阅读DZNEmptyDataSet源码笔记

发表于

组成

分类：

  • UIScrollView (DZNEmptyDataSet)
  • UIView (DZNConstraintBasedLayoutExtensions)

协议：

  • DZNEmptyDataSetSource
  • DZNEmptyDataSetDelegate

类：

  • DZNEmptyDataSetView
  • DZNWeakObjectContainer

UIScrollView (DZNEmptyDataSet)

使用运行时添加的属性：

  • emptyDataSetSource
  • emptyDataSetDelegate
  • isEmptyDataSetVisible

使用runtime Swizzling为reloadData添加方法：

  • dzn_reloadEmptyDataSet

    即当tableView或collectionView 调用reloadData方法时会执行dzn_reloadEmptyDataSet。这是整个框架的核心方法。

dzn_reloadEmptyDataSet方法

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- (void)dzn_reloadEmptyDataSet
{
  	//1.是否能显示 empty dataset view
    if (![self dzn_canDisplay]) {
        return;
    }
    
  	//2.一、询问emptyDataSetDelegate是否应该显示  二、itemsCount是否为0：tableView根据tableView:numberOfRowsInSection方法，collectionView根据 collectionView: numberOfItemsInSection:方法
    if (([self dzn_shouldDisplay] && [self dzn_itemsCount] == 0) || [self dzn_shouldBeForcedToDisplay])
    {
      	//3.创建empty dataset view(空数据View)
        // Notifies that the empty dataset view will appear
      	//3.1通知emptyDataSetDelegate代理，dataset view即将显示
        [self dzn_willAppear];
      
        //3.2 创建
        DZNEmptyDataSetView *view = self.emptyDataSetView;
        
        if (!view.superview) {
          	//3.3添加到ScrollView
            // Send the view all the way to the back, in case a header and/or footer is present, as well as for sectionHeaders or any other content
            if (([self isKindOfClass:[UITableView class]] || [self isKindOfClass:[UICollectionView class]]) && self.subviews.count > 1) {
                [self insertSubview:view atIndex:0];
            }
            else {
                [self addSubview:view];
            }
        }
        
      	//3.4 清理，重置约束以
        // Removing view resetting the view and its constraints it very important to guarantee a good state
        [view prepareForReuse];
        
      //3.5 添加你提供的自定义View
        UIView *customView = [self dzn_customView];
        
        // If a non-nil custom view is available, let's configure it instead
        if (customView) {
            view.customView = customView;
        }
        else {
            // Get the data from the data source
           //3.6 根据emptyDataSetSource提供的数据，配置空数据View的子View
          //具体代码太长，为避免干扰省略
        
          //3.7 通知emptyDataSetDelegate 空数据View已显示
        // Notifies that the empty dataset view did appear
        [self dzn_didAppear];
    }
    else if (self.isEmptyDataSetVisible) {
      	//4.空数据View清除操作
        [self dzn_invalidate];
    }
}