方法UIView(UIViewHierarchy)
willMoveToSuperview：，这个方法保证能拿到自己的superView
2、UIScrollView的保持垂直或水平的弹簧效果，这样才能滚动看到拉取的效果
alwaysBounceVertical
alwaysBounceHorizontal
3、对scrollView的contentOffset、contentSize、scrollView.panGestureRecognizer的state进行监听
4、添加action-target及callback的执行操作
