UITabView/UICollectionView 全选问题

SkySeraph July. 30th 2016

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The Issue

Recently in my new project I need to select all the cell data in my UITabViewCell and UICollectionViewCell, and need to do some operations with all the cells(like delete etc.), What I do as follows:

UITabView

private func selectAll(select: Bool) {
    let numSections = mListTableView?.numberOfSections
    if let numSections = numSections {
        for numSection in  0 ..< numSections{
            let numItems = mListTableView?.numberOfRowsInSection(numSection)
            if let numItems = numItems {
                for numItem in 0 ..< numItems {
                    selectCell(NSIndexPath(forRow: numItem, inSection: numSection), select: select)
                }
            }
        }
    }
}

private func selectCell(indexPath : NSIndexPath, select: Bool) {
    if mListTableView?.cellForRowAtIndexPath(indexPath) != nil {
        let cell = mListTableView?.cellForRowAtIndexPath(indexPath) as! DownloadListViewCell
        //cell.setSelected(select, animated: true)
        cell.setSelectForDelete(select)  // select status UI in UITabViewCell
        mDownloadList[indexPath.row].selectToDelete = select  // Pojo data
    }
}

UICollectionView

private func selectAll(select: Bool) {
    let numSections = mMyOfflineCollectView?.numberOfSections()
    if let numSections = numSections {
        for numSection in  0 ..< numSections{
            let numItems = mMyOfflineCollectView?.numberOfItemsInSection(numSection)
            if let numItems = numItems {
                for numItem in 0 ..< numItems {
                    selectCell(NSIndexPath(forRow: numItem, inSection: numSection), flag: select)
                }
            }
        }
    }
}

private func selectCell(indexPath : NSIndexPath, flag: Bool) {
    if mMyOfflineCollectView.cellForItemAtIndexPath(indexPath) != nil {
        let cell = mMyOfflineCollectView.cellForItemAtIndexPath(indexPath) as! MyOfflineCollectionViewCell
        cell.setSelect(flag)
        if flag {
            mMyOfflineCollectView.selectItemAtIndexPath(indexPath, animated: true, scrollPosition: UICollectionViewScrollPosition.None)
        }else {
            mMyOfflineCollectView.deselectItemAtIndexPath(indexPath, animated: true)
        }
        mMyofflinesData[indexPath.row].needDelete = flag
    }
}

But, The problem is , I can only select the visible cell when I scoll down or up, or do operations

Solutions in NetWork

UICollectionView cellForItemAtIndexPath is nil

cellForItemAtIndexPath returns nil after force scrolling to make it visible

Select all the cells in UITableView

Easier way to select all rows in UITableView

tableView.cellForRowAtIndexPath returns nil with too many cells (swift)

tableView.cellForRowAtIndexPath(indexPath) return nil

The real Solution

The real problem happened at the cellForRowAtIndexPath / cellForItemAtIndexPath, Which defined in Apple as follows:

public func cellForRowAtIndexPath(indexPath: NSIndexPath) -> UITableViewCell?
// returns nil if cell is **not visible** or index path is out of range

public func cellForItemAtIndexPath(indexPath: NSIndexPath) -> UICollectionViewCell?

When the cell is not visible, the cellForRowAtIndexPath will return nil,
So, it’s not the right way to do the cell select operation out the
UITableViewDataSource in cellForRowAtIndexPath (UITabView), you should do it separate. The right way as follows:

func tableView(tableView: UITableView, cellForRowAtIndexPath indexPath: NSIndexPath) -> UITableViewCell {
    let cell = tableView.dequeueReusableCellWithIdentifier(DOWNLOAD_LIST_CELL_INDENTIFIER, forIndexPath: indexPath) as! DownloadListViewCell
    cell.selectionStyle = UITableViewCellSelectionStyle.None
    // ...
   cell.setSelectForDelete(self.mDownloadList[indexPath.row].selectToDelete)// select status UI in UITabViewCell
    // ...
    return cell
}

private func selectCell(indexPath : NSIndexPath, select: Bool) {
    mDownloadList[indexPath.row].selectToDelete = select // Pojo data
    mListTableView?.reloadData() // reloadData
}