为什么 Xcode 在我的 'if' 子句中显示警告 'Will never be executed'？

Question

我想在我的 tableview 背景上显示 note/label when/if 没有要加载的数据，或者正在获取数据等

我看不出我做错了什么。 Xcode 在这行代码上显示警告 "Will never be executed"：if mostUpTodateNewsItemsFromRealm?.count < 1 {

方法在这里

    override func numberOfSectionsInTableView(tableView: UITableView) -> Int {

    // create a lable ready to display
    let statusLabel: UILabel = UILabel(frame: CGRectMake(0, 0, self.tableView.bounds.size.width, self.tableView.bounds.size.height))
    statusLabel.textColor = globalTintColor
    statusLabel.textAlignment = NSTextAlignment.Center
    self.tableView.backgroundView = statusLabel
    self.tableView.backgroundView?.backgroundColor = colourOfAllPickerBackgrounds

    // 1) Check if we have tried to fetch news
    if NSUserDefaults.standardUserDefaults().valueForKey("haveTriedToFetchNewsForThisChurch") as! Bool == false {
        statusLabel.text = "Busy loading news..."

    } else {
        // If have tried to fetch news items = true
        // 2) check church has channels
        let numberOfChannelsSubscribedToIs = 0
        if let upToDateSubsInfo = upToDateChannelAndSubsInfo {
            let numberOfChannelsSubscribedToIs = 0
            for subInfo in upToDateSubsInfo {
                if subInfo.subscribed == true {
                    numberOfChannelsSubscribedToIs + 1
                }
            }
        }
        if numberOfChannelsSubscribedToIs < 1 {
            // if no channels
            // show messsage saying you aren't subscribed to any channels.
            statusLabel.text = "Your church hasn't setup any news channels yet."

        } else {

            // 3) if we have tried to fetch news AND the church DOES have channels
            // check if we have any news items to show
            if mostUpTodateNewsItemsFromRealm?.count < 1 {

                // If no news items
                statusLabel.text = "Your church hasn't broadcast and news yet."
            } else {
                // if have tried to fetch AND church has channels AND there ARE news items
                // remove the background image so doesn't show when items load.
                self.tableView.backgroundView = nil
            }
        }
    }
    // in all circumstances there will be one section
    return 1
}

Answer 1

您的代码首先创建了一个常量：

let numberOfChannelsSubscribedToIs = 0

然后你检查它是否小于1:

if numberOfChannelsSubscribedToIs < 1

既然是常数，就永远不会变。这意味着 if 子句将始终被执行。因此，else 子句永远不会被执行。

所以首先你需要创建这个常量变量：

var numberOfChannelsSubscribedToIs = 0

那就改一下：

if subInfo.subscribed == true {
    numberOfChannelsSubscribedToIs + 1
}

对此：

if subInfo.subscribed == true {
    numberOfChannelsSubscribedToIs += 1
}

这样，numberOFChannelSubscribedToIs可以是0以外的数字，else子句就可以执行了。

var和let差别很大！

为什么 Xcode 在我的 'if' 子句中显示警告 'Will never be executed'？

Why does Xcode show warning 'Will never be executed' on my 'if' clause?

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