使用runtime关联对象将视图添加到视图的类目里

//get方法
- (RJCircularLoaderView*)rj_circularLoaderView
{
RJCircularLoaderView *loaderView = objc_getAssociatedObject(self, @selector(rj_circularLoaderView));
if (!loaderView) {
loaderView = [RJCircularLoaderView new];
objc_setAssociatedObject(self, @selector(rj_circularLoaderView), loaderView, OBJC_ASSOCIATION_RETAIN_NONATOMIC);
}
return loaderView;
}//添加在视图上
- (void)startLoader
{
RJCircularLoaderView *loaderView = self.rj_circularLoaderView;
loaderView.frame = self.bounds;
[self addSubview:loaderView]; loaderView.progress = ;
}